Home |
Search |
Today's Posts |
#1
|
|||
|
|||
20hz to 20Khz , yea right!
|
#2
|
|||
|
|||
20hz to 20Khz , yea right!
|
#3
|
|||
|
|||
20hz to 20Khz , yea right!
Flash,
Besides all that Mark said, you can't measure loudspeakers by playing tones in a typical room in a typical house. If you take it outside, far away from ambient noises, you'll have half a shot at it. --Ethan |
#4
|
|||
|
|||
20hz to 20Khz , yea right!
Flash,
Besides all that Mark said, you can't measure loudspeakers by playing tones in a typical room in a typical house. If you take it outside, far away from ambient noises, you'll have half a shot at it. --Ethan |
#6
|
|||
|
|||
20hz to 20Khz , yea right!
In article ,
says... "Mark" wrote in message th.net... In article , says... I have had no luck in measuring speaker response at low frequency's, Then you may not be using the right tools. What tools do you use? What is needed is a measurement mic that is calibrated to the device being used for the test measurements. I've personally used a number of different set-ups, from a number of different manufacturers. My favorite for best bang for the buck is the Audio Control Industrial SA 3052. There are plenty of other devices that will do a respectable job as well. First off, you should Never use a stereo mic (or any stereo set up) for measurement purposes. You are guaranteed to get inaccurate results. Secondly, the mic is only part of the equipment. What else are you using? Never? Yes, never. If what you're interested in is the frequency response from a single driver or cabinet, you want to make that measurement from one point in space. By using a stereo setup I can collect two data streams rather than one, I can compare the streams and quickly analyse microphone placement and any other abnormalities. Standard measurement is done at 1 meter, on axis. Period. (Unless, of course, you're creating a polar chart.) Any abnormalities that exist are a result of either poor driver/box design, or space-induced aberrations. And speaking of which, I note in a different response of this thread that you put nominal weight on the influence of the space in which you're testing. I would suggest that Ethan is dead-on in his comment, _particularly_ when the concern is low-frequency response. By testing in a confined space that is Not truly anechoic, you're guaranteed to introduce abnormalities in the response curve. I have access to / a collection of equipment, some built by HP other stuff designed and manufactured for the BBC or others. All the HP gear uses HPIB which is not what is the most convenient, The A2D - D2A card in the PC is a much quicker and generates the same results (But much quicker) I have a number of amplifers, but typically use a Class A 2n3055 based 60 watt mono amp, It has acceptable characteristics for the type of measurement that I usually do, 20Hz to 20Khz on / off axis at 1w / 1m / 1khz. Microphones is the biggest issue as I have not yet found anything that I am really happy with. I can use the Shures, I have some clone shure that are very flat from 60hz to 20Khz and cost like $60 each! (vs 3 grand for the shures) (I can compensate in software for the low end droop or use a opamp based corrector that was build before I started with the PC based A2D card. I have a nice transducer (Probably from a bridge or Crane) that works from a few Hz. None of which matters if the measurement tool and the microphone are not calibrated _To Each Other_. Otherwise you're fooling yourself into thinking you're getting accurate measurements. and a flat panel with a transducer is the only repeatable method of measuring the output, Balderdash. Now thats a technical response!, Alright, here's the longer response. _Any_ calibrated mic/tool combination designed for the job will accurately measure to 20 Hz (and lower) within its own tolerance. Ok, Can some one tell me what mics / transducers I need to be using to get accurate low frequency measurements. Not just 'use your ears' as this is far too subjective! As I indicated, it isn't just a matter of choosing a mic. If the mic and measurement tool aren't calibrated to each other, than accuracy is, at best, a crap shoot. -- Mark The truth as I perceive it to be. Your perception may be different. Triple Z is spam control. |
#7
|
|||
|
|||
20hz to 20Khz , yea right!
On Sun, 23 Nov 2003 02:44:43 -0800, "The Flash" wrote:
I have had no luck in measuring speaker response at low frequency's, I can measure from ~60Hz to 20Khz with near 100% repeatability (How accurate is questionable) I have questioned a number of speaker builders and a couple of companies that 'tune' speakers the answers given on what they measure with and how the do the tests give serious rise to the claims at low frequency. Almost any speaker system sold today claims 20Hz to 20Kz response yet this is so far from the truth I cannot understand how they dare claim such figures. I have yet to find ANY speaker system using an 8 inch driver that has the ability to produce 40hz or lower frequencys as they all have fallen so far down in output level as to be useless. How do you measure the responese at 20Hz?, I have tested a few speakers and basically I cannot get accurate (repeatable) data at much below 60Hz, even using a borrowed shure KSM141 stereo pair in omnidirectional gives vague results ($3000 for the mic's!) I have come to the conclusion that you are really measuring air displacement at anything under 30Hz and a flat panel with a transducer is the only repeatable method of measuring the output, how one calibrates said device is open for discussion. (Oh one firm told me that they use a laser to measure the low frequency of their speakers, check this out for novel! They place a small piece of reflective foil on the base driver, and shine a laser beam on it, they then apply signal and measure via 'laser' the deflection, Also they place a passive radiator 1 meter infront of the driver unit and use the same method to measure its deflection. The apply a 'correction factor' and the produce the frequency response data (company builds very expensive car and home audio subs!) I thought up my own method for eliminating the effect of the room on bass measurement (although, no doubt it has been done before). The main feature is to place the (pressure) microphone within the speaker and to compensate by 12 dB/oct. Normally I use a MLS and filter out higher frequencies, say above 100Hz, with a brick wall FIR filter using Coooledit. The 12 dB/oct compensation is also done in a similar way, either to the input MLS or to the output recording. This sort of pre-filtering can give a large increase to the signal to noise of the meaasurement. There must be some restrictions on the accuracy of this method but the only one I can think off at the moment is that the wavelength must be large compared to the internal dimensions of the speaker. The meaasurement includes the effect of any port and of the enclosure flexing. There is probably an assumption that the air is compressed adiabatically. The pressures involved are, of course, small if the mic is not to be overloaded. |
#8
|
|||
|
|||
20hz to 20Khz , yea right!
On Sun, 23 Nov 2003 02:44:43 -0800, "The Flash" wrote:
I have had no luck in measuring speaker response at low frequency's, I can measure from ~60Hz to 20Khz with near 100% repeatability (How accurate is questionable) I have questioned a number of speaker builders and a couple of companies that 'tune' speakers the answers given on what they measure with and how the do the tests give serious rise to the claims at low frequency. Almost any speaker system sold today claims 20Hz to 20Kz response yet this is so far from the truth I cannot understand how they dare claim such figures. I have yet to find ANY speaker system using an 8 inch driver that has the ability to produce 40hz or lower frequencys as they all have fallen so far down in output level as to be useless. How do you measure the responese at 20Hz?, I have tested a few speakers and basically I cannot get accurate (repeatable) data at much below 60Hz, even using a borrowed shure KSM141 stereo pair in omnidirectional gives vague results ($3000 for the mic's!) I have come to the conclusion that you are really measuring air displacement at anything under 30Hz and a flat panel with a transducer is the only repeatable method of measuring the output, how one calibrates said device is open for discussion. (Oh one firm told me that they use a laser to measure the low frequency of their speakers, check this out for novel! They place a small piece of reflective foil on the base driver, and shine a laser beam on it, they then apply signal and measure via 'laser' the deflection, Also they place a passive radiator 1 meter infront of the driver unit and use the same method to measure its deflection. The apply a 'correction factor' and the produce the frequency response data (company builds very expensive car and home audio subs!) I thought up my own method for eliminating the effect of the room on bass measurement (although, no doubt it has been done before). The main feature is to place the (pressure) microphone within the speaker and to compensate by 12 dB/oct. Normally I use a MLS and filter out higher frequencies, say above 100Hz, with a brick wall FIR filter using Coooledit. The 12 dB/oct compensation is also done in a similar way, either to the input MLS or to the output recording. This sort of pre-filtering can give a large increase to the signal to noise of the meaasurement. There must be some restrictions on the accuracy of this method but the only one I can think off at the moment is that the wavelength must be large compared to the internal dimensions of the speaker. The meaasurement includes the effect of any port and of the enclosure flexing. There is probably an assumption that the air is compressed adiabatically. The pressures involved are, of course, small if the mic is not to be overloaded. |
#9
|
|||
|
|||
20hz to 20Khz , yea right!
In article , "The Flash" wrote:
I have had no luck in measuring speaker response at low frequency's, I can measure from ~60Hz to 20Khz with near 100% repeatability (How accurate is questionable) I have questioned a number of speaker builders and a couple of companies that 'tune' speakers the answers given on what they measure with and how the do the tests give serious rise to the claims at low frequency. Almost any speaker system sold today claims 20Hz to 20Kz response yet this is so far from the truth I cannot understand how they dare claim such figures. I have yet to find ANY speaker system using an 8 inch driver that has the ability to produce 40hz or lower frequencys as they all have fallen so far down in output level as to be useless. Well its does produce it, no? How do you measure the responese at 20Hz?, I have tested a few speakers and basically I cannot get accurate (repeatable) data at much below 60Hz, even using a borrowed shure KSM141 stereo pair in omnidirectional gives vague results ($3000 for the mic's!) I have come to the conclusion that you are really measuring air displacement at anything under 30Hz and a flat panel with a transducer is the only repeatable method of measuring the output, how one calibrates said device is open for discussion. (Oh one firm told me that they use a laser to measure the low frequency of their speakers, check this out for novel! They place a small piece of reflective foil on the base driver, and shine a laser beam on it, they then apply signal and measure via 'laser' the deflection, Also they place a passive radiator 1 meter infront of the driver unit and use the same method to measure its deflection. The apply a 'correction factor' and the produce the frequency response data (company builds very expensive car and home audio subs!) I guess you could compute response measuring the deflection of a sealed box driver. The passive technique seems like it would work, but it doesn't seem better than simply using a microphone in front of the box on a flat plate. If you measure the deflection of a passive diaphram its deflection properties must be fully understood to intrepret anything. greg |
#10
|
|||
|
|||
20hz to 20Khz , yea right!
In article , "The Flash" wrote:
I have had no luck in measuring speaker response at low frequency's, I can measure from ~60Hz to 20Khz with near 100% repeatability (How accurate is questionable) I have questioned a number of speaker builders and a couple of companies that 'tune' speakers the answers given on what they measure with and how the do the tests give serious rise to the claims at low frequency. Almost any speaker system sold today claims 20Hz to 20Kz response yet this is so far from the truth I cannot understand how they dare claim such figures. I have yet to find ANY speaker system using an 8 inch driver that has the ability to produce 40hz or lower frequencys as they all have fallen so far down in output level as to be useless. Well its does produce it, no? How do you measure the responese at 20Hz?, I have tested a few speakers and basically I cannot get accurate (repeatable) data at much below 60Hz, even using a borrowed shure KSM141 stereo pair in omnidirectional gives vague results ($3000 for the mic's!) I have come to the conclusion that you are really measuring air displacement at anything under 30Hz and a flat panel with a transducer is the only repeatable method of measuring the output, how one calibrates said device is open for discussion. (Oh one firm told me that they use a laser to measure the low frequency of their speakers, check this out for novel! They place a small piece of reflective foil on the base driver, and shine a laser beam on it, they then apply signal and measure via 'laser' the deflection, Also they place a passive radiator 1 meter infront of the driver unit and use the same method to measure its deflection. The apply a 'correction factor' and the produce the frequency response data (company builds very expensive car and home audio subs!) I guess you could compute response measuring the deflection of a sealed box driver. The passive technique seems like it would work, but it doesn't seem better than simply using a microphone in front of the box on a flat plate. If you measure the deflection of a passive diaphram its deflection properties must be fully understood to intrepret anything. greg |
#11
|
|||
|
|||
20hz to 20Khz , yea right!
"The Flash" wrote in message ...
I have had no luck in measuring speaker response at low frequency's, I can measure from ~60Hz to 20Khz with near 100% repeatability (How accurate is questionable) I have questioned a number of speaker builders and a couple of companies that 'tune' speakers the answers given on what they measure with and how the do the tests give serious rise to the claims at low frequency. Almost any speaker system sold today claims 20Hz to 20Kz response yet this is so far from the truth I cannot understand how they dare claim such figures. Almost ANY speaker system? You haven't looked at many speaker systems if that's your claim. Further, a specification such as "20 Hz to 20 kHz" is, in an of itself, pretty damned meaningless. You have left out a crucial portion of the specification, the tolerance of the amplitude response within those limits. I have yet to find ANY speaker system using an 8 inch driver that has the ability to produce 40hz or lower frequencys as they all have fallen so far down in output level as to be useless. Determined how? How do you measure the responese at 20Hz?, You measure it with microphones and ancillary equipment that is up to the task. For myself, I have a number of Bruel & Kjaer, ACO, GR and pther microphones that have verified flat response to well below 20 Hz. Some of the B&K 1/2" capsules, for example, are within +-1/2 dB from approximately 3 Hz to 30 kHz and above. The remainder of the measurement and analysis chain has similar properties: the primary measurement chain is DC coupled, for example. Secondly, the size of the venue required for accurate measurements is inversely proportional to the frequency you need to measure. Even using techniques such as gated or windowed measurement, the distance to the first reflection surface is a prime determinant of how low you can measure. You want to measure 20 Hz accurately? Then you need to find a room where the distance between the speaker/microphone and the NEAREST surface is a minimum of 25 feet. I have tested a few speakers and basically I cannot get accurate (repeatable) data at much below 60Hz, even using a borrowed shure KSM141 stereo pair in omnidirectional gives vague results ($3000 for the mic's!) $3000 for microphones that were NEVER designed to be used as measurement microphones, ESPECIALLY at low frequencies. These are recording microphones, NOT measurement microphones. I have come to the conclusion that you are really measuring air displacement at anything under 30Hz and a flat panel with a transducer is the only repeatable method of measuring the output, That may be the conclusion you came to, but that conclusion just happens to be quite wrong. The physical stimulus that the ear responds to as sound are periodic pressure variations of a sufficient amplitude and within certain frequency limits. That's it. As long as a device can detect these pressure variations, it can be used to measure sound. The problem with you big flat panel method is that it assumes, quite incorrectly, that the imnpinging waves are planar: unless you are VERY far away from the speaker, such the wavefronts are no longer spherical, it isn't going to work. The smaller the diaphgragm of the microphone, the less it is affected by such a problem. That's one reason why measurement microphones have very small diaphragms: they are essentially point transducers over a wide range of frequencies. how one calibrates said device is open for discussion. One calibrates it by throwing it in the nearest landfill and going out an learning the proper ways of measuring acoustic phenomenon. (Oh one firm told me that they use a laser to measure the low frequency of their speakers, check this out for novel! They place a small piece of reflective foil on the base driver, and shine a laser beam on it, they then apply signal and measure via 'laser' the deflection, Well, gee golly, since it can be shown on physical first principles that the requirement for a constant sound pressure level (that would mean flat frequency response) from a piston radiator is simply a displacement which goes as the reciprocal of the square of frequency, then if you know the displacement, which you can measure with a pretty high degree of accuracy, then you can, over the piston range of the driver, DIRECTLY and UNAMBIGUOUSLY determine the total acoustic power as: Pa = p/(2 pi c) * (Sd w^2 X)^2 where p = density of air, typ. 1.18 kg/m^3 c = velocity of sound, typ 343 m/s Sd = emissive area of the diaphragm in m^2 w = radian frequency X = displacement of the diaphragm, in m. the method is HARDLY novel at all, as it is well understood and utilized in the field. If provides, for example, a means of measuring acoustical power output without the confounding innaccuracies of microphones, rooms and such, though the microphone innaccuracies are not a problem if you use proper microphones to begin with. More to your notion that it is "novel," you might want to modify that opinion when you discover the technique is described in nearly every text on acoustics. Also they place a passive radiator 1 meter infront of the driver unit and use the same method to measure its deflection. Well, not quite, I believe you are completely misinderstanding what they told you. I would suggest you look up "reciprocity methods." The apply a 'correction factor' and the produce the frequency response data (company builds very expensive car and home audio subs!) Hardly any correction factor needed: simply understand what's going on and that you are simply relying on the physical first principles of sound. What's wrong with that? Compare that to using recording microphones whose measurement capabilities are entirely unknown, in a room of unknown characteristics, using unknown poorly calibrated and undoubtedly poorly controlled techniques by someone who has little or know experience in measurement and acoustics... I'd not bet good money on getting ANY reliable data out of the latter. |
#12
|
|||
|
|||
20hz to 20Khz , yea right!
"The Flash" wrote in message ...
I have had no luck in measuring speaker response at low frequency's, I can measure from ~60Hz to 20Khz with near 100% repeatability (How accurate is questionable) I have questioned a number of speaker builders and a couple of companies that 'tune' speakers the answers given on what they measure with and how the do the tests give serious rise to the claims at low frequency. Almost any speaker system sold today claims 20Hz to 20Kz response yet this is so far from the truth I cannot understand how they dare claim such figures. Almost ANY speaker system? You haven't looked at many speaker systems if that's your claim. Further, a specification such as "20 Hz to 20 kHz" is, in an of itself, pretty damned meaningless. You have left out a crucial portion of the specification, the tolerance of the amplitude response within those limits. I have yet to find ANY speaker system using an 8 inch driver that has the ability to produce 40hz or lower frequencys as they all have fallen so far down in output level as to be useless. Determined how? How do you measure the responese at 20Hz?, You measure it with microphones and ancillary equipment that is up to the task. For myself, I have a number of Bruel & Kjaer, ACO, GR and pther microphones that have verified flat response to well below 20 Hz. Some of the B&K 1/2" capsules, for example, are within +-1/2 dB from approximately 3 Hz to 30 kHz and above. The remainder of the measurement and analysis chain has similar properties: the primary measurement chain is DC coupled, for example. Secondly, the size of the venue required for accurate measurements is inversely proportional to the frequency you need to measure. Even using techniques such as gated or windowed measurement, the distance to the first reflection surface is a prime determinant of how low you can measure. You want to measure 20 Hz accurately? Then you need to find a room where the distance between the speaker/microphone and the NEAREST surface is a minimum of 25 feet. I have tested a few speakers and basically I cannot get accurate (repeatable) data at much below 60Hz, even using a borrowed shure KSM141 stereo pair in omnidirectional gives vague results ($3000 for the mic's!) $3000 for microphones that were NEVER designed to be used as measurement microphones, ESPECIALLY at low frequencies. These are recording microphones, NOT measurement microphones. I have come to the conclusion that you are really measuring air displacement at anything under 30Hz and a flat panel with a transducer is the only repeatable method of measuring the output, That may be the conclusion you came to, but that conclusion just happens to be quite wrong. The physical stimulus that the ear responds to as sound are periodic pressure variations of a sufficient amplitude and within certain frequency limits. That's it. As long as a device can detect these pressure variations, it can be used to measure sound. The problem with you big flat panel method is that it assumes, quite incorrectly, that the imnpinging waves are planar: unless you are VERY far away from the speaker, such the wavefronts are no longer spherical, it isn't going to work. The smaller the diaphgragm of the microphone, the less it is affected by such a problem. That's one reason why measurement microphones have very small diaphragms: they are essentially point transducers over a wide range of frequencies. how one calibrates said device is open for discussion. One calibrates it by throwing it in the nearest landfill and going out an learning the proper ways of measuring acoustic phenomenon. (Oh one firm told me that they use a laser to measure the low frequency of their speakers, check this out for novel! They place a small piece of reflective foil on the base driver, and shine a laser beam on it, they then apply signal and measure via 'laser' the deflection, Well, gee golly, since it can be shown on physical first principles that the requirement for a constant sound pressure level (that would mean flat frequency response) from a piston radiator is simply a displacement which goes as the reciprocal of the square of frequency, then if you know the displacement, which you can measure with a pretty high degree of accuracy, then you can, over the piston range of the driver, DIRECTLY and UNAMBIGUOUSLY determine the total acoustic power as: Pa = p/(2 pi c) * (Sd w^2 X)^2 where p = density of air, typ. 1.18 kg/m^3 c = velocity of sound, typ 343 m/s Sd = emissive area of the diaphragm in m^2 w = radian frequency X = displacement of the diaphragm, in m. the method is HARDLY novel at all, as it is well understood and utilized in the field. If provides, for example, a means of measuring acoustical power output without the confounding innaccuracies of microphones, rooms and such, though the microphone innaccuracies are not a problem if you use proper microphones to begin with. More to your notion that it is "novel," you might want to modify that opinion when you discover the technique is described in nearly every text on acoustics. Also they place a passive radiator 1 meter infront of the driver unit and use the same method to measure its deflection. Well, not quite, I believe you are completely misinderstanding what they told you. I would suggest you look up "reciprocity methods." The apply a 'correction factor' and the produce the frequency response data (company builds very expensive car and home audio subs!) Hardly any correction factor needed: simply understand what's going on and that you are simply relying on the physical first principles of sound. What's wrong with that? Compare that to using recording microphones whose measurement capabilities are entirely unknown, in a room of unknown characteristics, using unknown poorly calibrated and undoubtedly poorly controlled techniques by someone who has little or know experience in measurement and acoustics... I'd not bet good money on getting ANY reliable data out of the latter. |
#13
|
|||
|
|||
20hz to 20Khz , yea right!
"The Flash" wrote in message ... "Mark" wrote in message th.net... In article , says... I have had no luck in measuring speaker response at low frequency's, Then you may not be using the right tools. What tools do you use? First off, you should Never use a stereo mic (or any stereo set up) for measurement purposes. You are guaranteed to get inaccurate results. Secondly, the mic is only part of the equipment. What else are you using? Never? By using a stereo setup I can collect two data streams rather than one, I can compare the streams and quickly analyse microphone placement and any other abnormalities. I would dearly love to sample 8 or more soundpoints at realtime but this is beyond my gear. I have access to / a collection of equipment, some built by HP other stuff designed and manufactured for the BBC or others. All the HP gear uses HPIB which is not what is the most convenient, The A2D - D2A card in the PC is a much quicker and generates the same results (But much quicker) I have a number of amplifers, but typically use a Class A 2n3055 based 60 watt mono amp, It has acceptable characteristics for the type of measurement that I usually do, 20Hz to 20Khz on / off axis at 1w / 1m / 1khz. Microphones is the biggest issue as I have not yet found anything that I am really happy with. I can use the Shures, I have some clone shure that are very flat from 60hz to 20Khz and cost like $60 each! (vs 3 grand for the shures) (I can compensate in software for the low end droop or use a opamp based corrector that was build before I started with the PC based A2D card. I have a nice transducer (Probably from a bridge or Crane) that works from a few Hz. I don't compensate for impedance/frequency change as this would results that would never be seen in the real world, so a crappy crossover can make a good driver look bad. and a flat panel with a transducer is the only repeatable method of measuring the output, Balderdash. Now thats a technical response!, Ok what I have found is that it seem almost all manuafctures fiddle the figures to make them look good, here is a classic. http://www.aperionaudio.com/products...onse_graph.jpg From the specs page they claim a 60Hz to 20Khz response! Yet their graph shows the speaker is more than 10dB down in output at 60Hz from its output at ~200Hz and again at the high end its ouput looks to be ~8dB down at 20Khz from 15Khz Ok, Can some one tell me what mics / transducers I need to be using to get accurate low frequency measurements. Not just 'use your ears' as this is far too subjective! try these people, they sell interesting FAST dataloggers, and if you want multichannel, use a reed relay or solid state switch box to multiplex your 'Mics' , as long as the source is the same for each run you then have multichannel. regards malcolm |
#14
|
|||
|
|||
20hz to 20Khz , yea right!
"The Flash" wrote in message ... "Mark" wrote in message th.net... In article , says... I have had no luck in measuring speaker response at low frequency's, Then you may not be using the right tools. What tools do you use? First off, you should Never use a stereo mic (or any stereo set up) for measurement purposes. You are guaranteed to get inaccurate results. Secondly, the mic is only part of the equipment. What else are you using? Never? By using a stereo setup I can collect two data streams rather than one, I can compare the streams and quickly analyse microphone placement and any other abnormalities. I would dearly love to sample 8 or more soundpoints at realtime but this is beyond my gear. I have access to / a collection of equipment, some built by HP other stuff designed and manufactured for the BBC or others. All the HP gear uses HPIB which is not what is the most convenient, The A2D - D2A card in the PC is a much quicker and generates the same results (But much quicker) I have a number of amplifers, but typically use a Class A 2n3055 based 60 watt mono amp, It has acceptable characteristics for the type of measurement that I usually do, 20Hz to 20Khz on / off axis at 1w / 1m / 1khz. Microphones is the biggest issue as I have not yet found anything that I am really happy with. I can use the Shures, I have some clone shure that are very flat from 60hz to 20Khz and cost like $60 each! (vs 3 grand for the shures) (I can compensate in software for the low end droop or use a opamp based corrector that was build before I started with the PC based A2D card. I have a nice transducer (Probably from a bridge or Crane) that works from a few Hz. I don't compensate for impedance/frequency change as this would results that would never be seen in the real world, so a crappy crossover can make a good driver look bad. and a flat panel with a transducer is the only repeatable method of measuring the output, Balderdash. Now thats a technical response!, Ok what I have found is that it seem almost all manuafctures fiddle the figures to make them look good, here is a classic. http://www.aperionaudio.com/products...onse_graph.jpg From the specs page they claim a 60Hz to 20Khz response! Yet their graph shows the speaker is more than 10dB down in output at 60Hz from its output at ~200Hz and again at the high end its ouput looks to be ~8dB down at 20Khz from 15Khz Ok, Can some one tell me what mics / transducers I need to be using to get accurate low frequency measurements. Not just 'use your ears' as this is far too subjective! try these people, they sell interesting FAST dataloggers, and if you want multichannel, use a reed relay or solid state switch box to multiplex your 'Mics' , as long as the source is the same for each run you then have multichannel. regards malcolm |
#15
|
|||
|
|||
20hz to 20Khz , yea right!
try these people, they sell interesting FAST dataloggers,
and if you want multichannel, use a reed relay or solid state switch box to multiplex your 'Mics' , as long as the source is the same for each run you then have multichannel. regards malcolm oops http://www.picotech.com/data.html |
#16
|
|||
|
|||
20hz to 20Khz , yea right!
try these people, they sell interesting FAST dataloggers,
and if you want multichannel, use a reed relay or solid state switch box to multiplex your 'Mics' , as long as the source is the same for each run you then have multichannel. regards malcolm oops http://www.picotech.com/data.html |
#17
|
|||
|
|||
20hz to 20Khz , yea right!
"The Flash" wrote in message ... Uh, I used to test in a anechoic chamber at the local university but don't now, Most anechoic chambers are useless below 100 Hz as well. I also tested other areas and found the following. You can test fine in you living room. Background noiselevel is typically 5OdB at home. You place a mat of acoustic foam on the floor, put yout mics up (1m away) place 4 more sheets of acoustic foam round the speaker and mic's and final sheet on top These knock 10dB off background noise Not at 20 Hz they don't. and stop echo, run up 1 watt at 1khz gives about 90dB in most case, this is 50dB above background ???. 50dB BG from 90 dB SPL gives 40 dB. and you can run a sweep test and get results the same as in an anechoic chamber. Again I think this is all smoke and mirrors stuff so that its 'too hard' to do yourself. Sure you can do that, and your measurement uncertainty is ????? TonyP. |
#18
|
|||
|
|||
20hz to 20Khz , yea right!
"The Flash" wrote in message ... Uh, I used to test in a anechoic chamber at the local university but don't now, Most anechoic chambers are useless below 100 Hz as well. I also tested other areas and found the following. You can test fine in you living room. Background noiselevel is typically 5OdB at home. You place a mat of acoustic foam on the floor, put yout mics up (1m away) place 4 more sheets of acoustic foam round the speaker and mic's and final sheet on top These knock 10dB off background noise Not at 20 Hz they don't. and stop echo, run up 1 watt at 1khz gives about 90dB in most case, this is 50dB above background ???. 50dB BG from 90 dB SPL gives 40 dB. and you can run a sweep test and get results the same as in an anechoic chamber. Again I think this is all smoke and mirrors stuff so that its 'too hard' to do yourself. Sure you can do that, and your measurement uncertainty is ????? TonyP. |
#19
|
|||
|
|||
20hz to 20Khz , yea right!
On Sun, 23 Nov 2003 12:29:42 -0800, "The Flash" wrote:
What type of / brand of mic are you using? I was not trying to make a very accurate measurement so I just used a cheap Panasonic WM-60AT price £2 http://rocky.digikey.com/WebLib/Pana...ata/WM-60A.pdf http://www.digikey.com/digihome.html |
#20
|
|||
|
|||
20hz to 20Khz , yea right!
On Sun, 23 Nov 2003 12:29:42 -0800, "The Flash" wrote:
What type of / brand of mic are you using? I was not trying to make a very accurate measurement so I just used a cheap Panasonic WM-60AT price £2 http://rocky.digikey.com/WebLib/Pana...ata/WM-60A.pdf http://www.digikey.com/digihome.html |
#21
|
|||
|
|||
20hz to 20Khz , yea right!
I have had no luck in measuring speaker response at low frequency's, I can
measure from ~60Hz to 20Khz with near 100% repeatability (How accurate is questionable) I have questioned a number of speaker builders and a couple of companies that 'tune' speakers the answers given on what they measure with and how the do the tests give serious rise to the claims at low frequency. Almost any speaker system sold today claims 20Hz to 20Kz response yet this is so far from the truth I cannot understand how they dare claim such figures. I have yet to find ANY speaker system using an 8 inch driver that has the ability to produce 40hz or lower frequencys as they all have fallen so far down in output level as to be useless. How do you measure the responese at 20Hz?, I have tested a few speakers and basically I cannot get accurate (repeatable) data at much below 60Hz, even using a borrowed shure KSM141 stereo pair in omnidirectional gives vague results ($3000 for the mic's!) I have come to the conclusion that you are really measuring air displacement at anything under 30Hz and a flat panel with a transducer is the only repeatable method of measuring the output, how one calibrates said device is open for discussion. (Oh one firm told me that they use a laser to measure the low frequency of their speakers, check this out for novel! They place a small piece of reflective foil on the base driver, and shine a laser beam on it, they then apply signal and measure via 'laser' the deflection, Also they place a passive radiator 1 meter infront of the driver unit and use the same method to measure its deflection. The apply a 'correction factor' and the produce the frequency response data (company builds very expensive car and home audio subs!) |
#22
|
|||
|
|||
20hz to 20Khz , yea right!
"Mark" wrote in message th.net... In article , says... I have had no luck in measuring speaker response at low frequency's, Then you may not be using the right tools. What tools do you use? First off, you should Never use a stereo mic (or any stereo set up) for measurement purposes. You are guaranteed to get inaccurate results. Secondly, the mic is only part of the equipment. What else are you using? Never? By using a stereo setup I can collect two data streams rather than one, I can compare the streams and quickly analyse microphone placement and any other abnormalities. I would dearly love to sample 8 or more soundpoints at realtime but this is beyond my gear. I have access to / a collection of equipment, some built by HP other stuff designed and manufactured for the BBC or others. All the HP gear uses HPIB which is not what is the most convenient, The A2D - D2A card in the PC is a much quicker and generates the same results (But much quicker) I have a number of amplifers, but typically use a Class A 2n3055 based 60 watt mono amp, It has acceptable characteristics for the type of measurement that I usually do, 20Hz to 20Khz on / off axis at 1w / 1m / 1khz. Microphones is the biggest issue as I have not yet found anything that I am really happy with. I can use the Shures, I have some clone shure that are very flat from 60hz to 20Khz and cost like $60 each! (vs 3 grand for the shures) (I can compensate in software for the low end droop or use a opamp based corrector that was build before I started with the PC based A2D card. I have a nice transducer (Probably from a bridge or Crane) that works from a few Hz. I don't compensate for impedance/frequency change as this would results that would never be seen in the real world, so a crappy crossover can make a good driver look bad. and a flat panel with a transducer is the only repeatable method of measuring the output, Balderdash. Now thats a technical response!, Ok what I have found is that it seem almost all manuafctures fiddle the figures to make them look good, here is a classic. http://www.aperionaudio.com/products...onse_graph.jpg From the specs page they claim a 60Hz to 20Khz response! Yet their graph shows the speaker is more than 10dB down in output at 60Hz from its output at ~200Hz and again at the high end its ouput looks to be ~8dB down at 20Khz from 15Khz Ok, Can some one tell me what mics / transducers I need to be using to get accurate low frequency measurements. Not just 'use your ears' as this is far too subjective! |
#23
|
|||
|
|||
20hz to 20Khz , yea right!
"Mark" wrote in message th.net... In article , says... I have had no luck in measuring speaker response at low frequency's, Then you may not be using the right tools. What tools do you use? First off, you should Never use a stereo mic (or any stereo set up) for measurement purposes. You are guaranteed to get inaccurate results. Secondly, the mic is only part of the equipment. What else are you using? Never? By using a stereo setup I can collect two data streams rather than one, I can compare the streams and quickly analyse microphone placement and any other abnormalities. I would dearly love to sample 8 or more soundpoints at realtime but this is beyond my gear. I have access to / a collection of equipment, some built by HP other stuff designed and manufactured for the BBC or others. All the HP gear uses HPIB which is not what is the most convenient, The A2D - D2A card in the PC is a much quicker and generates the same results (But much quicker) I have a number of amplifers, but typically use a Class A 2n3055 based 60 watt mono amp, It has acceptable characteristics for the type of measurement that I usually do, 20Hz to 20Khz on / off axis at 1w / 1m / 1khz. Microphones is the biggest issue as I have not yet found anything that I am really happy with. I can use the Shures, I have some clone shure that are very flat from 60hz to 20Khz and cost like $60 each! (vs 3 grand for the shures) (I can compensate in software for the low end droop or use a opamp based corrector that was build before I started with the PC based A2D card. I have a nice transducer (Probably from a bridge or Crane) that works from a few Hz. I don't compensate for impedance/frequency change as this would results that would never be seen in the real world, so a crappy crossover can make a good driver look bad. and a flat panel with a transducer is the only repeatable method of measuring the output, Balderdash. Now thats a technical response!, Ok what I have found is that it seem almost all manuafctures fiddle the figures to make them look good, here is a classic. http://www.aperionaudio.com/products...onse_graph.jpg From the specs page they claim a 60Hz to 20Khz response! Yet their graph shows the speaker is more than 10dB down in output at 60Hz from its output at ~200Hz and again at the high end its ouput looks to be ~8dB down at 20Khz from 15Khz Ok, Can some one tell me what mics / transducers I need to be using to get accurate low frequency measurements. Not just 'use your ears' as this is far too subjective! |
#24
|
|||
|
|||
20hz to 20Khz , yea right!
Uh, I used to test in a anechoic chamber at the local university but don't
now, I also tested other areas and found the following. You can test fine in you living room. Background noiselevel is typically 5OdB at home. You place a mat of acoustic foam on the floor, put yout mics up (1m away) place 4 more sheets of acoustic foam round the speaker and mic's and final sheet on top These knock 10dB off background noise and stop echo, run up 1 watt at 1khz gives about 90dB in most case, this is 50dB above background and you can run a sweep test and get results the same as in an anechoic chamber. (were not interested in its frequency response or efficency at 40 dB any way!) Again I think this is all smoke and mirrors stuff so that its 'too hard' to do yourself. None of us live inside a anechoic chamber and speakers sound awful when played inside one (no natural room reverberation) Alot of this smacks of the car makes 'economy mpg' by driving at 56Mph round an oval test circut. Something that we all do.... "Ethan Winer" ethanw at ethanwiner dot com wrote in message ... Flash, Besides all that Mark said, you can't measure loudspeakers by playing tones in a typical room in a typical house. If you take it outside, far away from ambient noises, you'll have half a shot at it. --Ethan |
#25
|
|||
|
|||
20hz to 20Khz , yea right!
Uh, I used to test in a anechoic chamber at the local university but don't
now, I also tested other areas and found the following. You can test fine in you living room. Background noiselevel is typically 5OdB at home. You place a mat of acoustic foam on the floor, put yout mics up (1m away) place 4 more sheets of acoustic foam round the speaker and mic's and final sheet on top These knock 10dB off background noise and stop echo, run up 1 watt at 1khz gives about 90dB in most case, this is 50dB above background and you can run a sweep test and get results the same as in an anechoic chamber. (were not interested in its frequency response or efficency at 40 dB any way!) Again I think this is all smoke and mirrors stuff so that its 'too hard' to do yourself. None of us live inside a anechoic chamber and speakers sound awful when played inside one (no natural room reverberation) Alot of this smacks of the car makes 'economy mpg' by driving at 56Mph round an oval test circut. Something that we all do.... "Ethan Winer" ethanw at ethanwiner dot com wrote in message ... Flash, Besides all that Mark said, you can't measure loudspeakers by playing tones in a typical room in a typical house. If you take it outside, far away from ambient noises, you'll have half a shot at it. --Ethan |
#26
|
|||
|
|||
20hz to 20Khz , yea right!
"The Flash" wrote in message ...
I have had no luck in measuring speaker response at low frequency's, I can measure from ~60Hz to 20Khz with near 100% repeatability (How accurate is questionable) You measure it with microphones and ancillary equipment that is up to the task. For myself, I have a number of Bruel & Kjaer, ACO, GR and pther microphones that have verified flat response to well below 20 Hz. Some of the B&K 1/2" capsules, for example, are within +-1/2 dB from approximately 3 Hz to 30 kHz and above. Can you give a recommend model of Bruel that you like? Bruel & Kjaer makes a wide variety of laboratory microphones that are intended for different purposes. They range in size from 1" diameter to 1/8", there are microphones intended for pressure, random incidence and such, carrier models for extremely low frequency and so on. I might usggest a visit to the B&K, ACO pacific and other websites for more information (q.v., bkhome.com). As to what Bruel & Kjaer microphone I "like," well, no insult intended, but it isn't a matter of what I "like," it's a matter of what is best suited for the task at hand based on technical considerations. I have a number of 4133 and 4134 that I use for common frequency response measurements. Please note that the price of these microphone is NOT cheap. You will find that by the time you are done with the impdeance converter/ preamplifier, powersupply and capsule, you're already up in the $2000 range. I have come to the conclusion that you are really measuring air displacement at anything under 30Hz and a flat panel with a transducer is the only repeatable method of measuring the output, One calibrates it by throwing it in the nearest landfill and going out an learning the proper ways of measuring acoustic phenomenon. You comments are most welcome but not vey helpful, I seem to be getting the feeling you are giving me the 'I've be doing it for decade and got really expensive gear, so my methods, results and opinions are gospel - do it my way or be burned at the stake as a heratic' Hold on there, bucko, YOU'RE the one who came riding into town yelling at everyone about how all this 20-20 kHz is bogus and declared the whole world of speaker measurement bogus and then declared a VERY well understood measurement paradigm as "novel." One starts to wonder if perhaps you are one of the 'Experts' that 'corrects' the measurments to what you 'know' is correct. Your attitude in your responses seems to show this blinded mentality. Sir, you make assumptions out of tyhin air. Never once did I say ANYTHING about correcting measurements, I talked about making measurements correctly. I suggest it's time you get down off your mighty steed and start learning instead of holding forth on topics about which you state quite clearly you know little about. (Oh one firm told me that they use a laser to measure the low frequency of their speakers, check this out for novel! They place a small piece of reflective foil on the base driver, and shine a laser beam on it, they then apply signal and measure via 'laser' the deflection, Well, gee golly, since it can be shown on physical first principles that the requirement for a constant sound pressure level (that would mean flat frequency response) from a piston radiator is simply a displacement which goes as the reciprocal of the square of frequency, then if you know the displacement, which you can measure with a pretty high degree of accuracy, then you can, over the piston range of the driver, DIRECTLY and UNAMBIGUOUSLY determine the total acoustic power as: Pa = p/(2 pi c) * (Sd w^2 X)^2 where p = density of air, typ. 1.18 kg/m^3 c = velocity of sound, typ 343 m/s Sd = emissive area of the diaphragm in m^2 w = radian frequency X = displacement of the diaphragm, in m. the method is HARDLY novel at all, as it is well understood and utilized in the field. If provides, for example, a means of measuring acoustical power output without the confounding innaccuracies of microphones, rooms and such, though the microphone innaccuracies are not a problem if you use proper microphones to begin with. I do undestand the theory, and I expect it would work well if the speaker was moving in piston motion. (An some of the car sub woofers with ridged aluminium cones would no doubt at low frequency) As ALL speaker cones do in the piston region of operation, below a frequency which is roughly determined when the wavelength reaches the circumference of the driver. For an 8" driver, that frequency is roughly 600 Hz, for example. However typical stereo speakers using either doped paper or pp cones won't, as you know the LF breakup happens quite early on these type of drivers due to the tradeoff of trying to give a wide response range with only 2 or 3 drives in most cases and stiff cone suspension. My humble suggestion, sir, is that you're experience in this area is not congruent with the rather large amount of data that is known and has been known for quite some time in this realm. The operation of drivers operating in the piston region has been very well studied, not by car audio or home audio speaker makers, most of whom, ESPECIALLY those in the car audio business, are clueless and work more on legenbd, rumor and unfounded assumption, but by the likes of MacClachlan, Beranek, Thiele, SMall, and many others. Some of these researchers did their work 60 years ago, and developed information that much of the speaker industry has yet to clue themselves in on. SHould you want a comprehensive set of references, I can start supplying such should you desire. More to your notion that it is "novel," you might want to modify that opinion when you discover the technique is described in nearly every text on acoustics. -Noted and yes I have seen it mention and was taught such things, but it was always theory and I had not heard of it done on audio speakers (however I do know it is done on building structures to measure characteristic) Well, again, you seem to be unfamiliar with the vast amount of literature on the topic. Indeed, far back in the 1970's, there is an extensive amount of literature in the technical press describing the characterisation of loudspeakers via such techniques. Anyone familiar with the theory is likely to be aware of these articles. I do know that laser scanning of drive to measure the breakup is done, but this was not what they were doing (So they said) Compare that to using recording microphones whose measurement capabilities are entirely unknown, in a room of unknown characteristics, using unknown poorly calibrated and undoubtedly poorly controlled techniques by someone who has little or know experience in measurement and acoustics... I'd not bet good money on getting ANY reliable data out of the latter. Well I have to say getting reliable data from 'experts' is not very successful! Not when you come charging in challenging a tpoic with which you are unfamiliar. You made some smeasurements and you ASSUMED without ANY supporting evidence that your methods have any validity. The apparently very narrow topic of measurement of acoustical phenomenon is, in fact, a very large, complex and quite fascinating one. You've not even touched on 1% of it. It's not something you're going to learn about via an Usenet article or two. You've not even touched on the issues of boundary conditions and nearfield vs farfield and diffraction effects, an entire sub-topic on suitable stimuli, of MLS vs impulse vs gated sine vs swept sine vs narrow band noise vs wide band noise vs averaged narrow-band analysis and so one and so forth. None of that. Despite that, you seem to have the attitude that you have just discovered some vast conspiracy or fraud, indeed the very title of your post states that. Yet, you clearly state that you know little or nothing about the basic principles involved. You claim to "understand the theory" that in the pistonic region of operation, there is a direct causal link between driver excursion, frequency and sound pressure level. If you are "familiar" with it as you claim, you coudn't possibly find the method "novel." It's a fundamental property that is taight in the very early stages of acoustical principles. All due respect, you don't even use the lexicon of the subject in a way that suggests you have any familiarity with the topic. You want some information? Fine, ask the questions. Don't come charging in like some expert, which you are not. The experts here are happy to answer your questions. Accusations such as "20hz to 20Khz, yea right!" are going to be dismissed as uninformed rantings that they are. |
#27
|
|||
|
|||
20hz to 20Khz , yea right!
"The Flash" wrote in message ...
I have had no luck in measuring speaker response at low frequency's, I can measure from ~60Hz to 20Khz with near 100% repeatability (How accurate is questionable) You measure it with microphones and ancillary equipment that is up to the task. For myself, I have a number of Bruel & Kjaer, ACO, GR and pther microphones that have verified flat response to well below 20 Hz. Some of the B&K 1/2" capsules, for example, are within +-1/2 dB from approximately 3 Hz to 30 kHz and above. Can you give a recommend model of Bruel that you like? Bruel & Kjaer makes a wide variety of laboratory microphones that are intended for different purposes. They range in size from 1" diameter to 1/8", there are microphones intended for pressure, random incidence and such, carrier models for extremely low frequency and so on. I might usggest a visit to the B&K, ACO pacific and other websites for more information (q.v., bkhome.com). As to what Bruel & Kjaer microphone I "like," well, no insult intended, but it isn't a matter of what I "like," it's a matter of what is best suited for the task at hand based on technical considerations. I have a number of 4133 and 4134 that I use for common frequency response measurements. Please note that the price of these microphone is NOT cheap. You will find that by the time you are done with the impdeance converter/ preamplifier, powersupply and capsule, you're already up in the $2000 range. I have come to the conclusion that you are really measuring air displacement at anything under 30Hz and a flat panel with a transducer is the only repeatable method of measuring the output, One calibrates it by throwing it in the nearest landfill and going out an learning the proper ways of measuring acoustic phenomenon. You comments are most welcome but not vey helpful, I seem to be getting the feeling you are giving me the 'I've be doing it for decade and got really expensive gear, so my methods, results and opinions are gospel - do it my way or be burned at the stake as a heratic' Hold on there, bucko, YOU'RE the one who came riding into town yelling at everyone about how all this 20-20 kHz is bogus and declared the whole world of speaker measurement bogus and then declared a VERY well understood measurement paradigm as "novel." One starts to wonder if perhaps you are one of the 'Experts' that 'corrects' the measurments to what you 'know' is correct. Your attitude in your responses seems to show this blinded mentality. Sir, you make assumptions out of tyhin air. Never once did I say ANYTHING about correcting measurements, I talked about making measurements correctly. I suggest it's time you get down off your mighty steed and start learning instead of holding forth on topics about which you state quite clearly you know little about. (Oh one firm told me that they use a laser to measure the low frequency of their speakers, check this out for novel! They place a small piece of reflective foil on the base driver, and shine a laser beam on it, they then apply signal and measure via 'laser' the deflection, Well, gee golly, since it can be shown on physical first principles that the requirement for a constant sound pressure level (that would mean flat frequency response) from a piston radiator is simply a displacement which goes as the reciprocal of the square of frequency, then if you know the displacement, which you can measure with a pretty high degree of accuracy, then you can, over the piston range of the driver, DIRECTLY and UNAMBIGUOUSLY determine the total acoustic power as: Pa = p/(2 pi c) * (Sd w^2 X)^2 where p = density of air, typ. 1.18 kg/m^3 c = velocity of sound, typ 343 m/s Sd = emissive area of the diaphragm in m^2 w = radian frequency X = displacement of the diaphragm, in m. the method is HARDLY novel at all, as it is well understood and utilized in the field. If provides, for example, a means of measuring acoustical power output without the confounding innaccuracies of microphones, rooms and such, though the microphone innaccuracies are not a problem if you use proper microphones to begin with. I do undestand the theory, and I expect it would work well if the speaker was moving in piston motion. (An some of the car sub woofers with ridged aluminium cones would no doubt at low frequency) As ALL speaker cones do in the piston region of operation, below a frequency which is roughly determined when the wavelength reaches the circumference of the driver. For an 8" driver, that frequency is roughly 600 Hz, for example. However typical stereo speakers using either doped paper or pp cones won't, as you know the LF breakup happens quite early on these type of drivers due to the tradeoff of trying to give a wide response range with only 2 or 3 drives in most cases and stiff cone suspension. My humble suggestion, sir, is that you're experience in this area is not congruent with the rather large amount of data that is known and has been known for quite some time in this realm. The operation of drivers operating in the piston region has been very well studied, not by car audio or home audio speaker makers, most of whom, ESPECIALLY those in the car audio business, are clueless and work more on legenbd, rumor and unfounded assumption, but by the likes of MacClachlan, Beranek, Thiele, SMall, and many others. Some of these researchers did their work 60 years ago, and developed information that much of the speaker industry has yet to clue themselves in on. SHould you want a comprehensive set of references, I can start supplying such should you desire. More to your notion that it is "novel," you might want to modify that opinion when you discover the technique is described in nearly every text on acoustics. -Noted and yes I have seen it mention and was taught such things, but it was always theory and I had not heard of it done on audio speakers (however I do know it is done on building structures to measure characteristic) Well, again, you seem to be unfamiliar with the vast amount of literature on the topic. Indeed, far back in the 1970's, there is an extensive amount of literature in the technical press describing the characterisation of loudspeakers via such techniques. Anyone familiar with the theory is likely to be aware of these articles. I do know that laser scanning of drive to measure the breakup is done, but this was not what they were doing (So they said) Compare that to using recording microphones whose measurement capabilities are entirely unknown, in a room of unknown characteristics, using unknown poorly calibrated and undoubtedly poorly controlled techniques by someone who has little or know experience in measurement and acoustics... I'd not bet good money on getting ANY reliable data out of the latter. Well I have to say getting reliable data from 'experts' is not very successful! Not when you come charging in challenging a tpoic with which you are unfamiliar. You made some smeasurements and you ASSUMED without ANY supporting evidence that your methods have any validity. The apparently very narrow topic of measurement of acoustical phenomenon is, in fact, a very large, complex and quite fascinating one. You've not even touched on 1% of it. It's not something you're going to learn about via an Usenet article or two. You've not even touched on the issues of boundary conditions and nearfield vs farfield and diffraction effects, an entire sub-topic on suitable stimuli, of MLS vs impulse vs gated sine vs swept sine vs narrow band noise vs wide band noise vs averaged narrow-band analysis and so one and so forth. None of that. Despite that, you seem to have the attitude that you have just discovered some vast conspiracy or fraud, indeed the very title of your post states that. Yet, you clearly state that you know little or nothing about the basic principles involved. You claim to "understand the theory" that in the pistonic region of operation, there is a direct causal link between driver excursion, frequency and sound pressure level. If you are "familiar" with it as you claim, you coudn't possibly find the method "novel." It's a fundamental property that is taight in the very early stages of acoustical principles. All due respect, you don't even use the lexicon of the subject in a way that suggests you have any familiarity with the topic. You want some information? Fine, ask the questions. Don't come charging in like some expert, which you are not. The experts here are happy to answer your questions. Accusations such as "20hz to 20Khz, yea right!" are going to be dismissed as uninformed rantings that they are. |
#28
|
|||
|
|||
20hz to 20Khz , yea right!
"Goofball_star_dot_etal" wrote:
I was not trying to make a very accurate measurement so I just used a cheap Panasonic WM-60AT price £2 ---------------------------------------- That's almost exactly what Behringer uses in ECM8000... |
#29
|
|||
|
|||
20hz to 20Khz , yea right!
"Goofball_star_dot_etal" wrote:
I was not trying to make a very accurate measurement so I just used a cheap Panasonic WM-60AT price £2 ---------------------------------------- That's almost exactly what Behringer uses in ECM8000... |
#30
|
|||
|
|||
20hz to 20Khz , yea right!
Flash,
Tony hit the salient high points, and I'll add this: I think this is all smoke and mirrors stuff so that its 'too hard' to do yourself. Not smoke and mirrors, acoustic interference. That's the real issue. And that's why even 1/12th octave pink noise tests are useless to obtain a true response within a room. None of us live inside a anechoic chamber Yes, but that's an entirely different issue. You said your stated goal is to measure the *speaker's* response. Well, if you meausre it in a room you're measuring far more of the *room's* response. --Ethan |
#31
|
|||
|
|||
20hz to 20Khz , yea right!
Flash,
Tony hit the salient high points, and I'll add this: I think this is all smoke and mirrors stuff so that its 'too hard' to do yourself. Not smoke and mirrors, acoustic interference. That's the real issue. And that's why even 1/12th octave pink noise tests are useless to obtain a true response within a room. None of us live inside a anechoic chamber Yes, but that's an entirely different issue. You said your stated goal is to measure the *speaker's* response. Well, if you meausre it in a room you're measuring far more of the *room's* response. --Ethan |
#32
|
|||
|
|||
20hz to 20Khz , yea right!
"The Flash" wrote in message ... I have had no luck in measuring speaker response at low frequency's, I can measure from ~60Hz to 20Khz with near 100% repeatability (How accurate is questionable) You measure it with microphones and ancillary equipment that is up to the task. For myself, I have a number of Bruel & Kjaer, ACO, GR and pther microphones that have verified flat response to well below 20 Hz. Some of the B&K 1/2" capsules, for example, are within +-1/2 dB from approximately 3 Hz to 30 kHz and above. Can you give a recommend model of Bruel that you like? Summerised I have tested in a number of different situation and with a collection of mics and such. what I have found is that it is easy to get a mike with a flat response from ~60Hz to ~20Kz, it seems that below this is where a specialist product is required. The remainder of the measurement and analysis chain has similar properties: the primary measurement chain is DC coupled, for example. Secondly, the size of the venue required for accurate measurements is inversely proportional to the frequency you need to measure. Even using techniques such as gated or windowed measurement, the distance to the first reflection surface is a prime determinant of how low you can measure. You want to measure 20 Hz accurately? Then you need to find a room where the distance between the speaker/microphone and the NEAREST surface is a minimum of 25 feet. I have tested a few speakers and basically I cannot get accurate (repeatable) data at much below 60Hz, even using a borrowed shure KSM141 stereo pair in omnidirectional gives vague results ($3000 for the mic's!) $3000 for microphones that were NEVER designed to be used as measurement microphones, ESPECIALLY at low frequencies. These are recording microphones, NOT measurement microphones. I have come to the conclusion that you are really measuring air displacement at anything under 30Hz and a flat panel with a transducer is the only repeatable method of measuring the output, That may be the conclusion you came to, but that conclusion just happens to be quite wrong. The physical stimulus that the ear responds to as sound are periodic pressure variations of a sufficient amplitude and within certain frequency limits. That's it. As long as a device can detect these pressure variations, it can be used to measure sound. The problem with you big flat panel method is that it assumes, quite incorrectly, that the imnpinging waves are planar: unless you are VERY far away from the speaker, such the wavefronts are no longer spherical, it isn't going to work. The smaller the diaphgragm of the microphone, the less it is affected by such a problem. That's one reason why measurement microphones have very small diaphragms: they are essentially point transducers over a wide range of frequencies. how one calibrates said device is open for discussion. snip good stuff from Dick I do undestand the theory, and I expect it would work well if the speaker was moving in piston motion. (An some of the car sub woofers with ridged aluminium cones would no doubt at low frequency) However typical stereo speakers using either doped paper or pp cones won't, as you know the LF breakup happens quite early on these type of drivers due to the tradeoff of trying to give a wide response range with only 2 or 3 drives in most cases and stiff cone suspension. more snip Compare that to using recording microphones whose measurement capabilities are entirely unknown, in a room of unknown characteristics, using unknown poorly calibrated and undoubtedly poorly controlled techniques by someone who has little or know experience in measurement and acoustics... I'd not bet good money on getting ANY reliable data out of the latter. Well I have to say getting reliable data from 'experts' is not very successful! I think Dick gave you good information. The B&K microphones are very expensive. Someone earlier posted a suggestion for a Panasonic capsule. These are available calibrated. The Behringer ECM8000 is more expensive, but still relatively cheap (£30). Either solution is far better than you have been using. Dick mentions the problem of reflections when doing in-room response. At low frequencies this can be dealt with using near field techniques, valid up to where the diaphragm reaches its piston limit. This is often several hundred Hz, allowing you to "stitch together" responses from different regions. Your assertion that it is not possible to get low frequencies using an 8 inch driver turns out not to be correct. I have a pair where the LF is done using 8 inch drivers in a bandpass enclosure. Those have a measured response which is 1dB down at 30Hz, and an overall response at 3dB down of 27Hz to 90Hz. Regards Ian |
#33
|
|||
|
|||
20hz to 20Khz , yea right!
"The Flash" wrote in message ... I have had no luck in measuring speaker response at low frequency's, I can measure from ~60Hz to 20Khz with near 100% repeatability (How accurate is questionable) You measure it with microphones and ancillary equipment that is up to the task. For myself, I have a number of Bruel & Kjaer, ACO, GR and pther microphones that have verified flat response to well below 20 Hz. Some of the B&K 1/2" capsules, for example, are within +-1/2 dB from approximately 3 Hz to 30 kHz and above. Can you give a recommend model of Bruel that you like? Summerised I have tested in a number of different situation and with a collection of mics and such. what I have found is that it is easy to get a mike with a flat response from ~60Hz to ~20Kz, it seems that below this is where a specialist product is required. The remainder of the measurement and analysis chain has similar properties: the primary measurement chain is DC coupled, for example. Secondly, the size of the venue required for accurate measurements is inversely proportional to the frequency you need to measure. Even using techniques such as gated or windowed measurement, the distance to the first reflection surface is a prime determinant of how low you can measure. You want to measure 20 Hz accurately? Then you need to find a room where the distance between the speaker/microphone and the NEAREST surface is a minimum of 25 feet. I have tested a few speakers and basically I cannot get accurate (repeatable) data at much below 60Hz, even using a borrowed shure KSM141 stereo pair in omnidirectional gives vague results ($3000 for the mic's!) $3000 for microphones that were NEVER designed to be used as measurement microphones, ESPECIALLY at low frequencies. These are recording microphones, NOT measurement microphones. I have come to the conclusion that you are really measuring air displacement at anything under 30Hz and a flat panel with a transducer is the only repeatable method of measuring the output, That may be the conclusion you came to, but that conclusion just happens to be quite wrong. The physical stimulus that the ear responds to as sound are periodic pressure variations of a sufficient amplitude and within certain frequency limits. That's it. As long as a device can detect these pressure variations, it can be used to measure sound. The problem with you big flat panel method is that it assumes, quite incorrectly, that the imnpinging waves are planar: unless you are VERY far away from the speaker, such the wavefronts are no longer spherical, it isn't going to work. The smaller the diaphgragm of the microphone, the less it is affected by such a problem. That's one reason why measurement microphones have very small diaphragms: they are essentially point transducers over a wide range of frequencies. how one calibrates said device is open for discussion. snip good stuff from Dick I do undestand the theory, and I expect it would work well if the speaker was moving in piston motion. (An some of the car sub woofers with ridged aluminium cones would no doubt at low frequency) However typical stereo speakers using either doped paper or pp cones won't, as you know the LF breakup happens quite early on these type of drivers due to the tradeoff of trying to give a wide response range with only 2 or 3 drives in most cases and stiff cone suspension. more snip Compare that to using recording microphones whose measurement capabilities are entirely unknown, in a room of unknown characteristics, using unknown poorly calibrated and undoubtedly poorly controlled techniques by someone who has little or know experience in measurement and acoustics... I'd not bet good money on getting ANY reliable data out of the latter. Well I have to say getting reliable data from 'experts' is not very successful! I think Dick gave you good information. The B&K microphones are very expensive. Someone earlier posted a suggestion for a Panasonic capsule. These are available calibrated. The Behringer ECM8000 is more expensive, but still relatively cheap (£30). Either solution is far better than you have been using. Dick mentions the problem of reflections when doing in-room response. At low frequencies this can be dealt with using near field techniques, valid up to where the diaphragm reaches its piston limit. This is often several hundred Hz, allowing you to "stitch together" responses from different regions. Your assertion that it is not possible to get low frequencies using an 8 inch driver turns out not to be correct. I have a pair where the LF is done using 8 inch drivers in a bandpass enclosure. Those have a measured response which is 1dB down at 30Hz, and an overall response at 3dB down of 27Hz to 90Hz. Regards Ian |
#34
|
|||
|
|||
20hz to 20Khz , yea right!
"The Flash" wrote in message ... Uh, I used to test in a anechoic chamber at the local university but don't now, I also tested other areas and found the following. You can test fine in you living room. Background noiselevel is typically 5OdB at home. Noisae isn't the problem . Speaker measurements in rooms are flawed becuse of the effects of standing waves. |
#35
|
|||
|
|||
20hz to 20Khz , yea right!
"The Flash" wrote in message ... Uh, I used to test in a anechoic chamber at the local university but don't now, I also tested other areas and found the following. You can test fine in you living room. Background noiselevel is typically 5OdB at home. Noisae isn't the problem . Speaker measurements in rooms are flawed becuse of the effects of standing waves. |
#36
|
|||
|
|||
20hz to 20Khz , yea right!
On Sun, 23 Nov 2003 09:11:31 -0500, "Victor"
wrote: "Goofball_star_dot_etal" wrote: I was not trying to make a very accurate measurement so I just used a cheap Panasonic WM-60AT price £2 ---------------------------------------- That's almost exactly what Behringer uses in ECM8000... I guess I am just lucky when it comes to measurements and boats. . . |
#37
|
|||
|
|||
20hz to 20Khz , yea right!
On Sun, 23 Nov 2003 09:11:31 -0500, "Victor"
wrote: "Goofball_star_dot_etal" wrote: I was not trying to make a very accurate measurement so I just used a cheap Panasonic WM-60AT price £2 ---------------------------------------- That's almost exactly what Behringer uses in ECM8000... I guess I am just lucky when it comes to measurements and boats. . . |
#38
|
|||
|
|||
20hz to 20Khz , yea right!
I thought up my own method for eliminating the effect of the room on
bass measurement (although, no doubt it has been done before). The main feature is to place the (pressure) microphone within the speaker and to compensate by 12 dB/oct. Normally I use a MLS and filter out higher frequencies, say above 100Hz, with a brick wall FIR filter using Coooledit. The 12 dB/oct compensation is also done in a similar way, either to the input MLS or to the output recording. This sort of pre-filtering can give a large increase to the signal to noise of the meaasurement. There must be some restrictions on the accuracy of this method but the only one I can think off at the moment is that the wavelength must be large compared to the internal dimensions of the speaker. The meaasurement includes the effect of any port and of the enclosure flexing. There is probably an assumption that the air is compressed adiabatically. The pressures involved are, of course, small if the mic is not to be overloaded. What type of / brand of mic are you using? |
#39
|
|||
|
|||
20hz to 20Khz , yea right!
I thought up my own method for eliminating the effect of the room on
bass measurement (although, no doubt it has been done before). The main feature is to place the (pressure) microphone within the speaker and to compensate by 12 dB/oct. Normally I use a MLS and filter out higher frequencies, say above 100Hz, with a brick wall FIR filter using Coooledit. The 12 dB/oct compensation is also done in a similar way, either to the input MLS or to the output recording. This sort of pre-filtering can give a large increase to the signal to noise of the meaasurement. There must be some restrictions on the accuracy of this method but the only one I can think off at the moment is that the wavelength must be large compared to the internal dimensions of the speaker. The meaasurement includes the effect of any port and of the enclosure flexing. There is probably an assumption that the air is compressed adiabatically. The pressures involved are, of course, small if the mic is not to be overloaded. What type of / brand of mic are you using? |
#40
|
|||
|
|||
20hz to 20Khz , yea right!
I have had no luck in measuring speaker response at low frequency's, I can measure from ~60Hz to 20Khz with near 100% repeatability (How accurate is questionable) You measure it with microphones and ancillary equipment that is up to the task. For myself, I have a number of Bruel & Kjaer, ACO, GR and pther microphones that have verified flat response to well below 20 Hz. Some of the B&K 1/2" capsules, for example, are within +-1/2 dB from approximately 3 Hz to 30 kHz and above. Can you give a recommend model of Bruel that you like? Summerised I have tested in a number of different situation and with a collection of mics and such. what I have found is that it is easy to get a mike with a flat response from ~60Hz to ~20Kz, it seems that below this is where a specialist product is required. The remainder of the measurement and analysis chain has similar properties: the primary measurement chain is DC coupled, for example. Secondly, the size of the venue required for accurate measurements is inversely proportional to the frequency you need to measure. Even using techniques such as gated or windowed measurement, the distance to the first reflection surface is a prime determinant of how low you can measure. You want to measure 20 Hz accurately? Then you need to find a room where the distance between the speaker/microphone and the NEAREST surface is a minimum of 25 feet. I have tested a few speakers and basically I cannot get accurate (repeatable) data at much below 60Hz, even using a borrowed shure KSM141 stereo pair in omnidirectional gives vague results ($3000 for the mic's!) $3000 for microphones that were NEVER designed to be used as measurement microphones, ESPECIALLY at low frequencies. These are recording microphones, NOT measurement microphones. I have come to the conclusion that you are really measuring air displacement at anything under 30Hz and a flat panel with a transducer is the only repeatable method of measuring the output, That may be the conclusion you came to, but that conclusion just happens to be quite wrong. The physical stimulus that the ear responds to as sound are periodic pressure variations of a sufficient amplitude and within certain frequency limits. That's it. As long as a device can detect these pressure variations, it can be used to measure sound. The problem with you big flat panel method is that it assumes, quite incorrectly, that the imnpinging waves are planar: unless you are VERY far away from the speaker, such the wavefronts are no longer spherical, it isn't going to work. The smaller the diaphgragm of the microphone, the less it is affected by such a problem. That's one reason why measurement microphones have very small diaphragms: they are essentially point transducers over a wide range of frequencies. how one calibrates said device is open for discussion. One calibrates it by throwing it in the nearest landfill and going out an learning the proper ways of measuring acoustic phenomenon. You comments are most welcome but not vey helpful, I seem to be getting the feeling you are giving me the 'I've be doing it for decade and got really expensive gear, so my methods, results and opinions are gospel - do it my way or be burned at the stake as a heratic' One starts to wonder if perhaps you are one of the 'Experts' that 'corrects' the measurments to what you 'know' is correct. Your attitude in your responses seems to show this blinded mentality. (Oh one firm told me that they use a laser to measure the low frequency of their speakers, check this out for novel! They place a small piece of reflective foil on the base driver, and shine a laser beam on it, they then apply signal and measure via 'laser' the deflection, Well, gee golly, since it can be shown on physical first principles that the requirement for a constant sound pressure level (that would mean flat frequency response) from a piston radiator is simply a displacement which goes as the reciprocal of the square of frequency, then if you know the displacement, which you can measure with a pretty high degree of accuracy, then you can, over the piston range of the driver, DIRECTLY and UNAMBIGUOUSLY determine the total acoustic power as: Pa = p/(2 pi c) * (Sd w^2 X)^2 where p = density of air, typ. 1.18 kg/m^3 c = velocity of sound, typ 343 m/s Sd = emissive area of the diaphragm in m^2 w = radian frequency X = displacement of the diaphragm, in m. the method is HARDLY novel at all, as it is well understood and utilized in the field. If provides, for example, a means of measuring acoustical power output without the confounding innaccuracies of microphones, rooms and such, though the microphone innaccuracies are not a problem if you use proper microphones to begin with. I do undestand the theory, and I expect it would work well if the speaker was moving in piston motion. (An some of the car sub woofers with ridged aluminium cones would no doubt at low frequency) However typical stereo speakers using either doped paper or pp cones won't, as you know the LF breakup happens quite early on these type of drivers due to the tradeoff of trying to give a wide response range with only 2 or 3 drives in most cases and stiff cone suspension. More to your notion that it is "novel," you might want to modify that opinion when you discover the technique is described in nearly every text on acoustics. -Noted and yes I have seen it mention and was taught such things, but it was always theory and I had not heard of it done on audio speakers (however I do know it is done on building structures to measure characteristic) I do know that laser scanning of drive to measure the breakup is done, but this was not what they were doing (So they said) Compare that to using recording microphones whose measurement capabilities are entirely unknown, in a room of unknown characteristics, using unknown poorly calibrated and undoubtedly poorly controlled techniques by someone who has little or know experience in measurement and acoustics... I'd not bet good money on getting ANY reliable data out of the latter. Well I have to say getting reliable data from 'experts' is not very successful! |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
When did home theater take over? | Audio Opinions | |||
Learning 30 tones from 20hz to 20khz | Pro Audio |