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Loudspeaker testing hardware?
Dear RATs,
a question posed by Mr. Turner about my new LS is now puzzling me: what kind of stuff is needed to test a loudspeaker? Is it possible to do it with some VERY cheap microphone and the sound card included in any PC? I don't want to spend a lot of $ in Bruel&Kjaer professional testing equipments.... Ciao Fabio |
#3
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Fabio Berutti wrote: Dear RATs, a question posed by Mr. Turner about my new LS is now puzzling me: what kind of stuff is needed to test a loudspeaker? Is it possible to do it with some VERY cheap microphone and the sound card included in any PC? I don't want to spend a lot of $ in Bruel&Kjaer professional testing equipments.... Ciao Fabio I am presently using an electret mic insert purchased from Hi Q products in Melbourne for aud $1.20 each. I bought 10, and all gave the same flat response as per their spec sheets for that model of electret mic. I fitted the insert into the end of a 12 mm copper pipe 300 mm long full of wool. Its clamped to a mic stand. The response is only flat from about 20 Hz to 8 kHz, and then rolls off at 6 dB / octave. So I placed an RC emphasis circuit in the mic amp, and made the recovered signal flat to 15 kHz, and after measuring many speakers, it must be about right enough to tell me if there are drastic problems. The test signal is pink noise, or white noise eq'd by 3 dB / octave across the band. My home brew tunable 3 decade range bandpass filter for measuring bands has a Q of about 12 at any F chosen, so if centred on 1 kHz, the poles are at 41 Hz each side of 1 kHz. The filter and noise source and mic amp are in the one box and use opamps to achieve what I want. There are calibrated mikes out there which may cost $100, and would probably be better, as would the use of a PC and program to analyse AF, 'Speclab' comes to mind. I do it the old fashioned way with a book and pencil with several takes in the room. These can be averaged, and a resultant response line drawn. The PC will be a lot faster. The results always seem to co-relate to what I hear. Drivers can be tested separately, then together, and the response of each driver plotted. When the phase of a driver is reversed, the results show up in the response. Its real shoe string budget stuff what I have done, but its a lot better than nothing at all. I have my eye on better gear, but the bills keep me poor, and I have to save up more. Even with better gear, the room effects still give +/- 3 dB graph undulations. Don't ever test with pure sine waves; you get a crazy +/- 12 dB variation with maybe 50 peaks and troughs, and a totally meaningless outcome. The more carpets and cushions, large bags of chopped foam in the room, the flatter your measurements will be. And the better the music will be. Its not as good as an anechoic chamber. If most music cannot be improved by adjusting the amplifier tone controls, then the speakers might be about right. I said might be. The pink noise room test will find the harder to hear other problems. Patrick Turner. |
#4
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"François Yves Le Gal" wrote: On Tue, 15 Feb 2005 13:49:01 GMT, "Fabio Berutti" wrote: Is it possible to do it with some VERY cheap microphone and the sound card included in any PC? You may consider using an affordable electret testing microphone, such as the Behringer ECM8000 together with a suitable preamp and phantom power (you can consider using a small mixer from Behringer). ECM8000 http://www.behringer.com/ECM8000/index.cfm?lang=ENG If you want to go for real cheap, you may build your own measuring mike from a Panasonic capsule. Most soundcards are OK. On the software side, you may use Audua Speaker Workshop (freeware), which is an excellent entry level solution. http://www.audua.com/ I downloaded this but I cannot get it to set itself up. It tries to use acrobat to open it, then comes up with a notice "document does not start with '%PDF' ". Another dead end? Patrick Turner. |
#5
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Patrick :
I got the same crazy peaks and troughs you mention when using sine waves to test speakers. I even got big fluctuations in readings if I stood within a few feet of the speaker and moved my arms around. I thought these were fluctuations caused by the room, so I gave up doing measurements. So your pink noise and band pass filter method interests me. Do you feed the pink noise through the filter then to the speaker, and measure the result ? or do you put the filter on the output of the mic ? By the way, since the original question was about equipment, what I use for a microphone is the analogue output from a RadioShack 33-2055 digital sound level meter. It has its own amplifier etc. Just connect an audio voltmeter to the output. There is a mod on the web somewhere showing how to extend the lower frequency response and remove the weighting to get a uniform frequency response. Thanks "Patrick Turner" wrote in message ... Fabio Berutti wrote: Dear RATs, a question posed by Mr. Turner about my new LS is now puzzling me: what kind of stuff is needed to test a loudspeaker? Is it possible to do it with some VERY cheap microphone and the sound card included in any PC? I don't want to spend a lot of $ in Bruel&Kjaer professional testing equipments.... Ciao Fabio I am presently using an electret mic insert purchased from Hi Q products in Melbourne for aud $1.20 each. I bought 10, and all gave the same flat response as per their spec sheets for that model of electret mic. I fitted the insert into the end of a 12 mm copper pipe 300 mm long full of wool. Its clamped to a mic stand. The response is only flat from about 20 Hz to 8 kHz, and then rolls off at 6 dB / octave. So I placed an RC emphasis circuit in the mic amp, and made the recovered signal flat to 15 kHz, and after measuring many speakers, it must be about right enough to tell me if there are drastic problems. The test signal is pink noise, or white noise eq'd by 3 dB / octave across the band. My home brew tunable 3 decade range bandpass filter for measuring bands has a Q of about 12 at any F chosen, so if centred on 1 kHz, the poles are at 41 Hz each side of 1 kHz. The filter and noise source and mic amp are in the one box and use opamps to achieve what I want. There are calibrated mikes out there which may cost $100, and would probably be better, as would the use of a PC and program to analyse AF, 'Speclab' comes to mind. I do it the old fashioned way with a book and pencil with several takes in the room. These can be averaged, and a resultant response line drawn. The PC will be a lot faster. The results always seem to co-relate to what I hear. Drivers can be tested separately, then together, and the response of each driver plotted. When the phase of a driver is reversed, the results show up in the response. Its real shoe string budget stuff what I have done, but its a lot better than nothing at all. I have my eye on better gear, but the bills keep me poor, and I have to save up more. Even with better gear, the room effects still give +/- 3 dB graph undulations. Don't ever test with pure sine waves; you get a crazy +/- 12 dB variation with maybe 50 peaks and troughs, and a totally meaningless outcome. The more carpets and cushions, large bags of chopped foam in the room, the flatter your measurements will be. And the better the music will be. Its not as good as an anechoic chamber. If most music cannot be improved by adjusting the amplifier tone controls, then the speakers might be about right. I said might be. The pink noise room test will find the harder to hear other problems. Patrick Turner. |
#6
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"François Yves Le Gal" wrote in message ... : On Tue, 15 Feb 2005 13:49:01 GMT, "Fabio Berutti" : wrote: : : Is it possible to do it with some : VERY cheap microphone and the sound card included in any PC? : : You may consider using an affordable electret testing microphone, such as : the Behringer ECM8000 together with a suitable preamp and phantom power (you : can consider using a small mixer from Behringer). : : ECM8000 http://www.behringer.com/ECM8000/index.cfm?lang=ENG : : If you want to go for real cheap, you may build your own measuring mike from : a Panasonic capsule. : : Most soundcards are OK. : : On the software side, you may use Audua Speaker Workshop (freeware), which : is an excellent entry level solution. : : http://www.audua.com/ Also, there are offers combining MLSSA and some fair quality microphones with calibrated response curves - just google around in eu :-) Rudy |
#7
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"Fabio Berutti" wrote in message ... | Dear RATs, | | a question posed by Mr. Turner about my new LS is now puzzling me: what kind | of stuff is needed to test a loudspeaker? Is it possible to do it with some | VERY cheap microphone and the sound card included in any PC? I don't want | to spend a lot of $ in Bruel&Kjaer professional testing equipments.... | | Ciao | | Fabio | | do you mind few MB in your mail box? -- -- .................................................. ........................ Choky Prodanovic Aleksandar YU "don't use force, "don't use force, use a larger hammer" use a larger tube - Choky and IST" - ZM .................................................. ........................... |
#8
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"François Yves Le Gal" wrote in message ... : On Tue, 15 Feb 2005 21:50:04 +0100, "Ruud Broens" : wrote: : : Also, there are offers combining MLSSA and some fair quality microphones : with calibrated response curves - just google around in eu :-) : : A solution around MLSSA costs more than 5,000 EUR... : Ok, cheaper solution: http://www.speaker-online.de/messtechnik/ most expensive solution there, with the MBC550, preamp, software EURO 498,- Rudy |
#9
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in article , François Yves Le Gal
at wrote on 2/15/05 4:32 PM: On Tue, 15 Feb 2005 21:50:04 +0100, "Ruud Broens" wrote: Also, there are offers combining MLSSA and some fair quality microphones with calibrated response curves - just google around in eu :-) A solution around MLSSA costs more than 5,000 EUR... Hence my assertion that it is the "gold standard." ;-) Jon |
#10
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"François Yves Le Gal" wrote in message ... : On Tue, 15 Feb 2005 22:41:30 +0100, "Ruud Broens" : wrote: : : most expensive solution there, with the MBC550, preamp, software EURO 498,- : : That's much more in the hobbyist league. : :-) : Well, it depends - take for instance us streetcar racing modded cars, owners there may spend 30.000 to 50.000 USD - yet the car may be impounded after a single 'race'... then all of a sudden audio seems like a very cheap hobby :-))) Rudy |
#11
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On Tue, 15 Feb 2005 13:49:01 GMT, "Fabio Berutti"
wrote: a question posed by Mr. Turner about my new LS is now puzzling me: what kind of stuff is needed to test a loudspeaker? Is it possible to do it with some VERY cheap microphone and the sound card included in any PC? I don't want to spend a lot of $ in Bruel&Kjaer professional testing equipments.... I can recommend WinAIRR, available from AudioXpress in the US for about $50. Others have mentioned several suitable microphones. Speaker testing at home is done in two bands; low frequencies are tested with a microphone in the very-near-field. Above a few hundred Hz, time-sampled measurements, using impulses, or noise that's shaped to have the mathematical characteristics of impulses, are manipulated by computer program to derive all kinds of cool info. Good fortune, Chris Hornbeck |
#12
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"François Yves Le Gal" wrote: On Wed, 16 Feb 2005 01:51:53 +1100, Patrick Turner wrote: Another dead end? The program is distributed as a .zip archive. If your PC tries to launch Acrobat, then you've got a serious configuration problem... Have you got Winzip or similar installed ? No, so do I try to download Winzip? Patrick Turner. |
#13
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Robert McLean wrote: Patrick : I got the same crazy peaks and troughs you mention when using sine waves to test speakers. I even got big fluctuations in readings if I stood within a few feet of the speaker and moved my arms around. I thought these were fluctuations caused by the room, so I gave up doing measurements. Fixed tone sine waves radiate from the speaker and all the reflected waves from the room also appear at the microphone, and depending on their power and phase these will tend to these will add to add or subtract to the amplitude recorded by the mic. One can also use a wobbulator, where the F is varied fast enough prevent reflected waves from adding or subtracting to the centre F waves. Pink noise contains all the bandwidth F over a period of time, with F and phase changing at random rates. So your pink noise and band pass filter method interests me. Do you feed the pink noise through the filter then to the speaker, and measure the result ? or do you put the filter on the output of the mic ? The pink noise is fed to the amp. It sounds like a large waterfall, with rumble and hiss. The microphone picks this up, and amplifies it, and passes the signal through the bandpass filter. The amount of energy for the band selected is then sent to a peak detector with a long time constant, and this is sent to a logarithmic amp to power a large scale analog meter with 0dB at the centre of the meter and +/- 20 dB each side. This way you can easily read across a 40 dB range of voltages. Set for 1 kHz, the meter needle sways a bit, since the 1 kHz band undulates at low frequency a little, but not badly enough to prevent getting a measurement after a few seconds of watching the needle. By the way, since the original question was about equipment, what I use for a microphone is the analogue output from a RadioShack 33-2055 digital sound level meter. It has its own amplifier etc. Just connect an audio voltmeter to the output. There is a mod on the web somewhere showing how to extend the lower frequency response and remove the weighting to get a uniform frequency response. The HF end of the band on those types of meters isn't too wonderful. In fact I wonder how accurate they are at all. I believe my set up to be more accurate than an SPL meter I could buy like that. But it did take a week or two to get it going right. I did it before I went on the net in 2000 so instead of hours at the PC each day, I was reading books and building and testing circuits. Patrick Turner. Thanks "Patrick Turner" wrote in message ... Fabio Berutti wrote: Dear RATs, a question posed by Mr. Turner about my new LS is now puzzling me: what kind of stuff is needed to test a loudspeaker? Is it possible to do it with some VERY cheap microphone and the sound card included in any PC? I don't want to spend a lot of $ in Bruel&Kjaer professional testing equipments.... Ciao Fabio I am presently using an electret mic insert purchased from Hi Q products in Melbourne for aud $1.20 each. I bought 10, and all gave the same flat response as per their spec sheets for that model of electret mic. I fitted the insert into the end of a 12 mm copper pipe 300 mm long full of wool. Its clamped to a mic stand. The response is only flat from about 20 Hz to 8 kHz, and then rolls off at 6 dB / octave. So I placed an RC emphasis circuit in the mic amp, and made the recovered signal flat to 15 kHz, and after measuring many speakers, it must be about right enough to tell me if there are drastic problems. The test signal is pink noise, or white noise eq'd by 3 dB / octave across the band. My home brew tunable 3 decade range bandpass filter for measuring bands has a Q of about 12 at any F chosen, so if centred on 1 kHz, the poles are at 41 Hz each side of 1 kHz. The filter and noise source and mic amp are in the one box and use opamps to achieve what I want. There are calibrated mikes out there which may cost $100, and would probably be better, as would the use of a PC and program to analyse AF, 'Speclab' comes to mind. I do it the old fashioned way with a book and pencil with several takes in the room. These can be averaged, and a resultant response line drawn. The PC will be a lot faster. The results always seem to co-relate to what I hear. Drivers can be tested separately, then together, and the response of each driver plotted. When the phase of a driver is reversed, the results show up in the response. Its real shoe string budget stuff what I have done, but its a lot better than nothing at all. I have my eye on better gear, but the bills keep me poor, and I have to save up more. Even with better gear, the room effects still give +/- 3 dB graph undulations. Don't ever test with pure sine waves; you get a crazy +/- 12 dB variation with maybe 50 peaks and troughs, and a totally meaningless outcome. The more carpets and cushions, large bags of chopped foam in the room, the flatter your measurements will be. And the better the music will be. Its not as good as an anechoic chamber. If most music cannot be improved by adjusting the amplifier tone controls, then the speakers might be about right. I said might be. The pink noise room test will find the harder to hear other problems. Patrick Turner. |
#14
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On Tue, 15 Feb 2005 23:44:46 +0100, François Yves Le Gal
wrote: On Tue, 15 Feb 2005 23:22:46 +0100, "Ruud Broens" wrote: then all of a sudden audio seems like a very cheap hobby Hmmm. Some ultra-fi rigs cost more than a couple of luxury cars. Ongaku anyone? You can buy a couple of luxury cars for $28,000? Where? -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#15
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"Patrick Turner" wrote in message ... So your pink noise and band pass filter method interests me. Do you feed the pink noise through the filter then to the speaker, and measure the result ? or do you put the filter on the output of the mic ? The pink noise is fed to the amp. It sounds like a large waterfall, with rumble and hiss. The microphone picks this up, and amplifies it, and passes the signal through the bandpass filter. The amount of energy for the band selected is then sent to a peak detector with a long time constant, and this is sent to a logarithmic amp to power a large scale analog meter with 0dB at the centre of the meter and +/- 20 dB each side. This way you can easily read across a 40 dB range of voltages. Set for 1 kHz, the meter needle sways a bit, since the 1 kHz band undulates at low frequency a little, but not badly enough to prevent getting a measurement after a few seconds of watching the needle. OK, understood. I will give this a try next time I am fooling around with speakers. Thanks. Robert. |
#16
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Hmmm... I suppose that my testing line-up will be the following:
- Chet Baker, "Broken Wings" on 180 grams vinyl - Thorens TD126 MkIII - Shure V15-VI - homebrew tube preamp (EF86+ECC88) - homebrew line amp (ECC81) - homebrew power amp (EC86/2A3) - mother-supplied microphones on the sides of my head - inboard analog signal processor (sometimes called brain) - 15yrs Barbancourt rum - Swiss bitter chocolate - European common cat if available (purring is a benchmark for 50Hz noise. American cats are surely tuned to 60) - 5kg hammer to smash the phone in case of incoming calls Definitely not scientific, but more fun. Anyway, I suppose that I'll do something, someday, with my PC sound card and a mike. The answers I got were quite helpful, thanks to all. Ciao Fabio "Fabio Berutti" ha scritto nel messaggio ... Dear RATs, a question posed by Mr. Turner about my new LS is now puzzling me: what kind of stuff is needed to test a loudspeaker? Is it possible to do it with some VERY cheap microphone and the sound card included in any PC? I don't want to spend a lot of $ in Bruel&Kjaer professional testing equipments.... Ciao Fabio |
#17
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"Fabio Berutti" wrote in message news : Hmmm... I suppose that my testing line-up will be the following: : : - Chet Baker, "Broken Wings" on 180 grams vinyl : - Thorens TD126 MkIII : - Shure V15-VI : - homebrew tube preamp (EF86+ECC88) : - homebrew line amp (ECC81) : - homebrew power amp (EC86/2A3) : - mother-supplied microphones on the sides of my head : - inboard analog signal processor (sometimes called brain) : - 15yrs Barbancourt rum : - Swiss bitter chocolate : - European common cat if available (purring is a benchmark for 50Hz noise. : American cats are surely tuned to 60) : - 5kg hammer to smash the phone in case of incoming calls : : Definitely not scientific, but more fun. : : Anyway, I suppose that I'll do something, someday, with my PC sound card and : a mike. The answers I got were quite helpful, thanks to all. : : Ciao : : Fabio Heh. Did you read about Sander's '0 feedback' - aware cat , on RAO ? ;-) Rudy: |
#18
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"Chris Morriss" wrote in message ... : In message , François Yves : Le Gal writes : On Tue, 15 Feb 2005 21:50:04 +0100, "Ruud Broens" : wrote: : : Also, there are offers combining MLSSA and some fair quality microphones : with calibrated response curves - just google around in eu :-) : : A solution around MLSSA costs more than 5,000 EUR... : : : : MLSSA is grossly out of date and frighteningly expensive. (And runs : under DOS!) : : Why not get a good quality sound card (like a DMX-6fire) and buy 'Sample : Champion'? Better than MLSSA performance at a fraction of the price. : -- : Chris Morriss heh, that's the soundcard installed in this computer I gave a link to a far cheaper solution, elsewhere in the thread. cheers, Rudy |
#19
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Hi Fabio,
funny list of testing equippment :-) But i agree. - European common cat if available (purring is a benchmark for 50Hz noise. We have 3 cats @ home and one or two of them sleeping in front of the speakers while Mozart is playing is a sure sign that all is okay. During the breadboard stage of my 807PP, once a cat jumped up and ran away as I switched the amp under construction on. Surely enough, it showed at the scope that the circuit at that time had stability problems at real speaker loads leading to slight parasitic oscillations. Obviously, the cat noticed that and didn?t like it :-) Tom -- |
#20
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I suppose that, being able to hear ultra-sounds up to 30 or 40K, our pets
can detect overtones due to instability or bad distortion products much better than us. In fact they are annoyed by many "technological" noises, particularly vacuum cleaners or other small electric motors AFAIK: the bearings'whistle must be like nails on the blackboard, for a cat. There are dogs trained to spot drugs or explosives... maybe it is possible to teach a cat to detect odd harmonics. Ciao Fabio "Tom Schlangen" ha scritto nel messaggio ... Hi Fabio, funny list of testing equippment :-) But i agree. - European common cat if available (purring is a benchmark for 50Hz noise. We have 3 cats @ home and one or two of them sleeping in front of the speakers while Mozart is playing is a sure sign that all is okay. During the breadboard stage of my 807PP, once a cat jumped up and ran away as I switched the amp under construction on. Surely enough, it showed at the scope that the circuit at that time had stability problems at real speaker loads leading to slight parasitic oscillations. Obviously, the cat noticed that and didn?t like it :-) Tom -- |
#21
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Fabio Berutti wrote: I suppose that, being able to hear ultra-sounds up to 30 or 40K, our pets can detect overtones due to instability or bad distortion products much better than us. In fact they are annoyed by many "technological" noises, particularly vacuum cleaners or other small electric motors AFAIK: the bearings'whistle must be like nails on the blackboard, for a cat. There are dogs trained to spot drugs or explosives... maybe it is possible to teach a cat to detect odd harmonics. One thing is for sure, cats sure don't need to be taught to detect odd dogs ;-) Miao, Patrick Turner. Ciao Fabio "Tom Schlangen" ha scritto nel messaggio ... Hi Fabio, funny list of testing equippment :-) But i agree. - European common cat if available (purring is a benchmark for 50Hz noise. We have 3 cats @ home and one or two of them sleeping in front of the speakers while Mozart is playing is a sure sign that all is okay. During the breadboard stage of my 807PP, once a cat jumped up and ran away as I switched the amp under construction on. Surely enough, it showed at the scope that the circuit at that time had stability problems at real speaker loads leading to slight parasitic oscillations. Obviously, the cat noticed that and didn?t like it :-) Tom -- |
#22
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Get yourself a Rane RA 27 or RA 30 and get on with life.
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