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#1
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Speaker ports
Suppose you are designing a ported speaker enclosure. Suppose this design wants two 2 inch ports @ 0.80 inches. Suppose also you are using 3/4" plywood. Must the port extend 0.80 into the internal volume of the speaker box or would the slightly less than .75 inches of the box material suffice? -- Les Cargill |
#2
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Speaker ports
On 1/17/2015 9:18 PM, Les Cargill wrote:
Suppose you are designing a ported speaker enclosure. Suppose this design wants two 2 inch ports @ 0.80 inches. Suppose also you are using 3/4" plywood. Must the port extend 0.80 into the internal volume of the speaker box or would the slightly less than .75 inches of the box material suffice? It depends on the designer and the design. You could glue a piece of 2" PVC pipe (2.375" OD, 2.05" ID) inside the port and trim it to length for what you think is the best sound. Or you could use a cardboard toilet paper roll if you want something easier to cut. Remember that there's a long history of toilet paper and NS-10 speakers. -- For a good time, visit http://mikeriversaudio.wordpress.com |
#3
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Speaker ports
On Sat, 17 Jan 2015 14:18:36 -0600, Les Cargill
wrote: Suppose you are designing a ported speaker enclosure. Suppose this design wants two 2 inch ports @ 0.80 inches. Suppose also you are using 3/4" plywood. Must the port extend 0.80 into the internal volume of the speaker box or would the slightly less than .75 inches of the box material suffice? The length of the port is used to determine the mass of air that is "bouncing" against the spring of the air inside the cabinet, so yes, that length is the total length of the port as calculated. Now it gets tricky. The moving mass of port air extends beyond the physical port for some distance - so called end effect - so you need to shorten the physical port to allow for it. In your design, that probably means a physical port length around zero. You should be able to refine the design parameters you feed into the programme to end up with a port length of at least a couple of inches in order to make it physically possible to build. The programme should be able to give you the end effect lengths that you subtract from the tube when building it. d |
#4
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Speaker ports
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#5
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Speaker ports
On 18/01/2015 7:18 AM, Les Cargill wrote:
Suppose you are designing a ported speaker enclosure. Suppose this design wants two 2 inch ports @ 0.80 inches. Suppose also you are using 3/4" plywood. Must the port extend 0.80 into the internal volume of the speaker box or would the slightly less than .75 inches of the box material suffice? The port length includes the baffle thickness, so the easiest way to do what you want is simply adjust the port diameter slightly to suit the baffle thickness you have. Even better, cut them undersize and then adjust their size and thus tuning of the finished box. Trevor. |
#6
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Speaker ports
On Sat, 17 Jan 2015 19:45:37 -0600, Les Cargill
wrote: (Don Pearce) wrote: On Sat, 17 Jan 2015 14:18:36 -0600, Les Cargill wrote: Suppose you are designing a ported speaker enclosure. Suppose this design wants two 2 inch ports @ 0.80 inches. Suppose also you are using 3/4" plywood. Must the port extend 0.80 into the internal volume of the speaker box or would the slightly less than .75 inches of the box material suffice? The length of the port is used to determine the mass of air that is "bouncing" against the spring of the air inside the cabinet, so yes, that length is the total length of the port as calculated. Now it gets tricky. The moving mass of port air extends beyond the physical port for some distance - so called end effect - so you need to shorten the physical port to allow for it. In your design, that probably means a physical port length around zero. That sounds like a feature, not a bug. This then becomes just a hole in the outer wall of the box. No tube required. I 'd expect a couple millimeters to not have much effect. If it does, cut a ring out of something to make it up. The "chuff" factor - "vent mach" in WinISD parlance - is 0.10; not bad at all. You should be able to refine the design parameters you feed into the programme to end up with a port length of at least a couple of inches in order to make it physically possible to build. The programme should be able to give you the end effect lengths that you subtract from the tube when building it. The program is WinISD and it just calculates a port length. I deliberately chose 2X2" because it has calculated a small - 0.5 cu. ft. box - that will need to be doubled in volume to actually be able to hold the speaker in question. The ports could be in the back, but 2x2" is about all you could afford for front-mounted ports. OK, your reasoning makes sense, but if you have doubled the box volume (for whatever reason), then you are headed well along the road to an infinite baffle design, and you probably don't need a port at all. d |
#7
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Speaker ports
In article ,
Les Cargill wrote: Suppose you are designing a ported speaker enclosure. Suppose this design wants two 2 inch ports @ 0.80 inches. Suppose also you are using 3/4" plywood. Must the port extend 0.80 into the internal volume of the speaker box or would the slightly less than .75 inches of the box material suffice? I'd generally glue another small square of plywood to the inside to make up the required length of port - unless very much longer than the thickness of the baffle. But the thickest baffle I've ever used is 12mm birch ply. Although never made PA sized speakers. -- *Do infants enjoy infancy as much as adults enjoy adultery? Dave Plowman London SW To e-mail, change noise into sound. |
#8
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Speaker ports
In article ,
Les Cargill wrote: Suppose you are designing a ported speaker enclosure. Suppose this design wants two 2 inch ports @ 0.80 inches. Suppose also you are using 3/4" plywood. Must the port extend 0.80 into the internal volume of the speaker box or would the slightly less than .75 inches of the box material suffice? ..75 is well within the margin of error anyway. You're going to have to do some cut-and-try work outdoors with a measurement system and see. You may even find the thickness of the box material adds too much delay. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#9
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Speaker ports
"Scott Dorsey" skrev i en meddelelse
... In article , Les Cargill wrote: Suppose you are designing a ported speaker enclosure. Suppose this design wants two 2 inch ports @ 0.80 inches. Suppose also you are using 3/4" plywood. Must the port extend 0.80 into the internal volume of the speaker box or would the slightly less than .75 inches of the box material suffice? .75 is well within the margin of error anyway. You're going to have to do some cut-and-try work outdoors with a measurement system and see. You may even find the thickness of the box material adds too much delay. I think the design is trying to explain to the designer that he should use larger and longer ports. A rectangular slit above the unit and one below comes to mind. --scott Kind regards Peter Larsen |
#12
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Speaker ports
"Les Cargill" skrev i en meddelelse
... Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there is one hump in the group delay that goes from 4ish to 8ish msec, around 75-80 Hz in the frequency response. In winisd you can fix any parameter and then see what happens to the design, so in case the port lenght is silly you try another area. If you err, then err to the side of the too long a port because the bass units Fs will get a wee bit lower in use. Do not err to the side of the too high tuning because it will give a "loose" sound with flappy transients. Oh, that btw. is the answer to whether a slightly too short port is OK, no, it is not redesign so that you have more length and lower air speed in port or make it a bit smaller. I didn't think that mattered so much until Quali-Fi service here in Denmark suggested that I should double the port area since I had room for longer ports, it was a surprising sonic improvement, unexpected because of my generally modest playback spl. Doubling the box nearly has to be more of a perturbation than 1.25 mm of port depth. But then again, ports are critically sensitive elements. Still, I am skeptical that "just take it outside and measure it" is going to allow enough accuracy to be able to tell. Measure the impedance curve, what sounds well to me is the setups where the lower impedance hump is equal to the higher one or larger, ie. generally systems that are tuned lower than optimally linear. (btw, this is not for me; it's for another participant on a different forum who has a speaker and is fishing for box designs ). But, surely, in fishing putting some bait on the hook, such as telling us what unit and what its parameters are may increase the chance for a good catch. Les Cargill Kind regards Peter Larsen |
#13
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Speaker ports
Peter Larsen wrote:
"Les Cargill" skrev i en meddelelse ... Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there is one hump in the group delay that goes from 4ish to 8ish msec, around 75-80 Hz in the frequency response. In winisd you can fix any parameter and then see what happens to the design, so in case the port lenght is silly you try another area. If you err, then err to the side of the too long a port because the bass units Fs will get a wee bit lower in use. Do not err to the side of the too high tuning because it will give a "loose" sound with flappy transients. Interesting. I was concerned that too long a port would fight the box. Still; moving from 20.00 to 1.97 inches diameter ( from 50.8 to 20.038 mm ) seems rather hairsplitting That gets it to a length of 0.75 inches. Since the ideal front design is 14"x14" for a steel guitar speaker, there was hardly room for a pair of 2" ports. They'd just have to go in back. Oh, that btw. is the answer to whether a slightly too short port is OK, no, it is not redesign so that you have more length and lower air speed in port or make it a bit smaller. I didn't think that mattered so much until Quali-Fi service here in Denmark suggested that I should double the port area since I had room for longer ports, it was a surprising sonic improvement, unexpected because of my generally modest playback spl. huh. That actually makes sense. Doubling the box nearly has to be more of a perturbation than 1.25 mm of port depth. But then again, ports are critically sensitive elements. Still, I am skeptical that "just take it outside and measure it" is going to allow enough accuracy to be able to tell. Measure the impedance curve, what sounds well to me is the setups where the lower impedance hump is equal to the higher one or larger, ie. generally systems that are tuned lower than optimally linear. True enough. (btw, this is not for me; it's for another participant on a different forum who has a speaker and is fishing for box designs ). But, surely, in fishing putting some bait on the hook, such as telling us what unit and what its parameters are may increase the chance for a good catch. It's an Eminence EPS-12C. I guessed ( incorrectly ) that this didn't matter It's not a bass driver at all; it's a guitar speaker. Fs is 49.17 Hz. I get the feeling it's really designed for infinite baffle. http://www.usspeaker.com/Eps12c-1.htm The gentleman will use it for pedal steel, presumably with a lowest note of C2 ( 69.4 cycles ). Les Cargill Kind regards Peter Larsen -- Les Cargill |
#14
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Speaker ports
On Sun, 18 Jan 2015 21:38:47 -0600, Les Cargill
wrote: Peter Larsen wrote: "Les Cargill" skrev i en meddelelse ... Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there is one hump in the group delay that goes from 4ish to 8ish msec, around 75-80 Hz in the frequency response. In winisd you can fix any parameter and then see what happens to the design, so in case the port lenght is silly you try another area. If you err, then err to the side of the too long a port because the bass units Fs will get a wee bit lower in use. Do not err to the side of the too high tuning because it will give a "loose" sound with flappy transients. Interesting. I was concerned that too long a port would fight the box. Still; moving from 20.00 to 1.97 inches diameter ( from 50.8 to 20.038 mm ) seems rather hairsplitting That gets it to a length of 0.75 inches. Since the ideal front design is 14"x14" for a steel guitar speaker, there was hardly room for a pair of 2" ports. They'd just have to go in back. Oh, that btw. is the answer to whether a slightly too short port is OK, no, it is not redesign so that you have more length and lower air speed in port or make it a bit smaller. I didn't think that mattered so much until Quali-Fi service here in Denmark suggested that I should double the port area since I had room for longer ports, it was a surprising sonic improvement, unexpected because of my generally modest playback spl. huh. That actually makes sense. Doubling the box nearly has to be more of a perturbation than 1.25 mm of port depth. But then again, ports are critically sensitive elements. Still, I am skeptical that "just take it outside and measure it" is going to allow enough accuracy to be able to tell. Measure the impedance curve, what sounds well to me is the setups where the lower impedance hump is equal to the higher one or larger, ie. generally systems that are tuned lower than optimally linear. True enough. (btw, this is not for me; it's for another participant on a different forum who has a speaker and is fishing for box designs ). But, surely, in fishing putting some bait on the hook, such as telling us what unit and what its parameters are may increase the chance for a good catch. It's an Eminence EPS-12C. I guessed ( incorrectly ) that this didn't matter It's not a bass driver at all; it's a guitar speaker. Fs is 49.17 Hz. I get the feeling it's really designed for infinite baffle. http://www.usspeaker.com/Eps12c-1.htm The gentleman will use it for pedal steel, presumably with a lowest note of C2 ( 69.4 cycles ). Les Cargill Kind regards Peter Larsen I was going to ask. Why are you porting this at all? Bottom E on a guitar is 82Hz, and the speaker cone is far better protected and supported in an IB box. Vox get away with open backs because their amplifiers are relatively low power compared to the speaker drivers. And they leave the backs open deliberately to roll off the bass for a cleaner sound. d |
#15
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Speaker ports
(Don Pearce) wrote:
On Sun, 18 Jan 2015 21:38:47 -0600, Les Cargill wrote: Peter Larsen wrote: "Les Cargill" skrev i en meddelelse ... Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there is one hump in the group delay that goes from 4ish to 8ish msec, around 75-80 Hz in the frequency response. In winisd you can fix any parameter and then see what happens to the design, so in case the port lenght is silly you try another area. If you err, then err to the side of the too long a port because the bass units Fs will get a wee bit lower in use. Do not err to the side of the too high tuning because it will give a "loose" sound with flappy transients. Interesting. I was concerned that too long a port would fight the box. Still; moving from 20.00 to 1.97 inches diameter ( from 50.8 to 20.038 mm ) seems rather hairsplitting That gets it to a length of 0.75 inches. Since the ideal front design is 14"x14" for a steel guitar speaker, there was hardly room for a pair of 2" ports. They'd just have to go in back. Oh, that btw. is the answer to whether a slightly too short port is OK, no, it is not redesign so that you have more length and lower air speed in port or make it a bit smaller. I didn't think that mattered so much until Quali-Fi service here in Denmark suggested that I should double the port area since I had room for longer ports, it was a surprising sonic improvement, unexpected because of my generally modest playback spl. huh. That actually makes sense. Doubling the box nearly has to be more of a perturbation than 1.25 mm of port depth. But then again, ports are critically sensitive elements. Still, I am skeptical that "just take it outside and measure it" is going to allow enough accuracy to be able to tell. Measure the impedance curve, what sounds well to me is the setups where the lower impedance hump is equal to the higher one or larger, ie. generally systems that are tuned lower than optimally linear. True enough. (btw, this is not for me; it's for another participant on a different forum who has a speaker and is fishing for box designs ). But, surely, in fishing putting some bait on the hook, such as telling us what unit and what its parameters are may increase the chance for a good catch. It's an Eminence EPS-12C. I guessed ( incorrectly ) that this didn't matter It's not a bass driver at all; it's a guitar speaker. Fs is 49.17 Hz. I get the feeling it's really designed for infinite baffle. http://www.usspeaker.com/Eps12c-1.htm The gentleman will use it for pedal steel, presumably with a lowest note of C2 ( 69.4 cycles ). Les Cargill Kind regards Peter Larsen I was going to ask. Why are you porting this at all? I don't know exactly. I suppose he wants a little more bass support. Steel goes lower than 6 string. Bottom E on a guitar is 82Hz, and the speaker cone is far better protected and supported in an IB box. Agreed. Vox get away with open backs because their amplifiers are relatively low power compared to the speaker drivers. And they leave the backs open deliberately to roll off the bass for a cleaner sound. d -- Les Cargill |
#16
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Speaker ports
Hi Don,
I was going to ask. Why are you porting this at all? Bottom E on a guitar is 82Hz, and the speaker cone is far better protected and supported in an IB box. It is a very low Qt unit, well into the "suited for horn loading range", so yes, it should be vented, I think an IB with this unit will sound thin. So I'll just re-iterate my suggestion of a slit shaped vent above and below the unit. A bit of finagling yields something like this as I see it early in the morning: box: 25 liters tuning: 60 Hz 2 vents as slits 30 centimeters long, 1 centimeter wide, 9 centimeters deep. The response should then be -5 dB at 80 Hz and sloping upwards to -1 dB around 250 Hz, that is about as much bass as you can get from that unit. It is not a standard tuning for the box, but as you said, too much bass in a guitar box can end up muddy. It is important to ensure a smooth inside finish of the vents. Box inside walls should probably be felt covered, 1 cm thick felt stapled in place, somewhat messy, not too flat and tidy. Make the box 32 liters to allow for it and for the loudspeaker magnet. Amplifier should if possible be highpassed at 60 Hz to protect loudspeaker from "hit all strings tranasients", somewhat depending on how powerful it is, RMS power for the unit is spec'd at 225 watts, the old JBL guideline was assume 30% for instrument use because of low crest factor and the risk of weird transients, ie. "somewhat safe to use with 60 watts amplifier". d Kind regards Peter Larsen |
#17
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Speaker ports
On Mon, 19 Jan 2015 06:24:18 +0100, "Peter Larsen"
wrote: Hi Don, I was going to ask. Why are you porting this at all? Bottom E on a guitar is 82Hz, and the speaker cone is far better protected and supported in an IB box. It is a very low Qt unit, well into the "suited for horn loading range", so yes, it should be vented, I think an IB with this unit will sound thin. So I'll just re-iterate my suggestion of a slit shaped vent above and below the unit. A bit of finagling yields something like this as I see it early in the morning: box: 25 liters tuning: 60 Hz 2 vents as slits 30 centimeters long, 1 centimeter wide, 9 centimeters deep. The response should then be -5 dB at 80 Hz and sloping upwards to -1 dB around 250 Hz, that is about as much bass as you can get from that unit. It is not a standard tuning for the box, but as you said, too much bass in a guitar box can end up muddy. It is important to ensure a smooth inside finish of the vents. Box inside walls should probably be felt covered, 1 cm thick felt stapled in place, somewhat messy, not too flat and tidy. Make the box 32 liters to allow for it and for the loudspeaker magnet. Amplifier should if possible be highpassed at 60 Hz to protect loudspeaker from "hit all strings tranasients", somewhat depending on how powerful it is, RMS power for the unit is spec'd at 225 watts, the old JBL guideline was assume 30% for instrument use because of low crest factor and the risk of weird transients, ie. "somewhat safe to use with 60 watts amplifier". d Kind regards Peter Larsen Extra damping on the walls of the box shouldn't be necessary. The internal Q is set by the driver and the port, so felt on the walls would be an added and unknown extra source of loss. And of course this is for sound production, not reproduction, so some character and resonance is probably to be considered a good thing. d |
#18
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Speaker ports
On 18/01/2015 10:10 PM, Dave Plowman (News) wrote:
In article , Les Cargill wrote: Suppose you are designing a ported speaker enclosure. Suppose this design wants two 2 inch ports @ 0.80 inches. Suppose also you are using 3/4" plywood. Must the port extend 0.80 into the internal volume of the speaker box or would the slightly less than .75 inches of the box material suffice? I'd generally glue another small square of plywood to the inside to make up the required length of port - unless very much longer than the thickness of the baffle. But the thickest baffle I've ever used is 12mm birch ply. Although never made PA sized speakers. Gee that's really doing it the hard way when you consider the port inertance is a factor of both the cross sectional area and length. So in this case a lot easier to adjust the port area slightly than length. When you must use a tube, the reverse is usually the case of course. Trevor. |
#19
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Speaker ports
On 19/01/2015 2:16 AM, Peter Larsen wrote:
"Scott Dorsey" skrev i en meddelelse ... In article , Les Cargill wrote: Suppose you are designing a ported speaker enclosure. Suppose this design wants two 2 inch ports @ 0.80 inches. Suppose also you are using 3/4" plywood. Must the port extend 0.80 into the internal volume of the speaker box or would the slightly less than .75 inches of the box material suffice? .75 is well within the margin of error anyway. You're going to have to do some cut-and-try work outdoors with a measurement system and see. You may even find the thickness of the box material adds too much delay. I think the design is trying to explain to the designer that he should use larger and longer ports. A rectangular slit above the unit and one below comes to mind. Why longer? Many designs simply use a hole cut in the baffle. Far easier when that is appropriate. As I said already, I'd simply cut smaller holes and tune the box by making them as large as necessary by measurement. Trevor. |
#20
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Speaker ports
"Don Pearce" skrev i en meddelelse
... On Mon, 19 Jan 2015 06:24:18 +0100, "Peter Larsen" wrote: .... It is important to ensure a smooth inside finish of the vents. Box inside walls should probably be felt covered, 1 cm thick felt stapled in place, somewhat messy, not too flat and tidy. Make the box 32 liters to allow for it and for the loudspeaker magnet. .... Extra damping on the walls of the box shouldn't be necessary. The internal Q is set by the driver and the port, so felt on the walls would be an added and unknown extra source of loss. If it was primarily or only a bass box I could agree and at least be willing to try. Felt suggested with the inernal Q in mind. I'll settle for half the walls, I'm thinking midrange standing waves causing midrange colouration via the ports, 32 liters is a small box. And of course this is for sound production, not reproduction, so some character and resonance is probably to be considered a good thing. As long as it is well sounding, yes. One could also use a partial diagonal bracing wall to break up standing waves so as to lessen any possible problem and make the midrange that comes out of the ports sound better. d Kind regards Peter Larsen |
#21
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Speaker ports
In article ,
Trevor wrote: I'd generally glue another small square of plywood to the inside to make up the required length of port - unless very much longer than the thickness of the baffle. But the thickest baffle I've ever used is 12mm birch ply. Although never made PA sized speakers. Gee that's really doing it the hard way when you consider the port inertance is a factor of both the cross sectional area and length. So in this case a lot easier to adjust the port area slightly than length. When you must use a tube, the reverse is usually the case of course. Depends, I suppose, on your woodworking skills and facilities. -- *Why is it that doctors call what they do "practice"? Dave Plowman London SW To e-mail, change noise into sound. |
#22
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Speaker ports
On 19/01/2015 10:38 PM, Dave Plowman (News) wrote:
In article , Trevor wrote: I'd generally glue another small square of plywood to the inside to make up the required length of port - unless very much longer than the thickness of the baffle. But the thickest baffle I've ever used is 12mm birch ply. Although never made PA sized speakers. Gee that's really doing it the hard way when you consider the port inertance is a factor of both the cross sectional area and length. So in this case a lot easier to adjust the port area slightly than length. When you must use a tube, the reverse is usually the case of course. Depends, I suppose, on your woodworking skills and facilities. Would be funny skills that find it easier to "glue another small square of plywood to the inside to make up the required length of port", than to simply cut a different size hole. But I guess I'll take your word for it that's easier for you. And I'll even assume the cost of extra material is no consideration in your case. Others may feel differently however. Trevor. |
#23
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Speaker ports
In article ,
Trevor wrote: Would be funny skills that find it easier to "glue another small square of plywood to the inside to make up the required length of port", than to simply cut a different size hole. But I guess I'll take your word for it that's easier for you. And I'll even assume the cost of extra material is no consideration in your case. Others may feel differently however. It's relatively easy to alter the length of the port by adding plywood etc to the back. Provided it's not that long. Enlarging a hole (bigger than a drill) may prove more tricky for some. You can buy adjustable length (telescopic) plastic tubes to use with ports. All sorts of ways to skin a cat. The best one will depend on the individual. -- *Can vegetarians eat animal crackers? Dave Plowman London SW To e-mail, change noise into sound. |
#24
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Speaker ports
Les Cargill wrote:
In this way, you can completely dial in the ideal port length to compensate for any errors in box volume calculation as well as variances in the drivers. I suspect this is outside the envelope of measurement. In that case, it's either not important, or else you need better measurement hardware in order to a proper design job. Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there is one hump in the group delay that goes from 4ish to 8ish msec, around 75-80 Hz in the frequency response. Doubling the box nearly has to be more of a perturbation than 1.25 mm of port depth. But then again, ports are critically sensitive elements. Still, I am skeptical that "just take it outside and measure it" is going to allow enough accuracy to be able to tell. That's entirely possible. The problem is that the simulation has even less accuracy in most cases. So either you need better measurement or better simulation, or else you need to not worry so much and live with the error. I will say that if you don't have good measurement, you are more likely to get a design that meets parameters on the first try with a sealed box design than a ported design. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#26
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Speaker ports
Les Cargill wrote:
If this was for manufacture, it'd be different - you'd be able to buy the right tooling, make proper jigs, all that. I was startled when I opened one of my Meyer UPA1A's long ago. He fit as much into that little cabinet as will go in there, including a special horn that must certainly have taken "proper jigs, all that". The result is reflected both in price, and in performance, both of them "up there". -- shut up and play your guitar * HankAlrich.Com HankandShaidriMusic.Com YouTube.Com/WalkinayMusic |
#27
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Speaker ports
On 21/01/2015 6:48 AM, Scott Dorsey wrote:
Les Cargill wrote: In this way, you can completely dial in the ideal port length to compensate for any errors in box volume calculation as well as variances in the drivers. I suspect this is outside the envelope of measurement. In that case, it's either not important, or else you need better measurement hardware in order to a proper design job. Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there is one hump in the group delay that goes from 4ish to 8ish msec, around 75-80 Hz in the frequency response. Doubling the box nearly has to be more of a perturbation than 1.25 mm of port depth. But then again, ports are critically sensitive elements. Still, I am skeptical that "just take it outside and measure it" is going to allow enough accuracy to be able to tell. That's entirely possible. The problem is that the simulation has even less accuracy in most cases. So either you need better measurement or better simulation, or else you need to not worry so much and live with the error. I will say that if you don't have good measurement, you are more likely to get a design that meets parameters on the first try with a sealed box design than a ported design. It's pretty easy for anybody with computer sound to make an impedance sweep these days, free software readily available, and that's all you need to tune the box. Not to mention you can also measure the driver for T/S parameters before you design the box. But yes, a sealed box is always easier to design and construct if that's what you want. Trevor. |
#28
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Speaker ports
Trevor wrote:
On 21/01/2015 6:48 AM, Scott Dorsey wrote: Les Cargill wrote: In this way, you can completely dial in the ideal port length to compensate for any errors in box volume calculation as well as variances in the drivers. I suspect this is outside the envelope of measurement. In that case, it's either not important, or else you need better measurement hardware in order to a proper design job. Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there is one hump in the group delay that goes from 4ish to 8ish msec, around 75-80 Hz in the frequency response. Doubling the box nearly has to be more of a perturbation than 1.25 mm of port depth. But then again, ports are critically sensitive elements. Still, I am skeptical that "just take it outside and measure it" is going to allow enough accuracy to be able to tell. That's entirely possible. The problem is that the simulation has even less accuracy in most cases. So either you need better measurement or better simulation, or else you need to not worry so much and live with the error. I will say that if you don't have good measurement, you are more likely to get a design that meets parameters on the first try with a sealed box design than a ported design. It's pretty easy for anybody with computer sound to make an impedance sweep these days, free software readily available, and that's all you need to tune the box. Not to mention you can also measure the driver for T/S parameters before you design the box. I have never had problems finding the manufacturer's published T/S parameters. But yes, a sealed box is always easier to design and construct if that's what you want. Trevor. -- Les Cargill |
#29
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Speaker ports
Les Cargill wrote:
I have never had problems finding the manufacturer's published T/S parameters. Sometimes those published parameters are pretty fictional. I'm not going to mention any particular manufacturers here, but a quick sweep in free air to determine Fs by ear will tell you who they are. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#30
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Speaker ports
On 23/01/2015 2:16 AM, Scott Dorsey wrote:
Les Cargill wrote: I have never had problems finding the manufacturer's published T/S parameters. Sometimes those published parameters are pretty fictional. I'm not going to mention any particular manufacturers here, but a quick sweep in free air to determine Fs by ear will tell you who they are. --scott And when they are not entirely fictional, they are often just ball park figures which don't allow for individual and batch variations. If I'm going to the trouble of designing and building a box, I'd rather take the time to measure the drivers first, and then tune the finished box. But each to their own. Trevor. |
#31
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Speaker ports
"Trevor" skrev i en meddelelse
... On 23/01/2015 2:16 AM, Scott Dorsey wrote: Les Cargill wrote: I have never had problems finding the manufacturer's published T/S parameters. Sometimes those published parameters are pretty fictional. I'm not going to mention any particular manufacturers here, but a quick sweep in free air to determine Fs by ear will tell you who they are. And when they are not entirely fictional, they are often just ball park figures which don't allow for individual and batch variations. If I'm going to the trouble of designing and building a box, I'd rather take the time to measure the drivers first, and then tune the finished box. But each to their own. I have a rebuilt white D123 made from original spareparts that has never been used, it is as hard as guitar loudspeaker. Very nice sounding midrange on home-coming test sans cabinet, seller suggested that a few days of sinewave might do it good ... not gonna do that, just playing will be fine - I don't want to loose the stability of the rear suspension but yes, it will change in use. Fortunately what it means is only that the initial bassreflex tuning will be on the lowish side. I think the specs are where they expect(ed) a played in loudspeaker to end up, do we have the designer (of at least one other D123 version, the worlds best 12" wideband loudspeaker unit) in the audience? Trevor. Kind regards Peter Larsen |
#32
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Speaker ports
On 27/01/2015 6:51 PM, Peter Larsen wrote:
"Trevor" skrev i en meddelelse ... On 23/01/2015 2:16 AM, Scott Dorsey wrote: Les Cargill wrote: I have never had problems finding the manufacturer's published T/S parameters. Sometimes those published parameters are pretty fictional. I'm not going to mention any particular manufacturers here, but a quick sweep in free air to determine Fs by ear will tell you who they are. And when they are not entirely fictional, they are often just ball park figures which don't allow for individual and batch variations. If I'm going to the trouble of designing and building a box, I'd rather take the time to measure the drivers first, and then tune the finished box. But each to their own. I have a rebuilt white D123 made from original spareparts that has never been used, it is as hard as guitar loudspeaker. Very nice sounding midrange on home-coming test sans cabinet, seller suggested that a few days of sinewave might do it good ... not gonna do that, just playing will be fine - I don't want to loose the stability of the rear suspension but yes, it will change in use. Fortunately what it means is only that the initial bassreflex tuning will be on the lowish side. I think the specs are where they expect(ed) a played in loudspeaker to end up, There were no T/S specs for that speaker when JBL designed it. (You were lucky to find the Fs at the time) It was before Neville Thiele had published his work I think, certainly before it was widely known and accepted. And IME, and I think according to Dick Pierce's vastly superior experience, "burn in" is not a one way street anyway. And fortunately some variations cancel themselves out. What does happen and is a far bigger problem these days IME is changes in design or materials between batches that are not accompanied by new T/S specs. That will *really* affect your box design if not careful. So measurement is always a good idea IMO. Trevor. |
#33
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Speaker ports
"Trevor" skrev i en meddelelse
... On 27/01/2015 6:51 PM, Peter Larsen wrote: I have a rebuilt white D123 made from original spareparts that has never been used, it is as hard as guitar loudspeaker .... I think the specs are where they expect(ed) a played in loudspeaker to end up, There were no T/S specs for that speaker when JBL designed it. (You were lucky to find the Fs at the time. It was before Neville Thiele had published his work I think, certainly before it was widely known and accepted. And when it was known nobody in their sane mind would design the white D123 version, according to the specs that come with winisd it should have a 200 liter box, according to the guidelines Duelund taught me - I don't know if they were his own or had some source - it is a unit for a closed box with its Qt around 0.45. With a room friendly box version it almost invariably ends up with a 4 dB boost around 60 Hz or - in a closed box - quite lame sounding. All assuming those specs are valid of course. And IME, and I think according to Dick Pierce's vastly superior experience, "burn in" is not a one way street anyway. Yes, quite well matching that speakers that have been left unused should have a play in before being evaluated, he did write about this over in ~.tech. And fortunately some variations cancel themselves out. What does happen and is a far bigger problem these days IME is changes in design or materials between batches that are not accompanied by new T/S specs. That will *really* affect your box design if not careful. So measurement is always a good idea IMO. Oh yes, most designers would prefer "loudspeaker unit" to be a constant rather than a variable! Trevor Kind regards Peter Larsen |
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