@bentoronto, I'm thinking that cab vibration(s) would show up in distortion measurements. Trick is separating that distortion from driver distortion. Perhaps a raw, unbraced cabinet and driver can be measured for distortion and a follow up with the same combination, after bracing, remeasured to show the difference.
The problem being mainly the joint between panel and diagonal strut also has to face shear forces and momentum which will cause the strut to bend. Diagonal bracing only works with real stiff struts and a firm (countersunk) joint.
Diagonal struts are much shorter, hence stiffer. I think you underestimate the strength of pva "stronger than the wood itself ". I tried to dismantle some of my old speakers, that stuffs damn strong.
I'll attest that PVA is typically stronger than the wood itself.
Yes, but not the typical harmonic distortion.
A cabinet resonance is not non-linear. It is fed energy in a consistent manner. It may mess with response.. it may relocate energy through the panels. These things won't show up as harmonic distortion.
I've only read the last couple of pages of this thread, so maybe I'm missing something important, but...
Something to consider is that the energy produced by the driver into the cabinet has to go "somewhere". Typically, its path is through the driver's diaphragm. The stiffer you make the cabinet, the more energy is transmitted through the diaphragm. Whether or not this detrimentally colors the sound is another question. There is some validity to making the cabinet vibrate beneficially, rather than making it as stiff as possible.
Something to consider is that the energy produced by the driver into the cabinet has to go "somewhere". Typically, its path is through the driver's diaphragm. The stiffer you make the cabinet, the more energy is transmitted through the diaphragm. Whether or not this detrimentally colors the sound is another question. There is some validity to making the cabinet vibrate beneficially, rather than making it as stiff as possible.
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To AllenB point, it is difficult to separate regular and irregular distortions. A couple of articles on audioxpress illustrate the methods involved in making such determinations.
However, the impact of cabinet vibration/resonance isn't a mystery. Apparently, there are studies dating back to '73 on the subject by various people. For instance, W.R. Stevens showed an undamped back panel producing peaks 10db lower than the driver's output. I'd think that qualifies as audible.
Measurement and Perception of Regular Loudspeaker Distortion | audioXpress
Measurement and Perception of Irregular Loudspeaker Defects | audioXpress
Speaker Design: Driver-Induced Vibrations | audioXpress
However, the impact of cabinet vibration/resonance isn't a mystery. Apparently, there are studies dating back to '73 on the subject by various people. For instance, W.R. Stevens showed an undamped back panel producing peaks 10db lower than the driver's output. I'd think that qualifies as audible.
Measurement and Perception of Regular Loudspeaker Distortion | audioXpress
Measurement and Perception of Irregular Loudspeaker Defects | audioXpress
Speaker Design: Driver-Induced Vibrations | audioXpress
I prefer to use the more explicit terms "linear" and "nonlinear" distortion since they make it clearer what is being discussed. Cabinet vibrations are linear and as such will show there effects in measurements of linear distortion, but they will not show anything in a nonlinear distortion measurement.
Can't find anything about audibility of cab vibrations and any kind of actual measurements of cab vibration in those links. Can you quote something and where we can find it, please?
A claim that a back panel is vibrating one-third the amplitude of the driver cone is quite extraordinary and difficult to believe. Can you double-check your claim, please.
I hope somebody will post audibility results or even brace versus no-brace mic results some day.
B.
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bentoronto,
References
1. D. A. Barlow, “Sound output of loudspeaker cabinet walls,” 50th AES Convention, Preprint Number: L-17, February 1975.
2. W. R. Stevens, “Sound radiated from loudspeaker cabinets,” 50th AES Convention, Preprint Number: L-16, February 1975.
3. P. A. Fryer, “Intermodulation Distortion Listening Tests,” 50th AES Convention, Preprint Number: L-10, February 1975.
4. Juha Backman, “Effect of Panel Damping on Loudspeaker Enclosure Vibration,” 101st AES Convention, Preprint Number: 4395, October 1996.
5. James Moriyasu “Panel Damping Studies: Reducing Loudspeaker Enclosure Vibrations,” Feb. ’02 audioXpress.
6. James K. Iverson, “The Theory of Loudspeaker Cabinet Resonances,” AES Journal, Volume 21 Number 3, April 1973.
7. A. Jones, “Loudspeaker driver de-coupling, a preliminary report,” Pioneer Electronics Tech.
^That was found in one of the posted links.
References
1. D. A. Barlow, “Sound output of loudspeaker cabinet walls,” 50th AES Convention, Preprint Number: L-17, February 1975.
2. W. R. Stevens, “Sound radiated from loudspeaker cabinets,” 50th AES Convention, Preprint Number: L-16, February 1975.
3. P. A. Fryer, “Intermodulation Distortion Listening Tests,” 50th AES Convention, Preprint Number: L-10, February 1975.
4. Juha Backman, “Effect of Panel Damping on Loudspeaker Enclosure Vibration,” 101st AES Convention, Preprint Number: 4395, October 1996.
5. James Moriyasu “Panel Damping Studies: Reducing Loudspeaker Enclosure Vibrations,” Feb. ’02 audioXpress.
6. James K. Iverson, “The Theory of Loudspeaker Cabinet Resonances,” AES Journal, Volume 21 Number 3, April 1973.
7. A. Jones, “Loudspeaker driver de-coupling, a preliminary report,” Pioneer Electronics Tech.
^That was found in one of the posted links.
Thanks - those are really intriguing titles.
But none of those papers are available at any non-extortion price to me or most members here. So could you just quote a bit for us since you seem to know what they say.
BTW, I am sure folks have been measuring cab vibration for 100 year. But we're interested in actual sound output, not wall vibration which is several logical steps away from my ears and barely commensurate.
I've almost given up asking about audibility, but if you could quote something, I'd be amazed.
B.
But none of those papers are available at any non-extortion price to me or most members here. So could you just quote a bit for us since you seem to know what they say.
BTW, I am sure folks have been measuring cab vibration for 100 year. But we're interested in actual sound output, not wall vibration which is several logical steps away from my ears and barely commensurate.
I've almost given up asking about audibility, but if you could quote something, I'd be amazed.
B.
Can't help you ben, like you I'm a broke senior. As some of this was summarized in all of the linked articles I'd of thought you'd be a little satisfied. Guess not.
As was indicated in the articles, speaker manufacturers test for such things as vibration audibility. Why bother? ... unless their rep would be put at stake. Who would ship a expensive product with a issue that could be identified by the end user? Surely there are degrees of acceptability and methods are employed to improve the products acceptability.
At what point do you, ben, feel cabinet vibration is minimized enough to not matter? Is there any degree of bracing necessary in your estimation? How much and what type of bracing do you feel is adequate? Not being confrontational but all I'm getting from your posts is that bracing wall vibration doesn't matter. This is clearly incorrect. Even I can hear it and I've got one bad ear 🙂
As was indicated in the articles, speaker manufacturers test for such things as vibration audibility. Why bother? ... unless their rep would be put at stake. Who would ship a expensive product with a issue that could be identified by the end user? Surely there are degrees of acceptability and methods are employed to improve the products acceptability.
At what point do you, ben, feel cabinet vibration is minimized enough to not matter? Is there any degree of bracing necessary in your estimation? How much and what type of bracing do you feel is adequate? Not being confrontational but all I'm getting from your posts is that bracing wall vibration doesn't matter. This is clearly incorrect. Even I can hear it and I've got one bad ear 🙂
Well if you haven't read stuff, maybe you shouldn't post it as documentation of the argument your are putting forward. "Guess not", eh?
And no, I am not so naive as to uncritically accept the wonderful good intentions of all speaker manufacturers.
On the other hand, if you want to see exemplary low distortion figures for a labyrinth/TL sub made from quarter-inch plywood, see post 5:
17 foot pipe sub 12-230 Hz ±5dB
(Yes, it vibrates quite a lot. Dunno what it would sound like if I made it from heavy Baltic Birch and hired some strong moving persons to help me lift it from my workshop to my music room.)
B.
And no, I am not so naive as to uncritically accept the wonderful good intentions of all speaker manufacturers.
On the other hand, if you want to see exemplary low distortion figures for a labyrinth/TL sub made from quarter-inch plywood, see post 5:
17 foot pipe sub 12-230 Hz ±5dB
(Yes, it vibrates quite a lot. Dunno what it would sound like if I made it from heavy Baltic Birch and hired some strong moving persons to help me lift it from my workshop to my music room.)
B.
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There was this bit, we discussed the energy going somewhere (damping), and the cabinet moving in order to produce that heat. A simple (but maybe not easy) bracing question.
That cabinet radiation can be as high as the driver itself shouldn't be controversial, it was shown in several papers I've come across when prepping for my box construction methods project. The one that sticks out I think was a BBC paper, for the life of me I can't find the paper but in the one attached they do reference this phenomenon by Bastyr and Capone.
There was discussion about this in my project thread, at the primary cabinet resonance it is almost transparent to sound. I measured this exact thing:
I'm still not wrapping my head around the cabinet not having nonlinear distortion. I suppose what happens when driven at its resonance vs any other frequencies might be different, so just focusing on *pure* signal at the resonant frequency being sent to a sound source, you guys are saying there would be no harmonics? I would think every physical material has some harmonic radiation when vibrating?
There was discussion about this in my project thread, at the primary cabinet resonance it is almost transparent to sound. I measured this exact thing:
I'm still not wrapping my head around the cabinet not having nonlinear distortion. I suppose what happens when driven at its resonance vs any other frequencies might be different, so just focusing on *pure* signal at the resonant frequency being sent to a sound source, you guys are saying there would be no harmonics? I would think every physical material has some harmonic radiation when vibrating?
No one is saying a panel can't be non-linear, rather that the process of resonance has nothing to do with non-linearity, and doesn't directly produce it. I suspect that what small amount of non-linearity there may be would be of little interest anyway, in the bigger picture.
No, there would not be any harmonics. Most nonlinearity requires large displacements, like a loudspeaker cone - some 100 -> 1000 x greater than a panel vibration. Look at Hook's law which shows that all stress-strain relationships are linear for small displacements. But yes, every material will have a nonlinear stress-strain relationship, it has to, but at what displacement level? Any sufficiently stiff enclosure is going to have very small actual displacements, so it is going to be linear.
But I do have sympathy for Ben's point: None of this has been shown to be a significant factor once some consideration for the enclosure has been made regarding its resonances. It may be a factor, never a large one, and will likely be masked by other system problems unless those other problems have been reduced to insignificance. As an absolute necessity, it's not, as a minor factor to be considered once all others have been dealt with is probably likely.
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Although I am confident that only the absolutely cheapest constructions have enough audible impact to have any impact...
I am trying to figure out the relation of wall vibrations to audible annoyance and convert the linear and not-so-linear into terms of human perception. Which after all, is the analysis we are really interested in.
Some vibrations arise from pressure inside the cab. Isn't that synched to the music (when wall tuning matches the music) and so not esp annoying?
Are non-linear plywood vibrations more annoying than linear ones? How does that relate to making guitars and violins?
B.
I am trying to figure out the relation of wall vibrations to audible annoyance and convert the linear and not-so-linear into terms of human perception. Which after all, is the analysis we are really interested in.
Some vibrations arise from pressure inside the cab. Isn't that synched to the music (when wall tuning matches the music) and so not esp annoying?
Are non-linear plywood vibrations more annoying than linear ones? How does that relate to making guitars and violins?
B.
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