just how much sound really comes out of the speaker cabinet? Its impossible to tell because you can't listen to it and the sound from the driver separately.
some folks have even said that the sound from the cabinet is many times that of the drive unit. But I can't hear any sound if I listen to the speakers cabinet from behind. In fact even if i put my ear up against the cabinet of my mdf speaker, there is only a faint sound coming through. Is it all lies?
The only good way to tell is to make two identical speakers except one made from a different material to the other. Has anybody done it?
Comparing lets say concrete vs mdf?
And how much mass would the cabinet have to have to dampen out or resist the transferred vibration from the drive unit to the cabinet?
some folks have even said that the sound from the cabinet is many times that of the drive unit. But I can't hear any sound if I listen to the speakers cabinet from behind. In fact even if i put my ear up against the cabinet of my mdf speaker, there is only a faint sound coming through. Is it all lies?
The only good way to tell is to make two identical speakers except one made from a different material to the other. Has anybody done it?
Comparing lets say concrete vs mdf?
And how much mass would the cabinet have to have to dampen out or resist the transferred vibration from the drive unit to the cabinet?
I think there's some mis-interpretation about "cabinet sound". If you go back to the Linkwitz article from the '70s, he used a phono cart placed in contact with the cabinet to find that at _some_ frequencies, the cabinet was indeed louder than the driver, due to panel resonances. Not _all_ frequencies.
He went further, and explored damping and decoupling the drivers to reduce this output...
He went further, and explored damping and decoupling the drivers to reduce this output...
It was also extensively researched by the BBC in the mid 70s. The Linkwitz piece was in Wireless World in 1978 or '79 and I think it's on his site. The BBC papers are on their website in the engineering archive.
http://downloads.bbc.co.uk/rd/pubs/reports/1977-03.pdf
http://downloads.bbc.co.uk/rd/pubs/reports/1988-14.pdf
http://downloads.bbc.co.uk/rd/pubs/reports/1977-03.pdf
http://downloads.bbc.co.uk/rd/pubs/reports/1988-14.pdf
My take on the subject....If you can feel the vibrations in the enclosure, no doubt it is producing sound...how much? I don't know. I'm sure someone out there has some data on such an experiment.
Now, run a frequency sweep on an enclosure & I'm sure the thing will sing like a little birdie...
I'm sure one could build an enclosure out of a Lead alloy that won't be set in motion by a driver......but more than a bit impractical.
Myself I'm experimenting with a local "Ironwood" Schinopsis balansae ....at a specific gravity of 1.24 and a Modulus of Rupture of 141.7 MPa (MegaPascals)..tough stuff. I found a local Furniture/Workshop who specializes in the working of the stuff. I should ask just how much it might be to create an enclosure, I've an idea how best to do it.. I think we need to make more "massive" enclosures to rectify this 'thorn-in-the-side' shortcoming.
______________________________________________________Rick.........
Now, run a frequency sweep on an enclosure & I'm sure the thing will sing like a little birdie...
I'm sure one could build an enclosure out of a Lead alloy that won't be set in motion by a driver......but more than a bit impractical.
Myself I'm experimenting with a local "Ironwood" Schinopsis balansae ....at a specific gravity of 1.24 and a Modulus of Rupture of 141.7 MPa (MegaPascals)..tough stuff. I found a local Furniture/Workshop who specializes in the working of the stuff. I should ask just how much it might be to create an enclosure, I've an idea how best to do it.. I think we need to make more "massive" enclosures to rectify this 'thorn-in-the-side' shortcoming.
______________________________________________________Rick.........
Impossible? Art Ludwig's research might change your mind: Loudspeaker construction
The rest of his site is equally enlightening to the neophyte, but seems largely forgotten today: Art Ludwig's Sound Page
GM
Also in :
BACKMAN, JUHA: Effect of panel damping on loudspeaker enclosure vibration, Preprint AES 101st Convention 1996 November 8-11 Los Angeles, California.
TAPPAN, PETERW.: LoudspeakerEnclosureWalls. Journal of the Audio Engineering Society, July
1962, reprinted in the AES Anthology Loudspeakers, vol. 1, pp. 88 -- 95, Audio Engineering Society, New York, 1978.
IVERSON,JAMES K.: The Theory of Loudspeaker Cabinet Resonances. Journal of the Audio EngineeringSociety, April 1973, reprinted in the AES Anthology Loudspeakers,vol. 1, pp. 312 -- 315, Audio Engineering Society, New York, 1978
Backman compares 9 test cabinets of different wall materials but otherwise identical constructions and measures the frequency responses as well as the cabinet vibration responses. The comparisons make interesting reading. My interpretation of the results are that the common materials mdf, plywood, particle board are all pretty poor on their own, but surprisingly particle board has some measurable acoustic advantages despite mechanical problems of fragility, moisture attack etc. All of these are improved by various damping methods. Veneer does nothing for damping. Lead is nowhere near as good as reputed elsewhere. Visco-elastic layers (CLD) made significant measured improvements to plywood.
An oft discussed situation, but one that is often poorly researched.
First, the correlation between the vibrations of a cabinet walls and the sound at the listening position is fairly small. This means that measuring the vibrations of the cabinet does not indicate how much sound is actually transmitted.
Then there is the problem of perception. Because one can hear the cabinet when the direct speaker sound is minimized does not mean that this sound would be audible once masked by the direct sound.
Measuring the differences in the far field from different cabinet constructions, I found the differences to be rather minimal. Once the cabinet is "decent", further vibration reductions did not appear to be measureable.
Hence, my conclusion is that a crummy cabinet may be a problem, but any well braced decent cabinet is not an issue.
That said, I use a lot of constrained layer damping, solid construction with cross bracing and so seeing the effects of added damping in my designs was not possible. I even reduced the damping considerably and could neither hear or measure any differences.
IMO, the damping of the material is more important than its mass or its stiffness. A well damped material with a high strength to weight ratio is ideal. Polyurethane planks appear to me to be ideal.
First, the correlation between the vibrations of a cabinet walls and the sound at the listening position is fairly small. This means that measuring the vibrations of the cabinet does not indicate how much sound is actually transmitted.
Then there is the problem of perception. Because one can hear the cabinet when the direct speaker sound is minimized does not mean that this sound would be audible once masked by the direct sound.
Measuring the differences in the far field from different cabinet constructions, I found the differences to be rather minimal. Once the cabinet is "decent", further vibration reductions did not appear to be measureable.
Hence, my conclusion is that a crummy cabinet may be a problem, but any well braced decent cabinet is not an issue.
That said, I use a lot of constrained layer damping, solid construction with cross bracing and so seeing the effects of added damping in my designs was not possible. I even reduced the damping considerably and could neither hear or measure any differences.
IMO, the damping of the material is more important than its mass or its stiffness. A well damped material with a high strength to weight ratio is ideal. Polyurethane planks appear to me to be ideal.
I do imagine that Mr. Geddes' cabinets are well damped, and don't resonate very much. My feeling is that un-damped cabinets can have a "smearing" effect due to high "Q" resonances that take some time to die down. Bracing only raises the frequency, but damping and decoupling of the drivers can help.
That statement ignores the fact that the energy available to excite the panel resonance is inversly proportianal to the square of the frequency
A high Q resonance also requires a large number/amount of input over a limited bandwidth to excite it, not something often seen in music.
So if you can make the panel ring at high frequency, and high Q, the liklihood of it ever getting excited by music becomes VERY low.
dave
I would certainly agree that a high Q resonance is a worse case as its ringing could go on longer than the musical signal and hence become unmasked. I think that once the resonances are damped, that the decay times are such that the sound will always be masked by the music. Clearly what frequency the resonances are at is less important than how long they ring. A massive stiff cabinet will push the resonances higher, but they may well ring longer. I'd rather have them lower in frequency but with a rapid decay.
Dave - could you support your first statement. I am not sure that I agree with it.
The issue with your second statement is complicated and I am also not sure that I would agree with it for the reasons that I state above. It could be a wash, at best, but I could never see it being better to push the resonances upward in frequency but less damped.
My position comes from decades of experience with noise control in automobiles. Stiff is good for ride and handling, but lose and well damped is better for noise. It was always a battle to compromise between the two.
Inverse square to the F, of course........... But let's say our perception of sound assumes a bell curve (Music content, not power) of F & for the resonance to fall smack square on that curve....the perception might be more pronounced.
So, assuming our theoretical loudspeaker is stand mounted mid-chest high, we get three different frequencies radiating away on three different axis. Would we not want those particular frequencies coming at us from "all" directions?
_____________________________________________________Rick......
So, assuming our theoretical loudspeaker is stand mounted mid-chest high, we get three different frequencies radiating away on three different axis. Would we not want those particular frequencies coming at us from "all" directions?
_____________________________________________________Rick......
Re; the "Q" of resonances. Many people instinctively assume that high Q must be worse than a more damped low Q. But this is not necessarily the case. What Barlow (Leak, sandwich cone fame) found many yrs ago was that when a resonance is damped (the peak lower but MUCH broader) it can then be excited by a much larger range of frequencies and was MORE audible as a consequence. All shown in his JAES (or Wireless World) paper from about 40yrs ago.
So the published work supports Dave's contention.
The best work I've seen tries to minimize decay time as that is what the ear responds to most sensitively.
Cheers, Jonathan
So the published work supports Dave's contention.
The best work I've seen tries to minimize decay time as that is what the ear responds to most sensitively.
Cheers, Jonathan
Last edited:
its just a preference whether you want to fix a large peak at one frequency or a shallow peak over a broader range. Both could be equally tricky
It is a suspicion i have been working under for over 30 years. In the last couple in one of my references (Berenak?) i found a supporting equation. I should have bookmarked it, as i have not been able to refind it.
dave
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.