Discussion on what materials to build speakers out of

[planet10]

Originally posted by MJL21193
I could have sworn you said mechanical vibration from the drivers operation was the biggest sourse of energy in the box. If so, low pressure, high pressure - doesn't matter.

I did, and building low pressure boxes just makes that more so...

dave

[planet10]

Originally posted by MJL21193
Damping is damping in any form. I provided a pretty accurate definition of damping earlier, didn't you read it?. Panel damping happens when a damping material contacts the panel (tuning fork I mentioned earlier).

A piece of wool felt or cotton felt placed next to a panel or a mass of loosely tufted polyfill have very little, if any, direct affect on the panel (and what they do directlt affect are only at higher frequencies). It is improtant to differentiate between airspace damping -- primarily intended to damp out reflection, standing waves, and higher harmonic pipe resonances -- from panel damping, which is intended to directly damp a panel. They are not the same beast at all.

dave

[MJL21193]

Originally posted by Ricky
I should like to add my tuppence worth to this.

At Arcaydis, I designed a cabinet in solid American White Oak and sold 20 pairs to a Canadian distributor. Every single pair came back. Why? Not because there was anything wrong with the speakers. The average humidity in Canada is 6%. The Oak literally "dried out". I found a remedy by laminating 8mm Oak to 12mm MDF in a flat press. Then I got the cold clinical edge.

There you have it: 20 pairs of speakers on the scrap heap because the designer didn't understand the limitations of solid wood, even here in the "sahara" like climate of Canada.
It's probably the first time in my life that ANYONE accused BC of being too dry

[planet10]

Originally posted by MJL21193
Two identical sound waves, of the same magnitude and phase approaching each other will cancel each other out, even at low frequencies. Are you disputing this?

Yes... you will get cancellation (& reinforcement) of the waveform but only at frequencies smaller than the cabinet dimensions and very much dependent on frequency & where you are considering the waveforms, These waveforms are actually mostly non-desructive and largely pass thru one another.

At low frquencies (wavelenghs longer than any cabinet dimension) the air acts as a lump and the 2 (or more) drivers act on the air as would a single larger driver (a woofer does not care what side of the box you mount the drivers on.

My favourite panel damping is and always has been carpet,... It's effective for breakup of standing waves and also is a very effective panel damping solution.

carpet tightly bonded to a panel should be effective at panel damping, As to standing waves it will have a very limited bandwidth related to its thickness and the material it is made out of. (here i am imagining your boxes lined with the orange shag carpet from the 60s/70s )

dave

[Ricky]

Hi all.

Whilst on the subject of cabinet resonance, does anyone know anything about the Celestion A1, A2 and A3?. Cabinet resonance was low on those.

Ricky.

[planet10]

Originally posted by MJL21193
It seems you have associated the use of damping with inferiior box construction.

No. What i am saying is that panel damping pushes the panels in extactly the opposite direction of what i am trying to achieve... it lowers panel resonance frequency by adding mass without increasing stiffness making it more likely that panel resonances will be excited and need to have the damping material. I didn't say it wouldn't work, it is just not as elegant (or as cost effective -- especially if you have to ship the box or lift it)

dave

[planet10]

Originally posted by Ricky
Whilst on the subject of cabinet resonance, does anyone know anything about the Celestion A1, A2 and A3?. Cabinet resonance was low on those.

Were those the exotic constrained layer "plastic" enclosures? I have heard positive things about those, but never seen any.

dave

[MJL21193]

Originally posted by planet10


A piece of wool felt or cotton felt placed next to a panel or a mass of loosely tufted polyfill have very little, if any, direct affect on the panel (and what they do directlt affect are only at higher frequencies). It is improtant to differentiate between airspace damping -- primarily intended to damp out reflection, standing waves, and higher harmonic pipe resonances -- from panel damping, which is intended to directly damp a panel. They are not the same beast at all.

dave

So, I guess what you are saying is that even though you are damping your panels, you like to say you're not.
The difference between the panel damping you do and one that is honest about it's intention is effectiveness. When the objective is to reduce panel vibrations, it can be addressed efficiently.
Take that same tuning fork and just touch it to the polyfil ever so slightly. Something magic happens.

[Ricky]

MJL21193

Please, if your gonna quote me, quote it all including the remedy which, incidentally, sold another 50 pairs on top of the 20 that got new cabinets with no problems.

[johninCR]

Originally posted by MJL21193
There you have it: 20 pairs of speakers on the scrap heap because the designer didn't understand the limitations of solid wood, even here in the "sahara" like climate of Canada.
It's probably the first time in my life that ANYONE accused BC of being too dry

Actually, it just shows that you need to know what you're doing. A friend exports solid wood doors to Canada with minimal problems. It just requires getting the wood to the appropriate level of water content and properly sealing it, as you mentioned before. I believe the real limitation with wood in speakers is like I mentioned earlier, that it transmits sound quite well. I'm unsure how well damping it from vibration will counter the ability of sound to travel along the grain structure.