Constraint Layer Damping(options)

[highfigh]

The answer is yes. The best resource is Vance Dickason's Loudspeaker Design Cookbook, Section 5.40. Also, consider the papers written by:

J. K. Iverson, The Theory of Loudspeaker Cabinet Resonances, JAES, April 1973.

Juha Beckman, Effect of Panel Damping on Loudspeaker Enclosure Vibration, 101st AES Convention, November 1996.

You wrote, "The air resonates sympathetically and unless the cabinet can move in response (which will alter the results), the sound is considered to be 'colored'. I think that you meant to say that if the cabinet walls move or resonate it will color the sound.

I think that it is good practice to reduce cabinet resonances as much as reasonable. There becomes an asymptote where the amount of money and effort applied to squelching resonances does not provide a good return on investment. I suspect that point is pretty variable depending on the manufactures' and DIY goals and budgets.

I should have asked if this has been done recently. Using info from '73, when testing equipment and damping materials were inferior to what are available now seems like trying to resurrect the past, although I would assume the differences aren't earth-shattering.

That money vs effort not equalling a good result is the Law Of Diminishing Returns, in Economics and yes, I did mean 'if', not 'unless', but by the time I caught it, it was too late to edit the post. Thanks for that.

 

[Loren42]

I should have asked if this has been done recently. Using info from '73, when testing equipment and damping materials were inferior to what are available now seems like trying to resurrect the past, although I would assume the differences aren't earth-shattering.

That money vs effort not equalling a good result is the Law Of Diminishing Returns, in Economics and yes, I did mean 'if', not 'unless', but by the time I caught it, it was too late to edit the post. Thanks for that.

Yes, not that much appears to have changed since 1973. MDF is still MDF, plywood is still plywood, and roofing felt is still roofing felt.

It may be true that advances in constraining material may exist, Green Glue being one of them, but the principles are the same.

The other thing those studies shows that you can quickly get toward that asymptote, but the last mile on the road to perfection is only a few dBs.

There are also many roads to successful cabinet design and manufactures have not rallied behind just one solution.

 

[highfigh]

Yes, not that much appears to have changed since 1973. MDF is still MDF, plywood is still plywood, and roofing felt is still roofing felt.

It may be true that advances in constraining material may exist, Green Glue being one of them, but the principles are the same.

The other thing those studies shows that you can quickly get toward that asymptote, but the last mile on the road to perfection is only a few dBs.

There are also many roads to successful cabinet design and manufactures have not rallied behind just one solution.

RE: MDF- it has changed a lot. A local store chain has some crap that actually bends pretty easily and it's 3/4" thick. I used it once and will never make that mistake again.

For the other advances used in speaker design, RTAs used to only be available to engineers and it's now possible to download RTA software at no charge. Some, like REW has waterfall plots and RT60 calculations. These would have cost thousands of dollars 15 years ago.

 

[MidnightSensi]

RE: MDF- it has changed a lot. A local store chain has some crap that actually bends pretty easily and it's 3/4" thick. I used it once and will never make that mistake again.

Just a guess, but recently there have been more formaldehyde free binders used to lower VOC outgassing. It's possible the MDF board you bought used a different (less stiff) binder. Again, just a guess.

There are also many roads to successful cabinet design and manufactures have not rallied behind just one solution.

They haven't been particularly creative either.

 

[highfigh]

Just a guess, but recently there have been more formaldehyde free binders used to lower VOC outgassing. It's possible the MDF board you bought used a different (less stiff) binder. Again, just a guess.



They haven't been particularly creative either.

When I worked for a sound contractor in the late '90s, part of the company was a cabinet shop and the foreman explained that MDF was more of a paper product than wood because of how it delaminates and shears. ALL of the MDF I had used previously had larger pieces than the crap I bought the last time and the crap looks more like liver sausage than little chips of wood. It's about the same color, too. I went to the same store and they have the same stuff, so I won't make the same mistake again. I know another cabinetmaker and he always goes to the lumber company I worked for after high school and I'll be getting all of my MDF from them. They have been in business for 110 years and they don't show signs of dying, even with the big box stores. Their quality is well above average, they have more people who know what they're talking about and their prices aren't really any more than the others when the quality difference is considered.

 

[Loren42]

"...and the crap looks more like liver sausage than little chips of wood..."

Ah, you have discovered the Soylent Green!

 

[Loren42]

RE: MDF- it has changed a lot. A local store chain has some crap that actually bends pretty easily and it's 3/4" thick. I used it once and will never make that mistake again.

For the other advances used in speaker design, RTAs used to only be available to engineers and it's now possible to download RTA software at no charge. Some, like REW has waterfall plots and RT60 calculations. These would have cost thousands of dollars 15 years ago.

You are speaking about quality of MDF and not necessarily a technological change in the composition of the structure.

As for RTA, that is just a tool to measure with.

How does either of those invalidate the studies I cited?