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Need help with back wave attenuation

1K views 2 replies 3 participants last post by  Mike P. 
#1 ·
I'm preparing for my next build, and I am looking for some clarification on this matter, which seems to go unanswered on all the threads I've searched. One of my goals in this build is to eliminate as much resonance and distortion from the cabinet as possible.

I've built many enclosures utilizing varying degrees of bracing to achieve a somewhat "inert" enclosure, which is usually where typical DIYers will stop. I understand that raising the resonance of each panel above the operating frequencies diminishes the sound radiating from the box, but my main question is: Where does that energy from the back of the driver go if the walls of the enclosure don't "absorb" it by resonating? Energy cannot just be "stopped" by dense or braced materials. It seems to me, that this just forces the energy to come back out the driver, causing distortion and time delay in the listening area.

I've read into constrained layer damping, and frictional damping with materials like fiberglass, which both absorb the energy by converting it, rather than reflecting it. Has anyone had remarkable success with particular designs that use these?

What if a waveguide or similar shape were implemented inside a sealed box to simply "bounce" the rear waves around enough to diminish them before they exit the cone again? Would this create other problems within the cabinet?
 
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#2 ·
You are talking about several things here.

First, the bracing has to be adequate to minimize panel resonance and is always necessary. You should also not brace a panel dead centre as this will give two panels with potentially the same resonance.

The energy from the driver should purely be used in compressing and expanding the air inside the enclosure which acts as a spring to bring the driver back to its resting position.

The size of the enclosure should not have any lengths that can resonate within the usable range of the driver, if it does then this is the sound that will be retransmitted out through a poorly designed system.
 
#3 ·
If a cabinet does have a dimension that can resonate within the usable range of the driver ( example-6 foot tall sonotube, 8 foot wide front stage box) then the issue can be appropriately dealt with with damping material.

Not sure about the waveguide theory, a few pounds of damping material is usually enough to minimize any reflections in a sealed sub.

 
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