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I am putting together a 8 cuft ported box with a CSS SDX-15. I am trying to decide if there is a need for damping material. The box will be braced fairly well with braces no more than 15" apart. This should drive the panel resonances up more than double the operating range.

Some say yes and some say no (and some say they can't tell the difference) to damping in ported boxes. What is the concensus?
 

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There are certain reasons to use a quality dampening agent such as OC705 or 8lb mineral wool. If the cabinet is large enough such that it is greater, in any dimension, than that of 1/4 the wavelength of any frequencies in the bandpass then use of dampening material would be beneficial. This is so because the dampening agent would aid in the removal of standing waves from the system. Also, a high quality dampening agent will remove mechanical noise, if any, as created by the sub.
 

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Or use open cell egg crate foam which is cheap and effective.
Egg crate foam is not an effective material in reducing standing waves in any appreciable manner. It might help with mechanical noise created by the components, but it simply does not absorb enough energy to be useful for the potential issue of standing waves. Simple physics dictate this statement as the egg crate foam has neither the mass or specialized material that allows it to have a high enough absorbency coefficient to be useful in such an application.
 

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The original question was if there is a need for damping material in a ported enclosure. The answer is yes, to damp the backwave of the subwoofer, reducing the "boominess or "hollow sound" as some describe it. Standing waves are a different issue where egg crate foam is not effective, and is dealt with by other means as you stated.
 

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The original question was if there is a need for damping material in a ported enclosure. The answer is yes, to damp the backwave of the subwoofer, reducing the "boominess or "hollow sound" as some describe it. Standing waves are a different issue where egg crate foam is not effective, and is dealt with by other means as you stated.
Fundamental standing waves are a non-issue, as today's smaller box dimensions won't support them. But suppressing midbass and midrange harmonics is a necessity, even well above the passband, as the motion of the cone creates harmonics. The only alignment where damping is actually detremental is folded horns, as their folds filter away the above passband harmonics anyway, while damping the chamber interferes with reactance annulling.
 
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