# Acoustic stuffing material



## kilgoretrout (Jun 2, 2008)

Hi, I am putting my own acoustic stuffing material in a pair of non-DIY monitors (Behringer B2020P), but I don't know exactly how to place go about placing it and how much to use. Any advice?


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## F1 fan (Jul 6, 2006)

If its a ported box its best to line the cabinet walls only,if its a sealed box then loosely stuffing the volume with polyester batting is fine.


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## keelay (Dec 11, 2008)

Forgive the noob question. But what is the best stuffing. I have an old memory foam 2" egg crate topper that I imagine (there I go again) would be decent lining for a speaker cabinet. Any thoughts?

-Kyle


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## 1Michael (Nov 2, 2006)

The egg crate is fine.


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## delphiplasma (Oct 22, 2008)

Acoustic wadding is a very fine point. I've carried out tests and they all seemed to produce different types of sound quality. The white polyester wadding was the worse. 

The best foam I’ve used is glass fibre foam. It is extremely effective.

Polyester/polyurethane foam blocks were only ok.

Long hair wool filling is probably second best to glass fibre foam.

The above were for Bass reflex and IB.

However, I would imagine in a transmission line, the foam block and long hair wool fillings would be best.

Subwoofers are definitely better with glass fibre filling.

These are my personal findings; however others may beg to differ?


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## avaserfi (Jul 5, 2007)

Intent determines what damping material is best. If one wants to remove internal reflections to minimize resonance than a high density material such as OC705 or 8lb mineral board is ideal. Sufficient use of such materials will eliminate any internal reflections caused by driver backwaves and/or modal behavior within a cabinet. This is application dependant - a typical sealed subwoofer may only need 2-4" on each side while a midrange cabinet would need to be stuff full to prevent any reflections.

Egg crate foam and poly fill have virtually no absorption ability and are not typically suited for such an application.


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## willy-be (Nov 15, 2006)

avaserfi said:


> Egg crate foam and poly fill have virtually no absorption ability and are not typically suited for such an application.


The Professionals disagree


> How does damping work?
> 
> In a sealed enclosure the driver moves in and out some distance. Multiplying the displacement distance by the surface area allows us to determine the volume of air pushed. While the front side of the woofer pushes air molecules which fill our listening areas with sound, the air in a sealed enclosure is compressed and expanded with the inward and outward motion of the driver. To more simply describe the situation in the box, we see that the quantity of air molecules in the box is fixed (it's sealed), while the motion of the driver's cone changes the volume of the sealed box.
> 
> ...


Tom Nousaine says.....
http://web.archive.org/web/20041027...gracaraudio.com/caraudio/resources/fiberfill/

Aloha,
WB


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## avaserfi (Jul 5, 2007)

The experts quoted here seem to primarily be focused on effective volume not acoustic signal absorption which is what I am referring too. These are two completely separate issues.

Of course, there are some potential negative effects from use of materials as I discuss alluded to within the quotes. The main potential issue is critical damping of a sealed midrange enclosures. Critical damping will cause an attenuation of lower frequency response, but critical damping can be fully remedied via equalization or crossover design.

In the end for acoustic signal absorption, which results in cabinet resonances, there is no superior alternative and materials such as egg crate foam and polyfill are virtually useless.


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## willy-be (Nov 15, 2006)

avaserfi said:


> The experts quoted here seem to primarily be focused on effective volume not acoustic signal absorption which is what I refer.


The effective volume increase is a function of the absorption of the acoustic signal.



> Proper use of materials I recommended will typically result in critical damping of midrange enclosures,


Critical damping of an enclosure can be accomplished using any number of damping materials. And the effects of the damping material can be measured by comparative impedance sweeps.



> In the end for acoustic signal absorption, which results in cabinet resonances, there is no superior alternative and materials such as egg crate foam and polyfill are virtually useless.


And the proof for this claim is in what peer reviewed research?


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## avaserfi (Jul 5, 2007)

willy-be said:


> The effective volume increase is a function of the absorption of the acoustic signal.


The effective cabinet increase is not due to absorption, but changed internal thermal characteristics of the cabinet.



> Critical damping of an enclosure can be accomplished using any number of damping materials. And the effects of the damping material can be measured by comparative impedance sweeps.


A material must have sufficient absorption characteristics for a given cabinet size to cause critical damping.



> And the proof for this claim is in what peer reviewed research?


Measured absorption coefficients by credible sources such as NRC labs.


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