Sound Deadening Your Box

[blsj1486 10+ year member]

Does lining the inside of your box with sound deadening do anything for the sound quality or loudness of your subs?

Thanks

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[dpom 10+ year member]

im not an expert but as long as the box is built right and sealed properly, i dont think you have to.

 

[Notloud00 10+ year member]

lol no. brace the box with some left over mdf on each side.

 

[Rudy 10+ year member]

Nope, waste of material. Sound deadener will do nothing for a properly built box.

 

[jrwalte 10+ year member]

Acoustical foam or polyfil can help, but not deadener.

 

[FoxPro5 5,000+ posts]

Nope, waste of material. Sound deadener will do nothing for a properly built box.

Depends on the material. A quality liquid deadener on semi-porous MDF will both increase the density and rigity of the structure. It may also help reduce the resonant frequency assuming the material is truly viscoelastic. If you LP your sub at 80 hz with a 12 dB slope, you're still playing 160 hz nearly half as loud. If that causes excitation of the MDF and you can audibly locate the box, that's not a good thing.

I got an estimated (not measured) 2-3 dB bump in the sub passband with two coats of VB-1 on the inside of mine. The box does indeed sound more dead/solid.

 

[FoxPro5 5,000+ posts]

Acoustical foam or polyfil can help, but not deadener.

Open cell foam vs a 60 hz wave that's 20 feet long? No, it will simply be ignored.

Polyfill has the effect of creating a greater inclosure volume, not any type of sound deadening what so ever. Go ahead and tape a bag of polyfill over the outside of your sub and listen to see what it does by way of affecting the sub output.

 

[audioholic 5,000+ posts]

When building a box, you want its resonant frequency to be outside the frequency window the subwoofer system will be expected to play. In other words, if the sub is gonna play 20-100 hz, you dont wan the box's natural resonant freq to be 60hz.

Knowing this, we must now look at how to achieve our goal. The box must be built to either resonate above 100hz, or below 20hz (for my example box). You lower res freq by adding mass, which is what the OP is suggesting by adding mat to the inside of the box.

The second way is to raise the res freq of the box. You do this by making it rigid. You can have a light, but strong box, that vibrates at a relatively high frequency (outside your playing range). You increase enclosure rigidity by, you guessed it, adding bracing.

Some home audio systems are designed to go below the operating range of the sub, by building the enclosure out of concrete. That works in a livingroom or basement, but not so much in a trunk. So the vast majority of car audio boxes are designed to be rigid, to raise res freq above the operating range... many times with the designer not even realizing it.

So knowing all this, you can now see why adding a mass loading mat to the inside of your box will be nothing but a waste of materials. The foams mentioned above are meant strictly for dispersing back waves, do not confuse that with deadening.

 

[FoxPro5 5,000+ posts]

lol no. brace the box with some left over mdf on each side.

Bracing has the effect of raising the resonant frequency. Not saying that's good or bad, just pointing out how to go about proper treatment (if any).

 

[audioholic 5,000+ posts]

Depends on the material. A quality liquid deadener on semi-porous MDF will both increase the density and rigity of the structure. It may also help reduce the resonant frequency assuming the material is truly viscoelastic. If you LP your sub at 80 hz with a 12 dB slope, you're still playing 160 hz nearly half as loud. If that causes excitation of the MDF and you can audibly locate the box, that's not a good thing.
I got an estimated (not measured) 2-3 dB bump in the sub passband with two coats of VB-1 on the inside of mine. The box does indeed sound more dead/solid.

You used it to lower the res freq of your box? What do you think the res freq of your box is? //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif