Constrained layer damping success!!!

[revboden]

I just built a subwoofer box using BB and MDF sandwiching "Schluter-KERDI" waterproofing membrane the resultant panels are so dead, when hit with a hammer all I hear is "thud".

Construction: I took one sheet of 3/4 inch mdf painted one side with latex primer, while the paint was still wet i rolled out the kerdi and used a legnth of 3" pvc pipe to roll out any air-bubbles, then painted the other side of the Kerdi with the latex primer and then laid the 3/4 inch BB on top. Set a bunch of bricks on top and let it dry.

Disclosure: I am not affiliated with "Schluter" in any way, I've just used their products to tile a lot of bathrooms and have this stuff just sitting around.

[revboden]

I also set screws in all four corners to keep everything lined up while the paint dried, dry time: seven days.

[c2cthomas]

Interesting! Ya got any photo's????

[revboden]

Correction: The Zinsser BONDZ is a urethane modified acrylic. Not latex.

c2cthomas,
Sorry, i didn't take any pictures, and as it's already built, it looks like any other 4.25ft^3 dual ported sub box with a 12" driver.

[CharlieLaub]

I seem to recall that Kerdi membrane is pretty pricey, but I don't know for sure. Is this available widely, e.g. at Home Depot? If not and/or it's expensive, what kind of substitute middle layer could you suggest?

-Charlie

[revboden]

CharlieLaub,
Yes, it is expensive. I'm a contractor so I get the stuff wholesale...

I've been thinking about using 2-3 mm Pond liner. it's basically inner-tube rubber my local pond supply shop has it for 85 cent per sq ft. with the appropriate adhesive should deaden any enclosure. must test. must learn. :P

[weltersys]

Originally Posted by revboden

CharlieLaub,
Yes, it is expensive. I'm a contractor so I get the stuff wholesale...

I've been thinking about using 2-3 mm Pond liner. it's basically inner-tube rubber my local pond supply shop has it for 85 cent per sq ft. with the appropriate adhesive should deaden any enclosure. must test. must learn. :P

Dead is good, but proper bracing can make panels quite dead without all the weight and expense.

If the stuff that is deadening is absorbing energy, output is reduced.

[planet10]

Originally Posted by revboden

when hit with a hammer all I hear is "thud".

What sound is a thud? Was the hammer blow on the inside of the box. MDF on the inside or outside?

LF, low Q is not the kind of sound you want back, particularily a woofer box.

dave

[revboden]

planet10,

When hit from the outside, It's the good thud or "thunk", think of a "thunk" ~300hz with a very very fast roll-off.

When hit from the inside the impact is damped so transmission to the outside is negligible (the "thunk" from the inside of the box is louder than the sound transmitted through the wall (I put my ear really close to the side being hit...)).

The MDF is on the inside, the edges were beveled and glued. Two shelf braces are used to split the top/bottom and the sides.

[kipman725]

how do you go about mounting the driver? is it mounted to the inner box or of the outer?