Something to absorb my subwoofer vibrations - Page 2

 

Cat litter is like sand, but not so dense. Watch out for "I can haz poop musik" :-)

 

 

some high density foam should do the work...

I'm sorry but I have to refute the sandbox technique.  It doesn't work effectively.  I'm a mechanical engineering student (senior, about to go to Masters school) and I designed a proper turntable isolation box.  I matched spring rates to the mass of the turntable and the plate it site on, and at 20Hz, only 1% of the vibrations go through, and at 150Hz, a fraction of 1% go through.

 

I have a paper written about it that I can send anyone who is interested.

 

Bottom line, sand does next to nothing -- and I can prove it mathematically.

 

 

Since all the sand particles are crammed together we can treat sand as a solid body, then the damping of the sinusoidal audio waves is extremely minimum for bass frequencies, as the waves propagate very easily through a solid medium.  You need to add something that actually absorbs amplitude.  Enter -- the spring.  Springs have a natural frequency at which they try to oscillate.  If we can make this natural frequency (k) below our hearing levels, say 10Hz or something like that, we can effectively remove all the frequencies that are transferred through the springs at higher frequency. 

 

Again, all this is in the paper, you could learn a lot!

Edited by wdahm519 - 9/26/11 at 8:24pm

i would like to see your paper

I sent you a PM.

 

EDIT:  Paper and data sent. 

 

If anyone else wants it, I'd be very happy to send it to you to be enlightened 

 

Word of warning though, its a technical paper (more or less).  

Edited by wdahm519 - 9/27/11 at 2:42pm

I use a kitty.

 

They used to do that in budget studios quite a few decades ago but it's a bit of a wives tale. The cardboard egg cartons absorb higher frequencies but have little affect on lower frequencies.

Although I haven't read your paper, what you are suggesting goes against the extremely well developed field of acoustics. While springs are used as part of the most efficient system of double shell construction in recording studios, it would not be correct to state that sand does next to nothing. Sand does have very good absorption coefficients and is commonly used in high end recording studio design for it's acoustic absorption and isolation properties. I wouldn't know how accurate your math is but decades of materials testing provides actual evidence that sand is a porous absorber, with good absorption characteristics for low frequencies.

I agree with Uncle Erik, that to help isolate a sub, sand is the easiest and most efficient material to use.

G
Edited by gregorio - 9/27/11 at 4:57pm

My Auralex Subdude should be in tomorrow, I'll post pics/results if you like.

2 Squash balls cut in half under a granite chopping board, use blue-tac under the sub.

"Sand does have very good absorption coefficients and is commonly used in high end recording studio design for it's acoustic absorption and isolation properties. " 

 

Not for bass frequencies, its not.

 

Also, it doesn't isolate.  Sand damps amplitudes of sinusoidal functions.  They are two different things.

Edited by wdahm519 - 9/27/11 at 8:37pm

How so? All frequencies are sinusoidal functions. Sand is commonly used in the construction of suspended floors for example, to dampen low frequency vibration and to isolate one recording environment from another. Sand is one of the best materials available for isolation using the MAM principle.

G

Yes, it damps the amplitude of the frequencies, but doesn't isolate whatever is sitting on top of the same from those frequencies. 

 

Here is the isolation table that I built.  Below is the data generated from my theory as to why this works... Inside the wooden chassis are four springs.  On top of these four springs is the top plate where the turntable sits on.  I actually have four sound isolation balls that I bought so the performance is even better than this but I don't feel like removing the balls and they can only help so why not.

 

 

 

 

So you see, at 20Hz, my turntable sees an amplitude 0.0586 times the amplitude of the 20Hz sine wave as it hits the isolation table (5.86%).  At 150Hz, this drops to 0.1%!

 

I can find a spring with a decreased K value that has ample displacement without buckling and achieve even less isolation at 20Hz if you really threw a fit about 5%. 

Edited by wdahm519 - 10/1/11 at 3:32pm