Hushmatt test.

JeremyC · Post by **JeremyC** » Sun Jan 01, 2006 12:01 pm

The other day OnYrMrk and myself got to talking about putting hushmatt foam on the inside of a box, and how it helped the speakers responce curve. Well I deceded to test the theory before I spent the money on some hushmatt (its pretty expencive).

So I took 3 layers of the medium dencity pollyfill matt, and stapled it to the bottom, and 3 sides of my box.(couldn't do the plexy glass side, but I will on my next box minus the window). I ended up with a 3/8 to 1/2 inch layer of polly on all 4 sides (same thickness of the hushmatt foam).

And the diffrence is,.................................. Heck if I know. I am waiting on the silicon to dry so I can put it all back together.

Don't worry, I will let you know in the morning.

William from NOLA · Post by **William from NOLA** » Sun Jan 01, 2006 12:11 pm

BAH, the suspense is killing me!!!!

OnYrMrk · Post by **OnYrMrk** » Sun Jan 01, 2006 12:45 pm

I like the usage of the hushmat foam. Seems the freq response is better, but without an rta to prove the theory, I just don't know.

ridr4lif · Post by **ridr4lif** » Sun Jan 01, 2006 1:53 pm

Hmm...im interested in the results as well. I havent built my box yet, this could be a good thing. It doesnt take up too much interior space though, does it? I wouldnt need to change the dims of the box, would i?

JeremyC · Post by **JeremyC** » Sun Jan 01, 2006 3:01 pm

OnYrMrk wrote:I like the usage of the hushmat foam. Seems the freq response is better, but without an rta to prove the theory, I just don't know.

Thats why I am testing it. Granted the results might be in my head (if I do notice a diffrnce) but for 10 bucks I figured it was worth a try.

Ridr, it shouldn't change the internals all that much. If anything it would make the box seem a little larger to the speaker. Remember this is just like adding 1 lb of polly per cubic ft of space. But instaed of doing it to compensate for a box that is to small, we are using a small amount around the inside of the box to help with SQ. (so the theory says)

Ryan from Ohio · Post by **Ryan from Ohio** » Sun Jan 01, 2006 5:47 pm

What about adding egg crate foam to the interor?

It would cancel out almost all waves on the back side...

I did some work awhile back on some test stands for JBL. THey had a 3' sq box. The interior was lined with this sharp (60 degree) foam, it was blue. You could stick your head in and yell and not hear crap... Quite eerie...

Jonathan · Post by **Jonathan** » Sun Jan 01, 2006 6:09 pm

Aperiodic Membranes are the better thing for this application. In car audio, they're the best thing you're going to get for a flat, predictable response and boxless sound.

Jonathan · Post by **Jonathan** » Sun Jan 01, 2006 10:05 pm

But basically with fill, you're converting the enclosure from Adiabatic to Isothermal. The fill just converts more energy into the form of heat and makes the enclosure more lossy (better damped), so in effect the air pushes less on the speaker. I think the bigger difference you'd notice is the flattening of the impedance peak, which won't be a humongous difference, but it's audible.

The main reason I'm not a fan of sealed enclosures from a SQ stance is because it's pretty much impossible to fully dampen the resonance of the enclosure. You can fill, foam, deaden a sealed enclosure all you want and it can still be outdone by a well designed ported enclosure, much less an AP or Transmission line. IB tends to have such a low resonance that it isn't a big issue. With sealed, nearly any application of a typical 10" or 12" sub in a car is going to have the resonant frequency at least above 40hz, but usually in the 50s and 60s, right in the meat of the bass range. It's also the point where the sub has the least control and the highest distortion. There is the argument that you can equalize it, but I think we all know that you can't really rid the audibility of a resonance. I think this is a lot of the reason that SQ competitors are doing more and more IB applications in vehicles, with some doing AP, but it's hard to hit cap with an AP membrane and your average SQ subwoofer.

joeyc · Post by **joeyc** » Mon Jan 02, 2006 5:22 am

well, how did it work? or did it work at all? I guess i am the first one up on the new day!! let me know jc or let us know i mean

JeremyC · Post by **JeremyC** » Mon Jan 02, 2006 11:03 am

Well so far Jonathan was right. It did make a noticable diffrence, and caused me to have to reset my Crosovers and PEQ. Now considering the Hushmatt is way more dence and better suited in an acoustic enviroment. I am sure the diffrence will be even more noticable.

I did notice a little loss in SPL from the sub. Again, it was small, and wasn't really noticeable till I started resetting my PEQ.

Over all, it was worth the time and money spent, and I will be putting hushmatt in my next box.

If anyone is interested. Here are my new settings.

Sub LPF 60 herts with a 24db slope
Mids HPF 80 herts with an 18db slope
Mids LPF 2K with a 12 db slope
Tweets HPF 2.5K with a 12 DB slope

That gave me about the flatest responce curve I could get with out using the PEQ.

As for the sound. So far I am pretty impressed, but ask me again in a few days and I will tell you if I am truely happy with it or not.

Hay Jonathan, I love your siginature. Thats probably the most true quote I have heard in a long time.