If you are talking about just dampening resonances, there are a lot of 1/2" and 3/4" foams that you can use on the insides of the speakers box. Parts Express and others sell it and many speaker kits come with it.
If you are talking about poly-fill and tuning, then it's a trial and error setup. I've seen many boxes that are about 75% filled with the stuff, but the end result is tuning the effective box size to achieve the proper bass balance. You are affecting the hump and roll-off by stuffing, as more stuffing makes the box "look" bigger to the waves inside. Obviously there is a theoretical end to this. Full stuffing is (IIRC) 25% more effective volume than the box alone.
But calculate all you want, the true test is to stuff, measure, restuff, remeasure, repeat.
Check out "damping" and "polyfill" at Parts Express -- a lot of good info, reviews, and recommendations there.
- stuff sealed enclosures with polyfill to damp all internal waves
- line ported enclosures with acoustic foam to damp reflected waves
In any sort of resonant enclosure (ported, passive radiator, transmission line, etc.) air needs to move. You line the walls with acoustic foam to absorb higher frequencies so they don't bounce around inside the box. The low frequencies that remain are what you hope will resonate and reinforce your low end. Here you generally tune the port length to tweak the bass response.
In a sealed box, air's got nowhere to go, so you fill the volume. Depending on how tightly you fill it, you will see subtle (to some) variations in bass response. Too much will attenuate the low end, too little will allow resonances to show up (best as I can describe). This one you tune by changing the fill density.
Now, in a 3-way with an open back mid, I'd:
- design an optimum ported box for the woofer using Unibox and T/S parameters
- seal off a chamber behind the mid/tweeter so they operate independently of the woofer
- stuff the mid/tweet chamber with polyfill since it's sealed
- put 1" or more acoustic foam on all interior walls except the baffle
- consider more foam, or a bit of polyfill at one end of a long box or around the port itself if things are still boomy after the port's tuned.
Pointers for tuning? Please your ears! You may need to train them first....
Room tuning isn't easy, but here's a great resource:
yea I run 24 channel Allen&Heath w/two QSC 1000 watt amps, two 31 band eq's, digital effects,etc. etc.
Even with all that I still need a a real time analyzer to help eq the room. I have an Onkyo 506, JBL back surrounds, JBL middle surrounds and I am rebuilding those chessy towers I bought. That is the reason fo all the questions. I also have an infinity center channel. My theater room is 16x30. I have a non audiophile wife. So all of these stuff I want to get is quite confusing for her. I know what sounds good. But I want great! But with a limited budget I am going to use everyone's kind advice. To build a very good room Thanks for all the replays. Garry
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