Insulation materials.

[Blaser]

Hello Friends!

I have read that filling subwoofer walls with an insulation material has for main target to make the enclosure act like a bigger one (enhance LF response). From the other side, I have also read that this helps with wall resonances.

Moreover, there are many types of insulation materials: Fiberglass, Fiberfill, Dacron, open cell foam, closed cell foam.....

Here are some points I would like to discuss:

- How much bigger the enclosure will appear? what's the rule?(related to thickness, wall length?)

- Should the insulation volume be substracted from the effective volume before insulation?

- What if the enclosure is big enough (LLT for ex.), is stuffing mandatory? What about the tuning frequency if the enclosure appears bigger than it is?

- What are the differences between insulation materials? Why use one and not the other type?

- When to apply insulation or not?

If others have questions, they are wellcome to add. Those who have answers are wellcome to educate!!

Thanks.

[buggers]

This is good stuff and it won't break the bank.
http://www.knoxfoam.com/cgi-bin/Soft....htm?E+scstore

[Blaser]

No no, I am not talking about prices... I am looking for scientific reasons. comparisons, whys....

[Ilkka]

Here's a good article that will cover at least some of your questions.

http://www.diysubwoofers.org/talksho...ages/41415.htm

[buggers]

I see what your saying. I use this material simply to make the box stop ringing, to make it dead.

[bigguy]

buggers wrote:

This is good stuff and it won't break the bank.
http://www.knoxfoam.com/cgi-bin/Soft....htm?E+scstore

which is better... their egg crate or the closed cell... or rough or smooth surface?

[buggers]

The closed cell for deadening the box, open cell for absorbing sound. I use the closed cell to line the box and then use fiberglass to fill the box if necessary. I dont believe it is as critical for subwoofers.

[Chester]

I use activated charcoal in perforated baggies in my sub... (its a diy sub)
http://www.kef.com/technology/acoustic/aceintro.asp

[grjohnso]

ACE is an interesting thing... Where did you get it, and how much does it cost? How would you rate it compared to conventional dampening/fill material?

[Chester]

http://www.kef.com/technology/pdfs/acewp.pdf
well first I looked at this whitepaper for a bit, I tried to find an approximate conversion factor; how much volume x volume of carbon would add to the box. my calculations were as follows (data taken from whitepaper)
-----------------------
2.8 liters of normal volume
2.2 liters carbon simulating
3.6+2.2=5.8 liters;
5.8/2.2=2.636 (factor of volume increase per volume of carbon)
------------------------
these numbers were derived from the text on the 6th page about the technology demonstration.
basically I get 2.6 cubic feet for every cubic ft of carbon in the box *below 90 hz (see graph in whitepaper)... anyways, KEF uses goretex fabric 'tubes' to enclose the activated carbon which is of a consistency of slightly heavier than styrofoam, 'sand granules' that will easily crumble and leave coal dust on whatever they crumble on... be sure to work outside on some grass or something if possible, or atleast an easy to clean area.
my carbon is in 'pouches' about the size of medium size zip lock baggies made of perforated plastic, normally landscaping material... the holes are just small enough that the carbon cannot get through; i will try and calculate out the volume of carbon used, i cant find my figures right now: I do know that i ordered two 40 lbs (80 lbs total) boxes of it, i have a little more than one box left over for future projects, I think it was around $66 per 40 lb box. I feel it works great as a dampener, in my sub I have noticed that due to teh vibrations, it 'settles' in the baggies very well and after while the baggies flatten and meld (is that a word? lol) together, (they take up the least space possible). I am considering putting a bit of rockwool in the sub however I dont want to open it... as far as the stuff working, I have used a dbx RTA-M mic hooked to my computer to measure the frequency response of the room (using the Room EQ Wizard program obtained on this forum), the bass response went to 15-14 hz, the calculated value with the carbon. This is including a 12db/oct cut below 37.5hz to account for cabin gain. I hope this helps a bit, I will try and find more links (i think i have a few patent links also) if you want them.

-Matt

EDIT: I found the carbon through Froogle (Google Products now?) I got the '20x40' grade (a measure of particle sizing), also, KEF's whitepaper shows differences between carcoal activated carbon and coconut shell activated carbon, i believe what I have is the coconut shell variation. cant remember why I choose that one

[Blaser]

I have read good things about rockwool....what do you think?

[Chester]

i have not done any 'analysis' between rockwool and plain insulation however i have found it to work very well. looking at absorption coefficents provided other places on the net, it works great

[shr-t]

Ilkka wrote:

Here's a good article that will cover at least some of your questions.

http://www.diysubwoofers.org/talksho...ages/41415.htm

I actually plotted a couple of figures of those numbers a while back, also converted to standard SI-units, here's it.

I've used just rockwool or some other standard construction materials, cabinet filling materials specifically made for speaker construction are usually overpriced and too light in my opinion(i.e. they have less of an effect than regular rockwool).