Home Theater Forum and Systems banner

1 - 11 of 11 Posts

·
Elite Shackster , HTS Moderator Emeritus
Joined
·
2,216 Posts
It depends on what you are trying to accomplish.

if you want to increase perceived volume, then packing material is required like the poly-fill or pillow fill, or in my 1st subwoofer -- the inards of one of those reading/bolster pillows. :)

if you want to cut down on cabinet resonances, then you need something that sticks to the walls to prevent or limit standing waves from forming. Then you are looking at the no-rez, foam core, or other panel-like stick on foam.

Ideally, you would have both in your speaker, although resonances are more important to tame in the lower frequencies. As for which foam -- I would go with the latter, because it has more volume with absorptive material for the same applied area.
 

·
Registered
Joined
·
133 Posts
Would you have to subtract the volume that the foam takes up from the interior volume of the cabinet? In other words, if the stuff is 3/4-inch thick, would you need to add 3/4-inch to the dimensions of the enclosure in order to achieve the tuning volume?
 

·
Elite Shackster , HTS Moderator Emeritus
Joined
·
2,216 Posts
That's tricky. It doesn't work the way you're thinking. Foam and stuffing actually make the cabinet seem larger from a "spring" perspective, but the wall dimensions themselves (with or without foam) determine the potential resonances and standing waves.

Stuffing is always a trial and error thing. Most instructions and books say to stuff until you get better results (with usually a bounding condition like 2 cuft stuffing or such).

Sorry it's not more of a solid yes or no. Like most things in speaker design, it's a trade.
 

·
Registered
Joined
·
316 Posts
The most effective broad band acoustic absorption materials are high density (4-8lbs^ft3) fiberglass and rockwool/mineral wool board products. These are standard fiberglass and/or mineral wool that has been compressed to a high density and set with a glue. The popular fiberglass is known as Owens Corning 705. The mineral wool based material has more names and is much cheaper (but equally as effective). These are the materials most commonly used in the highest quality acoustic absorption treatments and anechoic chamber surfaces. Most foams are of dubious quality and will not likely come close to matching the same performance per thickness. Foams that do come close to matching the performance will be very costly, such as Auralex, which has been verified by 3rd party lab analysis.

I recommend staying away from gimmick materials like no-rez and most acoustic foams(Auralex being an exception of course). The mineral wool board is so effective that 2" mounted against a solid surface (this is called A type mount) will prevent acoustic oscillation/reverberation nearly absolute, down to about 250 Hz, with a gradual less effectiveness as you go below this point. It is effective into the high treble region (assuming you don't cover it with a material that reflects treble). Locally to me, a 6 pack of 2" thick x 24" wide x 48" high mineral wool board pieces cost under $40. Keep in mind, this is as good as it gets for broad band acoustic absorber material. You can only do worse (and likely will using generic foams and such). I do recommend covering the fiberglass/mineral wool with a thin cheap foam or acoustic transparent cloth in the cabinet to prevent the fibers from escaping the port(if ported) and to prevent fibers from possibly entering driver venting holes.

-Chris
 

·
Registered
Joined
·
316 Posts
Do you have a source and manufacturer/model for the mineral wool board?
First, you should search for local insulation contractors. The industrial/commercial establishments. They will have the best price and of course no shipping charges (being a local pick-up).

If you have to order online, here are a couple of sources(btw, 6 or 8 lb. density will act almost identically so far as broadband acoustical absorption, so don't assume the 8 lb. stuff that costs more is of any benefit acoustically):

http://www.atsacoustics.com/item--Roxul-Rockboard-60-Case-of-6--RB60.html

http://www.acoustimac.com/index.php...ion=com_virtuemart&Itemid=1&vmcchk=1&Itemid=1

-Chris
 
1 - 11 of 11 Posts
Top