Fabric for absorbers  

Any fabric that has a relatively loose weave will work just fine. Acoustically transparent fabrics simply allow high frequencies to pass through as easily as low frequencies. If you can blow through a swatch without your face turning colors, it will be sufficiently acoustically transparent.

alinor --

Your impulse to experiment, rather than purchase, is a good one.

I would suggest some DIY panels. Get some 1x4 lumber (or ripped plywood) and make a rectangular frame as high as your ceiling and, say, thirty inches wide. Cover the two faces with some inexpensive black fabric -- I would suggest the black "shade fabric" in the Home Depot Garden Dept (or Landscaping Chintz Cloth, if you're really frugal) -- and fill the intervening three inches with whatever you can find that is cheap and absorptive. (My suggestion: Visit a local carpet shop and ask them for carpet and/or padding scraps, if you're too shy to go dumpster-diving.) If you want to get fancy, outfit the long edges of these Shoji-screens with hinges so that they can interlock.

You should be able to make eight of these babies for less than a hundred bucks (and a little time). With them, you will be able to impose more noticeable changes to your acoustics than a thousand dollars worth of those little triangular pillows.

My advise is to go to a fabric shop such as Joanne's, go straight to the clearance rack, and pick several yards of a fabric that goes best with your room decor. If you can blow through the fabric and see a small amount of light through it, odds are it will be fine for panel absorbers. If you are looking to make upper bass panel absorbers you can use a denser fabric to provide more resistance to air movement.

I have a very large bass trap spanning the entire front ceiling of my room (~12') that is approximately 24" deep and 13" high. I filled that space with mineral wool and covered the front face with black Velveteen. My thinking on this was that the velveteen would reflect high frequencies but that the low friequencies I was hoping to tame would pass through the velveteen and into the massive amounts of mineral wool in the trap. Is this a reasonable assumption?

Out,

> I have a very large bass trap spanning the entire front ceiling ... the low frequencies I was hoping to tame would pass through the velveteen <

Yes, in theory this is true. Exactly what kind of bass trap do you have?

--Ethan

Hello,
I am also looking into making treatments myself. Where can I buy rigid fiberglass #703 or #705?

Thanks,

Derrick

Ethan,

Well, I suppose bass trap makes it sound more technical than it is. I simply framed a large space at the front of my HT where the ceiling meets the front wall. It doubles as a bit of a shadow box. I initially was going to put my rather large center channel in it (it was wired for that purpose) with either side serving as bass traps but I decided to put the CC on the stage on a stand instead so I used the whole front (only my IR repeater is in there now). So I have drywall covering the bottom and an open face toward the listening position. I stuffed the whole thing with Roxul Safe N Sound Mineral wool (several bags worth) and covered the front with black velveteen.

Having seen plenty of bass trap designs (including yours Ethan) I thought that this might prove useful for taming bass as there is at least 34 cubic feet of heavy insulation in there (if my math is right...). Initially I was going to go with GOM fabric but it was very expensive and not particularly attractive. I saw many designs that had plywood or hardboard for a facing so I figured acoustical transparency was less important for a low frequency bass trap.

Unfortunately, I have no idea if it is helping or not. I have no basis for comparison as it has been there as long as I've had equipment in the room. I'm not unhappy with my bass but I think there is still a lot of room for improvement. I also stuffed my riser with mineral wool and left some holes in the face to try to trap some bass at the rear (floor) of the room. What do you think Ethan? Does this sound like a reasonable solution? I don't have any rigid fiberglass but I figured the volume of mineral wool should compensate for density...

alinor
If black is your thing - ponte works well. It looks just like grill cloth & is used as such by many.
Holds the fiberglass wool well.

I describe one way to use it here.
http://www.avsforum.com/avs-vb/showt...hreadid=389309


Good Luck
E

Derrick,

> Where can I buy rigid fiberglass #703 or #705? <

Look in your local Yellow Pages under Insulation Suppliers and Contractors, and also under Heating & Air Conditioning.

--Ethan

Out,

> So I have drywall covering the bottom and an open face toward the listening position. I stuffed the whole thing with Roxul Safe N Sound Mineral wool (several bags worth) <

With that much fiberglass I'm sure it's helping - probably a lot - though it would help even more without the sheetrock underneath which is blocking some of the waves from entering from that direction. I'll also mention that adding a similar amount of fiberglass spread out around the room in other corners will help even more.

> I also stuffed my riser with mineral wool <

That probably prevents it from ringing and vibrating more than it adds bass trapping in the room. If only because the riser is in the center of the floor rather than in a corner or flat against the rear wall.

> I don't have any rigid fiberglass but I figured the volume of mineral wool should compensate for density <

Yes, this is true. All you need is to spread more such absorption around the room.

--Ethan

Ethan,

Thanks for the advice. Would it be worthwhile to cut ports of some sort in the drywall to allow some sound to enter or would this create more resonance issues than it would solve? How big would the ports have to be?

My riser actually extends all the way to the back wall. It is ~6' deep and 12' wide by 10" tall and may help a bit (I hope).

I put a bookshelf on my back wall in hopes of creating a bit of diffusion but it is only about 3' wide so this is not an ideal solution for all seating positions. My wife is reluctant to let me put anything else like corner traps in back. Maybe with time she will be more open to the idea...

OL,

> Would it be worthwhile to cut ports of some sort in the drywall <

It would be even better to open the entire bottom up, or at least make the openings as large as possible.

--Ethan

Ethan,

I don't think that would work structurally. With over a foot thick of mineral wool resting on it, I think any pure fabric solution would bulge out in a very aesthetically damaging way. I'll give it some thought.

Outs,

> With over a foot thick of mineral wool resting on it <

You can get 1/2 inch by 1 inch pine sticks, or equivalent, and put them every six inches or so as supports. Or something along those lines.

--Ethan

For covering, nothing beats grillcloth.