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PartTimeProjects Hanging Bass Traps

Bass traps are commonly used to treat the acoustics of a room. You will find them in studios and movie theaters where they control echos and tame boomy bass to make it tighter and more precise. They "absorb" the bass, rather than reflect or redistribute it. Bass traps are commercially available or you can make your own.

Essentially a bass trap is a fiberglass pillow- fiberglass wrapped in "batting" wrapped in a loose weave fabric. A hanging bass trap is a hanging fiberglass pillow that is put in a wooden frame. You can put "rigid" Owens Corning 703 (I used 2" thick OC703) into a frame and hang it or compress some 6" thick ceiling insulation with hardware wire/ chicken wire and frame and hang that. The raw insulation is covered with "batting" (or Dacron) and then some soft fabric, such as burlap. Batting and burlap, as well as other fabrics, can be found at quilting stores, such as "Yardage Town." Batting is thick polyester or wool that people use as the inside of quilts and pillows. It comes in huge rolls of varying thicknesses, 1", 3/4" or 1/2" are common. So here we have a cross between DIY audio and DIY quilting...exciting no?

Mineral wool can be used instead of fiberglass, and may be cheaper. Most traps, including mine, are 24" wide by 48" high as this is the size of the fiberglass insulation panels, as well as the size of most commercially available mineral wool panels. Mine are 3.5" thick with 1" poly batting around the fiberglass with the entire thing somewhat compressed in the frame.

OK, here is how I made two hanging bass traps.

Step 1: Get the stuff, paint and assemble the frame.

Raw materials laid out.
Painting the frame elements.
Assembling the frame with rigid corner brackets.

Step 2: Inserting the Fiberglass, batting, and fabric, technique #1

Cutting up a roll of batting (1" thick).
Covering the fiberglass.
Additing Velcro (R) to hold.
Pushing into frame.
Fastening to back of Frame.

Notes: You see here that the fiberglass is faced front and back with the batting, and all of it is covered with burlap. Pegboard holds the assembly in the frame and adds stiffness. You can glue the fabric to the pegboard but I found that it sits in there tightlywith friction and no actual fastening is necessary. With this technique the fiberglass edges are not covered with batting but they are covered with the burlap fabric, and they are mostly inside the frame. You don't want fiberglass fibers shooting around your room so be careful. You see that the backing on my traps are mostly open vs. a lot of other traps that cover the entire back in pegboard. I found that the metallic corner supports add sufficient rigidity and left the back partially covered for more absorption for sounds that pass through the trap, are reflected off the wall, and come in the back.

Step 2: Inserting the Fiberglass, batting, and fabric, technique #2

Cutting the fiberglass to size.
Wrapping and sewing up
the fiberglass in batting
that's right - SEWING!
Attaching to the frame

Notes: Here I have wrapped the fiberglass in the batting and stitched it closed at the back. I stitched it by hand if you can believe that. Hey, most people try to avoid sewing when they make these but be a man and get your needle and thread out! By wrapping it this way I was able to avoid the exposed fiberglass under the fabric, its all covered with batting, even the tops and bottoms becuase the batting was a little long. You also see how to cut the fiberglass, use gloves to avoid the scratchy fibers. This one was made a little shorter than the 48" fiberglass sheets.

Step 3: Hanging up the frame

Here is the frame with the fiberglass.
Unit #1
Adding threaded inserts, long bolts
and a picture frame holder set
for wall mounting.
Unit #2
Adding top hooks for
ceiling mounting.

Here you see the finished frame and the challenge is to hang it. For hanging on a wall I used a standard picture frame rigging, eyelets and a metal line. To keep the unit spaced from the wall I put in three threaded 1/4" inserts with 5" bolts. The bolts go in about 1" and ensure that the frame is 4" from the wall that it is mounted on with the string. For ceiling hanging, I located the ceiling studs and put in metal eyelets, and then very carefully measured where corresponding ones would go on my frame. Seems to have worked out ok. Note that the fabric kind of puffs out the front and back, about 3.5" thick alltogether, 24" wide and 48" tall (if you don't cut them to make them smaller). I could have put the batting around the entire frame and stapled the burlap to the frame backside, preventing the somewhat reflective wood edges from being exposed, but I actually never thought of this until now, and I like the look of the blue frames so I'll keep thins as-is for now.

Ok, and now we have it finished. Hanging 2 traps reduced echo in the room and improved imaging. I am working on more room treatments so I'll post more on this when they are all done...

Now lets see how much we spent, to see if this DIY effort was worth it.

Item Price
Ceiling Hooks $0.98
Frame Hooks $0.98
Frame Anchors $1.12
lag bolts $3.00
Frame mounts $1.96
Wall mounts $2.50
Metal cord $1.96
screws & fasteners $8.00
Rigid angle corner supports x8 $9.00
Wood & cuts $8.00
Pegboard & cuts $8.00
Owens Corning 703/ 2 pieces $33.00
5 yards 1" batting $19.90
5 yards burlap $14.90
1 quart paint (blue) $8.00
Paintbrush/ roller $10.00
Sandpaper & hand sander $12.00
Total Cost - 2 units $143.30
Total Cost - each $71.65

Is this a good deal? Note, I made these in 2007.

In 2007, Ready Acoustics Sold bass traps at the following prices (though they are much higher now):

These prices may be slightly misleading, I used 2" thick Owens Corning 703, and 1" thick poly batting for an overall thickness of 3.5", but the 703 comes in cheaper 1" thick sheets as well, and batting comes in cheaper (thinner) thicknesses. I don't know whether the broadband traps use the cheaper 1" thick 703 or the more expensive 2" thick stuff that I used, or what kind of batting they use, if any. Either way you see that you save some money (but not a lot of money) making these by yourself. The more you make the more you save, I could reuse the paint and some other pieces, and I have a lot of left over batting and a little burlap. However it appears that you don't save quite as much as expected by making these yourself (at least as compared to Ready Acoustics) and you may end up with something not quite as professional looking as the store-bought version. Worth it? For me: Sure. I have the satisfaction of knowing what's in there and had fun using a bunch of tools making it myself the way I wanted.

Likewise, in 2007, RealTraps sold 4.25" thick "Mondotraps" for $299 and 3.25" thick "Minitraps" for $199. My traps are 3.5" thick so fall somewhere between the two.

I could have made mine cheaper if I used wire mesh to compress 6" thick standard fiberglass insulation instead of trying to buy Owens Corning or other "rigid" fiberglass. I could have used cheaper mineral wool instead of fiberglass. Or I could have made thicker, more expensive, traps by doubling up on the insulation.