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 Bass Trap 

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The Large, Bass Tweak

Hear what other people have to say:

"Those things are huge!" - Steffen Damgaard, Contractor for H&N Enterprises.

"You're crazy, you've gone too far this time, you are obsessive compulsive for audio" - Jim Tsutsui

Purpose:  To build a bass trap that will effectively smooth out the bass frequency response of a room.

If you ever noticed that bass sounds louder or quieter at specific notes no matter what sub you use, this may be a cause of room resonances.  These bass traps are designed to control bass frequencies by targeting the high pressure regions of the room such as corners.  By slowing down the air movement in these regions through a mesh of fiberglass, these traps help reduce standing waves within a room.

These bass traps are ASC trap clones that are slightly modified.  Effective in diameters ranging from 8, 12, 16, to 20, these are usually built in length 3 or 4 feet.  Generally, the larger the trap, the more effective.  Larger traps are also more effective at controlling deeper bass.
These acoustic treatments have both audible, and measurable results.

Key Benefits

bulletCan raise the volume of room dips, which parametric equalizers cannot.
bulletHelps absorb ambient noise thus quieting the listening environment.
bulletReduces the effects a room has on bass.

Description

Approx. $45 Per Trap DIY (as opposed to Retail Options of $245+ EA)

Quantity: 4 bass traps for placement at each upper corner of room, or 2 stacked in front corners.

Dimensions:  4 feet high, 16 inch diameter end caps.  Approx 17" actual diameter with burlap and polyester.

Weight = ~20lbs fully assembled

Color = White Burlap

Flame Retardant = None added

As for the materials list, I purchased extra with contingency in mind  (room for error).  Below you fill find the exact numbers for what I used to build 4 bass traps.

STORE MATERIAL Quantity Unit Cost per Unit Total Cost
Home Depot Fiber Glass Insulation 3.5" thick.  15"w x 32'L roll (R-13) 4 EA $8.80 $35.20
Home Depot 3/4" A-Grade MDF 2 EA $19.99 $39.98
Home Depot 4' high galvanized Steel Hog wire fence, 50ft roll. 1 EA $26.99 $26.99
Home Depot Arrow T2025 Hand Staple Gun and pack of staples 1 EA $19.99 $19.99
Home Depot 2250 feet 70lb Sisal Twine (You won't use it all) 1 EA $8.80 $8.80
Wal-Mart Yard of Burlap 10 YD $1.48 $14.80
Wal-Mart Yard of Polyester Batting (48" wide) 6 YD $2.27 $13.62

Total w/o tax

$159.38

 Estimated Total Cost 

$175.00

 

Directions:

Note: Staple Gun can be any brand, the one I used wasn't very powerful but it still worked.  If I did it again I'd probably pay a little more and get a heavy duty model or use an air/electric powered stapler.

Hit Counter "Hit me baby one more time"

Figure 1

Make square cuts with table saw

  Figure 1:  I actually didn't use that exact layout because I made mine from scraps.  This would be a simple layout if you were to make 16" diameter traps with 2 center braces 12" large.  You'll need to make 8 large circles, and 16 smaller circles to make 4 traps.

Figure 2:  Here my friend Steffen made a simple circle jig that fits on a band saw.  It involves a single screw that I put in the center of the circle.  (Remember to mark the center with a cross).  We made two holes in the jig, one for a 12" diameter circle, and the other for a 16" diameter.  This proved to be very effective in making circles, It was also easier and way less messier than using a router.

Figure 3:  I had to cut about 24 circles but it didn't take that long considering how fast the jig pumped them out.

Figure 4:  Here we see the circles and Makita hand drill I used.  The nail gun will be used to shoot some brads when gluing the smaller disc to the larger disc.  (For the end caps)

Figure 5:  Using a jigsaw and no clamps I just rotated the disc by hand making inner circles in the smaller discs  (To allow air to pass through the braces to form one big chamber).  Since we'll be using 2 inner braces for each trap, I made 8 of the smaller circles into these donut shaped braces.  I cut a 6" hole in the 12" circles so that left a 3" border which is plenty strong.  With the remaining 8 smaller circles you do not have to cut inner braces in them but you could as it might cut the weight down of the tubes a bit.  I just glued them and nailed them in the center of the end caps.  To find the center I drilled a hole in the middle of the small disc and matched it with the center of the large disc.

Figure 6:  Remember to cut 1.5" from the inner hog wire because the end caps are both 3/4".  If you don't then the outer hog wire won't be able to staple to anything.  Save the scrap from the top as it can come in very handy when cut into "U" pieces that can be used as clamps for holding the hog wire to itself as seen in figure 9.  Also, be careful with the hog wire as it is very sharp and springy.  I didn't wear gloves or pants like I should and ended up a few scrapes.

Figure 7:  Staple the braces in place, it's easy if you rest it on the wire as shown.  My friend and I built these together to save time.

Figure 8: Cut the fiberglass into sections to be wrapped around the wire.  They should not overlap but should bunch closely together to form a seal around the inner chamber.  I used two strands of twine I wrapped around the cylinder, tied, and trimmed.  Three sections will not cover the 4 foot length so I cut one section in half for the top as seen in figure 8.  When applying the 2nd layer, put the half cut section at the bottom instead of the top again, and make the seam on the opposite side.

Figure 9: We cut the excess hog wire into "U" shaped pieces that were then bent to be used as clamps that held the hog wire to itself.  We did this because we had no wire but will probably use this on the other traps as it worked very well.  See the first picture for where we put the clamps, it took one person to pull the wire together and the other to bend the clamp in place. 

I really think it's optional to seal the top part and places where fiberglass meets with caulk.  The fiberglass ends up being bunched up pretty well so I only caulked one of the traps as an example for those wondering what it would look like.

Figure 10: Wrap the outer hog wire fence around the fiberglass.  Then use the excess wire you cut from the top as "U" clamps.  The excess wire will make plenty of these clamps but you could always make more with the extra fence.  These will hold very strong if you chose a strong welded fence.

What I did was staple the wire a few times on the sides touching the floor in (figure 10), and then pull the wire together and clamp.  Put about 7 clamps up the seam, it's easy with the trap on its side with one hand pulling the wire together and the other hand bending the clamp in place.  If you spiral wound the fiberglass tight this will be no problem.

Figure 11: Next, cut the string if it's too tight and let if fluff out.  Cut the polyester into 4 equal sections and wrap the outside with it and tape the ends.  Sew the burlap into four 4.5ft high x 5.0 ft sections and then wrap the traps and sew down the seam.  (May need a woman's help with this one).  Staple the burlap on top of the disc, and then you can add another decorative end cap to cover the staples, or finish the trap however you wish.

Figure 2

Cut out the circles and donuts

Figure 3

Cut circles with jig on band saw or use router.

Figure 4

8 small donuts, 8 small circles, and 8 large circles.

Figure 5

Glue end caps, we used a nail gun along with a bead of wood glue.

  Figure 6

Cut wire to proper length and width.

Figure 7

Staple end caps and brace in place.  Brace rests on inner wire during stapling.

 

Figure 8

Wrap the first layer of fiberglass, Tie each one in place by wrapping it with twine.

Add 2nd layer of fiberglass, secure with twine.

 

Figure 9

After 2nd layer, spiral wrap the entire bundle tightly.

Seal with silicone

 
Figure 10

Use the custom "U" shaped clamp scraps to secure the fence to itself and staple the fence to the end caps.

 
Figure 11

Add polyester, tape, burlap, and staple.

 
 

FINISHED

Lightly sweep or vacuum the burlap and you're ready to install them.  

The Test and Review

<< Click on to enlarge graph

Response Measurement:

On the left is a graph of before/after results of actual in room response.  This is with two finished traps stacked on top of my subs in the front corners of the room.  I did have two other traps but they were against the back wall and were not finished (Had black trash bags taped over them for dust free transportation).  I do know that flimsy plastic does not affect bass so I suppose that this experiment involves 4 traps all together. 

Although it seems minimal on paper, the sonic differences these four traps created are quite substantial.  Bass has become more detailed, I can hear more distinct transients, and overlapping of notes.  The bass has also lost the "ringing" and boomy sound it once had during certain songs and movies.  In addition to controlling bass, these traps have also contributed to a more silent room and have further reduced ambient noise.  What's quite surprising is that the bass volume did not drop with the traps, but increased the volume as a result.  This is due to a reduction of first order standing waves that causes nulls (bass cancellations) at the listener position.  You can see this in the graph where the volume dip at 63hz which was then considerably reduced with the bass traps.  I believe that increasing the SPL at dips is where bass traps really shine as it's very hard for equalization to reduce nulls.

I am however disappointed in that the traps did not EQ the response to within +/-3db like I had hoped, but I suppose +/-4db isn't bad either.  $45 per trap, and about 20 hours of work to find the best methods may not be worth it to everyone, but it's certainly an audiophile tweak to consider for those wanting to improve the bass of their room.

Test 2:

<To be continued...  more testing with different rooms, and different trap/sub positioning>

Conclusion: 

If you're crazy about bass and equalization can't fix all your problems then these are for you.  If you've got a small room like mine and the bass is bloated in the upper bass range then these can make your room acoustically larger.  It pleases me that they made an immediately noticeable audible difference and the response has improved throughout the entire room and not just one seating location.  However, don't expect any miracles in your frequency response, and don't expect these to be easy and interior design friendly.

Click Here to go back to HouR Audio***

Pricing

Description SKU # Price
  sku-bt1 n/a
  sku-bt2 n/a
  sku-bt3 n/a

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Copyright 2003 Chris Tsutsui
Last modified: 06/25/03