Cutting Rigid Fiberglass for Bass Trap: link to short video - AVS Forum
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post #1 of 72 Old 07-18-2006, 06:31 AM - Thread Starter
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...break this out from the master thread...

Well... after making my first purchase towards this project 6 months ago I finally had the time (where the wife and kids were gone) to make my first "superchunk" style, corner, bass trap.

For the larger trap I used
3 - pieces of a JM equivalent to OC703, 2" thick.
1 - FRK panel.
3 - 48"x1" dowels (from HD)
1 - 2'x2' 1/4" hardboard panel (from HD)
6 - screws
about 2 yards of speaker cloth from Joanns Fabrics

You can check out the superchunk info here . I used the 24" pattern on the 3 pieces of fiberglass, and also added the full panel of FRK in front of that. To cut the triangles I used a straight-edge to score the panel with a utility knife, first lightly, then a little deeper. This created an internal channel for the $10 electric carving knife that I used to make the final cut. By the way, this method of scoring then cutting works really well. The internal channel guides the carving knife to the point where you could literally make the cut with little concentration.

Check out the short video of me doing my cuts, here. Please note I could not find my mask, so that is part of an old t-shirt covering my face. Also, since I filmed this myself, my technique is not perfect. Really I just wanted to show how easy this stuff is to work with so you people on the fence can just go do it.

The frame is made from the hardboard panes cut a little shorter than in half, diagonally. I used a hand saw because I don't own many power tools. The triangle was estimated using a dry-fit of the 1" dowel, the triangular fiberglass, and the 2" of the FRK.

The bolt of speaker cloth at Joanns was wide enough to use a straight peice of fabric.

I'll try to measure the FR at a later date. I want to make a few more panel first.

...just excited to share...
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post #2 of 72 Old 07-18-2006, 06:33 AM - Thread Starter
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Okay... here are a few shots from the second trap I made. Since this one was a little smaller than the first, I used 3/4" dowels. It is basically the same as the first trap, but without the front panel with FRK. This makes the top and bottom triangle a little smaller, which is what I wanted.

There are a few more shots in my gallery.

Empty Frame:


Laying in the wedges:


Getting ready for the final stretch and staple...


Finished product:


The dowel that goes in the corner is peppered with staples... it ain't pretty but it works.
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post #3 of 72 Old 07-18-2006, 06:34 AM - Thread Starter
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Going back to the first trap...
Here are some shots of the beefier panel I made. In this case I put another piece of 2'x4'x2" FRK in front of the wedges and made the top and bottom panels a little larger. It came out very nice, imho. So nice, my wife said it looked good without me asking her opinion!



...and a view on the top...


EDIT
Here's a link

and one of three sketches in my gallery:
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post #4 of 72 Old 07-18-2006, 06:37 AM - Thread Starter
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post #5 of 72 Old 07-18-2006, 09:21 AM
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Excellent! Good job with the video. Also good for anyone who wants to see what the rigid fiberglass is "like". That's the thing to pont them to.
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post #6 of 72 Old 07-18-2006, 10:07 AM
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Good tip on the electric carving knife.
thanks

I just can't help but think that somewhere a flock of turkeys is giving you a standing ovation
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post #7 of 72 Old 07-18-2006, 11:26 AM
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Can you tell a difference by listening (not just on a graph)? I have spare weekend (alone) coming up and would like to build some of these babies. I think my room is pretty smooth but everyone always seems pleased with superchunks so I figured it's time to give it a whirl.
Thanks!!

edit: I see you still have a few more to build. I'll wait. patiently this time
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post #8 of 72 Old 07-18-2006, 03:03 PM
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When building the next one, would you please take a picture (and post it) of the FRK panel in place, before you start wrapping the speaker cloth around the frame? I'm having trouble visualizing how this panel is placed, and a picture would really help.

Thanks in advance,
ND
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post #9 of 72 Old 07-19-2006, 06:30 AM - Thread Starter
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Quote:
Originally Posted by johnnykretentiv View Post

Can you tell a difference by listening (not just on a graph)? I have spare weekend (alone) coming up and would like to build some of these babies. I think my room is pretty smooth but everyone always seems pleased with superchunks so I figured it's time to give it a whirl.
Thanks!!

edit: I see you still have a few more to build. I'll wait. patiently this time

I am sure you read this in the other thread... I'll repost for consistency.
--
I'd love to give you a complete a/b, but that will be a while. I want to do some first-reflection treatment (6 more 2'x4' panels to make) and it will be a while before I can do some critical listening. I also will want to re-calibrate and re-eq the room with the treatments (I'll save the current curve for a potential, future a/b with and without the treatements.)

That said, I did do a little listening. There is a Chemical Brothers track that has a series of long, reverse bass sweeps. These sweeps are very revealing of the FR response of the room. They then go into a deep, musical bass beat which, in the worst of set-ups could sound obviously late (i.e. lots of smear and delay). I did notice it being tighter and smoother, but again, without an a/b session it could all be in my head
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post #10 of 72 Old 07-19-2006, 06:50 AM - Thread Starter
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Quote:
Originally Posted by ND23 View Post

When building the next one, would you please take a picture (and post it) of the FRK panel in place, before you start wrapping the speaker cloth around the frame? I'm having trouble visualizing how this panel is placed, and a picture would really help.

Thanks in advance,
ND

Hi-

My next panels (for this run of treatments) will only be single, 2'x4' panels. In other words, I won't be able to take pics.

On the other hand, let me try to describe what I did. Forget the hardboard triangles on the top and bottom for a minute and just foucs on the trianglular pieces I cut. The are right triangles with 2' hypotenuse. (Remember the panel was cut from 2'x4' down to 2'x2' squares. Each of those squares were cut into 4 triangles, hence the 2' hypotenuse.)

Take a look at this pic:


That face we are looking at is 2' wide. Now imagine just walking up to that with a 2'x4', 2" thick piece of rigid fiberglass that happens to be FRK. It would fit perfectly (in theory) flush against that face. Still ignoring the frame, from the top we would see a right triangle sitting on top of a wide, skinny rectangle.

Make sense so far? When describing this over the phone I made my buddy draw stuff in the sand...

If we draw a second , right triangle that is larger than the first one, we can size it so it covers both the smaller triangle and the wide skinny rectangle that is flush with the hypotenuse. This leaves a small area on either side of the rectangle that has no rigid fiberglass.

If you look at the shot again of the smaller panel, you can see I spaced the fiberglass triangles away from the right corner to allow some room for the support dowell (3/4" in this case, and 1" for the larger panel). Again, if you draw this out you can draw a right triangle that covers the small triangle, the rectangle, and the dowels nicely. I also cut the corners off of the triangles so the speaker cloth wrapped nicely with the dowels and the top and bottom of the frame.

Geez... with all of this typing I should have just google-sketched it... maybe later today or tomorrow...

EDIT Here's a link

and one of three sketches in my gallery:


Hope this helps,
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post #11 of 72 Old 07-19-2006, 08:40 AM
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Quote:
Originally Posted by Tweakophyte View Post

Geez... with all of this typing I should have just google-sketched it... maybe later today or tomorrow...

Thanks for taking the time to explain (very hepful indeed!)... and a sketch would be great! Just one more question: when adding the FRK panel to the front, does the paper side face out into the room, or in to the stack of triangles? I assume it's out into the room, but wanted to confirm.

I like the idea of cutting down the corners of the hardboard top/bottom, or even rounding them to match the profile of the attached dowels.

If I wanted to make a floor-to-ceiling version of this (8' tall), does anyone know where could I get 8' long wooden dowels? I tried to find them at Home Depot and Lowe's last week for a closet remodel project, and could only find metal closet rods in that length. Wooden dowels were 4' long max. Hopefully I won't have to find a way to "join" two 4' dowels to make an 8' dowel.

They look great!
ND
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post #12 of 72 Old 07-19-2006, 09:36 AM
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You Rock!

Though I must admit I cringed a little when that terrorist picked up the electric knife.

PS: on the 8' dowel question... make em 4' high and stack em?

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post #13 of 72 Old 07-19-2006, 09:47 AM
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Quote:
Originally Posted by ND23 View Post


If I wanted to make a floor-to-ceiling version of this (8' tall), does anyone know where could I get 8' long wooden dowels? I tried to find them at Home Depot and Lowe's last week for a closet remodel project, and could only find metal closet rods in that length. Wooden dowels were 4' long max. Hopefully I won't have to find a way to "join" two 4' dowels to make an 8' dowel.

How about making a "shelf" like the top and bottom in the middle. Then there is support half way up, and the 4' dowels connect into it. It would be like making 2 of these and staking them, but only one board in between the 2 sections of triangles instead of 2.

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post #14 of 72 Old 07-19-2006, 10:01 AM
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Great thread! I really like the video clip!

For anyone interested, I recently made some speaker stands and incorporated some bass-trapping capacity in the design. Pics are near the end of my theatre photo album, at:

The Tanglewood Bijou

I didn't take the time to do a before & after sound analysis, I just did this on an empirical basis...

Mike Moss
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post #15 of 72 Old 07-19-2006, 10:29 AM
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Neat idea on those speaker stands.

Scott R. Foster
Ready Acoustics
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post #16 of 72 Old 07-19-2006, 10:42 AM
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Quote:
Originally Posted by Chiahead View Post

How about making a "shelf" like the top and bottom in the middle. Then there is support half way up, and the 4' dowels connect into it. It would be like making 2 of these and staking them, but only one board in between the 2 sections of triangles instead of 2.

Yeah, like a "Big Mac!" (bun, burger, bun, burger, bun)

Now why didn't I think of that?

Thanks!
ND
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post #17 of 72 Old 07-19-2006, 02:53 PM
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ND - Look for wooden closet rods, or stair hand rails. I've seen them at HD in several locations. Over by the finish trim, in the closet organization section and where the outdoor deck supplies are. May be laid out differently in KS...

I need to try this as well. I need a few that are 7-8' in length/height...

Kevin -

In an average home theater room there are 1,257 objects Chuck Norris could use to kill you, including the room itself. There are no weapons of mass destruction. Just Chuck Norris.
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post #18 of 72 Old 07-19-2006, 06:52 PM
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Quote:


when adding the FRK panel to the front, does the paper side face out into the room, or in to the stack of triangles?

Actually for bass traps, the FRK does face the room.

Great work on the traps. They should really improve the low end of your room. I didn't see this, but are you placing in both back corners and are you going floor to ceiling or just the one shown?

"There's a lot of badness in the world, Danny"
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post #19 of 72 Old 07-20-2006, 06:41 AM - Thread Starter
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Quote:
Originally Posted by sdspga View Post

Actually for bass traps, the FRK does face the room.

Great work on the traps. They should really improve the low end of your room. I didn't see this, but are you placing in both back corners and are you going floor to ceiling or just the one shown?

Thanks. I have one in each of the back corners of the room, at half-height. I can't go full-height because of vents, soffits, and sconces. In one corner there is the modified version, and in the other there is just a regular superchunk (so I can save a little room for the equip. rack). Ideally you want symmetry...
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post #20 of 72 Old 07-20-2006, 06:46 AM - Thread Starter
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Hi-

I added these sketches to my gallery and modified the posts above. Here they are as attachments...
LL
LL
LL
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post #21 of 72 Old 07-20-2006, 06:59 AM - Thread Starter
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Quote:
Originally Posted by Chiahead View Post

How about making a "shelf" like the top and bottom in the middle. Then there is support half way up, and the 4' dowels connect into it. It would be like making 2 of these and staking them, but only one board in between the 2 sections of triangles instead of 2.

Hi-

This is not a bad idea, but whatever approach is used needs to make sure the dowels are rigid enough to not flex when you wrap them with fabric. At 48" long both the 1" and the 3/4" did well. The 3/4" could not have been much longer. I also found it harder to pick a straight, not warped piece of the 3/4". Finally, the modified superchunk was more rigid, in part because if the 1" surface area, and in part because the full piece of FRK acted to stabilize the front part.
-------
Btw...
There is one more step that I did with the smaller superchunk that is optional. I took some light adhesive (the 3M for photos) and sprayed a little between each wedge. The face of each wedge was placed on a flat surface as I built it up. The reason I did that was so, when I stacked the the wedges the part facing the room would have a nice clean line. I made two 2' tall wedges when I did that.
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post #22 of 72 Old 07-21-2006, 06:16 AM - Thread Starter
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Quote:
Originally Posted by BIGmouthinDC View Post

Good tip on the electric carving knife.
thanks

I just can't help but think that somewhere a flock of turkeys is giving you a standing ovation

It was a $10 Black and Decker model from Walmart...
...and don't call my fellow AVSers "turkeys"
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post #23 of 72 Old 07-21-2006, 07:51 AM
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Did you spray the FRK panel with the black paint (before covering it with the speaker cloth), or was there no need?
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post #24 of 72 Old 07-21-2006, 09:15 AM
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Thanks a lot for the detailed instructions. one question, where did you get the JM equivalent to OC703, 2" thick and the FRK panel.
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post #25 of 72 Old 07-21-2006, 09:51 AM
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The video is excellent.

I used a magic marker instead of the razor knife but it's obvious that with the cut from razor blade, the electric knife has a guide.

HH
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post #26 of 72 Old 07-21-2006, 11:15 AM
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Quote:
Originally Posted by Tweakophyte View Post

I'd love to give you a complete a/b, but that will be a while. I want to do some first-reflection treatment (6 more 2'x4' panels to make) and it will be a while before I can do some critical listening. I also will want to re-calibrate and re-eq the room with the treatments (I'll save the current curve for a potential, future a/b with and without the treatements.)

Would you by any chance be taking pics and making a thread for your 2'x4' panel project?
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post #27 of 72 Old 07-22-2006, 07:24 AM - Thread Starter
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Quote:
Originally Posted by ND23 View Post

Did you spray the FRK panel with the black paint (before covering it with the speaker cloth), or was there no need?

Hi-

No, I did not. I had a concern that I would need to, but was too excited to want to wait for paint to dry. The speaker cloth I am using (from Joann's fabrics) seems to work really well. I am not even sure I needed to spray paint the frame black like I did. Btw, the smaller version (with no FRK) is not sprayed or anything and you can't see the yellow.
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post #28 of 72 Old 07-22-2006, 07:31 AM - Thread Starter
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Quote:
Originally Posted by zfc6e View Post

Thanks a lot for the detailed instructions. one question, where did you get the JM equivalent to OC703, 2" thick and the FRK panel.

The Johns Manville equivalent is JM 814 (make sure it's the 3psf density).

click on spin glass

I got mine just off of 70 and Colorado (in Denver, but you can search here).
click on the HVAC when you search

A big nod to Bob Gold's site, and other's who have helped vet out which material to use.
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post #29 of 72 Old 07-22-2006, 07:35 AM - Thread Starter
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Quote:
Originally Posted by George Montemayor View Post

Would you by any chance be taking pics and making a thread for your 2'x4' panel project?

Hi-

Sure. I'll probably snap some pics and post them here (and in my gallery)... but compared to this corner trap, it will seem easy. it won't require any cuts (other than HD or Lowes) and I already found some nice, thick, felt feet... you'll see

Quote:
Originally Posted by Husker Harley View Post

The video is excellent.

Thanks...and those pics you posted helped me.
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post #30 of 72 Old 07-24-2006, 07:55 PM
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nice bass traps tweak

I got a question about them. I know you havent ran any tests yet, but how low (hz) do you think you traps will be affective to?

thx

Trevor
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