...break this out from the master thread...

Well... after making my first purchase towards this project 6 months ago :eek: 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 (http://forum.studiotips.com/viewtopic.php?t=535) . 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. (http://video.google.com/videoplay?docid=3067566258802658704) 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...

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:
http://gallery.avsforum.com/data/507/medium/cornertrap_99_Small_.JPG

Laying in the wedges:
http://gallery.avsforum.com/data/507/medium/cornertrap_99_10_Small_.JPG

Getting ready for the final stretch and staple...
http://gallery.avsforum.com/data/507/medium/cornertrap_99_12_Small_.JPG

Finished product:
http://gallery.avsforum.com/data/507/medium/cornertrap_99_13_Small_.JPG

The dowel that goes in the corner is peppered with staples... it ain't pretty but it works.

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! :D

http://gallery.avsforum.com/data/507/medium/cornertrap_99_1_Small_.JPG

...and a view on the top...
http://gallery.avsforum.com/data/507/medium/cornertrap_99_5_Small_.JPG

EDIT
Here's a link (http://gallery.avsforum.com/showphoto.php/photo/21646/cat/507)

and one of three sketches in my gallery:
http://gallery.avsforum.com/data/507/medium/Bass_Trap3.jpg

...placeholder... if needed...

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.

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

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 :)

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

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 ;)

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:
http://gallery.avsforum.com/data/507/medium/cornertrap_99_10_Small_.JPG

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 (http://gallery.avsforum.com/showphoto.php/photo/21646/cat/507)

and one of three sketches in my gallery:
http://gallery.avsforum.com/data/507/medium/Bass_Trap3.jpg

Hope this helps,

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

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?

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.

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 (http://tanglewoodbijou.myphotoalbum.com)

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

Neat idea on those speaker stands.

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? :o

Thanks!
ND

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 -

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?

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...

Hi-

I added these sketches to my gallery and modified the posts above. Here they are as attachments...

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.

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" :p

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

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 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

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? :)

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.

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 (http://www.jm.com/insulation/performance_materials/2685.htm)

I got mine just off of 70 and Colorado (in Denver, but you can search here).
click on the HVAC when you search (http://www.jm.com/locator/mqlocator.exe?link=find)

A big nod to Bob Gold's site, (http://www.bobgolds.com/AbsorptionCoefficients.htm) and other's who have helped vet out which material to use.

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 ;)

The video is excellent.
Thanks...and those pics you posted helped me.

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

wouldnt it be more efficient if it was a resonator ?
like here :http://www.jocaviacousticpanels.com/uk/products/synt.roundbasscorner/index.shtml
good response from 31hz to 125hz. i will experiment it soon (starting with one then 2)

fiberglass itself would need to be much bigger in volume to start being efficient at low FQs no ?

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

Hi-

Thanks...
I got the idea for these traps from the StudioTips fourm. Here is a link to a comparison of some types of bass traps. (http://forum.studiotips.com/viewtopic.php?t=536) They did some measurements of an Auralex MegeLERND, a corner trap, and a superchunk (with the larger, 34" face). I would imagine my bass traps are somewhere between the corner trap and the Superchunk performance, and closer to the Superchunk. Thickness, distance from the wall, and surface area (for total absorbtion) play into it.

Someone with more expertise would need to come in and forecast how low... I would guess as low as 40-50hz.

One thing people that measure these things will tell you is any measurement below 125hz is very tough. You cannot compare one test to another (though I believe you can compare a relative number made during a single test).

wouldnt it be more efficient if it was a resonator ?
like here :http://www.jocaviacousticpanels.com/uk/products/synt.roundbasscorner/index.shtml
good response from 31hz to 125hz. i will experiment it soon (starting with one then 2)

fiberglass itself would need to be much bigger in volume to start being efficient at low FQs no ?

I am not sure... this one might be good to put on the master thread.

We'd really need to know what the material of those traps are made of. It might be the same as the Auralex MegaLERND. If so, the superchunk comes pretty close for a fraction of the price. I think my trap cost maybe $50, with most of the cost going to the rigid fiberglass.

As far as it being a resonator, I thought they worked across a narrow band. With broadband absorbers it comes down to material (and its density), surface area, and location, both distance from wall, and number of planes it touches (i.e. corner).

Again, I am just learning and think this would be better for the master thread.

hi
hi agree cost efficiency, you beat them :)

now, it seems this model has a wide spectrum of absorption and not one FQ in particular (for which often a resonator with a membrne is tuned on). this is why i find i interesting. the megalernds even are not efficient imho. foam is good up to 80hz maximum. but not below. only "membrane" based system work i think.

no other choice than to test it...

the most expensive but VERY efficient way of having great bass at all the seating area is a wall of subwoofers, either the full width or the two front sides vertically. (or both :D ).
but this an expensive solution. imagine for instance 6 or 8 $999 subs or even more expensive. virtually you cancell all room modes, the line of subs absorb also the bounced back wavelengths instead of the wall against which they sit. they (i think) play sort of resonators themselves, the launch bass but absorb the bounced back bass.

Sweet thx for the info. It would be nice with that much coverage down to the 40ish area, even lower if possible. :)

Hi-

snip

I would guess as low as 40-50hz.

One thing people that measure these things will tell you is any measurement below 125hz is very tough. You cannot compare one test to another (though I believe you can compare a relative number made during a single test).

Hey Tweak:

That is a good guess I think... but a lot depends on what we mean by "effective".

If we are talking about the frequency range at which the device's performance drops out of the stratosphere of sabin numbers per unit we enjoy when we use corner mountings then I think you are dead on the money. At about 40 - 50 Hz we are going to see the a big droop.

But, you need to recognize that just because a device has dropped back to the more rational absorption performance range we might expect to see in the rest of the room - for example, the levels we see in a wall mount - that doesn't mean it isn't working anymore. To me that is just an indication that the "free ride" we get from corner mounting stops and we have to go back to “normal” performance expectations.

Look at the phenomena this way... a pair of 32" faced 703 SuperChunks running from floor to ceiling is going to add something on the order of half a dozen sabins per linear foot of corner treated at 100 Hz. That is a shocking number when you consider the device has 2.66 SF of face per linear foot and therefore 2.66 sabins would mean an "open window" of that size - no reflection of sound whatsoever. At first blush the idea you might get 6 SF or so of “open window” for every 2.66 SF of treatment seems to defy physics. Its an acoustical black hole, Wow!

But cool as that is, it aint magic. Instead its a byproduct of resonant behavior. Corner mounted porous absorbers typically exhibit a sharp peak in performance - typically somewhere in the 63-100 Hz bands. This little elf has been dubbed the "100 Hz peak" for lack of a better name. The 100HP moves around a bit, and gets broader or sharper, depending on the topology of the construct [wedge versus panel], the density of the foam or mineral fiber, whether you have upholstery and what kind of fabric is used, whether you space the devices or mount them edge-to-edge, whether you capture tri-corners, and the overall thickness and face dimension, etcetera.

The basic concept is however pretty straight forward, namely that porous absorbers in corners are a mass-spring resonate system. The air in the corner is the spring, held in place by the room’s walls, and the panel or wedge of absorbent material is the mass. Mineral fiber or foam, naked or upholstered, panel or wedge, thick or thin, big face or small face... doesn't matter. They are all mass-spring systems with a resonance kick somewhere around 100 Hz, and, that kick has a front side and a backside on a measurement graph. You reckon [I think] that the backside of the free ride starts running uphill somewhere around 40 to 50 Hz - and from everything I have seen, that is a fair statement, but concluding that this means no work can be done using a porous absorber south of say 63 Hz does not follow.

Expressions of this peak can be quite large [on the order of a 50% increases over the median absorption outside the peak center band], and can appear very sharply expressed. Or, they can be so subtle as to not look "peaky" at all, but rather a gentle rise and fall. There are ways to soften the peak - and to broaden it - or you can even make it more "peaky" by adding a membrane [a generally nutty idea IMO - but it could fit the need for a particular application just so].

But, keep in mind that whatever you study as to this effect, to some degree the actual effect is masked by the 1/3rd octave band reporting technique. For example, a peak straddling a pair of bands could be quite "peaky" but not show up that way in the graphs – alternatively a peak of exactly the same magnitude but which falls completely in a single band will have a much more dramatic expression on a graph.

This is part of why it always best measure for low frequency performance in situ as the intrinsic properties of devices are hard to measure very low in the band, such measurements are hard to interpret [even if you know everything about how they were taken], and the results in any given room will vary enormously even using the same devices when you vary the placement. There are a number of "known good" devices, and known good treatment placement schemes, but nothing can beat verifying the installation with an on site measurement system [and a professional acoustician too if you can swing it].

PS: A couple of other comments:

The idea that foam doesn’t work as well as mineral fiber is falsehood. Acoustic foam works great... non-acoustic foam does not. By the same token, there are thermal insulation materials that have excellent acoustic properties, and ones that do not.

Comparing absorption measurements at 100 Hz even or even lower, can be done both rationally and usefully provided you have all the information. It takes some intellectual honesty and a keen understanding of what you are looking at, but a lot can be learned from comparing measurements - even between measurements taken by different labs –if you have full details of the measurement procedures [sample size, sample placement, the % Uncertainty of the measurements, etcetera]. When measurements are proffered absent these details comparison becomes quite dicey stuff as you suggest, especially below about 80 Hz. This is not so much a limitation of the science – though physics does come into play - but rather, the key limitations are artificial constraints created by researchers and manufacturers who hide data.

Tweakophyte,

Awesome video, info and attitude. I loved it all, and it is very helpful.

Thanks for posting mate!

Joel DuBay

Scott-

Thank you for the comments. I am still digesting them!
--------
Joel-

No prob!

Hi-

Well... I built 3 of the 4 panels I had planned on. Two of the panels were for the front wall, and the other 2 were for the first reflection points on the side wall.

...then I asked for my wife's help...

She barfed all over all of the panels. :( In the end I "negotiated" keeping the 2 panels on the front wall. I post pics in the next few days.

The good thing is I got to do some listening. It was a short listening session, late at night (so lower volumes) and I could hear a definite tightening of the mid-bass. This run was the first 3 songs on U2's Joshua Tree. "Where the Streets Have No Name" has many strums of the same note in a row, so you can really focus on them. The notes were smoother and more distinct.

I also checked out a bit of Dave Brubeck "Time Out". On the "Blue Rondo..." track the Piano and Bass play the bass line in unison, and again, the same note in a row. Now for the fun part (as many tweaks create)... I heard something new in the music... a slight dissonance between the bass and the piano. I think, because the fundamental got out of the way so to speak, the tonal color of the bass became more clear. It was subtle but distinct. I had a similar experience with "Take Five".

Like I said, I'll try to post more pics this week.

Sounds to me like you got some treatments for sale ;-)

This is the same thing I'm struggling with in my family-room wannabe theater. Just how do I sneak treatments in? Or is the better question, when do I start building a dedicated theater in the basement?

Bobby

Here are some pics:


http://gallery.avsforum.com/data/507/medium/More_HT_00_Medium_.JPG

http://gallery.avsforum.com/data/507/medium/More_HT_02_Medium_.JPG

http://gallery.avsforum.com/data/507/medium/More_HT_12_Medium_.JPG

I used some chair glides and thich felt to give my panels some space away from the wall. I found that I liked having the space away from the front wall for deeper absorbtion, but the side walls looked better with thinner panels... until my wife saw them...

http://gallery.avsforum.com/data/507/medium/More_HT_05_Medium_.JPG

Nice stuff Tweak!

What's the WAF hurdle... why does she object... is it a color thing?

I actually made 2 sets of panels. For the first one I used 1x3 MDF. Even when I pre-drilled the holes, the MDF split. Also, over the 4' span it sagged enough to bother me when I hung it on the wall.

You can see one of the splits here (lower right corner):
http://gallery.avsforum.com/data/507/medium/More_HT_01_Medium_.JPG

For the second one I used B or better, pine 1x4s. I used the 6' lengths because I had trouble finding a straight board in the other lengths. I still had to spend some time in the lumber pile to find some good, straight 6' boards. Each panel took 3 boards. Two boards were cut 1/16" short of 4'. The remaining board was cut 1/16" shy of 25 1/2" (so the inside dimension is 2').

I cut them slightly short for two reasons. First, with a perfect cut at these lengths there would be a great, friction fit. Second, the guys at HD are careless with their cuts. I had to return one set because it was 1/4" too long (you could see his mark, and many of the cuts were out of square. (Don't go there before close on a Saturday night!)

The frames are held together with two 3 1/2" screws in each end. I tapped in some wire brads to hold the rigid fiberglass towards the front of the panel. I don't have pics, but I found it easier to wrap the frame and have the "seam" of the fabric be in the middle. I used some light, spray adhesive to hold the fabric together.

Hope this helps!

Nice stuff Tweak!

What's the WAF hurdle... why does she object... is it a color thing?
Thanks Scott.

It could be the color, but in the end I think she did not like the idea of "things" hanging on the wall. We agreed to make this room as "normal" looking as possible, and the panel take that away for her. I may try with her again.

I think I got my 80% performance with just the 2 panels. I am also going to do some small treatments in the shadow box area. The center sounds great at is it and I think the sub acts as a diffuser, but I have the rigid fiberglass, so I might as well play around. :D

In my next theater I will have room treatments as part of the plan, and make the walls with GOM or some other fancy fabric that SHE can pick out. ;)

snip...

or some other fancy fabric that SHE can pick out. ;)


I think you are on to something there Tweak. :cool:

I found it easier to wrap the frame and have the "seam" of the fabric be in the middle. I used some light, spray adhesive to hold the fabric together.

Tweak - thanks for sharing! I followed everything, right up until this quote. Can you explain more? Are you saying that you did not staple the fabric to the back (wall side) of the frame?

ND

Tweak - thanks for sharing! I followed everything, right up until this quote. Can you explain more? Are you saying that you did not staple the fabric to the back (wall side) of the frame?

Hi-

No, I stapled. Let me try to explain (until I can post a pic). I can use this for an example for now:
http://gallery.avsforum.com/data/507/medium/More_HT_02_Medium_.JPG

See how the frame is in the center of the fabric? If I folded the sides over they would meet in the middle of the frame. I could still staple the perimeter of the fabric (which I basically did) but the fabric in the middle would still be a little loose (it was).

Since I was hanging them horizontally on the wall, the bottom piece of the fabric was really sagging. I lightly sprayed some adhesive (#45?) on the fiberglass and stuck it so it would not sage. The top piece of fabric still drooped a little.

None of this matters if you don't want to wrap the back of the frame. Since I have kids, I did.

Make sense?
---
Btw, the way I did the first frame is I shifted the frame over so one side of the fabric met the first edge with little overlap. The second side of the fabric reached all the way around and back to that same side (so the piece on the left stapled on the right). It worked, but it was a bit of a pain to do and made that side of the frame a little bulky.

That helps! Thanks, and good job!

ND

The Johns Manville equivalent is JM 814 (make sure it's the 3psf density).
I got mine just off of 70 and Colorado

Can you tell me exatly where you got it? I'm getting tired of the run-around from the box stores and contractors trying to get the OC703. You'd think I was asking to date their wife, or daughter, or something...

I have been looking for but not finding

source for oc3 (or whatever today's recommended foam for panels and superblocks is - how about john mansvile

source for frk - actually, what is frk - t looks like spun glass

source for acoustic cloth.


I searched but, a reference to a forum entry would be fine.

Hi-

FRK is something like Foil Reinforced Kraft paper. It is used where you don't want to absorbe the high-frequencies.

I just used speaker cloth from JoAnns Fabrics. You can find a 40-50% of coupon if you sign up for their mailing list.

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

click on spin glass (http://www.jm.com/insulation/performance_materials/2685.htm)

I got mine just off of 70 and Colorado (in Denver, but you can search here).
click on the HVAC when you search (http://www.jm.com/locator/mqlocator.exe?link=find)

A big nod to Bob Gold's site, (http://www.bobgolds.com/AbsorptionCoefficients.htm) and other's who have helped vet out which material to use.

I like this type of bass trap a lot, but I was a bit surprised when I found out how much it would cost to buy all the rigid figerglass insulation I would need. I can't find anywhere locally that carries anything equivalent to the JM or OC stuff and the places online seem to be about $70 for six 2'x4' panels. So, for two 7.5' tall corner traps using the 34"x24"x24" section, it would cost $280 + shipping just for the insulation!

Would stuffing an equal wieght (45 lbs) of normal fluffy fiberglass insulation into a triangular collumn of the same size would produce similar results?

I'm having trouble finding the density of fluffy fiberglass. From some info I got on Geisen's DIY bass trap page (http://webpages.charter.net/jdgeisen/BassTraps/BassTrap2.htm), I calculated 1.125 pcf. I called OC, and the person I talked to said 0.53 pcf. The 0.53 pcf value is almost identical to a value of 0.54 pcf that I calculated for blown insulation from some other info I got from the web. I'm waiting on a return call from Owens Corning, to see if we got mixed up on which insulation type the density was for.

If anybody happens to know this density info, could you let me know? Or if someone knows how much a roll weighs and what it's dimension are, I could calculate it that way.

Thanks,
-Stephen

I think I paid about $9 per sheet for the JM... I've heard that $8-12 is normal. Shipping will kill you. Did you look for HVAC insulation on the JM or OC sites?

I can't answer the fluffy question...

I tried calling all the places listed on OC's and JM's website around where I live and none of them have, or said they could get, the rigid fiberglass boards.

I just got a confirmation from the very helpful people at Owens Corning that the fluffy stuff has a typical density between 0.5 and 0.6 pcf. This means that, using the fluffy stuff, the cost for the insulation would be about $180 for two 7'5 foot tall 24"x24"34" triangular collumns. This doesn't include materials to build a light frame to stuff the fluffy stuff into.

So... it's not as much of a cost saver as I had hoped. I'm going to check some other stores around to see if I could get the fluffy insulation cheaper anywhere. I'm hoping that the loose insulation meant to be blown into place will be cheaper. I'll let you know what I find out.

-Stephen

very good work

Hi-

Thanks... too bad I couldn't find my 3m filter mask!

I have a quick question. I may need the traps aforementioned. Can I make the traps, and add a poster over them, or does that defeat the purpose?

Also, could I lay a clearish/see through fabric over the poster, over the treatment to make it more attractive to the lady?

I have a quick question. I may need the traps aforementioned. Can I make the traps, and add a poster over them, or does that defeat the purpose?

Also, could I lay a clearish/see through fabric over the poster, over the treatment to make it more attractive to the lady?


bump

bump


anyone?? Help???? :-)

I have a quick question. I may need the traps aforementioned. Can I make the traps, and add a poster over them, or does that defeat the purpose?

Also, could I lay a clearish/see through fabric over the poster, over the treatment to make it more attractive to the lady?



????

????

Dude, chill! 4 posts in 36 hours asking the same question in the same thread? Take a pill! Eventually someone who knows the answer will answer. Until then, breathe in, breathe out, breathe in, breathe out...

I have a quick question. I may need the traps aforementioned. Can I make the traps, and add a poster over them, or does that defeat the purpose?

Also, could I lay a clearish/see through fabric over the poster, over the treatment to make it more attractive to the lady?

If the trap is in the back of the room you'll probably be okay placing a thin, paper poster over the front of it. In the back of the room you usually want to have a reflective surface for the high frequencies. The low frequency waves go right through. For the rear of the room I don't think fabric will matter too much.

On the other hand, in the front of the room you often want a broad-band absorber, so the fabric should be acoustically transparent (or close to it) and the poster would not be good. You'll get a better response in the acoustic treatments mast thread.

Thanks,
PS If you get a chance would you clean up some of the bumps you put in? Thanks.

If the trap is in the back of the room you'll probably be okay placing a thin, paper poster over the front of it. In the back of the room you usually want to have a reflective surface for the high frequencies. The low frequency waves go right through. For the rear of the room I don't think fabric will matter too much.

On the other hand, in the front of the room you often want a broad-band absorber, so the fabric should be acoustically transparent (or close to it) and the poster would not be good. You'll get a better response in the acoustic treatments mast thread.

Thanks,
PS If you get a chance would you clean up some of the bumps you put in? Thanks.


sure, how do I clean them up, I am not sure what that means.

sure, how do I clean them up, I am not sure what that means.

You can "edit" (not quick edit) your posts and delete them. (I'll do the same to this post when you are done.) It will help streamline the thread.

Thanks,

Hello folks. At the risk of adding yet another project to my yet to be undertaken home theatre build, could somebody enlighten me as to the purpose of the bass trap? I get that a bass trap is used to improve your rooms frequency response, but, what are bass traps made specifically to do? Do they mainly reduce peaks or do they affect nulls, or do they work their magic on a little of both? Do you simply measure your rooms frequency response and then design your bass trap from their?

Hello folks. At the risk of adding yet another project to my yet to be undertaken home theatre build, could somebody enlighten me as to the purpose of the bass trap? I get that a bass trap is used to improve your rooms frequency response, but, what are bass traps made specifically to do? Do they mainly reduce peaks or do they affect nulls, or do they work their magic on a little of both? Do you simply measure your rooms frequency response and then design your bass trap from their?


I'm not sure what they actually do, but I do know that they work. When I first started doing a theater in my garage, the sound was absolutley horrible. I had a concrete floor, and reflective surfaces everywhere. I added carpet, and that helped dramatically to make it not so much of an echo chamber. Problem was, the bass was still boomy and out of control. I then went to Home Depot and got bales of R-13 fiberglass and stacked them in the corners, from the ceiling to the floor. Even though this was very much a ghetto-style solution, it actually worked. The bass was no longer boomy and out of control, but much more tight and crisp. Hard to explain, but it's something you can hear right away after you add the treatments.

Now, I'm totally redoing the theater, and I got rid of all those bales of fiberglass, cause I want to make it look nice, and not so ghetto-style. In the front corners, I'm going with the superchunk method, with the oc703. Unfortunately, I couldn't find the oc703 anywhere locally, and I paid thru the nose to get it, but hopefully it will actually even improve upon the bales of fiberglass I had before.

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! :D

http://gallery.avsforum.com/data/507/medium/cornertrap_99_1_Small_.JPG

...and a view on the top...
http://gallery.avsforum.com/data/507/medium/cornertrap_99_5_Small_.JPG

EDIT
Here's a link (http://gallery.avsforum.com/showphoto.php/photo/21646/cat/507)

and one of three sketches in my gallery:
http://gallery.avsforum.com/data/507/medium/Bass_Trap3.jpg

Just what I need to tame the 10-SVS infrabass set up monster!... :D

-THTS

I have this notion it would be extremely easy to create some 8"x8"x4' rigid fiberglass "boxes" for all the ceiling/wall intersections in my 11'x11'x8' room. Add some simple absorption panels (carpeting "squares" or a few pro acoustical panels) strategically placed on the walls and ceiling and I might be able to tame my Boomville room and still have it look fairly decent.

I'd cut 2'x4'x2" rigid fiberglass panels into 3 sections lengthwise (8"x4'x2"), then glue 4 of them together to create a 8"x8"x4' "boxes." I think I can cover them so they'll remain rigid and velcro them to all the intersections, no real frame necessary. (I'd use thin poster board glued to the sides that will go against the ceiling and walls, then wrap only the visible area in speaker fabric.)

I'd create some larger traps of the same material for the front soundstage of my room. I don't think this will look as good as the triangular corner traps, but those are not practical for my space.

What do you think?

Anyone have any more pictures of custom made superchunk? I am getting some help from my wood worker and need some examples for him.

Thanks

I'm in the middle of trying to figure out what type of acoustic treatment is worth the bother in my room. I'll have my speakers fairly close to the corners, but I can't do the big "super chunk" type corner traps. I'll be able to put an acoustic absorption trap directly above the screen (about 2 feet wide, 11 feet long, 5" thick running along the top of the screen). And since the entire screen wall is open at this point - the dry wall taken off - there is the option of not finishing that cavity with drywall, but instead filling it with acoustic absorption, covering the entire screen wall behind the speakers. I suppose that follows the type of "dead end" (at the speakers) "live end" concept.

Anyone advise if that is a good plan? I'll have a very big sofa in my 15 x 13' room, thick carpet, curtains etc. One of my worries is going a bit too far with absorption and ending up with a "dead" sounding room. Especially as I'll be listening to 2 channel music as well as movie sound.

^^^ Thread kill?