[Rob Babcock]

Well, it's not fancy but I got my first one done.  My plan was to paint the wood so the corners didn't peek through the burlap but I decided better the ugly but functional trap today than a pretty trap that doesn't get built for months.  I built a frame of 1"x2"s with a 16" x 17" or so board for a top and bottom.  The filling is Roxul S'n'S oriented vertically in bottom half (to avoid cutting) with 15" x 16" pieces stacked on top.

Here are some pics before I got the fabric on.  Sorry about the mess and that the second one is a little blurry (must have wiggled). But you get the idea.





I will build a matching one for the opposite corner and I need to build a smaller version to sit on top, so it covers the whole corner wall-to-ceiling.  And I'm planning to do a shorter version for another corner where space concerns prevent using something taller (plus a shorter version can be used for a surround speaker stand).

[jk@home]

Nice job. That's the beauty of DIY, one can do custom sizes for any situation.

If you have already covered them then it's too late, but in lew of painting the wood for a better color blend behind the burlap, one may be able use a colored tape slapped on the wood. Quicker and less messy than paint.

[timind]

Lookin good!
Curious about the weight of this trap? Also, where did you get the filler material? Was it less expensive than just purchasing a prebuilt trap from someone like GIK?

[lokie]

Curious as to what frequency range you are trying to "modify"... And other goals you are targeting.

Are you going to show some before and after measurements?

[AKLegal]

Looks good.  I have made a few that look exactly like yours. 

What I did and what you may want to do is measure frequency response in the corners of your room individually and not just the listening position.  Then look for the peaks and nulls and then build a trap with materials that are best for absorbing those particular frequencies.  To do that you would use a porous absorber calculator like this one http://www.acousticmodelling.com/multi.php

So say you have a issue at 30hz.  A 16 inch deep trap with 2 inches Owens Corning 705 closest to the room side and 14 inches of SnS between the OC and the wall would be better than straight up SnS for 16 inches.  But if your issue is with 80 hz then 16 inches of SnS is better by far but 16 inches of R-30 is even better (although I would probably still choose safe n sound in that situation).  http://tinyurl.com/lh7b523   

It took about a year but I was able to transform my room this way.  In one corner I even ended up with a 12 inch deep trap with the first layer (the side facing out into the room) being 2 inches of Roxul Rockboard 60 and the remaining 10 inches being Fluffy R-30 material.  You can really mix and match to get a custom solution. 

The calculator is easy to use just make sure to select "Komatsu (2008)" for the porous model on the left side of the page.  Here are some common values for absorption materials.

Common pa.s values:
Pink R-30 insulation -  4000 pa.s
Safe N Sound - 8,000 pa.s
Owens corning 703, Rockboard AFB (or equivalent) - 16,000 pa.s
Owens corning 705, Rockboard 60(or equivalent) - 30,000 pa.s
Rockboard 80 - 45,000 ~ 50,000 pa.s (I haven't found a agreed upon rating for it)

[Rob Babcock]

Lookin good!
Curious about the weight of this trap? Also, where did you get the filler material? Was it less expensive than just purchasing a prebuilt trap from someone like GIK?

I used 16" x 3" x 47" batts of Roxul Safe'n'Sound.  A bundle is 12 batts, and this trap took maybe 8 (with a bit of the last piece left over).  It's easily moveable by one person, so not super heavy.  The frame is 1" x 2" sticks with a solid bottom and cap.

Curious as to what frequency range you are trying to "modify"... And other goals you are targeting.

Are you going to show some before and after measurements?

Maybe, but not soon.  It's a work in progress, probably be later this summer before I am done.

[Rob Babcock]

Looks good.  I have made a few that look exactly like yours. 

What I did and what you may want to do is measure frequency response in the corners of your room individually and not just the listening position.  Then look for the peaks and nulls and then build a trap with materials that are best for absorbing those particular frequencies.  To do that you would use a porous absorber calculator like this one http://www.acousticmodelling.com/multi.php

So say you have a issue at 30hz.  A 16 inch deep trap with 2 inches Owens Corning 705 closest to the room side and 14 inches of SnS between the OC and the wall would be better than straight up SnS for 16 inches.  But if your issue is with 80 hz then 16 inches of SnS is better by far but 16 inches of R-30 is even better (although I would probably still choose safe n sound in that situation).  http://tinyurl.com/lh7b523 

Those calculators are useful but have some serious limitations and aren't always accurate.  OC 705 is good stuff, though.  The room I'm treating isn't my main room but a smaller one. 
Every room is different but there are some near-univerals; corners are almost always in need of bass trapping. 

My plan is to install floor-to-ceiling soffit traps in the front corners, 2'x4'x4" traps (made of Roxul Rockboard 60/80) straddling the wall/ceiling junctions on all 4 walls the mid-points, large bass traps on the side walls at first reflection points, traps in the back wall/ceiling trihedral corners and a shorter soffit trap in the floor/wall junction corner in the left rear.  The layout and the location of immovable features (doors and windows, other things I can't move) dictate some compromises.

Once I get all the trapping I can reasonably manage I'll apply judicious equalization to a sub.  The room isn't large enough to "need" a sub but in my experience it's easiest and most effective to offload bass to a sub and deal with the low end through a combination of EQ and physical treatment.

[Glenn Kuras]

Rob GREAT JOB!! 

[Housteau]

I like the idea of a square soffit vertical corner trap.  Had I not already had a bunch of triangular cut sections I would have built similar ones for the corners behind my listening seat.  Who knows, after I get home and get the chance to do my room tuning, maybe I still will.

[Rob Babcock]

Okay, I did a second one tonite.  It's short to fit in a spot where I can't go higher and it's sturdy enough to use as a speaker stand.  It's built but I didn't have time to apply the fabric.  The top is made of 1"x2" sticks and the bottom is solid.  I have a solid piece cut for the top which I'll put on after I do the cloth.  I stuck on three short feet on the bottom to make sure it was solid.  The insulation is Roxul S'n'S with one batt of Thermafibre since I was a chunk short of Roxul.

The trap is 42" tall x 16" x 17".  The only minor annoyance is that I intended to make it 41.5" tall but forgot to include the 1/2" for the top square. 

Here are a few pics.

[Rob Babcock]

Lookin good!
Curious about the weight of this trap? Also, where did you get the filler material? Was it less expensive than just purchasing a prebuilt trap from someone like GIK?

Ooops, forgot to address the material.  I bought the Roxul S'n'S at the local Lowe's.  IIRC it was $48 for a package of a dozen batts (4" x 16" x 47" long).  Counting the lumber and fabric along with the rock wool I have maybe $75 in the whole project.  Probably a few bucks worth of screws and hardware but that's something I always have around.  Much cheaper than getting stuff from GIK, at least at first blush.  If you count the time (and you should I suppose) and running around getting stuff it's closer.  However, buying one from GIK it would have looked a helluva lot nicer than mine!   I'll snap some pics with the fabric on it but it's a stark monolith.  I was too lazy and impatient to paint the frame black before upholstering it and the weave of burlap is really open, so the one-by's show through a bit.

I like to DIY, and I have a good range of tools and space to work.  It's also nice to be able to fabricate something the exact size I need (although I sometimes miss the mark a bit ).  Sometime I'll pick up a panel or three from GIK just to see how bad it makes my upholstery skills look!

[spence]

Hi Rob,
   Your traps look great! I've been following your build over on the GS site too. I'm ready to wrap mine, but I'm really curious as to the benefit of using Safe n' Sound compared to JM R-30 when building traps this size. The R-30 is only $15 per bundle compared to $48 for the S n' S. I've read that there's little difference in the two when traps are this large. I'd love to hear opinions on this.

My local fabric shop suggested that I run velcro down one edge of the fabric and apply that edge to the frame first, then wrap the fabric right around the traps and staple the other side to the frame. That way, you can open the trap easily if needed. They have a newer type of burlap that isn't nearly as fuzzy or flaky like the regular type of burlap. It actually looks pretty nice and comes in about 20 colors.

Dave

[Glenn Kuras]

  Sometime I'll pick up a panel or three from GIK just to see how bad it makes my upholstery skills look!

Just take your time and let your wife (if you have one) grade you! 

[Rob Babcock]

Hi Rob,
   Your traps look great! I've been following your build over on the GS site too. I'm ready to wrap mine, but I'm really curious as to the benefit of using Safe n' Sound compared to JM R-30 when building traps this size. The R-30 is only $15 per bundle compared to $48 for the S n' S. I've read that there's little difference in the two when traps are this large. I'd love to hear opinions on this.

All the research I've done and experience of the years has made me feel that that regular fluffy isn't as good as rock wool until you get into really large traps, like Superchunks.  But I'll be honest- part of it is simply that I don't like working with it.   Rock wool is pretty rigid, easy to cut and better to handle (IMOHO).

My local fabric shop suggested that I run velcro down one edge of the fabric and apply that edge to the frame first, then wrap the fabric right around the traps and staple the other side to the frame. That way, you can open the trap easily if needed. They have a newer type of burlap that isn't nearly as fuzzy or flaky like the regular type of burlap. It actually looks pretty nice and comes in about 20 colors.

Dave

That's a slick idea!  I'll have to look into that.  An acoustic treatment isn't like a PC case that you know you'll have to open periodically but it still sounds like a good idea.

[James Romeyn]

deleted

[spence]

The only reason you'd need to get into the trap is if the insulation would settle after a while. Or now that I think about it, if the material starts to sag, you can always undo the Velcro side, pull it snug, then reattach it - much easier than pulling staples!

[Rob Babcock]

Yeah, it would be nice.  Where did you find this nicer grade of burlap?  I have the common stuff that's around $3.99/yard at all the craft stores.  It's cheap and has a really open weave but realistically it doesn't need to be that open for a corner trap.  Some reflection would be okay for he upper freq range.  I know many people will glue FRK or plastic to the rock wool to create a membrane effect but I didn't want to mess with it just now.  Down the road I might do so, reupholster the tall trap, paint the wood and add a membrane.

In halfhearted defense of my laziness it really is a matter of doing something now even it could be better.  Often I let perfection be the enemy of the good.  Even if my traps could be made more effective at least I'm getting good performance now.

[Rob Babcock]

Okay, got some fabric on it.  I got a $4.96 bed sheet from Wal-Mart; that way I only had to sand the corners, no worrying about wood showing through.   I also decided maybe grey was better than another black "monolith".  You can see from the different shots that I have a piece cut to cover the top.  As of right now it's not attached, still deciding if I should stain it a dark color first.

Here are a few pics (please pardon the mess):







You can see it without the top on it in this last picture.  The seam is highly visible on the front edge relative to the camera but that's not an issue since that corner faces the, well, corner.



BTW, as luck would have it the top does just barely clear the item I hoped it would!   That gains me another 2" of wall space in an area that's already a tight fit.

[spence]

Rob,
   The burlap I saw was at my local fabric shop. It has a tighter weave than the burlap of old, but still very easy to breathe through, and it's not as hairy or dirty like I remember seeing in the past. I'm trying to decide on which color to get. I'll also be putting paper on the face of my traps. A huge roll at Lowes is about $10. If I were you, I'd iron that bed sheet to get the folds out. You can also dye it if you want a different color. It all depends on how nice you want it to look.

[Rob Babcock]

A little late to iron it now.  Plus, what's an iron?   I think it will smooth out a little as it hangs.  The trap is in a corner where it's hard to see anyway.  That corner is dark enough that I might not even bother to stain the top.