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  Topic Review (Newest First)
09-04-11 01:00 PM
streetcore
Re: Bass traps for asymmetrical set-up in L-shaped apartment?

So I got some R40 pink insulation 11"x24"x48" and have been experimenting a bit with it in the right corner. It's going to require some cutting and/or squishing to fit it into my triangle, but I think the layout below will be the easiest. It's two pieces standing vertically in an L-shape, and I'll build a brace with netting to support the top layer for a full 8 feet. Before I start cutting I thought I'd see if you guys had any comments. How critical is it to fill the empty space in the triangle as seen below? Since the spaces left are so small, I can't imagine it would make much difference.

I've also attached some before and after waterfalls, and it does seem to make a difference. I did some quick listening tests too, and there did seem to be a bit more clarity and less boominess (is that a word?)

Thanks,

Andrew
08-31-11 05:50 PM
streetcore
Re: Bass traps for asymmetrical set-up in L-shaped apartment?

I don't mind you giving me a hard time, especially since you're providing so much useful information and I obviously don't know what I'm talking about.

I didn't really understand that the thickness of the pink stuff varied so much and that it could be fluffed up to make it thicker. My comparisons were only based on the dimensions of the low priced R12. I actually expected it to settle a bit after installation, and I thought maybe it should be compressed to make it denser, so I was thinking that 3.5" of pink stuff would occupy approximately the same volume as 3" of OC703.

I now understand that I can get much thicker insulation for a bit more money. The OC R-40 is available at my local HomeDepot for $59.77 with a rated thickness of 11". Maybe I should consider that?

Quote:
SAC wrote: View Post
What we have proposed is not some abstract concept. It has been done many times in reality, for substantial savings.
Can you provide any links to traps that have been built like this? I did a lot of google searching last night trying to find examples of people who had built traps with pink fluffy stuff, but couldn't find any. In fact, most of the results I found where people saying not to use it. Examples include: "The pink stuff is good for in the walls only. Completely useless for bass traps or diffusers", "you need density for bass traps- the pink insulation(probably wall or ceiling insulation) won't do much for you", "The pink stuff just isn't dense enough for bass traps. You want something like Owens and Cornings 703 or 705".

I assume we can disregard those statements since we're talking about a trap with a thickness of 12" or more, but it would still be nice to see some examples.

As for the netting, I'm sure if I look around a bit I can find a better price, but that was the lowest price, and smallest quantity, I found find at my Home Depot.

Anyway... thanks again for the additional info. I'm sure I'll figure this out eventually.
08-31-11 03:52 PM
SAC
Re: Bass traps for asymmetrical set-up in L-shaped apartment?

Very ‘interesting’ calculations and comparisons, as the performance of the two variations are not even close to being equivalent.

At Lowes, one can source Roxul Safe’n’Sound 8-Pack 24"Wx4’L x R-30 Fiberglass Insulation Batts for $47.87, which has the additional benefit of also lacking a formaldehyde based binder.

BTW, you do not want insulation with a Kraft/FRK applied layer.

Also, I would consult Bob Gold's database or obtain measured specs from the manufacturer before you assign equivalency in absorptive performance of the semi-rigid material! Neither thickness nor density are valid indicators of equivalence - rather gas flow resistivity is.

Considering that R-30 is rated at a thickness of 8.5 inches and can be fluffed substantially beyond this for our purposes (I would suggest ~10 inches), which is actually useful, the effective depth is actually substantially increased.

Assuming that it is fluffed to 10” deep and placed vertically, you could make a trap that is nominally 30 inches deep (at least on the wider side) and 48” wide!

It would take at least 22 - 4’ semi rigid panels to achieve slightly less than the same volume of fill provided by ~8 panels of fluffy stuff. And due to the variance in gas flow resistance, the performance would not be equivalent.

A quick search found Dalen 7-Foot by 20-Foot Bird-X Net 3/4-Inch Mesh for $7.27. We can find it for the prices you cite, but just how many traps are you considering making!? That’s enough netting material to put full sized traps in every corner of your house AND the neighbors! And as we previously mentioned, we have routinely sourced this at Wal-Mart for ~$5, and less if you are savvy with the end of the summer clearances in their garden department, eliminating the need to even check with Farmtek.

And after all is said and done, with the referenced materials, we could literally make several corner traps for the price of a semi-rigid design that each outperform the semi-rigid option, not to mention that a 24” faced 4” semi-rigid panel with a 4” gap is not even in the same ballpark performance-wise, and that is far lower performing than an equivalent Superchunk format constructed of semi-rigid panels that is still outperformed by the suggested 'fluffy stuff' construction with lower gas flow resistance.

What we have proposed is not some abstract concept. It has been done many times in reality, for substantial savings.

So, I’m not trying to give you a hard time, except to say that with just a LITTLE research, you can dramatically cut the costs and increase the performance. We make this as difficult as we like. And in the end, the compromises you make only come back to seriously degrade the comparative performance. But if it were me, I would be interested in obtaining the maximal return with respect to actual acoustical performance with respect to the investment of cost and effort. But of course each is free to do as they choose. My interest is that you don’t make it any more difficult than it is! Good luck!
08-31-11 01:17 PM
streetcore
Re: Bass traps for asymmetrical set-up in L-shaped apartment?

Quote:
SAC wrote: View Post
I hope that allays a few fears and makes things a bit simpler (and cheaper!)
I was at Home Depot last night pricing things out and I don't think it's going to be any cheaper to use pink insulation. In fact I think it might be more expensive and more complicated.

The cheapest pink insulation I could find was Owens Corning R12 3.5"x15"x47", 20pcs per package, for $38.99. The plastic netting was much more than I expected at $25.99 for 36"x25'. Metal net was cheaper at $16.97 for 48"x25', but it would be harder to work with.

If my calculations are correct, I would need at least two packs of insulation, maybe three, plus the netting and wood for the framing. In order to hold the netting in place, I think the frame would also be more complicated and require more wood than a frame built to hold rigid fibre board. In fact, many of the designs I've seen for traps built with OC703 have no frame at all.

So the cost of the corner trap with pink insulation would be at least $100 plus the wood for the framing and the fabric to cover it.

However, I can also get 4 sheets of 3"x24"x48" unfaced OFI48 here in Toronto (the equivalent of OC703) for about $45. One package is enough to build a Superchunk with a 24" face, and two packs would be enough for an SC with a 36" face. If I built the Studiotips Corner Absorber I would only need six sheets, would only have to make a couple cuts, and might not need any framing at all.

If we compared the cost to build a large triangle as we described above, I would need 16 - 24"x48" sheets cut into two diagonally. That would be about $180, but I wouldn't require any netting and minimal framing. So I think the costs are actually pretty close.

So I hate to say it, but I'm kind of back to where I started, and I think the cost and convenience of working with the rigid fibre board is leading me back in that direction.
08-29-11 09:51 PM
SAC
Re: Bass traps for asymmetrical set-up in L-shaped apartment?

A few thoughts.

First, the fibers are not loose, and I always wonder why folks think these things are 'active' and that the fibers somehow grow feet and migrate.

Also, just to allay additional fears and to put things into perspective, Fiberglass is an irritant ONLY.The pink fluffy stuff has minimal binder as opposed to the semi-rigid material (and also a good reason to explore Knauf Ecose semi-rigid equivalents). Funny, I seldom hear anyone concerned that sawdust is listed as an a carcinogen and that 'natural' fibers such as cotton, wool, hemp, etc are literally MUCH more dangerous than Fiberglass or basaltic fibers that if breathed/ingested, harmlessly dissolve in less than 2 weeks. Compare that with natural fibers that do NOT dissolve and cause such ailments as byssinosis.

Of course, it follows that best practices and (un)common sense are ALWAYS advised regardless of whatever materials are employed!

All of that said, you enclose the material behind a loose weave cloth boundary such as unbleached muslin reinforced with supportive orchard bird netting. You then build a face frame with a stretched materiel that straddles the actual trap leaving about an inch gap between the outer and inner fabric panels. Thus any casual contact, etc., with the external surface never disturbs the contents. There should be no reason for there to be any disturbance of the material, let alone movement other than settling, at all.

I hope that allays a few fears and makes things a bit simpler (and cheaper!)
08-29-11 09:09 PM
streetcore
Re: Bass traps for asymmetrical set-up in L-shaped apartment?

I get it now. I was going back to my original thoughts about a Superchunk trap with a 24" face and 16" depth. The other drawing I did was based on a Studiotips Corner Absorber, which has more depth. Thanks as well for the additional info about why the corner placement will outperform the planar application. I was wondering about that.

I think this final idea might be doable. However, I am a bit concerned about using lose pink fibreglass, and don't want those fibres working their way out into the room and my lungs. Would there be any problem sealing the face of the trap with plastic?

Cheers,

Andrew
08-29-11 08:26 PM
SAC
Re: Bass traps for asymmetrical set-up in L-shaped apartment?

Yes and no!

I am NOT proposing that you radically cut the depth almost in half!!! That will have significant detrimental effects on a porous velocity based absorber.
If you want some 'trim unobtrusive' treatment, you need to explore pressure based tuned resonant traps - the easiest of which to obtain are the RPG Modex tuned modules.

Leave the original wall interface dimensions and simply straddle that region with the face frame and fill.
08-29-11 08:18 PM
streetcore
Re: Bass traps for asymmetrical set-up in L-shaped apartment?

I just noticed you added a picture to your post. I guess we are on the same page.

I'm up for cheaper and more effective, but I'm not sure I'm following you. Are you suggesting something like this?
08-29-11 08:07 PM
SAC
Re: Bass traps for asymmetrical set-up in L-shaped apartment?

A few suggestions that are not only more effective, but much less expensive.

For the corner bass trap, stop messing with expensive OC703 panels and the additional complexity of complex multi-element face frames and simply make a Superchunk corner trap that straddles the entire space that you are imagining being treated with a corner trap and adjacent panels.





The additional space that is filled by the resultant hypotenuse is negligible in terms of room use, but substantial in terms of bass absorption.

And fill the entire corner region with cheap fluffed 'pink fluffy stuff' available at any home improvement store. Just provide a few horizontal layers of plastic orchard bird netting (cheap at any nursery supply or Wal-Mart in season) dividing the Superchunk into sever 2-3' compartments. You can fill these with fluffed 'pink fluffy stuff' and the netting will minimize the insulation settling and compressing due to gravity as the mass will be less in each compartment and it will not all press on the lower portions.

This will outperform the Superchink made with the more expensive lower performing semi rigid OC703.

{Part of the reason the corner placement will outperform the planar application is that some of the energy reflects ;laterally off the wall surface and is directed 'sideways' through the absorbent material, effectively increasing the reactive area whereby the energy interacts with the absorptive material. In other words, porous traps are velocity based devices. Velocity goes to zero near a boundary, so by moving the absorbent material further out from the wall, you lower the effective frequency that corresponds to the maximum velocity quarter wave spacing, and then you also further increase the amount of interaction by having some if the energy be redirected off the wall as it travels 'sideways' over a longer path through the absorbent material, thus increasing the energy dissipation.}

And its MUCH simpler to construct as well! A case where the easier cheaper alternative outperforms the more expensive and complex variation.
08-29-11 07:46 PM
streetcore
Re: Bass traps for asymmetrical set-up in L-shaped apartment?

Quote:
SAC wrote: View Post
Regarding the proposed traps, you might consider a Superchunk style corner trap using the 'cheap pink fluffy stuff" and utilizing several pieces of plastic orchard bird netting to create several partitions that will act to support the material such that it will not compress as much over time.

Also note that a 3 inch panel mounted adjacent to a wall will not act as a bass trap. in fact, a 3 " panel with a 3" gap, utilizing Rockwool, will only exhibit an ~.3 absorption coefficient at 100 Hz! In fact, a 4 inch panel with a 4" gap is about the 'smallest' you want to use for a broadband (mid and higher) absorptive panel.

To be effective below 100 Hz, you need to go with at least a 6" panel with a 6" gap ([email protected] Hz and [email protected] Hz).
So there's seems to be some consensus that a Superchunk in the right corner is a good start, but the effectiveness of any further treatment of the wall beside the right speaker is still questionable.

If I was going to use a 4 to 6" thick panel of OC703 with a 4 to 6" gap, could I skip the Superchunk and just fill that 4'x8' side wall with the panel from the back wall to the door? Something like the picture below might suit my aesthetic concerns better, and be easier to build, than separate corner and side panels, especially if then need to be so thick.

Thanks again for the incredibly detailed response. I'll take some more time to read and digest the ETC info.
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