Soffit Type Bass Trap

klh · « **on:** 13 Dec 2005, 11:43 pm »

I have devised a plan for a soffit like bass trap using Bonded Logic cotton insulation. I would buy two 4 packs of the R-19 5.5" x 24" x 94" sheets of the insulation. I would then cut each in half lengthwise and laminate them together (so the combo would be 12" x 11" x 94". I would then put a ring of them at the wall/ceiling corner all the way around the room, and suspend them in the air so that they rest 2" from the ceiling and 2" from the wall. They would then be covered with acoustically transparent, attractive cloth. Each 4 pack only costs $52.50, so that is a heck of a lot of healthy bass trapping for only $105. What do you guys think?

BTW, they also have 3.5" x 16" (or 24") x 94" peices rated to R-13. They come in 10 and 8 packs, respectively, and cost $63.15 and $75.00 per bundle, respectively. They would work nicely for first reflections.

ctviggen · « **Reply #1 on:** 13 Dec 2005, 11:49 pm »

That sounds good, but I wonder what the real effect would be. Do you plan to take any tests?

ScottMayo · « **Reply #2 on:** 14 Dec 2005, 12:15 am »

R-19 has limited absorption ability. Use enough of it, and yes, it helps. But you might be better off with OC 703.

I have a ceiling soffit trap (based on 703), and I do get good bass control.

klh · « **Reply #3 on:** 14 Dec 2005, 12:42 am »

Hmmm... that's too bad. Kind of seemed too good to be true... at least in terms of cost. Scott... you posted on your bass traps, didn't you? I vaguely remember that, but haven't had the chance to look back through the threads.

klh · « **Reply #4 on:** 14 Dec 2005, 01:03 am »

Here's a link to the acoustic properties of Bonded Logic cotton insulation...

http://www.bondedlogic.com/UltraTouchSpecSheet.pdf

The Bass Buster from Sensible Sound Solutions discussed in a previous Soffit thread has identical numbers and costs $39 per 4" x 2' x 4' panel. The cost per 48" of the 5.5" x 24" x 94" bonded logic stuff is less than $7. Interesting difference.

ScottMayo · « **Reply #5 on:** 14 Dec 2005, 01:42 am »

Quote from: klh

Hmmm... that's too bad. Kind of seemed too good to be true... at least in terms of cost. Scott... you posted on your bass traps, didn't you? I vaguely remember that, but haven't had the chance to look back through the threads.

I've got 3 kinds of bass trapping in my room, all of it hand built and none of it was any fun. I poured out OC 703 like water. I suffered as no man has ever suffered. (OK, that's over the top. I itched some and sweated a lot). But the bass is pretty clean now.

JohninCR · « **Reply #6 on:** 17 Dec 2005, 09:41 pm »

KLH,

I think you are on the right track, but something to keep in mind for trapping bass is that it's magnitude more effective when you form a sealed air volume and your absorbant material inside will dissipate the bass and turn it into heat.

Along the lines of your idea something easy and effective would be to use the ceiling/wall corners to form a triangular panel bass trap around the ceiling of the room. 1 runner along the wall and 1 on the ceiling. Staple up some fiberglass or if you prefer, the cotton insulation. Then close it up with plywood or sheetrock and seal the edges and the trap is done. To tune some of the traps tuned to frequencies, just attach some wood scraps to the center of some of the panels before installing them to lower their resonant frequency. You'd probably need to do some HF absorption to the reflective surface angles you've added, but that's easy enough to do on the exterior using acoustical tiles or an absorbant covered by material without detracting from the operation of your panel bass traps.

This forum seems to be dominated by expensive solutions which is fine when you have the money to throw at a problem, however, there are a myriad of cheap and effective DIY solutions that solve the same acoustic problems. A little research and sweat equity can go a very long way.

bpape · « **Reply #7 on:** 17 Dec 2005, 10:08 pm »

Just for clarification...

The Bonded Logic material and the Bass Buster are very similar and are made via the same materials and similar process. Some things to note:

The Bonded Logic is available at that price IF you buy a bunch of it. The Bass Buster is priced that way for 1 piece. If you buy more, the price goes down. The best quantity I've found for that price is 50 24x94 pcs. For a reasonable quantity, it's more like $18-$25 for a 24x94 plus shipping.

The Bass Buster is a full-size 24x48 pc (not that this is a big deal) where the Bonded Logic is 24x94 and would need to be cut into 2 pcs that are 24x47. The Bass Buster is already cut to size and is also dyed charcoal. The Bonded Logic is in medium blue only (natural state of recycled cotton) and comes in 94" batts. The cutting and dying do have a manufacturing cost associated with them.

Don't get me wrong. You can absolutely save money buy buying bulk material. When you do, there is also increased shipping cost involved as well as more time spent on your end.

ctviggen · « **Reply #8 on:** 18 Dec 2005, 02:04 am »

This book has quite a few ideas for bass traps (along with data therefore):

http://www.amazon.com/gp/product/0071360972/qid=1134871388/sr=1-1/ref=sr_1_1/104-6955198-2829510?s=books&v=glance&n=283155 They have an angular bass trap that's cheap and easy.

klh · « **Reply #9 on:** 18 Dec 2005, 05:33 am »

Thanks for the tips and responses. The bonded logic stuff is sold locally, so I can go pick it up. Also, the price I got is per bundle, and they know I'm only getting two. I guess I'm just a very lucky person. I'm reluctant to use 703 or 705 because I'd like to create a soffit and cutting rigid fiberglass is something I'd really like to avoid. The health risks and skin irritation don't sound fun at all... plus the cost is quite a bit higher. Ideally I'd build a soffit made of 4" 705 and treat the first reflection points with 2" 703, but that would be rather expensive. We'll see. Thanks again.

BTW, the idea of keeping the bonded logic in the corners but spaced slightly away from the wall was based on Nathan's ideas at 8th Nerve. His theory is interesting... a ring of bonded cotton measuring 11"x12" and suspended 2" from the wall and ceiling and going all the way around the room would be a DIY attempt at what he is doing. I'm wondering how that would work as a bass trap compared to 705 across the corner either as a soffit or triangle.

ctviggen · « **Reply #10 on:** 18 Dec 2005, 12:59 pm »

The problem with bass traps is that they typically need to be large (even resonant chambers are on the order of bass wavelengths, so they're large). You typically need mass for this. Nathan's products (specifically, the corner and seam products) are too small for much bass trapping. The work very well for midrange and upper range trapping but not so well for bass. 703 and 705 are recommended as they're dense and help to trap bass.

If you have a room that's open and you don't care what it looks like, you can develop a very good bass trap by making a corner trap from plywood and filled with insulation. The Handbook of Acoustics gives data on such a trap. This trap works by letting the plywood ring (thereby taking bass energy and converting it to heat/movement) and any sound that gets through the plywood would get further absorbed by the insulation. You can paint the plywood. This will not provide midrange absorption however.

bpape · « **Reply #11 on:** 18 Dec 2005, 02:40 pm »

If you can get the Bonded Logic at that price for 2 bales (that's techically equivalent to 16 pcs of Bass Buster for those keeping score...) and you can go pick it up instead of having to pay shipping, go for it. It will do a great job in the soffits.

For broadband bass control, consider bonding a kraft/foil (FSK) scrim to the exposed surface. If you can't get the FSK, even some decent kraft paper will do a good job.

klh · « **Reply #12 on:** 20 Dec 2005, 09:31 pm »

The 8th nerve line I was referring to was the adapt line. His thinking is definitely nonconventional. I would love to get the 705, I just don't want to deal with cutting it, and, undfortunately I would have to given the placement of windows and doors within the room.

ScottMayo · « **Reply #13 on:** 20 Dec 2005, 09:42 pm »

Quote from: klh

The 8th nerve line I was referring to was the adapt line. His thinking is definitely nonconventional. I would love to get the 705, I just don't want to deal with cutting it, and, undfortunately I would have to given the placement of windows and doors within the room.

For what it's worth, cutting 703 is trivial - I use a yardstick and a steak knife. You get simple, clean cuts, and very little mess. It's also fireproof, moisture resistant, uninteresting to bugs and doesn't seem to break down over time.

klh · « **Reply #14 on:** 21 Dec 2005, 12:18 am »

Bpape...

I was at your website and in particular looking at the Mineral Wool. In order to do a soffit... I would cut the 2' x 4' x 4" lengthwise into two so one sheet would get me a soffit 12" tall and 16" deep (and 48" long). I like that because it is asthetically pleasing. In order to do that, I would need five 3 packs ($240) to cover all of the wall/ceiling corners. To make the soffits out of bonded cotton as previously described, I would need to get 2 bundles of the bulk 5.5" x 24" x 94" insulation (you sell that for $268).

Which of those two choices would work better at broadband bass absorption in your opinion, and why? Since the cost (and your profit) is comparable, I'd like to know what you prefer.

If anyone else has an opion please chime in.

bpape · « **Reply #15 on:** 21 Dec 2005, 04:51 pm »

Well, first of all, the Mineral Wool would cost you more. The cotton pricing inlcludes the shipping cost where shipping the mineral wool would be in addition to that price.

All else being the same (thickness and surface area), the Mineral Wool will do a better job in the deep bass due to it's additional density. The cotton will have an absorbtion hump around 200-300Hz over and above what the mineral wool would do. If your room needs that, and many do - especially if you have single layer drywall instead of double layer, this may be an advantage.

The other thing to consider is ease of cutting. The Mineral Wool cuts very easily provided you have a very sharp knife - a bread knife works wonderfully on the 8lb materal. The cotton is a bit more difficult but can be done - it just takes more patience and a blade that is very thin like a double edged razor blade type.

Lastly, unless you're going to bond a facing like FRK to it, you also must consider the mid and high frequency differences of the material. Here, the cotton will do a superior job when dealing with shallow angles of incidence.

To select the proper treatment, I'd want to know exactly what the rest of the room is like, how it will be mounted, if it's faced, etc. Since it's in a soffit, the ability of the cotton to bounce back to shape instead of getting 'dented' like 703 and mineral wool can may not be a concern but thought I'd mention it.

Optionally, you can do a mix of the 2 where you'd do multiple layers of mineral wool from the wall out and then finish the face with the cotton product. This assumes that you cut the other dimension and that the sides of the soffits are also open to the room and not drywalled.

They can both be very effective products - just depends on the situation and what the room needs in your particular application. If it were me, I'd probably do Mineral Wool in the vertical corners stacked solid in triangles and cotton in the soffits faced with kraft paper. If you're not doing the vertical corners, then I'd probably mix it with cubes of mineral wool in the tri-corner portion of the soffits and cotton elsewhere. I could then use the leftover from the second bale to make some parts of the soffit more dense.