Membrane absorber bass trap - anyone made these?

[hemster]

Dec 2, 2014 5:17:45 GMT -5 yves said:

Dec 1, 2014 22:38:02 GMT -5 pedrocols said:

Precisely!

Well... as much as I hate to rain on your parade, the answer to this question has already been provided in the first link I posted (and by none other than Ethan Winer himself, for that matter........).

I've researched more and realize that the rigid fiberglass batt is easy to keep propped up. I was originally thinking of the floppy 701-type batts but these 703 FRK (and even more so the 705) are quite rigid. Saves me the hassle of more woodworking. 

[yves]

Dec 2, 2014 5:32:17 GMT -5 hemster said:

Dec 2, 2014 5:17:45 GMT -5 yves said:

Well... as much as I hate to rain on your parade, the answer to this question has already been provided in the first link I posted (and by none other than Ethan Winer himself, for that matter........).

I've researched more and realize that the rigid fiberglass batt is easy to keep propped up. I was originally thinking of the floppy 701-type batts but these 703 FRK (and even more so the 705) are quite rigid. Saves me the hassle of more woodworking. 

Yes, but before you proceed, here is a link to a discussion thread that you might also want to read first.

www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/887562-wood-panel-bass-trap.html

As you can see, the wood panel type of bass traps are NOT recommended if your room is not large enough, and the fact they are tuned bass traps also means that you need to work out the correct absorption frequencies or else they simply will not work for your specific room acoustic analysis plot.

[hemster]

Dec 2, 2014 5:43:44 GMT -5 yves said:

Dec 2, 2014 5:32:17 GMT -5 hemster said:

I've researched more and realize that the rigid fiberglass batt is easy to keep propped up. I was originally thinking of the floppy 701-type batts but these 703 FRK (and even more so the 705) are quite rigid. Saves me the hassle of more woodworking. 

Yes, but before you proceed, here is a link to a discussion thread that you might also want to read first.

www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/887562-wood-panel-bass-trap.html

As you can see, the wood panel type of bass traps are NOT recommended if your room is not large enough, and the fact they are tuned bass traps also means that you need to work out the correct absorption frequencies or else they simply will not work for your specific room acoustic analysis plot.

The room is 15 ft x 26 ft x 9 ft. If that's too small for a wood panel trap than I need to rethink this. It's confusing because Ethan says these traps work well for a small room also! link. 

I have very little space in the front 2 corners. The screen and speakers pretty much take up the width, so placing a corner trap is unworkable. 

[yves]

Dec 2, 2014 5:53:34 GMT -5 hemster said:

Dec 2, 2014 5:43:44 GMT -5 yves said:

Yes, but before you proceed, here is a link to a discussion thread that you might also want to read first.

www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/887562-wood-panel-bass-trap.html

As you can see, the wood panel type of bass traps are NOT recommended if your room is not large enough, and the fact they are tuned bass traps also means that you need to work out the correct absorption frequencies or else they simply will not work for your specific room acoustic analysis plot.

The room is 15 ft x 26 ft x 9 ft. If that's too small for a wood panel trap than I need to rethink this. It's confusing because Ethan says these traps work well for a small room also! link. 

I have very little space in the front 2 corners. The screen and speakers pretty much take up the width, so placing a corner trap is unworkable. 

I think the article is actually pretty clear on this:

Please understand that the bass traps described in this article are intended mainly for larger rooms. For rooms smaller than 25 by 15 feet you'll do better with broadband bass traps made from thick rigid fiberglass placed in the room corners, them more on the front and rear walls if possible. Small rooms have peaks and nulls at all frequencies, so broadband absorption is better than the tuned traps shown in this article.

Thick, porous bass traps like the ones I described are broadband absorbers, whereas wood panel bass traps are tuned to one specific frequency, and this frequency is determined by both the thickness of the panel and the thickness of the insulation inside it. Use the REW waterfall plot to find out at which frequencies you want to tune your wood panel bass traps, and don't be afraid to seek out more advice from Ethan on his forum: forums.musicplayer.com/ubbthreads.php/forums/24/1/Ethan_Winer_The_Audio_Expert

That said, I think your room is just big enough, but you should consider to always start out with broadband bass traps first, and only add the tuned type after that if still necessary, as Glenn Kuras of GIK Acoustics points out in the thread I linked.

P.S. - The corners between the walls and ceiling (where 3 surfaces meet) are excellent locations for thick, triangular bass traps:


...And because your ceiling is 9 ft. high, I'm sure there will be enough space for an even bigger soffit bass trap than this guy has:

[hemster]

Thanks. I'll be talking with Ethan on this subject as well as the merits of using OC 703 vs. OC 705.

[jlafrenz]

Dec 2, 2014 16:55:32 GMT -5 hemster said:

Thanks. I'll be talking with Ethan on this subject as well as the merits of using OC 703 vs. OC 705.

I'm interested to see what he has to say about this. I am planning on building some superchunk style traps and since your post it has me wonder if the ones you linked might be a better option. The room is quite small so based upon the specs provided for ideal room size, the superchunk is probably still the best. I would still like to hear Ethan's thoughts on how they compare though.

[yves]

He tested OC 703 vs. OC 705 and then he wrote an article about it:
ethanwiner.com/density.html

However...
www.avsforum.com/forum/91-audio-theory-setup-chat/608026-owens-corning-703-vs-705-a.html

So, if straddling a corner with it (leaving an air gap behind it), the denser OC 705 wins, but if you decide to increase the thickness of the insulation beyond a certain thickness, ideally, you will want to replace it with a different type of insulation that has a lower gas flow resistivity. This is because, if the gas flow resistivity is too low, a too significant part of the bass waves will travel right through the bass trap and then simply back again without getting absorbed by it, whereas, if this resistivity is too high, a too significant part of the bass waves won't be able to penetrate deep enough into the bass trap to be able to be absorbed by it.

As for Supertips SuperChunk bass traps, I think the main reason why a lot of people go for Safe'n'Sound mineral wool instead of pink fluffy fiberglass, even despite the fact they're building them at least 24" thick, is because either they still don't know that the pink fluffy stuff gives better absorption at this kind of thickness, or they think that it's just too much of a pain to work with. Personally, I, think it's very easy to work with after you've figured out how to keep it in place without it starting to compress under its own weight as I explained earlier, but still. I prefer Knauf mineral wool with 'Ecose technology' because it doesn't contain any formaldehyde so it's odorless, and, some say, less hazardous to human health / less irritable to those who are sensitive to formaldehyde, etc.. (If you go to www.gikacoustics.com you'll notice that the Ecose logo is actually on their homepage, so IMO it's worth).

For cosmetics, it is common practice to cover a frame in breathable fabric stapled around the back of the frame and stick it in front of the bass trap (leaving a narrow air gap in between, as doing this will keep the front face of the bass trap from touching the fabric so it will look tidy). In addition, you could cover the exposed surfaces of the insulation in a layer of polyester wool batting to prevent loose fibers from escaping through the cosmetic fabric and getting airborne. Polyester wool also absorbs sound, very similar to the fluffy insulation itself, and you don't usually have to worry about making a large enough room sound too dead, so the FRK membrane, that reflects mid and high frequencies so that it can prevent a room from sounding too dead, might not be a good idea (i.e., it depends). The rigid fiberglass that comes with the FRK is expensive, and, if added to the front face of thick bass traps such as the SuperChunks, the relatively high gas flow resistivity of this rigid fiberglass might actually even cause the improvement in bass trapping performance, that can be had from the FRK membrane, to be cancelled out. The fact some later adjustments might be feasible on the inside of these thick bass traps is another reason why I prefer to add, instead of rigid fiberglass, polyester wool batting (reinforced with plastic orchard netting / chicken wire fencing / etc. if necessary, to keep it flush), as the batting (and possibly netting / wire fencing) are easy to open up gently at the top in such way that none of the fluffy insulation behind it can start to escape in the process.

[jlafrenz]

yves... do you happen to have some more links that show pink is better than Safe N Sound for superchunk? I have gone back and forth on this and often see conflicting information and opinions. I would like to get some more insight on this.

[hemster]

Dec 2, 2014 17:15:31 GMT -5 jlafrenz said:

Dec 2, 2014 16:55:32 GMT -5 hemster said:

Thanks. I'll be talking with Ethan on this subject as well as the merits of using OC 703 vs. OC 705.

I'm interested to see what he has to say about this. I am planning on building some superchunk style traps and since your post it has me wonder if the ones you linked might be a better option. The room is quite small so based upon the specs provided for ideal room size, the superchunk is probably still the best. I would still like to hear Ethan's thoughts on how they compare though.

Ok, I heard back from Ethan. Below is the conversation we had:

I asked:

I'm contemplating building a couple of plywood panel traps for my theater to place under the screen on the front wall. Unfortunately I do not have the room for chunky panels in the corners. The room size is 15' x 25' x 9'which I understand is just large enough for panel traps.

Question I have is: would I be better served using 6" deep traps stuffed with OC 703 instead? The goal is to make the bass less boomy sounding. I do have mid/high absorbers in the room so would I then use OC FRK (with the scrim facing outwards into the room) to avoid making the room too dull?

Ethan replied:

Yes, bass traps made from rigid fiberglass are a better choice than wood panel traps in a room that size. I also agree that you should use FRK fiberglass for all bass traps that are in corners or otherwise away from reflection points. I don't think you need to worry about making the room good dead sounding, but the FRK also increases absorption at bass frequencies which is always useful.

So I'll plan accordingly for thick fiberglass traps with 703 FRK. Even though 705 is more rigid it has lower gas permeability and may lessen the absorption effect. Still researching this... 

[jlafrenz]

I'm glad that Ethan touched on using FRK with traps in corners as I have been trying to determine if trying to add something similar to the superchunk design I am wanting to build would be worth it. It sounds like it would be. Now the question is what material to use. I was scoping this out some "builders paper" as it appears to be (or similar to) Kraft paper which is what the pink fluffy has.

[deltadube]

Dec 3, 2014 14:49:06 GMT -5 hemster said:

Dec 2, 2014 17:15:31 GMT -5 jlafrenz said:

I'm interested to see what he has to say about this. I am planning on building some superchunk style traps and since your post it has me wonder if the ones you linked might be a better option. The room is quite small so based upon the specs provided for ideal room size, the superchunk is probably still the best. I would still like to hear Ethan's thoughts on how they compare though.

Ok, I heard back from Ethan. Below is the conversation we had:

I asked:

I'm contemplating building a couple of plywood panel traps for my theater to place under the screen on the front wall. Unfortunately I do not have the room for chunky panels in the corners. The room size is 15' x 25' x 9'which I understand is just large enough for panel traps.

Question I have is: would I be better served using 6" deep traps stuffed with OC 703 instead? The goal is to make the bass less boomy sounding. I do have mid/high absorbers in the room so would I then use OC FRK (with the scrim facing outwards into the room) to avoid making the room too dull?

Ethan replied:

Yes, bass traps made from rigid fiberglass are a better choice than wood panel traps in a room that size. I also agree that you should use FRK fiberglass for all bass traps that are in corners or otherwise away from reflection points. I don't think you need to worry about making the room good dead sounding, but the FRK also increases absorption at bass frequencies which is always useful.

So I'll plan accordingly for thick fiberglass traps with 703 FRK. Even though 705 is more rigid it has lower gas permeability and may lessen the absorption effect. Still researching this... 

here is a good read Hemster for your choice of 703 or 705 with or with out frk

ethanwiner.com/density.html

for my money safe n sound ... value value ...

great table of absorption here

www.bobgolds.com/AbsorptionCoefficients.htm

[hemster]

^Thanks delta. I did get that from Ethan and had read it. The key part was when he said " in all tests of 12 panels the FRK facing improved absorption from the lowest 41 Hz mode to the 200 Hz upper limit" which is why I'm considering it (i.e. 703 FRK).

[deltadube]

Dec 3, 2014 22:28:23 GMT -5 hemster said:

^Thanks delta. I did get that from Ethan and had read it. The key part was when he said " in all tests of 12 panels the FRK facing improved absorption from the lowest 41 Hz mode to the 200 Hz upper limit" which is why I'm considering it (i.e. 703 FRK).

the frk only a made a little bit more .. nothing major..

check out

safe n sound here

www.bobgolds.com/AbsorptionCoefficients.htm

no frk ..

[deltadube]

my mini super absorber lol.. I sit my subs on these

[deltadube]

no more boomy bass here



white is 4ft x 2ft x 6in blue is 6ft x2ft x 6in and the red is 4ft x 2ft x 3in.. safe n sound.. blue one is on an angle to the corner big air pocket makes the trap more efficient ..

cheers..

[hemster]

At 3" depth Safe & Sound is about the same as 703 plain (i.e no FRK) but considerably pricier. Stacking 2 layers of 3" 703 would do the trick I think. Data below:

PRODUCT	THICKNESS	MOUNTING	DENSITY	125 Hz	250 Hz	500 Hz	1000 Hz	2000 Hz	4000 Hz	NRC
703, plain	3" (76mm)	on wall	3.0 pcf (48 kg/m3)	0.53	1.19	1.21	1.08	1.01	1.04	1.10
703, FRK	3" (76mm)	on wall	3.0 pcf (48 kg/m3)	0.84	0.88	0.86	0.71	0.52	0.26	N/A

So plain is more effective as a broadband absorber. If there's any danger od making the room too dead-sounding, then FRK can be deployed to reflect more of the mid/high frequencies. 

In speaking with Ethan, he says not to worry too much about making the room too dead (unless one has many many mid/high absorbers in the room).  

[yves]

Dec 3, 2014 9:55:14 GMT -5 jlafrenz said:

yves... do you happen to have some more links that show pink is better than Safe N Sound for superchunk? I have gone back and forth on this and often see conflicting information and opinions. I would like to get some more insight on this.

www.acousticmodelling.com/multi.php

As for the conflicting information, SuperChunks are way more than 30 cm ( ~1 ft.) thick, so for those you should use fluffy:
www.gearslutz.com/board/9446651-post12.html
Please note, density is not the same thing as gas flow resistivity. Gas flow resistivity, or air flow resistivity numbers are not usually provided by the manufacturers of insulation products, but you can search on Gearslutz forum for 'flow resistivity' and find some interesting threads like this one:
www.gearslutz.com/board/studio-building-acoustics/625978-common-gas-flow-resistivity-numbers.html

[yves]

Dec 3, 2014 19:23:24 GMT -5 jlafrenz said:

I'm glad that Ethan touched on using FRK with traps in corners as I have been trying to determine if trying to add something similar to the superchunk design I am wanting to build would be worth it. It sounds like it would be. Now the question is what material to use. I was scoping this out some "builders paper" as it appears to be (or similar to) Kraft paper which is what the pink fluffy has.

Yes, Kraft paper (the kind of paper that grocery bags are made of) can be used as a very effective replacement for the FRK membrane found on OC 703 FRK / OC 705 FRK. For it to work well, however, you'll need to apply some kind of correct bonding between the paper and the insulation, and, IMO the best choice for that would be 3M Super 77 spray glue. Super 77 is kind of expensive, you need to spray the right amount, spray evenly, allow it to dry for up to 1 minute or so before putting the kraft paper onto the sprayed surface (but don't wait too long, as it dries pretty fast), and make sure not to breathe in too much of the fumes from this stuff because else it will give you a really strong headache for sure. However, the fibers in the pink fluffy insulation are simply too loose to tidily be glued to a piece of paper IMO, as the surface of the pink fluffy is not very flat, and I think you'll run the risk of soaking it when you press the paper against it.

[yves]

Dec 3, 2014 22:34:00 GMT -5 deltadube said:

the frk only a made a little bit more .. nothing major..

That was also my point when I wrote about using, instead of rigid fiberglass, plastic orchard netting (etc.) combined with polyester wool batting. It just provides an easy way to keep the pink fluffy insulation in place, that's all.

[yves]

Dec 3, 2014 23:02:42 GMT -5 hemster said:

At 3" depth Safe & Sound is about the same as 703 plain (i.e no FRK) but considerably pricier. Stacking 2 layers of 3" 703 would do the trick I think.

Like I said, density is not the number you need to be looking at. Instead, it's the gas flow resistivity that matters.

In speaking with Ethan, he says not to worry too much about making the room too dead (unless one has many many mid/high absorbers in the room).  

That was also my point when I wrote about the orchard netting + polyester wool batting.