Membrane absorber bass trap - anyone made these?

[hemster]

I'm seriously considering making a couple of these bass traps. The biggest advantage to wood panel membrane absorber variety is that they don't need to be too bulky and are more efficient than a regular fiberglass-only/Rockwool-only type bass trap. Wood panel bass trap also has insulation but that serves a different purpose - it dampens the sound waves that are transmitted to it from the wood panel and avoids putting the sound waves back into the room in the form of resonance. 

I would like to know how others have handled the challenge of keeping the fiberglass/rock wool held up in a vertical  position. 

Below is a schematic from Ethan Winer on the bass trap:

[Chuck Elliot]

Nov 30, 2014 18:01:14 GMT -5 hemster said:

I'm seriously considering making a couple of these bass traps. The biggest advantage to wood panel membrane absorber variety is that they don't need to be too bulky and are more efficient than a regular fiberglass-only/Rockwool-only type bass trap. Wood panel bass trap also has insulation but that serves a different purpose - it dampens the sound waves that are transmitted to it from the wood panel and avoids putting the sound waves back into the room in the form of resonance. 

I would like to know how others have handled the challenge of keeping the fiberglass/rock wool held up in a vertical  position. 

Below is a schematic from Ethan Winer on the bass trap:

link?

[jlafrenz]

You might want to read on some of the FRK type fiberglass options. It is a similar concept where it reflects the higher frequencies and absorbs the lower frequencies. I found the link on Ethans site that discusses them. I plan on reading it and am interested to see if it discusses this type of trap vs. a 4" or thicker trap typically used for low end absorption. Also curious how this compares to a typical panel with a air gap behind it.

Here is a link to the entire article.

ethanwiner.com/acoustics.html

[hemster]

Here's the link below. Sorry, I should have posted it in my OP.

Ethan Winer's article on bass traps

[hemster]

Nov 30, 2014 18:12:33 GMT -5 jlafrenz said:

You might want to read on some of the FRK type fiberglass options. It is a similar concept where it reflects the higher frequencies and absorbs the lower frequencies. I found the link on Ethans site that discusses them. I plan on reading it and am interested to see if it discusses this type of trap vs. a 4" or thicker trap typically used for low end absorption. Also curious how this compares to a typical panel with a air gap behind it.

Here is a link to the entire article.

ethanwiner.com/acoustics.html

Yes, I am considering the FRK type. Per Ethan, "705-FRK" is nearly six times more absorbent than foam at 125 Hz! 

Kinetic bass traps like the one being discussed here depend on the damping properties of the fiberglass to contain the energy from a low freq. sound wave. The wooden panel that is sound-facing acts as a flexible membrane that just bend in response to the received sound wave, The wave is then dampened by the insulation and not rebroadcast as a resonant wave. This is important because you really want the sound wave received to be absorbed (at whatever frequency it was at the time) and not have to deal with multiple other sound waves at harmonic frequencies. 

I know that my link to the figure and reference is contained in the URL cited by jlafrenz. Ethan Winer is an authority when it comes to sound absorption! 

[pedrocols]

I truly appreciate the kind of information he provides but stuff is kind of pricey....You'd be better off going the DIY route....

[hemster]

Nov 30, 2014 19:53:18 GMT -5 pedrocols said:

I truly appreciate the kind of information he provides but stuff is kind of pricey....You'd be better off going the DIY route....

I'm talking the DIY method only. I will make my bass traps but just need to figure out how to keep the insulation vertical. It's a matter of learning from my esteemed colleagues here on the lounge or waiting until the inspiration strikes me!   

[jlafrenz]

My initial thought for keeping the the fiberglass rigid in this case it to build a frame that is larger in depth and allows for an air gap in front of the fiberglass and behind. You could easily cut some corner braces that would help support the frame and provide the spacing necessary. Here is a pick from one of my DIY acoustic panel threads that shows how I used a small corner brace to also provide an air gap. You would just need to make the frame deeper and use another set of braces 2" in front of the other set to wedge the fiberglass between.

[hemster]

I read that original post. I'm lazy and don't have the means to cut 45^o angles. Maybe I can buy a miter saw. 

Question: will those angled braces hold most insulation panels? Some I've seen in Lowe's are quilt floppy. 

[jlafrenz]

What you see at home improvement stores is typically Roxul Safe and Sound or similar insulation bats. They are not as rigid as the Roxul 60 or Owens Corning 703/705 that you would get from an acoustics supplier.

[deltadube]

Nov 30, 2014 20:48:46 GMT -5 hemster said:

I read that original post. I'm lazy and don't have the means to cut 45^o angles. Maybe I can buy a miter saw. 

Question: will those angled braces hold most insulation panels? Some I've seen in Lowe's are quilt floppy. 

nice 10 inch chop saw is a great toy to have... looks great under the tree!!!

what are you going to use as a membrane this is the top secret stuff...?

cheers

[deltadube]

Nov 30, 2014 18:01:14 GMT -5 hemster said:

I'm seriously considering making a couple of these bass traps. The biggest advantage to wood panel membrane absorber variety is that they don't need to be too bulky and are more efficient than a regular fiberglass-only/Rockwool-only type bass trap. Wood panel bass trap also has insulation but that serves a different purpose - it dampens the sound waves that are transmitted to it from the wood panel and avoids putting the sound waves back into the room in the form of resonance. 

I would like to know how others have handled the challenge of keeping the fiberglass/rock wool held up in a vertical  position. 

Below is a schematic from Ethan Winer on the bass trap:

I use the safe and sound roxul for my bass traps.. 6 inches thick 2 layers of 3inches.. make the frame a 1/2 inch smaller to hold
the roxul on all sides so its snug fit.. get the 23 x 47 inch stuff so its nice and wide across the corners.. go 6 ft to 8 ft high..

get some 200 thread count cotton bed sheets at Walmart and staple down the back then wrap from the back across the front to the back and
staple down works great with practice.. I use 2x4s for the frame .. the sheets give the insulations a rounded look..

cheers

try a couple of these simple traps in your front you will go wow... before you try the more complex ones..

[jlafrenz]

Nov 30, 2014 20:48:46 GMT -5 hemster said:

I read that original post. I'm lazy and don't have the means to cut 45^o angles. Maybe I can buy a miter saw. 

Question: will those angled braces hold most insulation panels? Some I've seen in Lowe's are quilt floppy. 

If you don't have the means to cut corner braces, you could always use something like these

www.lowes.com/pd_451252-37672-851144_0__?productId=4461065&Ntt=corner+braces&pl=1¤tURL=%3FNtt%3Dcorner%2Bbraces&facetInfo=

Quite a bit more expensive than just using the left over wood. Depending on how many panels you plan on making, you are probably better off investing in a saw you can use for future projects.

The other option you have is instead of using a 45 degree corner brace, you could cut some 1x2's to fit across the top and bottom to create a slot within the frame to hold the insulation. You would lose the benefit of it bracing the frame in the corner though.

[linvincible]

The drawback of these is that they are hard to tune to a given frequency
There are some calculations to consider that involve the surface and weight of the membrane.
Do you know which frequency you need to absorb best?
In my case I had to absorb a 95Hz frequency and that made me need two layers of truck cover sheet of the highest weight (is it what it's called?) which wasn't convenient, because the glue that would have to be applied would have a weight to consider too... And after you get it right then you can't re-tune it!
In the end I went for a Helmotz absorber. They work like a bass reflex tube in speaker cabinet : there is a ratio to work out between the volume of air in the absorber and the tube (you can have multiple tubes) and this will give you the work frequency.
You can then work on the tubes to fine tune/re-tune.
I made 4 of them already, 2 for myself and 2 for a friend. On mine I used PVC tubes of 75mm diameter that are replaceable and telescopic in case I need to re-tune the whole thing.
At my friend's we just drilled holes in the front side, using the thickness of the material and diameter of the holes (and quantity of holes) to make the tubes. It was much faster and easier to build!
I can provide the calculation sheet for membrane and helmotz absorbers if you like, it's all in french though (but numbers and units should be readable!)

[hemster]

Helmholz absorbers are usually tuned to a specific problem frequency. Membrane ones are good for a range which is why I like them. As these will go under my screen they need to be inconspicuous and not bulky. My sub is centered under the screen so I'll use 2 traps flanking the sub. In a membrane trap the job of the insulation is to prevent reflection of waves back out the front into the room (i.e. resonance).

I'll get some rigid Roxul 60 boards from an acoustics supplier. Then I'll use a couple of 1x2" strips all around the inside of the box frame to hold it in place. For bracing the box I can use right-angled "L" brackets. The membrane can simply be a sheet of plywood or for a better finish, a sheet of birch/oak which are available pre-sanded. Lastly, instead of mounting the traps on the wall, I plan to place them on the floor, positioned a couple of inches away from the wall. This adds to the absorption properties.

^That's the plan. Now to find some time to do the work!

[yves]

If you have a large enough room, be sure to also check out his other article on bass traps.

ethanwiner.com/basstrap.html

Note that, in a small room, you are better off treating as many corners of the room with bass traps as possible, and that also includes the corners between the walls and ceiling, according to Ethan himself.

The main benefit of simply straddling as many corners of the room as possible with rigid (standard size, 2 ft. by 4 ft.) sheets of 'FRK' type Owens Corning 703 fiberglass comes from the fact these sheets are extremely easy to install because they are so rigid, and because bass waves tend to build up in every corner of a room, and also because the 'FRK' membrane slightly improves bass absorption if pointing it into the room. However, OC 703 (FRK) is relatively far more expensive than Roxul Safe'n'Sound, whereas the latter is so floppy it will easily start to sag if you don't build a wood frame around it to support it. So, I learned from Ethan that you could decide to use rigid sheets of fiberglass that are only 2 inches thick, as they are cheaper than the 4 inches thick ones, yet will also give you the FRK membrane on the front face of your bass traps (that is, if you decide to go for the OC 703 FRK), and then just put slabs of cheap Roxul in the cavity behind it in order to increase the amount of bass absorption.

The rigid OC 703 FRK will keep the floppy slabs in place, thereby allowing you to avoid having to spend extra time, money and effort on building wood frames. Further, if the thickness of your bass traps measures roughly 12 inches or more, you'll get better bass absorption by using less dense insulation material, e.g. very cheap pink fluffy attic insulation instead of the Safe'n'Sound. Unless you are building very thick bass traps, though, you should just choose whichever is cheaper or more easily available to you. If piling many slabs of Roxul on top of eachother, then to prevent them from compressing under their own weight, you can divide the tall pile into multiple, smaller piles, each of which are supported at the bottom. (See www.gearslutz.com/board/6278486-post20.html and www.gearslutz.com/board/6366455-post32.html for details on this, and on how to improve the final aesthetics.)

[autiger]

Dec 1, 2014 3:48:35 GMT -5 hemster said:

Helmholz absorbers are usually tuned to a specific problem frequency. Membrane ones are good for a range which is why I like them. As these will go under my screen they need to be inconspicuous and not bulky. My sub is centered under the screen so I'll use 2 traps flanking the sub. In a membrane trap the job of the insulation is to prevent reflection of waves back out the front into the room (i.e. resonance).

I'll get some rigid Roxul 60 boards from an acoustics supplier. Then I'll use a couple of 1x2" strips all around the inside of the box frame to hold it in place. For bracing the box I can use right-angled "L" brackets. The membrane can simply be a sheet of plywood or for a better finish, a sheet of birch/oak which are available pre-sanded. Lastly, instead of mounting the traps on the wall, I plan to place them on the floor, positioned a couple of inches away from the wall. This adds to the absorption properties.

^That's the plan. Now to find some time to do the work!

Don't forget that the article said they need to be sealed (air tight) or the waves will escape wherever the air escapes. But I figured you had this planned already. Just for anyone who hasn't read the link.

[hemster]

Yep, that's critical for a sealed enclosure trap. Best to glue or caulk all the edges of the plywood membrane so there's no air leaks. Also, pick a piece of plywood that doesn't contain any knot holes!

[pedrocols]

Nov 30, 2014 20:08:49 GMT -5 hemster said:

Nov 30, 2014 19:53:18 GMT -5 pedrocols said:

I truly appreciate the kind of information he provides but stuff is kind of pricey....You'd be better off going the DIY route....

I'm talking the DIY method only. I will make my bass traps but just need to figure out how to keep the insulation vertical. It's a matter of learning from my esteemed colleagues here on the lounge or waiting until the inspiration strikes me!   

Precisely!

[yves]

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

Nov 30, 2014 20:08:49 GMT -5 hemster said:

I'm talking the DIY method only. I will make my bass traps but just need to figure out how to keep the insulation vertical. It's a matter of learning from my esteemed colleagues here on the lounge or waiting until the inspiration strikes me!   

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........).