# Building some DIY absorption panels. Need help with questions.



## Jetjones (Jan 29, 2012)

I have decided to build some absorbtion panals for the first reflection points and possibly some more for the front wall. I have some questions that I can't seem to find the answer for, so if anyone can give me some answers to these questions, then I will be greatful. 

First, is regular roxul ok to use and which thickness should I get? 3i inch? 5&1/2 inch? 

Second, should the roxul be compressed any, and if so, how much should it be compressed? Or should I build my frame to hold the roxul at its uncompressed thickness?

Third, does there need to be an airspace between the roxul and the back of the frame? Does it matter what the back of the frame is made of? If not then I will probably just use plywood in the back. If there does need to be an airspace between the back of the frame and the roxul, how much air space is needed? 

Fourth, does it matter what kind of fabric I use to cover these panels? Or more specificly, are there any types of fabric that are bad to use? I would imagine that my wife will want to use some sort of nice looking fabric so I just want to make sure that I don't end up using something that would take away from the performance of the panels. I have seen some people post about the breath test or what ever so can someone please explain that to me?

I will start building the frames tomorrow and will post pictures of everything along the way.


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## bpape (Sep 14, 2006)

Different place in the room will benefit from different thicknesses and densities. Do not compress it. You'll only hurt performance. When you say 'regular roxul' what are you referring to? There are at least 4 different densities.

Air space in the rear will only help extend how low a particular panel will reach into the low frequencies. If you're hanging them right on a wall and any gap is inside the frame, a back is fine - otherwise don't.

For the cloth, just get something that you can breathe through relatively easily. From a home theater video perspective, you'd also like to avoid any fabric that has any sort of shine to it.


Bryan


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## SAC (Dec 3, 2009)

*Broadband panel absorbers:*
For broad band absorbent panels, the best material density characteristics are either ~3lb/ft^3 Fiberglas or 4 lb/ft^3 mineral wool.

The minimum configuration that should be considered for a broadband panel is 4" thick with a 4" boundary gap. (Any thinner and the effective low frequency extension suffers.)

This configuration effectively behaves similarly to an 8” thick panels placed flush to the wall by virtue that the actual absorptive material is moved out from the boundary closer to the maximal 1/4 wave velocity point of the lowest frequency that corresponds to that distance.


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## Jetjones (Jan 29, 2012)

bpape said:


> Different place in the room will benefit from different thicknesses and densities. Do not compress it. You'll only hurt performance. When you say 'regular roxul' what are you referring to? There are at least 4 different densities.
> 
> Air space in the rear will only help extend how low a particular panel will reach into the low frequencies. If you're hanging them right on a wall and any gap is inside the frame, a back is fine - otherwise don't.
> 
> ...


What thickness would you recommend for the first reflection points on the side walls? I am not sure what the different types of roxul consist of, can you recommend any that would work best, or any that I should not use? As far as air space in the rear, how much do you recommend? What did you mean by? "..any gap inside the frame, a back is fine - otherwise dont". I was under the assumption that the panels needed a plywood back to them, but now I am confused, is it better to not use a wooden back to the frame? Does the roxul have a paper backing materal or any other backing material that I should be concerned with?


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## Jetjones (Jan 29, 2012)

SAC said:


> *Broadband panel absorbers:*
> For broad band absorbent panels, the best material density characteristics are either ~3lb/ft^3 Fiberglas or 4 lb/ft^3 mineral wool.
> 
> The minimum configuration that should be considered for a broadband panel is 4" thick with a 4" boundary gap. (Any thinner and the effective low frequency extension suffers.)
> ...




Hey SAC, thanks for your help! You are awesome! I am free all day so call me when you get a chance!


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## bpape (Sep 14, 2006)

If you can swing it and you have response problems down relatively low from the reflections, then the 4" with a 4" gap would be great. Sometimes, the response problems aren't low enough to require that and you can get by with say 4" with a 1-2" gap.

What I meant on the gap was if you're going to put a hard back on the panel, then spacing them off the wall doesn't really buy you anything. So, if you wanted the gap and a hard back, the outer frame would be say 6" or 8", with just 4" of material toward the front, then mount it flush with the wall.

Hope that makes more sense.

Bryan


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## HTip (Oct 10, 2011)

I also built DIY-absorbers. In fact I've just placed some pictures in my topic of the build. I had someone (10 years experience in acoustics) design them after a RT60 measurement and he tuned every panel to a specific frequency. The treated frequency is determined by the following factors:
- the covered area of the board (only attached at the sides)
- the material of the board (I used 3mm Meranti)
- the absorption material (mineral wool as SAC stated). The boards should be able to stand on their own. I used 2" thick Rockwool industrial boards.
- the gap between the board and the mineral wool. Normally between 1.5 and 2".
- the gap between the mineral wool and the back wall. The bigger the gap the more efficient the low frequencies are absorbed.

I would also suggest to put diffusers (i.e. QRD) on the reflection points instead of absorbers. The sound stage will remain wide without the flutter echo. Absorbers can be placed anywhere in the room and are still effective.

For reference see my topic: http://www.hometheatershack.com/for...54859-chamber-dreams-how-made.html#post499706


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## Jetjones (Jan 29, 2012)

Ok so I had the pleasure of speaking with a very intelligent man (SAC) with regards to acoustics, and now I feel a lot better about treating my room and acheiving the best results. I am going to go ahead and start building my absorbtion panals, but, I am going to hold off on the diffusers and bass traps until I have some more time to talk to SAC and pick his brain a little more. Hopefully I can get the necessary components together to start using REW so that I have a battle plan and know what needs to be done. I am planning on using the absorbtion panals to treat the reflection points on the side walls. Then after I get the ETC measurements I will start on the diffusers so that I know how many diffusers I am going to need, as well as where to place them. 


First, I am going to build 4 absorbtion panals. I am still trying to get a general idea of what to construct them out of. I am thinking that I will use a retangular 2 x 4 frame that is 3 feet by 4 feet with 4 inch thick roxul, then I will build some spacers that hold the panel to-and-away from the wall. I am going for a 4 inch thick panel with 4 inches of space behind the roxul. 

I don't know anything about the diffusers or bass traps at this point. I hope to be able to talk with SAC about this in the next few days so that I can come up with a game plan on how to construct them. As soon as I get time to start on the absorbtion panels, I will post pics of the entire process from start to finish, and also the same goes for my diffusers and bass traps!


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## aLittletank (Dec 25, 2011)

FWIW I used 1/2" plywood for my frames. I had home depot rip (our local HD ROCKS!) a plywood sheet into 2.5" strips and used that to frame 2" OC 703 rigid fiberglass. One 2.5" strip across the back for support was all that was needed. A full plywood back would be overkill. We wrapped the fabric around and stapled it. An electric nail gun made the frames easy to assemble. 

I choose to use GOM fabric because of the acoustic and fire ratings.







































I will probably add 2"spacers to the backs at some point.


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## Owen Bartley (Oct 18, 2006)

Looks good, dude! The panels seem to fit in to your room nicely. How did yours impact the sound in the room? Did you notice a clear difference before and after? If so, I hope it was an improvement in the sound!


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