DIY absorption panels

***UPDATE***....see link for portable/stand mounted panel below.

Here's a fundamental absorptiona panel design that is easy, inexpensive, and effective. I chose to use Owens Corning 703 though Roxul SafeNSound is a good alternative (but it takes 3" thickness in SafenSound to perform like 2" OC 703). I found 2" thick 2'x4' 703 panels locally at an industrial insulation supply house for $8/ea. A few other supply houses in the area were almost twice as expensive so be sure to shop around. Roxul SafeNSound can be special ordered from Lowes and it's about $60 for a bale of eight 3" thick 2'x4' panels. I think the 703 has a slight edge in performance, but I wouldn't hesitate a second to substitute with the Roxul (I have panels made from both OC703 and SafeNSound in my listening space). The only downside to using SafeNSound is it's not as rigid and smooth as 703 so it tends to look "lumpy" when used in a non-nested design (absorption media not nested inside the frame). This is significant because with the media nested inside the frame you have less absorptive surface area and no airspace between the boundary layer (wall) and absorption media. This will decrease the panel's absorption in the mid to upper bass region and the only way around it is to mount the panel away from the wall (around a foot or more ideally).

For the frame I used 1"x4" pine screwed together. Angle brackets could be employed as well but it is an additional expense that adds up quickly if you are building several panels. A screwed together frame with corner gussets gives just as much strength and rigidity as the corner brackets for less money and that's the construction method I used on some larger panels (gussets were made from 1/4" plywood). The backing material is muslin cloth and the facing material is speaker grill material but muslin or burlap could be used as facing material as well and you have a variety of decor friendly colors to choose from with those two fabrics. Here's a step by step.

1. Build your frame. I made these 2'x2' but you can build them to just about any size you want. Most of my panels are 2'x4' and this size is probably best for first reflection absorption. 2'x2' are probably better suited if you have one (or two arranged vertically) behind each speaker and one behind the equipment rack. Again, mine are just screwed together with two #8x1.5" wood screws per joint with all holes pre drilled to prevent splitting but metal corner brackets could be used as well.

2. Lay out your backing material. This will be behind the absorption media and will create a surface for it to rest on. Just drape it over the frame as you're going to staple it to the frame next.

3. Staple the backing material to the frame. I like to start with one side and get it all stapled down then go to the opposite side, pull it taut, and staple it down repeating with the remaining two sides. Again, you want it nice and taut. Trim your excess material away once you're done.

4. Cut absorption media to size (if necessary). You can see I've set the 703 on top of the backing material. This is the basic configuration coming together.

5. Lay out your facing material and locate absorption media. Spread the facing material out across your working surface and get all the wrinkles out. Then lay your absorption media on top of that and leave enough excess material around the sides to allow it to wrap over the sides of the absorption media, the sides of the frame, and back around the frame so it can be stapled. For instance, I used 4" of 703, the 1x4 is 3.5", and I gave myself 1.5" to staple, so I allowed 9" excess material beyond the absorption media.

6. Lay your frame on top of absorption media. You want the backing material against the absorption media rather than having the absorption media nested inside the frame. This creates airspace between the absorption media and the boundary surface (wall) which, like I mentioned earlier, makes the panel more effective at absorbing upper and mid bass content.

7. Cut your facing material and staple it to the frame. What you're going to do here is bring the facing material up and over the absorption media and frame and staple it to the edge of the frame opposite the edge the backing material is stapled to.

8. Trim edges and fold your corners. Trimming in self explanatory, folding the edges is something you'll have to play with as there are few different ways to skin the cat. I just make sure the folds are on opposite sides so they can be inconspicuously located on top and bottom of the panel so as to not be visible when hung on the wall.

9. Admire your finished panel (but not the crappy, low res picture of mine)

Mount it on the wall with picture hangers or whatever method you prefer. You can also build stands for them easily enough to get mobile panels that can be moved around the room for experimentation and also to get them positioned away from the wall for better absorption of mid and upper bass content. Total cost for this little 2'x2' panel with 4" thick of 703 (or a 2'x4' with 2" thick 703) came to just under $20 and could have been less if the facing material would have been muslin.

Keep in mind the thickness of the absorption media layer will have an effect on LF performance. A 4" or 6" thick panel will have better LF absorption performance (below 125 Hz) than a 2" or 3". For first/early reflection points at side wall and ceiling a 2" or 3" panel is generally utilized. For front and rear walls, where an accumulation of LF content is often concentrated (especially near and in corners, including corners formed by wall/ceiling junction), the thicker panels can be beneficial. A 2" thick panel of OC703 spaced approximately one foot from the wall will give effective absorption down to 125 Hz. If the panel is mounted on the wall you'll need 4" of thickness to get effective absorption down to 125 Hz.

See my other threads for absorption panel placement, DIY broadband corner absorbers ("superchunk" style bass traps) and DIY diffusion panels. All these treatments...the absorption panels, broadband corner absorbers, and diffusion panels..... are the fundamental acoustic room treatments that will really get your room acoustics under control. Do a YouTube search for "Ethan Winer" for good tutorials on how to implement these treatments.

http://audiokarma.org/forums/showthread.php?t=446798

http://www.audiokarma.org/forums/showthread.php?t=433749

http://www.audiokarma.org/forums/showthread.php?t=535105

http://www.audiokarma.org/forums/showthread.php?t=547132

****Portable/stand mounted absorption panel build....****

http://www.audiokarma.org/forums/showthread.php?t=572781

nice method and i like the way the backing material is against the absorption media rather than having the absorption media nested inside the frame.
They might slide tho..
Ethan Winer is good too Thanks

highcut28 said:

nice method and i like the way the backing material is against the absorption media rather than having the absorption media nested inside the frame.
They might slide tho..
Ethan Winer is good too Thanks

Click to expand...

Thanks. I've made six panels utilizing this method (but 2'x4' instead of 2'x2') and one of the panels routinely has to be handled and I've had absolutely zero issues with the absorption media "sliding" (I presume that's what you're talking about). It's simply not an issue as the rigid fiberglass creates a bit of friction against the backing material and doesn't move across it very easily.

So I'm thinking if I made these 2x4 then can they just sit on the ground or do they need stands? Is 48" above the floor high enough to hit the reflection points of my Vandies?

I don't have a scientifically supported answer to your question Tromba, but I'd hypothesize that you'd want them positioned so they are near-centered in the plane of your mid and HF drivers relative to the height of your head above the floor. For instance, if your mid and HF drivers are about three and a half feet above the floor and your head when in your seated listening position is about three feet off the floor I'd want the center of the absorber near three feet off the floor. It may be just fine if they are resting on the floor since that would put a 4' tall panel a foot above your head and six inches above the HF driver, but I'd personally probably experience better "psychoacoustic" results if I saw the panel about a foot or two off the floor....under the premise of more room reflections are being absorbed a bit more evenly (rather than having four feet of the upper half of the wall with no absorption). One foot off the floor would put the center of the panel three feet off the floor and the top of the panel three feet from the ceiling. Two feet off the floor would center the panel on the wall with two feet of wall above and below the panel. I think anywhere in this range would be what I'd go for.

That makes sense. It's what I was thinking but I've got windows all around so I'd have to use some kind of stands.

Where to place things like these are not easy unless you're building a room from the start. For example, bass traps. I've read your other thread on building those. But my Vandersteen 2Ci manual says 2' from the side wall and 1' from the back. Since I think there's a rear reflecting driver, I don't know what that means in terms of bass traps in the corners behind them. Then again I have the window problem and can't actually mount anything on walls, so they'd have to be in stands also

tromba said:

That makes sense. It's what I was thinking but I've got windows all around so I'd have to use some kind of stands.

Where to place things like these are not easy unless you're building a room from the start. For example, bass traps. I've read your other thread on building those. But my Vandersteen 2Ci manual says 2' from the side wall and 1' from the back. Since I think there's a rear reflecting driver, I don't know what that means in terms of bass traps in the corners behind them. Then again I have the window problem and can't actually mount anything on walls, so they'd have to be in stands also

Click to expand...

Yeah, I just caught your comment in an older thread (that I contributed to but failed to keep up with) that made mention of only being able to have a corner absorber with a 12" face. I don't know how effective it would be if the actual cubic area/volume of absorption of what I did was reduced by half, but I wouldn't expect it to absorb frequencies as low as what a 24" face corner absorber could. You might want to look into a tube trap type absorber like this....

http://teresaudio.com/haven/traps/traps.html

....but even with those the bigger they are the lower the frequencies they will effectively absorb. I'm considering building some for my room for the rear corners where I have obstructions that prevent me from fitting triangular corner broadband absorbers, but I plan on mine being at least 18" OD.

I wouldn't sweat there being any adverse effects wrt absorption on the front wall and corners behind your Vandees. It'll help, if anything.

It's been a few weeks since I read a lot of this so I'll have to go back... but I was wondering what makes an effective bass trap. Surface area? If I have a 4" thickness of 2' x 4' or a 4 inch thickness of 1' x 8' -- that's the same surface area. Would each of those function the same as a bass trap?

Maybe a round one in each corner would be as effective?

It's not surface area that makes it effective....it's thickness. It all boils down to absorbing as much of the soundwave as you can at any given frequency. As you know, the lower the frequency the longer its wavelength. The greater the distance the soundwave has to travel through the absorption medium (and this could include chambered air space as well....hence the tube traps) the lower the frequency the absorber will absorb. If you look at the ASC tube traps you'll see they are available in different diameters. As the dia. of the traps increases so does their ability to absorb lower frequencies. This is why my absorption panels are 4" thick rather than 2"...so they can effectively absorb frequencies lower in the bandwidth. It's also why I elected to utilize a design that has airspace between the fiberglass and the boundary layer. The airspace will actually aid in enabling the panel to absorb frequencies lower in the bandwidth. Similar thing with my panels at sidewall first reflection. I have them about one foot out from the wall so I can get a good "buffer" between the panel and the boundary layer (wall).

RevMen, you want to step in and clean this up for me.

Again.

tomlinmgt said:

It's not surface area that makes it effective....it's thickness.

Click to expand...

but the thickness would be 4" in either case -- whether it's only 4 feet tall and 24" wide, or 8 feet tall and 12" wide.

tomlinmgt said:

It all boils down to absorbing as much of the soundwave as you can at any given frequency.

Click to expand...

would a 24" width do better here? It's a wider target!! I don't see much on tall bass traps (although those round ones looked interesting) so I've wondered what part is the most important - height, width, placement? (assuming a 4" thickness as a constant)

Both surface area and thickness matter. More surface area means more sound waves come into contact, means more sound gets absorbed. Thicker absorbers stand off from a boundary further, meaning they act on lower frequencies.

tromba said:

It's been a few weeks since I read a lot of this so I'll have to go back... but I was wondering what makes an effective bass trap. Surface area? If I have a 4" thickness of 2' x 4' or a 4 inch thickness of 1' x 8' -- that's the same surface area. Would each of those function the same as a bass trap?

Click to expand...

No.

RevMen said:

Both surface area and thickness matter. More surface area means more sound waves come into contact, means more sound gets absorbed. Thicker absorbers stand off from a boundary further, meaning they act on lower frequencies.

Click to expand...

assuming a constant 4" thickness, the surface area of 24" by 4' and 12" by 8' is the same amount of surface area.

So does the shape of the surface area matter?

Sorry, I should've been more clear when I said "thickness" and shouldn't have said surface area didn't matter because in a general sense it does. However, specific to your question about thickness in the corner absorber I was referring to thickness in a horizontal plane, not the thickness of the panel. Whether it's 2" or 4" thick doesn't matter as it's going to be laid on its side and stacked anyway. Visualize it like this.....imagine you take a triangle and fit it into a corner resting on the ground. Looking down at it you can see that the base of the triangle (side opposite the right angle) is a certain distance from the corner. As the triangle gets bigger so does the base and so does the distance of the face from the corner. Just throw down the trusty old Pythagorean theorem and you'll see what I'm talkin about. Take for instance my corner absorber which is a triangle with legs of 17" and a base (absorber face) of 24". This creates a triangle with a height of 12" which is going to be the thickest part of the absorber wrt how much absorbing medium the soundwave has to penetrate on a horizontal plane. Your proposed absorber would create a triangle with 8.5" legs, a base of 12", and a height of 6"....so the thickest part of your corner absorber would be only 6". So yes, more frontal surface area (the face of the absorber/base of the triangle) will equate to greater absorber thickness (and volume) since as the base of the triangle increases so does the height of the triangle which is going to be the distance between the corner and the face of the absorber.

Look at it this way....if you're in a boat and you drive by the shore you create a wake (sound wave) that will hit the shore and return another wave back into the body of water. If the shore is lined with cattails (absorber) you will weaken the return wave and the thicker and denser that stand of cattails the less strength the return wave will have. There's a bit more to it than that when you're talking about trapping different sound frequencies but suffice it to say the thicker the absorber the lower the frequencies it will trap. Speaking hypothetically, your 12" face corner absorber (6" thick from corner to face) may only absorb frequencies down to 200 hz whereas a 24" face corner absorber (12" thick from corner to face) could absorb frequencies down to 80hz.

As far as height goes the taller you make it the more absorber volume you'll have and the more effective an absorber it becomes. I made mine three feet tall simply because I had obstructions in the lower half of my corners but it also makes the absorbers less cumbersome if they are in two smaller sections rather than one tall one.

Gottcha now..... Makes sense.

more DIY Panels







Here is a panel that I made out of 700 series Dow. I spray adhesived fabric to the insulation. The frame is 2 1/2 inch pine with a 3/16 strip dadoed into inside edge. This allowed me to not fully edge wrap the panel as the strip hid the edge. I was able to hold the insulation in with 2 wires across the back held with screws. If you are doing a few it takes very little time per.

Thanks for this thread ya'll! I made mine a tad differently, but the idea all came form here and what a difference!

Tom and Rev, I have a question for you guys. I made my panels with sound-proofing fiberglass insulation from Lowe's. The barrels are 8" thick and I compressed them to fit my 1x3 panels. Essentially, I have 8" of soundproofing in a nice 1x3 box. It sounds a world of a difference and I am currently making a few more. Looking at the picture I currently have just 2 2x4 foot panels behind my 2 main speakers, but will be adding another 2x2 foot panel underneath those panels, as well as a wide 1x8 panel foot under the screen for the center speaker, and another 2x4 foot panel to the wall on the right of the stereo rack to cover first wave reflections. My questions are this: in squeezing 8" of the soundproofing into a 3" thick box did I loose any absorption properties or does this even matter so long as the same thickness was met (8")? And second, why is having an air-space behind the panel necessary, if any? Should I re-think my panel and add a couple of inches of lift? What benefit would I get?

Thanks, JN

Hi Jimmy. are you going for reflections or absorbtion? If absorbtion, you might be better off putting panels in the corners. If you put too many panels on the front wall, it might sound too dead. What does the back of your room and first reflection points look like?

I think I have the back covered pretty well because of our large diagonal sofa and my desk. I *think* I need to concentrate on both absorption and tame some reflections. Since I have forward radiating speakers (as oppossed to dipoles) in the front I should probably want to absorb all rear soundwaves. This is the thought for building the lower 2x2 foot panels and 1x10 foot panel under the screen - to stop these speakers rear reflections. The other 2x4 foot panel to the right of the gear rack would be my first reflection point from the right speaker. The left speaker is much more challenging and will probably be a compromise because there is no wall on the left side to close the gameroom. It's an open floor plan and on the left are our stairs that take us to the first floor of our 2 story home. Right now the room sounds great. It's amazing how big of a difference just 2 panels can make. I think I could gain a bit more room control by adding the remaining panels. I've given this a lot of thought and have run several DRC tests. It's the actual amount of sound proofing fiberglass that i don't quite understand. I don't know if compressing the fiberglass would have an impact on the absorption properties? I would guess not because you can buy sheets of compressed sound panels.

JN