Easy and Cheap DIY Absorption Panels

03Apr15

Background:

In my own small room I doubt I’ll ever achieve enviably flat frequency response. However, one area I have managed to make significant improvement in is reducing unwanted reflections using absorption panels. Aside from properly dialing in a subwoofer, I can’t think of anything else that has made the sound quality difference to my own system that these panels have.

There are many excellent DIY instructions for acoustic absorption panels online. Here, here, and here are online instructions that I looked at carefully. But when I do a project like this I like to look at as many instructions as I can before I do it in the way that makes sense to me, so I hope that others will look at what’s out there and then also benefit from my humble contribution. My cost for 6 panels was under $25 / panel.

records

side

Difficulty:

Really easy. Personally, I doubt I’ll ever have the patience to make something truly nice out of wood, but I’m happy with how these turned out both aesthetically and functionally. Only the most basic tools are required: drill, saw, staple gun, scissors.

Materials:

  • 2” Owens Corning 703 rigid fiberglass boards (2’ x 4’). ~$17 / panel bought as a six pack.

These fiberglass boards are sold as insulation, but it is the most common product used to make acoustic panels (even most of the commercial products use it). As far as I am able to determine, there is no physical store in my area that sells this stuff (not at Home Depot, Lowes, or any other similar store I checked with). I bought a six pack of it on Amazon for ~$100 including shipping. (Alternatively, rockwool is a slightly cheaper product that is popular and works about as well, and if you are squeamish about fiberglass you may consider this “natural” product instead.)

Note: When I first constructed DIY panels, I made two 2” panels and two 4” panels by placing two OC 703 boards together in a deeper frame. My thinking at the time was that the 4” panels would function as bass traps and at least start to make a positive difference in the lower frequencies. As I learned more (and measured), I realized that to make a difference in the frequencies much below the Schroeder frequency (where sound becomes omnidirectional) one has to go to town with these bass traps to a degree beyond what I’m currently prepared for. Instead, I decided to turn each 4” panel into two 2” panels to concentrate only on mid and high frequency reflections. Problems with the lower frequencies, such a nasty peak around 125 Hz, I hope to address with EQ (or an Audyssey upgrade).

oc703_13

  • 1.5 yards (per panel) of acoustically transparent fabric.

I went with broadcloth at Joann Fabric with a 60% off coupon. Came to about $5 / panel. Alternatively, I know there are always 40% off Hobby Lobby coupons online that one can use for any single item. More or less the same cloth is sold there. Any fabric that one can easily breath through should be adequate.

broadclothcategory

  • 1” x 3”  (~12.5’ per panel) whitewood boards. $4.

You could use poplar, common, pine, or anything similar. I chose whitewood because it was cheap and I liked the look of it. I correctly guessed that it would look pretty good after being sanded and finished.

  • A box of 1.5” screws for $5.

I used gold-plated for aesthetic reasons.

  • Wood finish (optional depending on design).

If one is using an exposed frame design (as opposed to pulling the fabric over the frame, see option 1 below), then some kind of finish may be desirable. I used clear semi-gloss polyurethane.

  • Mounting hardware.

Just about anything one might use to mount a relatively heavy picture would be fine for this task. Some people use picture wire. I found it simple enough to just use brackets (and plastic anchors into drywall).

Assembly:

1. Place wood around fiberglass boards on ground. Lay wood against fiberglass boards and carefully mark cuts. Frame should fit snugly (but not too snugly) around fiberglass boards.

2. Drill pilot holes. You may want to use a counter sink to make space for screw heads and prevent splitting. (If you don’t have a counter sink, a larger drill bit 1/8” into the pilot hole should do the trick.)

counter sink

3. At this point you’d probably want to sand and apply finish if desired.

drying

4. On flat surface, insert screws using drill. 

frame

5. Cut fabric to at least 6” beyond the size of the panel.

6. Place fabric around fiberglass panels and into frame. Pull fabric tight all the way around. (See option #1 below for alternate design where frame is not exposed.)

7. I stapled fabric to frame in a few places to help keep it in place. I also put some screws into the sides of the frame as below. Since the frame is 2.5” and the panels 2”, these screws keep the panels from pushing back into the frame.

screw

8. You may consider calling it done here, but I started thinking about the fiberglass fibers becoming airborne as I moved the panels around. (Not sure how much of a concern this actually is, but with two small children, I figure better safe than sorry.) I actually considered just stapling a large piece of cardboard to the back, which I believe would have worked fine. But since I didn’t have a piece of cardboard large enough, I actually ended up using some weed barrier fabric we had laying around.

barrier

Optional design with covered frame:

For the ceiling clouds, I pulled fabric all the way around frame. The most important thing here is to get the corners looking good, which I only did OK at. Similar idea to wrapping a present.

clouds

clouds 2

I want to mention that this is not our living room. My wife, who was happy to get all stereo equipment out of the living room, has been miraculously tolerant of me basically doing what I want in our small family room (aka “daddy’s listening room”).

 couch

Measurements:

The following measurements were taken in this small, mixed-use room. There are currently eight panels total. In my space I was able to hit the majority of first reflection points on the ceiling, back walls, and side walls.

These measurements were taken using Room EQ Wizard and an UMIK-1 USB calibration microphone. This is the ETC graph, where the x-axis is milliseconds and the y-axis can be thought of as volume. The peaks then correspond to reflections arriving at the main listening position milliseconds after bouncing off walls/ceiling/floor/furniture/etc. (Austin Jerry’s guide has been an invaluable resource when learning about this program.)

Here is my room with no acoustic treatment and the curtains open:

curtains open

For reference, here is the room with the curtains closed (windows at first reflection points on side and back walls):

curtains closed

And here is a measurement with all eight panels in place:

after treatment

According to what I understand, -20 dB reduction (or a quarter perceived volume) of reflections is considered a reasonable goal, which I am close to achieving.

But how does it sound?

Even operating in my small, much-less-than-ideal room I’m stunned at what these panels have done to improve sound quality. Rather than producing pleasant reverberations (as reflections beyond 20 milliseconds or so as might occur in a larger room might), these more immediate reflections subconsciously give our brains clues as to the location of the loudspeaker. When undesirable reflections are reduced, I’ve found that the imaging is vastly more precise. Instruments or vocals now seemed to be so precisely from the center of the room that several times I found myself getting out of my chair to make absolutely sure I hadn’t turned on some up-mixing feature that would cause music to play from my center channel. A very cost effective upgrade, in my opinion.

Please comment if these instructions have been helpful to you or if there is anything unclear!

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2 Responses to “Easy and Cheap DIY Absorption Panels”

  1. Panels looks great! Your first attempt looks better than mine did. And I can’t agree more: a little acoustic treatment really makes a world of difference in a room. It has literally taken my studio from a slow living room project studio to a professional studio with its own commercial location.

    I’m honored that you mentioned my Weekly Creations tutorial and glad it assisted your project in some way. Cheers, and thanks for the mention!

    http://weeklycreations.com/2012/09/09/week-16-tutorial-how-to-make-sound-absorption-acoustical-panels/


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