Building Sound Absorption Panels


#21

Flutter Echo Attenuation Prototype Absorber #1

With a borrowed drill, mitering hand saw, and a few other borrowed tools, I was able to build my first attempt at a frame.

Wood Selection
Without access to a table saw, my material choices are currently limited to precut measurements such as 1X4 (3/4” X 3-1/2”) or 5/4X6 (1” X 5-1/2”)

In these sizes, the two main varieties of wood planks available were framing lumber and decking boards. Decking is well finished, structural wood that is a bit heavy for this purpose. Framing lumber is not pretty but was the better option. It’s surprisingly cheap too.

Note: If using 1X4 framing lumber, look through the stack to find sufficiently straight boards as some planks were better suited for boomerangs than absorber frames. Clamping everything into place first does help with drilling the holes straight and preventing your project from becoming a parallelogram absorber.

Even then, the only way I could think to keep the boards straight was to screw a short and a long side together, making an L shape for the absorption material to sit in.

Screws
The wood screws were selected to be used on a variety of materials and sizes. #8 X 2-1/2” is probably larger than necessary for 1X4 planks. This is my guess at logical screw placement. It’s the fewest number of screws that accounted for everything. And of course we are countersinking all screws!


This screw placement attaches all sides of the wood planks with the fewest number of fasteners possible. The backing board is also screwed to the side beam at the center point to help prevent warpage.

Summary
So far so good. Because the purpose of these absorbers is to attenuate flutter echo, this frame should work well enough.

Perhaps we’ll try hole sawing the planks in some places to increase the absorption area. I’m not sure the wood is strong enough.

Both the cover fabric I have on order and the insulation itself are fireproof. These 1X4’s are the only flammable part of this prototype. If I can acquire (or get access to) a table saw, I will make the next prototype frame from a sheet of MDF instead of lumber as MDF is a lot less flammable. The center plank is intended to help hold soundproofing insulation in place as well as help straighten the frame. If you have ideas of how to improve this design, please share them.

Thank you for playing along, your feedback is appreciated.


#22

To second, acoustic treatment and soundproofing are distinctly separate. With treatment, you want a choice of absorption over the audible spectrum, as well as zones within a space (LEDE etc). Soundproofing is a more expensive (and expansive) scope, ideally you suspend the room within a room. Without referencing a specific manufacturer, I can say there are some very effective and pretty affordable non-foam treatment panels on the market.


#23

About ten years ago I was working on a documentary about life in the Bombay slum of Dharavi (https://www.nfb.ca/film/dharavi_slum_for_sale/). One of our subjects was a brilliant young jazz/fusion drummer who was making a soundproof practice room for his fusion band in the tannery area of the slum. He fitted the entire interior with mattresses… it worked quite well, but the heat and humidity in that room had to be experienced to be believed. We used to shoot for ten/fifteen minutes, then everyone would leave the room to relax and smoke a cigarette outside and drink gallons of water. Unfortunately he didn’t make the cut, but he was a great guy.


#24

imho, remember to 'trust your ears
many recordings were made by
some modifications to the room, putting the mics whete they sound best, and recording
people making -'music ('playing)

sun studios


van gelder’s parent’s house

daniel lanois’ old oxnard theatre 'studio

even sound city (old vox factory, some sonic modifications, and yet idiosyncratic still…


of course, mixing/mastering rooms have different requirements… :slight_smile:


#25

For someone with untrained acoustic ears, is there a tool I can use to “measure” the frequency response of the room, or at least to my ears? Moved into a new, smaller room and while it has more soft surfaces it’s very boomy.

Edit: I used the “room control” switch on the back of my hs8s and it made a huge difference. Much more natural to my ears now.


#26

Room EQ Wizard is probably the most used because it is relatively easy to use and free. You will need to purchase an ultra-linear response microphone - the website has a few recommendations. I use a Behringer ECM8000 that I picked up used for $30-40 but I would probably recommend a USB model with built in calibration if I had to do it over again. Still, you can get good results doing what I did.

Word of caution: this is a free program but can get very deep. There are numerous tutorials on the web out there - I would look at a lot of them before going down this path to make sure you understand what you are getting into.

Just to play devil’s advocate and to skip to the punchline… Unless you are already in a world class studio, your results will undoubtedly be:

  • Your bass looks wonky as hell and you need some bass traps in the corner
  • These bass traps will improve the sound to your ears but you may not “see” the results you are after in the software
  • You will add absorption at your first reflection points (the walls on either side of your ears)
  • The results get marginally better. Building panels kind of sucks.
  • You will contemplate adding an overhead cloud panel
  • Your improved low end brings more attention to the splashiness of your high end in the room
  • You will watch a lot of YouTube videos on the topic and realize that not everyone knows what they are talking about
  • You will build more panels anyway
  • You will read about “ideal” room dimensions and briefly assess your carpentry/contracting skills
  • Maybe add some more panels.
  • Is my room too dead?

EDIT: I kid, mostly. For real, you may just start with building a few bass traps and first reflection panels as this will probably be at least part of the solution to the problem that you find. My project became a bit of a rabbit hole, if you can’t tell.


#27

hahaha thanks! Actually flicking the room control switch on the back of the monitors got my 90% there so I’ll see where I’m at when the room isn’t a moving mess. I can think of one corner in particular which I think is misbehaving.


#28

Here’s my frame design for 2" OC 703 (rigid fiberglass) absorber panels. 2" is not necessarily adequate for every situation (it’s not quite thick enough for full broadband absorption), but this frame design uses readily available materials that are easy to work with and it is very lightweight and strong. The only power tool you need is a good impact driver or drill. It is made slightly more effective by putting some space behind it to create an air gap. I hope that this design can be helpful for someone.

When we renovated my studio building, we tore down a bunch of walls that were framed with 2 1/2" steel framing material, and I realized that these studs fit perfectly around the edge of 2" rigid fiberglass, so I set out to create a frame that uses them. I used 2’ x 4’ panels from ATS acoustics. (Please pardon the mess in these pictures!)

The first step is cutting the steel framing members to the proper dimensions. It cuts easily with tin snips but gloves are necessary because the edges are sharp (also always use gloves when handling fiberglass). I used track (headers/footers) for the short edges (2’) and studs for the long edges (4’).

Next I slipped the 4’ studs (long edges) over the long edges of the fiberglass panels. It fits snugly and stays in place.

Then the 2’ track (short edges) is fitted over the short edges. I made sure that the corners lined up nicely and then fastened the corners together using sheet metal screws (two screws for each corner—front and back). It takes a little bit of pressure to get the screws started but goes quickly with a good driver. Once all the screws are in place, the frame is super rigid.

The next step is to cover the panels in fabric, but first I had to cover the sharp edges of the steel framing so that it didn’t snag or tear the fabric. For this I simply used Gorilla Tape (heavy duty permanent duct tape). This was actually the most time-consuming step (I also covered old screw holes, etc. because I was using salvaged steel framing—my stuff was pretty gnarly; you won’t need as much tape with new material).

The fabric covering is Guilford of Maine FR701. It isn’t cheap but it looks beautiful, is acoustically transparent and (perhaps most importantly) is fire rated. I cut the fabric to 36" width, so that there was at least 3 inches of overhang on the long edges to wrap around the back (this would need to be wider if you’re using thicker fiberglass/studs). I kept the 64" height (the size of a roll of FR701) in the long dimension, so there is additional overhang on the short edges. I imagine this stretching process would be similar for wood or other frames.

I don’t have as much photo documentation of the wrapping process because I had to work fairly quickly. I used 3M Super 77 according to the manufacturer’s directions and put down cardboard (the OC 703 boxes) to protect work surfaces. I also used a respirator to protect my lungs and brain cells. I carefully aligned the panel and the fabric, and then sprayed one long metal edge of the panel with a thin coating of adhesive, taking care to prevent adhesive from getting on parts of the panels where I didn’t want it (especially the front). After waiting about 60 seconds or so (the time is dependent on heat and humidity), the adhesive becomes very tacky and I could carefully press the fabric against the first long edge to secure. The first edge is critical to getting a nice smooth appearance. Fortunately the Super 77 doesn’t dry immediately so there’s a little time to revise if it doesn’t go perfectly. At this point I only glued the edges, not the overhang on the back of the panel. There’s a lot of waiting for glue during this process, so make sure you have a good podcast to listen to. I recommend Welcome to Night Vale or S-Town.

After the first edge dried a bit and felt secure, with the panel on its back I folded the fabric over the front of the panel and prepared to secure the opposite long edge. The critical part here is pulling it very taut so that there are no sags or lumps on the front of the panel (I didn’t always do it perfectly). You can’t tell in the photo, but I found that it helped if I allowed the long edge to hang over the edge of the table so that I could pull the fabric downward. I sprayed the metal edge of the frame and waited ~60s, then pulled the fabric straight down (toward the floor/back of the panel) and pressed against the metal edge to secure. The FR701 has a little bit of stretch to it but not too much, and it’s this stretching process where I really appreciated working with this fabric. Again, I only glued the edges at this point, not the overhang.

Here are the steps where I’m missing some good photos, and it’s also the hardest to describe in text— Sorry! There’s a little room for creativity with how you fold the extra fabric back to create a neat appearance.

I glued both short edges the same way—working one side at a time, gluing only the edges, not the overhang (yet). I found that I didn’t have to stretch as much in the long dimension if the fabric was already very taut in the short dimension.

With all four edges secured, there are little folds in the fabric extending at approximately a 45° angle from each of the four corners. Using some additional spray glue, I came up with a way of folding those little triangular flaps around the edge and over the back to create neat little right triangles that are visible on the long edges. I also experimented with wrapping this overhang like a Christmas present but found that I liked the triangles on the long edge better. After this is done, I glued down all of the additional loose fabric and folds to the back of the panel—there’s no stretching at this point, just tidying up.

Finally, I used two strips 2" x 24" of 5/8" plywood to attach mounting hardware to the back of each panel. The thickness of this wood determines the air gap behind the panel. One strip has a French cleat picture hanger and the other simply has self-stick felt furniture pads (to protect the wall). The strip of plywood is pre-drilled and attached to the frame using long fine-thread drywall screws. I found that it was important to be super precise with measuring at this step to make it easier to level the panels when they’re installed. In retrospect I would have painted the edges of the plywood to match my wall because it is visible.

That’s basically it. It took me a few days to build 24 of these panels. Being only 2" thick means that they won’t absorb much LF, but I have found that they are effective at cutting down reflections in my live room and much better than any foam. My vocal booth is covered in these and it is dry as a bone. I also use them as spot treatments for reflection points in the control room, in combination with superchunk bass traps. And because they are so lightweight, I was able to suspend them from the ceiling with chains to cut down on flutter echoes in drum overheads and in the iso booth.



Steel framing is sold in 3-5/8", 4", 5-1/2" + widths, and I’m hoping to experiment with this basic design with thicker rigid fiberglass. This could be easily adapted for different sizes and purposes.

Sorry for the long post—I’ve been meaning to write this up since I built these two years ago. I hope that this will be helpful for someone. I would also be happy to share my design for superchunk bass traps for anyone who is interested. Just let me know!


#29

I attempted to google this, but I couldn’t find a good answer. Are acoustic panels safe for a sometimes mischievous dog or 3.5 year old nephew? Does fabric (or cacao bean bags) adequately seal in the mineral/glass fibers (and is rockwool “safer” in that regard?)


#30

This doesn’t directly answer your question, but my SO is a commercial interior architect, and even though we music folk associate fiberglass acoustic panels with audio studios, they are much more common than I ever realized in offices, schools, restaurants, etc. Most modular cubicle walls are rigid fiberglass. Commercial building codes (in most US cities) are very strict about health and safety, so these products wouldn’t get installed if they weren’t deemed to be safe. Granted, commercial applications are using professionally-built panels, and those manufacturers are responsible for making sure they are safe.

In my experience, fiberglass (in panels or wall batting) doesn’t seem to become airborne unless it’s agitated by being cut or moved, so I don’t worry about about it with absorbers after they’re installed. My bigger concern is the VOCs and chemicals used in the insulation manufacturing process, which can off-gas and be harmful after installation. However, from my own research and conversations with construction folks, insulation is far less toxic than it was even ten or fifteen years ago, and I haven’t experienced anything worrying with my DIY acoustic treatment.

Knauf ECOSE insulation uses 60% recycled material and contains no formaldehyde, phenol, acrylics or artificial colors, which theoretically makes it safer. It comes in soft batts and rolls, as well as rigid panels (like OC 703). I used batts of ECOSE when I built my bass traps, but I decided to go with OC703 for wall absorbers.

As for fabric, I don’t think that any fabric will seal in gasses or VOCs. Burlap (like coffee bags) is a pretty loose weave, so perhaps it would allow fibers to escape, but I doubt it unless you’re bumping or moving panels often. I don’t know what incentive a dog or 3.5 y/o nephew would have in trying to eat fiberglass. Maybe just secure them well so they don’t get knocked around?


#31

Fantastic information, thank you!

Also, rereading your panel design post, I feel like there’s a lot of potential to having such a rigid frame. I have been thinking about things like fastening hinges to multiple panels and casters to create portable room dividers (which you could also fold these up to create more “broadband” 4" and 6" traps).