DIY Acoustic Panels

[geo3]

So I've been looking at getting room treatments for my living room. But Professional panels are expensive and the foam squares from Amazon kind suck.  So... DIY it? 

The quality panels you can get from places like GIK Acoustics or Music City are essentially just a fancy enclosure filled with mineral wool or something similar. Since that's readily available at my local Lowe's I figured it couldn't be to hard.  Everything  I needed to build these I either already had or got from Lowe's with the exception of the fabric which I got from Hobby Lobby. 

 

Results first:
3 of the six, one of each color.

 

 

Mounted on the wall

 

 

Tools:
You'll need: Saw, Stapler, Scissors, Power Drill 

Materials:
Lumber 2x4x92 Fir wall studs, $40 for 12

 

Rockwool insulation, $54 for 12 batts  These are the 3in thick kind. If you want to trap lower frequencies you can buy thicker 5.5 inch batts or double stack these one in front of the other.  Though you'll need to build a thicker frame using 2x6 planks. 

 

Fabric. $210 for 30 feet of this fabric. I could almost definitely find cheaper fabric. 

 

Wood screws 8x3, $5

 

Hanging hardware,  <1$

Process:
Cut your lumber to size, I chose 33.5x50 inches because that fits 2 rockwool batts side by side. Remember to account for the thickness of the frame itself.

 

Screw the corners together. 3 screws per corner seemed sturdy enough.

 

Lay the fabric out on a table and place the frame on top of it. Cut it to length then staple the edges to the back side of the frame. 

 

Cut and tuck fabric under itself to form neat corners. 

 

The rockwool simply layers in place. Since they insulation and the lumber are both intended for wall construction the fit each other perfectly. The thickness is just right.  Touching it is rather itchy though so maybe use gloves. 

I'll add a backing fabric to these later, but for now the insulation seems to stay in there pretty snuggly. 

 

Attach mounting hardware. 

 

Backing fabric and wire mounting

 

[Needfuldoer]

Homemade sound traps are great, and this is the way to make them!

 

DO NOT think you can cheap out and just glue packing foam or mattress pads to the wall, though! That stuff is flammable.

[cmndr]

Also be aware that you can 2x the performance of many of these by doubling their frame thickness - think going from 2" thick to 4" thick with just an extra wood frame against the wall - still the same amount of rockwool up at the front. 

[geo3]

8 hours ago, cmndr said:

Also be aware that you can 2x the performance of many of these by doubling their frame thickness - think going from 2" thick to 4" thick with just an extra wood frame against the wall - still the same amount of rockwool up at the front. 

Extending the frame isn't necessary, just getting an air gap behind  them is enough. This can be done with rubber stand offs, but it makes mounting a bit more tricky. I'll do this  eventually.  

[Ahoy Hoy]

Common misconception which all the YouTubers and streams don't know. It’s more affective to space out room acoustic panels foam etc then have it all in one area. So if you have four panels put one on each wall instead of the YouTube way of all of them sat behind you or in front and having three blank walls and a highly reflective roof.

I can’t remember the numbers off my head from the study or my uni education on it (was only one lesson on this subject) but it’s something around 20% better reduction spacing it out then clumping it. (Don’t quote me though that’s a off the head from a memory ten years ago)

[cmndr]

4 hours ago, Ahoy Hoy said:

Common misconception which all the YouTubers and streams don't know. It’s more affective to space out room acoustic panels foam etc then have it all in one area. So if you have four panels put one on each wall instead of the YouTube way of all of them sat behind you or in front and having three blank walls and a highly reflective roof.

I can’t remember the numbers off my head from the study or my uni education on it (was only one lesson on this subject) but it’s something around 20% better reduction spacing it out then clumping it. (Don’t quote me though that’s a off the head from a memory ten years ago)

Generally speaking you want to place them at the first reflection points. Practically speaking, people do this at the side walls and SOMETIMES the ceiling. 
There is some logic to having gaps between panels since it decorrelates the reflections but for the left/right sides it's usually sensible to extend the panel so that it covers the reflections from both the left and the right speaker. 

Generally the best practice for doing stuff with sound is having a mix of absorption and diffusion. Absorption is often cheaper/easier to do when it comes to making panels (though things like bookshelves with objects in them are their own brand of diffusion). There's also ongoing research about hybrid absorption/diffusion panels. 
 

[geo3]

5 hours ago, cmndr said:

Generally speaking you want to place them at the first reflection points.

 

Yes, but also you want stuff in the corners for standing waves that develop from room modes.  I'll probably be making soffit versions of these by stacking 3 insulation batts.

 

5 hours ago, cmndr said:

Generally the best practice for doing stuff with sound is having a mix of absorption and diffusion. Absorption is often cheaper/easier to do when it comes to making panels (though things like bookshelves with objects in them are their own brand of diffusion). There's also ongoing research about hybrid absorption/diffusion panels. 

Generally. Absorption is usually always good, diffusion is much more situational. Diffusers are not only a lot more work and cost to build, but they significantly harder to design correctly. You can't just do the random block thing, the shape has to be mathematically calculated to be effective. 

[cmndr]

I used the word "generally" a lot because a ton of audio things are basically just rules of thumb. 

Computationally "solving" a lot of things just doesn't work. The systems are too chaotic. 

Bass traps in corners and along edges makes sense in general. 

I have seen diffusers work VERY well at reducing echoes though.
When I say seen, I mean the office I work at has TONS of wood/metal diffusers and it otherwise looks like a place I'd expect to have AWFUL echoes. Pieces of 2x2 spaced 2" apart across an entire wall REALLY scatter a lot of sound surprisingly well.  Same with the HUGE sheets of metal that have the company logo "dotted" into them with the dots being of different sizes. I had similar designs at 3 different offices. 

 

This is the only example I could get away with publicly sharing https://www.zgf.com/work/404-google-spruce-goose

When I worked in that office it wasn't horribly echoey. 

I won't claim it's the BEST solution for "audiophile grade sound" but basically ANYTHING not bad beats a bare wall. 

The next time I move, I might very well end up making diffusers out of alternating 1"x2" + 2"x2" wood pieces as a fun DIY project

 

I definitely wouldn't get to THIS -

but I don't think I need to... 

With that said, I'll probably do a DEEP dive before doing any real DIY projects 1-3 years from now since scattering, diffusion and absorption are non-trivial and I'm still generally of the mind that absorption is harder to mess up and provides more benefit. I'm still somewhat amused by the ideal of placing a trellis on a wall with like... fake plants/leaves/ivy interspersed since that SHOULD be effective for frequencies past 1000Hz or so if I can get it "random" enough. 

Think 1-2 of these, spaced out a bit and not at a perfect angles relative to the wall. 
https://www.homedepot.com/p/Outdoor-Essentials-72-in-Wood-Diamond-Lattice-Trellis-418750/313618278

 

It'll be a fun engineering project for my "make the ultimate man cave" project (will likely involve converting a garage - think cabinets placed against the garage door so I can use the air as cheap insulation, absorption/diffusion overhead, 9.4.6 speakers, etc. 

[geo3]

55 minutes ago, cmndr said:

I won't claim it's the BEST solution for "audiophile grade sound"

Yeah, that's the crux of it. Obviously a random uneven surface will  scatter sounds. The goal in a listening environment would be to do that in an even way across some particular segment of the spectrum. 

[cmndr]

1 minute ago, geo3 said:

Yeah, that's the crux of it. Obviously a random uneven surface will  scatter sounds. The goal in a listening environment would be to do that in an even way across some particular segment of the spectrum. 

Full disclosure, I'm more of a statistician than I am an electrical engineer or physicist. In statistics, "just randomize it" is often a VERY effective strategy. 

The view I have with room reflections is that "correlations" in how sound is reflected off of walls result in comb filtering and that screws with sound quality at the listening position. 
A sufficiently erratic set of reflection surfaces would decorrelate the sound reflections, partially mitigating this - ideally, across at a wide range of frequencies.

The way I look at it is the more erratic the surface (when it comes to generating reflections) the better from a sound perspective. This is likely to be non-intuitive though since wavelengths vary so much in size. (these will be off by like 10-15%) If 100Hz is around 10' then 1000Hz is around 1' and 10KHz is around 1' you pretty much need to have a bunch of half inch extrusions doing all sorts of erratic things to achieve this... which is hard. Hence fake plant leaves as an idea. And a trellis that's 3" from the wall and maybe another offset trellis 4" from that (potentially with the trellises 45 degrees different from each other). And 4" of sound absorption panels behind all that. 

[geo3]

With backing and alternate mounting hardware .

 

[H713]

I can attest to the "random diffusers" thing working remarkably well. 

 

My lab is a bit of a disaster in general - think the EEVblog lab, only about twice the density. I've got shelves on almost all of the walls, and said shelves are pretty full. The floor is concrete, though in practice the amount of floor available for reflections is relatively limited. The ceiling is also somewhat diffusive, as I've got more crap stored between the floor joists (iceboat runners, a few rolls of sailcloth, pieces of ash for making iceboat battens, etc). My bench (which also has my test speakers on shelves above it) is somewhere in the middle of the room. 

 

I don't have the data handy, but I did some qualitative acoustic measurements of the system and the lab in general, and it's quite good. It's not perfectly flat, but it's better than most of what people use as listening rooms. 

 

 

A tip I have found for cheap acoustic treatment is corporate surplus - Most modern office suites have acoustic treatment of some sort in them, otherwise the big, open spaces would make meetings and conversation impossible. Inevitably, every time a restyling is done, these are replaced. Only downside is that you don't get a whole lot of choice over the color. Our lab, for example, got rid of a bunch that were puce. 

 

[geo3]

Making soffit/corner traps, to deal with room modes (the first set of panels are meant to deal with reflection points). These are the same rockwool batts as before, but 3 stacked on top of each other, for a 47 x 15.25 x 10.5 inch volume of absorption.  

 

The frame is made from 1x3s instead of 2x4s and are a lot trickier to assemble. I need to pre drill the screw holes with these planks to have them not split immediately. 

 

[geo3]

Finally done. Most of the hold up was finding a way to mount these. Settled on these drywall mounting hooks and eye loops. 

 

And here they are mounted:

 

I've got 4 in total, 2 on each side wall in the rear of the room. I'll likely add 4 more, and additional 1 on each side and one center front wall and center rear wall.