DIY Acoustic Panels

Pogre

Pogre

Audioholic Warlord
This video popped up in my feed and I actually found it pretty interesting. This guy does a pretty thorough test of different sound absorbing materials before settling on towels. I haven't shopped for towels in a while so not sure how cost effective it is, but they are very effective and look nice.

 
ryanosaur

ryanosaur

Audioholic Ninja
Haven’t had a chance to watch this vid... but a lot of the stuff that gets used is... unhealthy. Rockwool and fiberglass? Eek! ;)
If I ever get to the point where I need to play with treatments on that level, I’ve been very intrigued by the idea of the combination diffuser/absorber.
 
Pogre

Pogre

Audioholic Warlord
Haven’t had a chance to watch this vid... but a lot of the stuff that gets used is... unhealthy. Rockwool and fiberglass? Eek! ;)
If I ever get to the point where I need to play with treatments on that level, I’ve been very intrigued by the idea of the combination diffuser/absorber.
What made this interesting for me was the fact that towels work so well. He sets up a mic outdoors above a speaker (same speaker behind him in the room where he's sitting. I wanna know what they are!) and played test tones through the different materials to see what damps the most sound energy. Towels blew everything away. You need like 7 or 8 per panel tho and I'd say thicker is better, so I'm guessing they're not "cheap" but probably more cost effective than buying from a manufacturer.
 
ryanosaur

ryanosaur

Audioholic Ninja
Hmmm... Alex's post is gone. I saw the email notification. Hmmm. :oops:

I just watched the vid, Pogre. Interesting. I do have some Spidey-Sense issues with his methodology (how his rig and microphone is set up, as well as the way he is more directly measuring sound passing through the material), but at least in the general consistency of his implementation, I gotta say... it looks somewhat promising.
My thought process is that in the combination of density of material and air inherent in the terry cloth fabric, that the stack helps create a good measure of absorptive properties. Some of the research I've done indicates that sometimes a layer of absorption, standing off from the wall, works better than the layer of absorption pressed up against the wall. I'm hesitant to go as far as saying one confirms the other, though. ;) Not without seeing a better test setup and tighter methodology, including more consistent application of material description, thickness, density, and measurement setup... including getting out of his rather lovely back yard and into an open field or large building where tighter controls can be implemented.

Its unfortunate that he doesn't give a better range of frequencies. He does frequencies ranging from 17-5 kHz at the beginning... and then adds 500 Hz, which nothing that thickness of about 1.5 or 1.75" will really work on. We do see an SPL reduction from the blocking of direct soundwaves in his test, and of course we can "hear" a difference in the recording quality of his treated room...
But he doesn't show us before-and-after room measurements to illustrate the actual level of frequency attenuation he acheives, much less whether his goal was a more acoustically dead space for production rather than what is desired for entertainment (some reflection is necessary). Reinforcing the point of frequency attenuation, it would be very helpful to know the performance of his panels in the midrange, more specifically between 1000 and 2500 Hz, say: Consider, this is the area (around 2 kHz) where our ears are also more susceptible to listening fatigue.

Personally, I would love to see a test of a range of materials that are more freindly to the living environment of our homes. The towels are cool, but what about Recycled Denim that is used for insulation? Perhaps a comparison to acoustic foam, as well as the Long Fiber Wool and Polyfill/Acoustuff common in various speaker damping applications, as well?

I'd like to see a set up that perhaps uses those towels, pressed against a perforated panel at the back with a small airspace behind. I'd like to see a better attempt at fighting the effect of gravity on woven material than just stitching some terry cloth together... perhaps some spray adhesive between layers along with the stitching? And then... How long until that white terry cloth front cover is disgustingly dirty and impossible to clean? :p For Cat's Sake, man, wrap it in acoustic fabric that won't be a flipping dirt magnet! ;) Add some color to your life, even if its eggshell grey just to offset your white walls! :D
 
Last edited:
KEW

KEW

Audioholic Overlord
What made this interesting for me was the fact that towels work so well. He sets up a mic outdoors above a speaker (same speaker behind him in the room where he's sitting. I wanna know what they are!) and played test tones through the different materials to see what damps the most sound energy. Towels blew everything away. You need like 7 or 8 per panel tho and I'd say thicker is better, so I'm guessing they're not "cheap" but probably more cost effective than buying from a manufacturer.
Nice video!
At the end of the video it shows two of his other videos. One was for a headphone stand and the other is for what appears to be the speaker he used for testing (with the dome tweeter), so you could Google that title to find out more about the test speaker.
Some comments/suggestions on his panel construction:
1) I don't know what wood he was using, but what I usually see in the stores around me has a bit more warp/bend/twist than what he used. YMMV, but it might make sense to fab the frames out of 3/4" plywood cut to strips. Even then, a thin board across the back to maintain the width may be useful to prevent the stretching of the towel from pulling the frame narrow in the middle.
2) He stapled the red towel to the back of the frame, then cut the towel using scissors. It looked like he cut the towel close to the staples which is likely to result in the towel being pulled out from under the staples over time since there are only a few threads between where the staple holds the towel and the cut edge. I would use Duco cement (tube glue) to glue the threads close to the staple together, or even better, after the staples like he shows, fold the towel back to the center of the frame and staple down, then glue.
3) this may not be needed and I would wait to see if it is a problem, but often when building a frame like this, to keep it square (the contact area of the boards at the corners is not much and a little bit of warp can mess up what little ability that corner has to hold the frame square), you measure the diagonals from opposite corners. They should be equal if the frame is square then you can use diagonal wires connected to tacks at the corners to hold it square. Here you would want to add some sort of felt or bumper to prevent the wall from being marred by the tack heads or the wires.
 
KEW

KEW

Audioholic Overlord
Hmmm... Alex's post is gone. I saw the email notification. Hmmm. :oops:

I just watched the vid, Pogre. Interesting. I do have some Spidey-Sense issues with his methodology (how his rig and microphone is set up, as well as the way he is more directly measuring sound passing through the material), but at least in the general consistency of his implementation, I gotta say... it looks somewhat promising.
My thought process is that in the combination of density of material and air inherent in the terry cloth fabric, that the stack helps create a good measure of absorptive properties. Some of the research I've done indicates that sometimes a layer of absorption, standing off from the wall, works better than the layer of absorption pressed up against the wall. I'm hesitant to go as far as saying one confirms the other, though. ;) Not without seeing a better test setup and tighter methodology, including more consistent application of material description, thickness, density, and measurement setup... including getting out of his rather lovely back yard and into an open field or large building where tighter controls can be implemented.

Its unfortunate that he doesn't give a better range of frequencies. He does frequencies ranging from 17-5 kHz at the beginning... and then adds 500 Hz, which nothing that thickness of about 1.5 or 1.75" will really work on. We do see an SPL reduction from the blocking of direct soundwaves in his test, and of course we can "hear" a difference in the recording quality of his treated room...
But he doesn't show us before-and-after room measurements to illustrate the actual level of frequency attenuation he acheives, much less whether his goal was a more acoustically dead space for production rather than what is desired for entertainment (some reflection is necessary). Reinforcing the point of frequency attenuation, it would be very helpful to know the performance of his panels in the midrange, more specifically between 1000 and 2500 Hz, say: Consider that that is the area (around 2 kHz) where our ears are also more susceptible to listening fatigue.

Personally, I would love to see a test of a range of materials that are more freindly to the living environment of our homes. The towels are cool, but what about Recycled Denim that is used for insulation? Perhaps a comparison to acoustic foam, as well as the Long Fiber Wool and Polyfill/Acoustuff common in various speaker damping applications, as well?

I'd like to see a set up that perhaps uses those towels, pressed against a perforated panel at the back with a small airspace behind. I'd like to see a better attempt at fighting the effect of gravity on woven material than just stitching some terry cloth together... perhaps some spray adhesive between layers along with the stitching? And then... How long until that white terry cloth front cover is disgustingly dirty and impossible to clean? :p For Cat's Sake, man, wrap it in acoustic fabric that won't be a flipping dirt magnet! ;) Add some color to your life, even if its eggshell grey just to offset your white walls! :D
Working off of your comments, I agree that there would definitely be a benefit to seeing measurements of exactly how much reduction he accomplished. Having graphical displays without any scale to quantify is always a bad idea.

I actually think tacking the layers with thread might be part of why it works so well. The layers are free to move with the sound waves as they absorb energy. My fear of using a spray adhesive is that it might convert the multiple supple layers in to a single (comparatively) stiff layer that would not absorb sound energy as well.
 
ryanosaur

ryanosaur

Audioholic Ninja
This is my favorite video for a simple panel build:
I would prefer to change up the material some, but you can see it is a more well conceived plan. :)
 
ryanosaur

ryanosaur

Audioholic Ninja
Working off of your comments, I agree that there would definitely be a benefit to seeing measurements of exactly how much reduction he accomplished. Having graphical displays without any scale to quantify is always a bad idea.

I actually think tacking the layers with thread might be part of why it works so well. The layers are free to move with the sound waves as they absorb energy. My fear of using a spray adhesive is that it might convert the multiple supple layers in to a single (comparatively) stiff layer that would not absorb sound energy as well.
Indeed, I thought of that too... and perhaps using a rod across the top, where the layers could be better fastened or secured would also help alleviate sagging, as well as eliminate the need for spot sewing the layers together.

I would add that in my study of transmission line builds, it seems to be well documented at this point that the fill material doesn't actually move. Therefore, I would be willing to propose that these towel layers wouldn't either. However, as I wrote before (and in agreement with you), I think it is in the layering of a dense material with air space inherent to the fabric, that may make this a potentially good material for such a project. :)
 
KEW

KEW

Audioholic Overlord
I would add that in my study of transmission line builds, it seems to be well documented at this point that the fill material doesn't actually move. Therefore, I would be willing to propose that these towel layers wouldn't either. However, as I wrote before (and in agreement with you), I think it is in the layering of a dense material with air space inherent to the fabric, that may make this a potentially good material for such a project. :)
Cool!
What I have always heard is in line with this blurb:
When sound waves travel through the air and strike wall- or ceiling-mounted noise reducing panels, fiberglass fibers or foam pores vibrate, increasing friction among the pores or fibers. These vibrations quickly reach a point where enough friction is created for the conversion of sound energy to kinetic (heat) energy, which is simply the energy of an object in motion. Since kinetic energy can’t be contained, it dissipates quickly, leaving no sound waves and, naturally, no sound.

So that begs the questions:
1) Is one source simply wrong?
2) Are different materials being used for different objectives (it also occurs that foam has been used for speaker grills as well as internally for damping)?

When you get the chance, please post a link to your source re: TL fill materials!
Thanks!
 
ryanosaur

ryanosaur

Audioholic Ninja
I'll try to find that when I have time... perhaps later today.
For now, what I recall is re: the idea that the damping of the TL actually slowed the speed of sound in the line via the movement of the fibers (as you describe above). This seems to have been generally debunked... assuming I understood correctly what I was reading. :p
*blushes
I'll try to follow up soon, if I can!
 
Alex2507

Alex2507

Audioholic Slumlord
Alex's post is gone.
Basically I only wanted to call the guy a wanker and a tosser that TLS ought to b!tch slap when he got back home for not knowing that reflection and transmission of sound were measured with the mic on different sides of the panel.

Those towels could have been reflecting sound and therefore the mic would record a reduced SPL on the wrong side of the panel. Rigid fiberglass with a 6lb/ft^3 is the ticket for absorption in lower frequencies OC705 IIRC. The OC703 is almost as good at 3 lb/ft^3. Mineral wool comes in 4 and 8 lb densities and is nearly as good but weight adds up fast, however it is about half the cost of rigid fiberglass.

Search for nibhaz on sound panels and bass traps for good info on panels. He had an understanding of it and produced informative post on the topic. I searched quickly for bass traps with his name for this result. The key with the fabric was that air be able to pass through it like you want to be able to breathe through it. There's a lot more to this than some joker with towels from the a second hand store and a mic. Caucasian, puh-lease.

Anyways it's been a while since I looked at the different types of insulation and their Noise Reduction Coefficients (NRC) but that's an average sampling 5 frequencies. The lowest frequency would be of most interest to us. Maybe 125 Hz.

Another quick search produced this thread that might be of interest as well. TLS talked about sound dampening in a speaker in the thread. My favorite part of that was getting Swerd going on brain cancer.

Sound absorption was a hot topic back in the day. Informative discussions took place but the brainiacs on the topic moved on. The best part of that jack off with the mic and camera was his accent. Who buys second hand towels? Anyway I deleted my post because it didn't offer much other than an insult and I didn't have the time or inclination to get into it.

There's also the consideration of so called absorbers acting more like diffusers and there's an argument for first reflections being a good thing with speakers that have good off axis responses. Alvin Foster of The Boston Audio Society has 2 foot thick absorbers behind his listening position because he doesn't care for reflected sound. It's a crazy topic that I was interested in way back but can't shed real light on now or then for that matter.

Here's a link with info on the Owens Corning products. Check out GIK Acoustics for what looks good. If you search for them in our forums, you'll likely find other the other manufacturers for comparisons. I would caution against is using a 24"x48" piece of insulation to build a panel around as it becomes huge and heavy. I made some way back with Mahogany frames and an air gap. They were just too big for ManTown.

My take away on panels was that while they worked to improve acoustics, better speakers worked better. I still have a GIK 242 hanging in the living room corner to address one problem but it's twin and my bigger and better DIY jobs all got given away.
 
Pogre

Pogre

Audioholic Warlord
I stirred up a bunch of poop, lol. Okay, so apparently this guy is a choad and doesn't understand panel absorption like I thought he did.

This is why I still hang out here. I learn stuff. To the uninitiated (me), that dude seemed to cover all his bases. Just shows how much more there is to know when it comes to audio and acoustics.
 
ryanosaur

ryanosaur

Audioholic Ninja
Ha! you can't polish turds unless you pick them up and handle them. And as Mythbusters proved, it is possible to polish a turd! :p Just have to find the right one... and this might not have been it. :D

Alex did more clearly state something I mentioned above, regarding methodology, that the towels may be blocking the soundwaves rather than absorbing them, hence the dramatic change in recorded signal.

I'm looking forward to checking out the links Alex brought up.

:)
 
Alex2507

Alex2507

Audioholic Slumlord
Just shows how much more there is to know when it comes to audio and acoustics.
My explanations aren't stellar because my understanding isn't perfect. An interesting question regarding coefficients is how they end up with a value greater than 1.0 ... and 'fake news' isn't the answer. :)

As always the best answer to any question is getting a bigger amp. :p
 

newsletter
  • RBHsound.com
  • BlueJeansCable.com
  • SVS Sound Subwoofers
  • Experience the Martin Logan Montis
Top