Testing If Fabric Is Suitable To Cover Porous Absorbers

[Elder]

Hello everyone, hope your day is going well

I am currently building some acoustic treatment for my office/home studio space. I had gone shopping in person at multiple places looking for some nice looking, breathable and affordable fabric to wrap the panels in, but then found a great deal online.

The fabric finally was delivered, but after inspecting it I noticed that the fabric weave was actually much tighter than expected. The most common advice that seems to be given online regarding suitable fabric is to do the "breath test".....I could barely exhale/blow through this stuff at all!

Being very concerned that this fabric would undermine all the efforts I was making to build these panels I had to come up with something to put my mind at ease, so I run some measurements using my UMIK-1 and REW. I took measurements with the mic at listening position, and also at the first refection points of the rooms side walls since I imagined the angle could increase high frequency reflectivity. Measurements were taken with the fabric zip tied over the end of the UMIK, and also with fabric off.

I was surprised to see that all measurements taken were all exactly the same, within margin of error.

So my question is, would I be wrong in assuming that since the measurements are all the same, my fabric is not actually reflecting in the high frequencies? Am I missing something here?

 

[DVDdoug]

I was surprised to see that all measurements taken were all exactly the same, within margin of error.

I'm not that surprised... If you still have some extra fabric, try listening through it.

And depending on what percentage of your walls are treated, much of the high-frequency reflections may never "see" the acoustic panels. (Those high-frequency soundwaves are small.)

 

[Elder]

I'm not that surprised... If you still have some extra fabric, try listening through it.

And depending on what percentage of your walls are treated, much of the high-frequency reflections may never "see" the acoustic panels. (Those high-frequency soundwaves are small.)

I'm relieved to hear that, thank you.

The fabric is not shiny or hard and light can be seen shining through it. The commonly mentioned "breath" test had me stressing out!

 

[Sal1950]

Measurements were taken with the fabric zip tied over the end of the UMIK, and also with fabric off.

That was a very tiny area of fabric, I'm not sure you could expect a measurable change.
Now absorption of high freq over a large panel area might be a different case.
I tend to believe in the breath test for picking material for acoustic panels.
I used some very cheap shear draperies I bought at WalMart.
You can slightly see the rockboard acoustic insulation underneath it but I know
the sound waves are getting thru for best absorption.
I used the gray ones on the left, the whites are less transparent to both sight and sound.

 

[Elder]

That was a very tiny area of fabric, I'm not sure you could expect a measurable change.
Now absorption of high freq over a large panel area might be a different case.
I tend to believe in the breath test for picking material for acoustic panels.
I used some very cheap shear draperies I bought at WalMart.
You can slightly see the rockboard acoustic insulation underneath it but I know
the sound waves are getting thru for best absorption.

Yes the area of fabric was miniscule, the diameter of the UMIK tip.

Do you happen to have any theories as to why a larger scale test could result in showing more high frequencies being reflected?

This whole thing seems very simple on the surface (sound gets through the fabric, so is not reflected) but I'm sure there could be complexities that I'm not aware of.

Seems to always be the case with these things!

 

[Sal1950]

Do you happen to have any theories as to why a larger scale test could result in showing more high frequencies being reflected?

I'm really not a acoustician, lol .
I can only relate what I read on the subject while doing the research for my room.
Putting the material directly up against the 1/2 of a UMIK just seems a whole different thing to me.
It would only be measuring the amount of absorbtion of X freq by 1/2sq" of material.
What the effect in a room of one 8sqft panel would be a different thing.
I THINK.
There's much smarter guys than me here. HELP

 

[ozzy9832001]

I'm willing to bet that even if you covered the entire room in the fabric it wouldn't make a dent in the audible high frequencies. And depending on the panels position, they may never come in contact with the panels.

 

[Elder]

I'm really not a acoustician, lol .

We definitely have that in common haha! Your help is still very much appreciated though.

 

[Elder]

I'm willing to bet that even if you covered the entire room in the fabric it wouldn't make a dent in the audible high frequencies. And depending on the panels position, they may never come in contact with the panels.

Interesting, thank you.

All I have to run off at the moment is whatever information I could gather from here at audioscience and another well known forum. There always seems to be so much focus on what the high frequency reflections are doing. Much of the discussions seem to revolve around this concern of acoustic panel fabric reflecting rather than absorbing or being transparent enough to allow the energy to be absorbed by the insulation material behind it.

The panels will be positioned everywhere in my small room. Rear wall, side walls, corners and ceiling. I guess what I'm concerned about is ending up with funky uneven decay times due to no absorption of the highs.

Everything I "think" I know though at this point could be completely wrong though of course, finding reliable sources for this type of information is difficult for me.

 

[dasdoing]

I have a hard time believing that any normal (=pourous) fabric can be reflective in any way. If there are losses in some NRC tests it's because they are absorptive, not reflective. You see even a 20Khz the wavelength is still 1,7cm.....bigger than any fiber.

 

[ozzy9832001]

Interesting, thank you.

All I have to run off at the moment is whatever information I could gather from here at audioscience and another well known forum. There always seems to be so much focus on what the high frequency reflections are doing. Much of the discussions seem to revolve around this concern of acoustic panel fabric reflecting rather than absorbing or being transparent enough to allow the energy to be absorbed by the insulation material behind it.

The panels will be positioned everywhere in my small room. Rear wall, side walls, corners and ceiling. I guess what I'm concerned about is ending up with funky uneven decay times due to no absorption of the highs.

Everything I "think" I know though at this point could be completely wrong though of course, finding reliable sources for this type of information is difficult for me.

In my experience, the only issues I've ever seen with high end frequencies is too much absorption. Generally speaking, it's rare to see much eq applied to them as well. We tend to just let them bounce around the room or use diffusion to scatter them.

The low frequencies and anything in that transition range tend to be the most problematic and usually where most people concentrate their efforts. In those cases, it's best to have some sort of limiter in place to prevent over absorption of the high end.

 

[Sal1950]

We tend to just let them bounce around the room or use diffusion to scatter them.

You don't seem to be following the thought process here, That's the whole reason for doing room treatments.
The object is not to have your room sounding like the inside of your shower stall.
You don't want the sound just bouncing all around and screwing up everything from frequency response at the
listening chair, making a mess of imaging and all the rest. The small amount I spent on materials for my panels
made one of the biggest improvements in sound quality per dollar I've ever experienced.
What we're discussing here is the fabric used "strictly for cosmetic effect" to cover the outside of the 2" absorbent
panels. If you spend $50 for a 4'x8'x2" acoustic absorbing panel but then cover it with a shower curtain, you not only
wasted your money but may even have made the rooms acoustic nature worse. You want something as transparent
as possible to let the highs get thru, to then be absorbed by the panel. You want much the same effect as you would
like for a speaker grill, one that lets all the sound thru it..

Superior Acoustic Panels and Sound Absorbing Panels with Free Acoustic Advice - GIK Acoustics

Our professionally handcrafted acoustic panels are sound absorbing panels for walls or ceilings that control and reduce noise, eliminate slap echo, and control comb filtering in a room, using the highest quality acoustic panel materials combined with superior construction methods. The objective...

www.gikacoustics.com

Acoustic Fabric - DIY Noise Reduction Panels | Canvas ETC .

Acoustic fabric wrapped around wall panels is often used in home theaters, recording studios, restaurants & hospitals for noise reduction. DIY your own!

www.canvasetc.com

 

[ozzy9832001]

You don't seem to be following the thought process here, That's the whole reason for doing room treatments.
The object is not to have your room sounding like the inside of your shower stall.
You don't want the sound just bouncing all around and screwing up everything from frequency response at the
listening chair, making a mess of imaging and all the rest. The small amount I spent on materials for my panels
made one of the biggest improvements in sound quality per dollar I've ever experienced.
What we're discussing here is the fabric used "strictly for cosmetic effect" to cover the outside of the 2" absorbent
panels. If you spend $50 for a 4'x8'x2" acoustic absorbing panel but then cover it with a shower curtain, you not only
wasted your money but may even have made the rooms acoustic nature worse. You want something as transparent
as possible to let the highs get thru, to then be absorbed by the panel. You want much the same effect as you would
like for a speaker grill, one that lets all the sound thru it..

Superior Acoustic Panels and Sound Absorbing Panels with Free Acoustic Advice - GIK Acoustics

Our professionally handcrafted acoustic panels are sound absorbing panels for walls or ceilings that control and reduce noise, eliminate slap echo, and control comb filtering in a room, using the highest quality acoustic panel materials combined with superior construction methods. The objective...

www.gikacoustics.com

Acoustic Fabric - DIY Noise Reduction Panels | Canvas ETC .

Acoustic fabric wrapped around wall panels is often used in home theaters, recording studios, restaurants & hospitals for noise reduction. DIY your own!

www.canvasetc.com

Why are you quoting me? I already stated the fabric wouldn't have any sonic effect.

I understand perfectly the reason behind the acoustic treatments.

I find absorbing the high end to be a waste of time and money. If any treatment were really necessary, I'd recommend diffusion. I'd prefer to keep that high end energy in the room. That money is better spent getting the low end and mid range under control. Over the course of getting the low end under control, the room will naturally become more absorbent and less reflective. Most people's goal is not to have a completely dead room. If you want a RFZ or a dead room you'll need more than a few panels.

 

[Sal1950]

I find absorbing the high end to be a waste of time and money. If any treatment were really necessary, I'd recommend diffusion.

We'll have to agree to disagree on that point.
Specially with a 5.2.4 surround rig like mine.
But even with 2ch, great imaging depends on a reasonable lack of
reverberation from the side walls.
YMMV

 

[Elder]

Appreciate the help everyone!

It seems that most of you are in agreement that this fabric will indeed not be reflective (potentially absorptive, but not reflective) which is what had me so concerned. I will be going ahead and using it to complete my porous absorbers.

Once all the treatment is complete I can return with before and after room measurements if anyone is interested. If not, have a great day everyone and see you all around on the forum

 

[Philbo King]

I used unbleached muslin from joann.com to cover mine both front and back. Worked fine, looks good, and was inexpensive at the time.

Edit: It's still listed at $2/yard

 

[ozzy9832001]

Appreciate the help everyone!

It seems that most of you are in agreement that this fabric will indeed not be reflective (potentially absorptive, but not reflective) which is what had me so concerned. I will be going ahead and using it to complete my porous absorbers.

Once all the treatment is complete I can return with before and after room measurements if anyone is interested. If not, have a great day everyone and see you all around on the forum

I'm always interested in the data.

 

[Sal1950]

Once all the treatment is complete I can return with before and after room measurements if anyone is interested. If not, have a great day everyone and see you all around on the forum

For sure, let us know how things work out.
I hope you get all your looking for.

 

[dasdoing]

we are data junkies

 

[Elder]

Before vs After Treatment (No Smoothing Obviously)

RT60 Before Treatment

RT60 After Treatment

Waterfall Before Treatment

Waterfall After Treatment

Spectrogram Before Treatment

Spectrogram After Treatment

As promised, some data!

Currently using a tiny pair of DIY bookshelf speakers that I decided to 3d print during covid as a fun little project, but sadly they aren't exactly good speakers lol. Would be great to see what's happening down in the low end, but that's going to have to wait until I have my new speakers. Decided to get the room sorted before speakers this time around!