Acoustic Treatments, 2" inches or 4" inches thickness?

[nibhaz]

Afterthought:

A lot of flutter echo can usually be tamed by eliminating parallel flat surfaces.

This can be accomplished by moving furniture and wall hangings around so that you minimize the number of flat surfaces on one wall from facing flat surfaces on the opposite wall. The best part about this is it’s free.

 

[Jack Hammer]

Techlord, Accoustic treatments can be a tad bit addictive, especially so when you notice a huge improvement right away. You may find that thicker panels are too bulky in some spots and that thinner are better suited for that location. Use what works best for not just sound but for aesthetics and practicality. You may end up making more panels of differing shapes and thickness later down the road. Point is make some thick and some thin, you'll likely be happy with both.

 

[highfigh]

Now I am confused getting two different opinions that are opposite of each other, now I don't know what to do! Maybe I should just hang a carpet on the wall...

What materials are considered broadband absorption?

This is the reason I recommended buying some fiberglass panels, cover them (less of a mess when they're moved repeatedly) and just play with the placement. Use the basic guidelines for placement and move them, listening for the differences.

Unfortunately, the problems are somewhat specific but trial and error will eventually solve them to a point. If you're problems with echo are all in the mid-range, 1"-2" should be fine and it will definitely make an audible difference. If you can, don't aim any of the speakers so the sound hits the opposite wall at a right angle. try a panel behind the front speakers, so the sound that goes behind them is absorbed. Put a panel to the sides of the front speakers where the sound hits the wall (this is the first reflection). This is important for the way the 'soundstage' is reproduced. If you have strong reflections from the sides, it can sound like the source isn't between the speakers, it'll sound like it's outside and that's not natural. If they wanted it to sound that way, they would use the side and/or surround speakers.

Find some source material that has a lot of percussive sounds. Also, find something with one person speaking- the sound of their voice will usually be centered.

Listen to the sound with no panels and put one behind each front speaker, with the panel's center at the outside edge of the speaker cabinet. Listen to the difference, playing the same source material. Now, put at least one panel between the front speakers, centered. Listen again for the differences. Place a panel to the sides of the front speakers unless you have something fairly large and irregularly shaped where the sound would reflect. You can use a small mirror to find this spot- if you can see the speaker in the mirror when you look from your main listening position, you'll hear the reflected sound. Again, listen to the differences. If you don't have a wall immediately behind you when you're in the main listening position, that may be all you need.

Human voice should sound very natural. If you hear something that's too strong or is missing, move the panels slightly. The way sound reflects is similar to the way light reflects- if the sound hits the surface at a 30 degree angle, it will reflect at a 30 degree angle. If it hits an irregular surface, the sound or light will scatter.

 

[Techlord]

All of my 2' x 4' wooden frames will have 1 1/2" inch of space behind the actual absorbing material, I'm starting out with three frames and will gradually add more. Does anyone think that microsuede will hindle the sound absorption vs burlap?

Thanks for all the helpful info!

Techlord.

 

[highfigh]

All of my 2' x 4' wooden frames will have 1 1/2" inch of space behind the actual absorbing material, I'm starting out with three frames and will gradually add more. Does anyone think that microsuede will hinder the sound absorption vs burlap?

Thanks for all the helpful info!

Techlord.

Microsuede is sold by most of the acoustical panel makers as an option to that oh, so attractive burlap. If you can breathe through it easily, it will work for this. If you blow though it and you notice resistance, use something else.

Personally, until I knew exactly how many panels I needed, I would use muslin (it's about $3/yard) first and then buy the good stuff. That way, you may be able to buy enough to get a discount.

 

[jostenmeat]

All of my 2' x 4' wooden frames will have 1 1/2" inch of space behind the actual absorbing material, I'm starting out with three frames and will gradually add more. Does anyone think that microsuede will hindle the sound absorption vs burlap?

Thanks for all the helpful info!

Techlord.

Microsuede is sold by most of the acoustical panel makers as an option to that oh, so attractive burlap. If you can breathe through it easily, it will work for this. If you blow though it and you notice resistance, use something else.

Personally, until I knew exactly how many panels I needed, I would use muslin (it's about $3/yard) first and then buy the good stuff. That way, you may be able to buy enough to get a discount.

This is an interesting query/discussion. Maybe stuff like microsuede can actually help reduce HF, at least for certain freq's, but for which are they more reflective?

I just browsed for a bit, and the brainiac Terry Montlick said the following recently:

Guilford Anchorage does not have very good acoustical transparency. My measurements show that it attenuates more than 3 dB at 2 kHz, and about 6 dB at 8 kHz. That is at least a doubling of panel space required at these higher frequencies, compared to FR701.

"SoundSuede" fabric is similar to Anchorage in performance. Dazian Janus measures a little better, with around 2 dB attenuation at 2 kHz, but 4 dB at 8 kHz.

I think if the goal is to have the fiberglass do all of the absorption, then use the blow through test. Even if blowing is zero hertz, it should be a good indicator of the transparency.

If, OTOH, HF attenuation is the goal, then I would look for that attribute with the covering.

I'm not really answering any questions.

 

[Techlord]

This is the reason I recommended buying some fiberglass panels, cover them (less of a mess when they're moved repeatedly) and just play with the placement. Use the basic guidelines for placement and move them, listening for the differences.

Unfortunately, the problems are somewhat specific but trial and error will eventually solve them to a point. If you're problems with echo are all in the mid-range, 1"-2" should be fine and it will definitely make an audible difference. If you can, don't aim any of the speakers so the sound hits the opposite wall at a right angle. try a panel behind the front speakers, so the sound that goes behind them is absorbed. Put a panel to the sides of the front speakers where the sound hits the wall (this is the first reflection). This is important for the way the 'soundstage' is reproduced. If you have strong reflections from the sides, it can sound like the source isn't between the speakers, it'll sound like it's outside and that's not natural. If they wanted it to sound that way, they would use the side and/or surround speakers.

Find some source material that has a lot of percussive sounds. Also, find something with one person speaking- the sound of their voice will usually be centered.

Listen to the sound with no panels and put one behind each front speaker, with the panel's center at the outside edge of the speaker cabinet. Listen to the difference, playing the same source material. Now, put at least one panel between the front speakers, centered. Listen again for the differences. Place a panel to the sides of the front speakers unless you have something fairly large and irregularly shaped where the sound would reflect. You can use a small mirror to find this spot- if you can see the speaker in the mirror when you look from your main listening position, you'll hear the reflected sound. Again, listen to the differences. If you don't have a wall immediately behind you when you're in the main listening position, that may be all you need.

Human voice should sound very natural. If you hear something that's too strong or is missing, move the panels slightly. The way sound reflects is similar to the way light reflects- if the sound hits the surface at a 30 degree angle, it will reflect at a 30 degree angle. If it hits an irregular surface, the sound or light will scatter.

I just ordered some burlap fabric (ivory in color) and have been looking at the NRC and all the absorption numbers with the different frequencies (125Hz, 500Hz. 1000 Hz. 4000 Hz. & Density) and have a question, using Owens-Corning 703 2" material as an example, if you take two pieces of 703 2" material with an NRC rating of 1.00 and stick two 703 2" material pieces together do you get 200% absorption? I'm looking to build a high frequency type acoustic panel to trap first and second reflections or at least tame them down a bit, most of my reflections are high, mid-range and low mid-range as my MK speakers are limited to 80Hz - 20kHz.

Thanks,
Techlord.

 

[nibhaz]

First you should realize that NRC ratings are merely an averaged performance rating based on rates of absorption at specific frequencies. Whilst this number is usually applicable to frequencies higher than the tested mid band frequencies, the same cannot be said for low end frequencies. However, since you are a merely concerned with mid-band and high frequencies absorption the NRC rating is a good metric for you to use in your endeavors.


The difference between a 2” panel and a 4” panel of OC 703 is going to be increased absorption at lower frequencies.


Looking at the blue traces only, which represent flush mounting, you will see the difference between a 2” panel and a 4” panel of 703.

2" OC 703



4" OC703



100% absorption is 100% absorption…you can’t’ absorb more sound than exist, though it is possible to have an NRC greater than 1 (full absorption) due to their methodology…

 

[highfigh]

I just ordered some burlap fabric (ivory in color) and have been looking at the NRC and all the absorption numbers with the different frequencies (125Hz, 500Hz. 1000 Hz. 4000 Hz. & Density) and have a question, using Owens-Corning 703 2" material as an example, if you take two pieces of 703 2" material with an NRC rating of 1.00 and stick two 703 2" material pieces together do you get 200% absorption? I'm looking to build a high frequency type acoustic panel to trap first and second reflections or at least tame them down a bit, most of my reflections are high, mid-range and low mid-range as my MK speakers are limited to 80Hz - 20kHz.

Thanks,
Techlord.

The NRC of 1.0 is only at certain frequencies, not broadband. If you go thicker, it works better at lower frequencies and if you want better absorption at other frequencies above that, increase the surface area, not the thickness. If you want HF absorption, you shouldn't be using 2". For that, 1" and a 1" space behind works fine. I would try it without the space first but it does work and the results are measurable.

 

[Techlord]

First you should realize that NRC ratings are merely an averaged performance rating based on rates of absorption at specific frequencies. Whilst this number is usually applicable to frequencies higher than the tested mid band frequencies, the same cannot be said for low end frequencies. However, since you are a merely concerned with mid-band and high frequencies absorption the NRC rating is a good metric for you to use in your endeavors.


The difference between a 2” panel and a 4” panel of OC 703 is going to be increased absorption at lower frequencies.


Looking at the blue traces only, which represent flush mounting, you will see the difference between a 2” panel and a 4” panel of 703.

2" OC 703



4" OC703



100% absorption is 100% absorption…you can’t’ absorb more sound than exist, though it is possible to have an NRC greater than 1 (full absorption) due to their methodology…

Thanks guys for all the helpful info, so going from 1" to 2" of OC 703 improves the mid-range since it's lower in frequencies and 4" go's even further into the lower frequencies? I'm thinking 3-4 2" OC 703 panels on the rear wall and two 1" panels directly behind the main L/R speakers, all the edges around the 703 material will be exposed for added surface area. I will staple the burlap onto the frames, then set the 703 material on to of the burlap. After that I will cover the whole 703 material with burlap again around the back of the frame and staple it all up. I do have a ton of mid-range and highs when compared with lower bass frequencies, the subwoofer is the only piece in my HT that produces bass frequencies, but have lots of lower mid-range also.

Regards,
Techlord.

 

[Techlord]

Hi everyone, I finding that my ivory white burlap fabric can be seen through to the wood backer frame, if the wood is showing through then what's to stop the Qwen's Corning 703 from showing through the burlap fabric? Is there another fabric that still transparent enough that doesn't show through the backer frame and Qwen's Corning 703? I hate to think I wasted my money of this fabric that I have now! Does anyone know what type of fabric is in this You Tube video?

Regards,
Techlord.

 

[just-some-guy]

how about a 2nd layer ?

 

[Techlord]

how about a 2nd layer ?

That is doable, it may or may not effect the blow through test. I just hope I have enough burlap left to finish all three panels using 2" OC 703 material, the place that I purchased the fabric is out of stock for now. I purchased six yards 56" wide and have used up three 2' x 4' pieces...

Thanks,
Techlord.

 

[Techlord]

Can someone list a few fabrics that are acoustically transparent? I would like to know so I don't go into a fabric store and buy the wrong fabric.

Thanks
Techlord.

 

[manlystanley]

Can someone list a few fabrics that are acoustically transparent? I would like to know so I don't go into a fabric store and buy the wrong fabric.

Thanks
Techlord.

I have the same question. Is the micro suede just as transparent as the burlap?? Specifically, what do you all think of this:

http://www.atsacoustics.com/item--Microsuede-Fabric-60-inch-wide--1027.html


Thanks,
Stan

 

[Weasel9992]

I have the same question. Is the micro suede just as transparent as the burlap?? Specifically, what do you all think of this:

http://www.atsacoustics.com/item--Microsuede-Fabric-60-inch-wide--1027.html


Thanks,
Stan

Absolutely, positively not. Terry Montlick has done tests on lots of different fabric types, including MicroSuede. The issue seems to be up in the highs, as you can imagine.

Frank

 

[manlystanley]

Absolutely, positively not. Terry Montlick has done tests on lots of different fabric types, including MicroSuede. The issue seems to be up in the highs, as you can imagine.

Frank

Thanks!!! I did a search for 'Terry Monlick' and found that he tested "one "microsuede" fabric, and it reflected 4 dB at 1 kHz. That's more than half the sound energy unabsorbed! ". Ouch!!!!

Is there a better product to use then this:
http://www.atsacoustics.com/item--Burlap-Fabric-56-Inch-Wide--1009.html

Thanks,
Stan

 

[Weasel9992]

I'm not a huge fan of microsuedes in general, but there are tons of other options. Guilford of Maine FR701 fabric is a fantastic option as is Guilford's Anchorage fabric.

Frank

 

[manlystanley]

I'm not a huge fan of microsuedes in general, but there are tons of other options. Guilford of Maine FR701 fabric is a fantastic option as is Guilford's Anchorage fabric.

Frank

What do you think of a 100% cotton covering for being sound transparent?? I was thinking that batik would look nice:

http://www.sewbatik.com/Products.aspx

Thanks,
Stan

 

[Weasel9992]

Depends completely on the thread count and/or whether it's a sateen finish. I know that anything below 200TC non-sateen is definitely transparent.

Frank