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3.5" or 5.5" thick acoustic panels?
Old 3 weeks ago
  #1
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3.5" or 5.5" thick acoustic panels?

I'm about to make some DIY acoustic panels using UltraTouch insulation and I need to decide whether to build 3.5" or 5.5" thick panels. The goal is to create a handful of broadband absorbers that can do double duty as bass traps when positioned in the corners.

My instinct is to go with the thicker panels since most people seem to agree that anything less than 4" isn't enough for dealing with low frequencies. But I've also read that UltraTouch actually becomes reflective to low frequencies when it's more than 4" thick. Is this a legitimate reason to avoid the 5.5" batts? The 5.5" and 3.5" cost the same but you get a few more batts in the 3.5" package. Should i go for the 3.5" and have a few extra panels to play with or stick to fewer but thicker panels?
Old 3 weeks ago
  #2
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A 4" trap with 4" airgap is minimum for a broadband trap for first reflection points. Its not a bass trap. You should go way thicker than 5 inches and use an alternate material IMO.
Old 3 weeks ago
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Thanks. An air gap is part of the plan; and broadband absorption at the first reflection points is the primary goal. Is ultra touch insulation not a good choice for broadband absorption ?
Old 3 weeks ago
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Quote:
Originally Posted by dustcloud View Post
Thanks. An air gap is part of the plan; and broadband absorption at the first reflection points is the primary goal. Is ultra touch insulation not a good choice for broadband absorption ?
I really havent looked into the ultra touch insulation all that much, and i dont believe i've ever seen it recommended by the pros. It seems pretty dense to me, but if you have GFR/density data you can share i could make a more difinitive statement.
Old 3 weeks ago
  #5
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It looks like Ultra touch has a GRF of ~ 15-20k/rayls:
Is Ultratouch Denim Insulation superior; Bass Buster

It seems to work well down to about 100Hz (3.5" = .95 NRC @ 125Hz). But its high GFR makes it ineffective for panels thicker than about 4". So, as you said, not the right material for bass traps. But it still seems like a good option for early reflection points.
Old 3 weeks ago
  #6
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Quote:
Originally Posted by dustcloud View Post
It looks like Ultra touch has a GRF of ~ 15-20k/rayls:
Is Ultratouch Denim Insulation superior; Bass Buster

It seems to work well down to about 100Hz (3.5" = .95 NRC @ 125Hz). But its high GFR makes it ineffective for panels thicker than about 4". So, as you said, not the right material for bass traps. But it still seems like a good option for early reflection points.
Thanks for the GFR data. Density and fiber size also play a large role, but based soley on GFR you'd be around .5 @ 100hz. Perhaps it would be fine for a first reflection point at 4" thick with a 4" airgap. It would be interesting to see how it looks in soundflow with all the correct data.
Old 3 weeks ago
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4"+4" air gap. GRF = 15. Density = 24 kg/m3
Attached Thumbnails
3.5" or 5.5" thick acoustic panels?-4in4airgap.png   3.5" or 5.5" thick acoustic panels?-4in4airgapmoredetails.png  

Last edited by JayPee; 3 weeks ago at 07:46 AM.. Reason: adding second pics for more details
Old 3 weeks ago
  #8
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Thanks for taking the time to share those graphs.

It's incredible how steep the drop in performance is below 100Hz.

How different would those graphs look without a 4" air gap? What range of frequencies would be impacted the most?

Also, I should have mentioned: according to the thread i linked to above, the density of Ultratouch is 19.2 kg/m3. I have no idea whether that figure is accurate or how much difference it would make.
Old 3 weeks ago
  #9
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Quote:
Originally Posted by dustcloud View Post
Thanks for taking the time to share those graphs.

It's incredible how steep the drop in performance is below 100Hz.

How different would those graphs look without a 4" air gap? What range of frequencies would be impacted the most?

Also, I should have mentioned: according to the thread i linked to above, the density of Ultratouch is 19.2 kg/m3. I have no idea whether that figure is accurate or how much difference it would make.
4" no air gap
Attached Thumbnails
3.5" or 5.5" thick acoustic panels?-screenshot_20191121-103032_firefox.jpg  
Old 3 weeks ago
  #10
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4", no air gap. GRF:15kPa.s/m3. Density: 19kg/m3.
Attached Thumbnails
3.5" or 5.5" thick acoustic panels?-4inchnoairgap.png  

Last edited by JayPee; 3 weeks ago at 07:31 PM..
Old 3 weeks ago
  #11
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You'll lose one octave of absorption.
Old 3 weeks ago
  #12
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In my experience ultratouch doesn't seem to regain its full depth. The stated 3.5" ends up at about 2.5", which fits nicely into 1x3 and 2x3 framing. The stated 5.5" probably ends up about 4".

Utilize the 93" batts to make tall and large panels. Surface area matters. Large air gaps will help a lot if you have the space for it.
Old 3 weeks ago
  #13
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Quote:
Originally Posted by Jason Foi View Post
...i dont believe i've ever seen it recommended by the pros.
I believe Newell uses cotton for porous absorption.
Old 3 weeks ago
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Wow. I was planning on using an air gap, but I've got to admit, part of me was thinking well maybe I could get away without one. Those graphs make it pretty clear that an air gap is critical.

Is it safe to say that without an air gap you could end up doing more harm than good to the response of a room? I'm imagining all that energy below 250Hz bouncing around stripped of any higher frequency content.
Old 3 weeks ago
  #15
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So how are we supposed to read the published acoustic specs for Ultra Touch in light of those graphs? Ultra Touch claims to have a very high NRC all the way down to 125Hz. But those figures are based on tests that used a 'Type A Mounting' which apparently means the material was directly mounted on the surface with no air gap. Are the published specs just not reliable? Or is there something else at play here?
Old 3 weeks ago
  #16
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Quote:
Originally Posted by johnnyc View Post
In my experience ultratouch doesn't seem to regain its full depth.
That seems to be a common complaint, even in construction jobs where its being installed behind drywall. Does it mean that a 3.5" batt is only going to deliver 2.5" performance? Or is it just something to keep in mind when planning the dimensions of the panels?
Old 3 weeks ago
  #17
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Quote:
Originally Posted by dustcloud View Post
That seems to be a common complaint, even in construction jobs where its being installed behind drywall. Does it mean that a 3.5" batt is only going to deliver 2.5" performance? Or is it just something to keep in mind when planning the dimensions of the panels?
It will increase the gfr value and decrease performance.

The test you see are for reverberation chambers and valid for large rooms, but not small room acoustics. You never acheive a reverberant field in a small room.

In all honesty, i would just use an alternate material. Roxul safe n sound would be comperable and performs well at 9" or pink fluffy at 12" or deeper. 36" of pink fluffy absorbs down to 20hz
Attached Thumbnails
3.5" or 5.5" thick acoustic panels?-screenshot_20191121-155254_firefox.jpg  
Old 3 weeks ago
  #18
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Quote:
Originally Posted by dustcloud View Post
That seems to be a common complaint, even in construction jobs where its being installed behind drywall. Does it mean that a 3.5" batt is only going to deliver 2.5" performance? Or is it just something to keep in mind when planning the dimensions of the panels?
It's a little bit of both. The main thing you want is total depth. If the material gets more compressed then GFR goes up. But performance wise there is not a drastic difference between compressed 2.5" with 5.5" air gap vs 3.5" with 4.5" air gap.

The thing you should decide first is how much depth you can realistically do.

Last edited by johnnyc; 3 weeks ago at 01:50 AM..
Old 3 weeks ago
  #19
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Quote:
Originally Posted by dustcloud View Post
So how are we supposed to read the published acoustic specs for Ultra Touch in light of those graphs? Ultra Touch claims to have a very high NRC all the way down to 125Hz. But those figures are based on tests that used a 'Type A Mounting' which apparently means the material was directly mounted on the surface with no air gap. Are the published specs just not reliable? Or is there something else at play here?
Low end response is fine but low mids are horroble. Why why why?

Absorbtion panels for early reflection

Welcome to enter the rabbit hole …
Old 3 weeks ago
  #20
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Thank you for the links. Lots to digest.

If i'm understanding everything correctly, the low frequency absorption specs are more or less useless because the test environments don't properly mimic the diffusion in real world scenarios. So even for broadband absorption at the first reflection points you need really thick panels and the GFR should ideally be matched to the thickness of the panel. Which is why Jason is recommending roxul and a lot of it.

What's considered low frequency here? When I play around with the calculator it seems like the drop in real world performance can start as high as 700Hz.

Also, it seems like the shape of the absorption curve can vary wildly based on the depth of the panel in relation to the size of the air gap. A 5.5" panel with a 4" gap has a relatively smooth curve but a 3.5" panel with a 4" gap has a lot of peaks and valleys throughout the midrange and it looks like you can get better results with a smaller gap.
Old 2 weeks ago
  #21
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Quote:
Originally Posted by dustcloud View Post
Thank you for the links. Lots to digest.

If i'm understanding everything correctly, the low frequency absorption specs are more or less useless because the test environments don't properly mimic the diffusion in real world scenarios. So even for broadband absorption at the first reflection points you need really thick panels and the GFR should ideally be matched to the thickness of the panel. Which is why Jason is recommending roxul and a lot of it.

What's considered low frequency here? When I play around with the calculator it seems like the drop in real world performance can start as high as 700Hz.

Also, it seems like the shape of the absorption curve can vary wildly based on the depth of the panel in relation to the size of the air gap. A 5.5" panel with a 4" gap has a relatively smooth curve but a 3.5" panel with a 4" gap has a lot of peaks and valleys throughout the midrange and it looks like you can get better results with a smaller gap.
To over simplify things terribly, the further away from the wall the front of the absorber, the deeper it will absorb. A full fiber fill with no airgap will offer smoother absorbtion within reason. The lower the GFR, the deep the trap must be, but the more efficient it will be at absorbing low frequencies

Low = 20hz-100hz more or less imo
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