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Predicting the absorption of a corner super chunk bass trap?
Old 18th March 2019
  #1
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Predicting the absorption of a corner super chunk bass trap?

What is the best way to model the absorption of a super chunk? I've just framed out the front corners of my control room with traps that are 60" (152 cm) across the face. The front corners of my room are dead space, so I just went as large as I could without worrying about effectiveness.

Now That I'm about to start addressing trapping for the back wall (where space is more of an issue) I figured it would be good to do some calculations to balance space vs. effectiveness for my back wall.

But when I sat down at SoundFlow, I realized I'm not sure how to calculate the absorptions of a triangular prism.

Any advice would be greatly appreciated!
Old 21st March 2019
  #2
Deleted 451f99d
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Quote:
Originally Posted by logjamparty View Post
What is the best way to model the absorption of a super chunk? I've just framed out the front corners of my control room with traps that are 60" (152 cm) across the face. The front corners of my room are dead space, so I just went as large as I could without worrying about effectiveness.

Now That I'm about to start addressing trapping for the back wall (where space is more of an issue) I figured it would be good to do some calculations to balance space vs. effectiveness for my back wall.

But when I sat down at SoundFlow, I realized I'm not sure how to calculate the absorptions of a triangular prism.

Any advice would be greatly appreciated!
Well I guess it depends a lot on where the sound waves are coming from, where the corner is, how the soundwaves within that corner are moving...

It is not as simple as just having a flat porous absorber and a soundwave hitting it at 90 degrees angle... but then again not every soundwave comes at a regular broadband absorber at 90 degrees either lol so we just take the 90 degrees I gues?! That seems logical... Still

I guess we have to make a premise here first in what "scenario" for what soundwave you want to calculate your absorption coefficient?


So I assume you want to look at these distances with red arrows and not really the green one and compare it with 1/4 wave lengths in order to know your "lowest" you can score... Those are the parts of your bass trap that would absorb the lower frequencies better. Of course some bass propagating vertically through the entire height of it would get some major friction.

Other than telling you these "somewhat" correct things I can't help you more because

1. I am a noob and I just made this up
2. In what actual scenario you want to calculate it for what bass sound direction is unknown...
Attached Thumbnails
Predicting the absorption of a corner super chunk bass trap?-sound-waves-33.jpg  
Old 21st March 2019
  #3
Deleted 451f99d
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Although I do have a question... isn't it logical that you want the rear wall to have the "as big as possible" rather than the front one?

English is not my native language, what exactly do you mean "dead space"? and why does your rear wall have "space problems"?

I have no clue about this... I designed my own studio and had tremendous help here to adjust things in order to get a flat sweep test and I had to ask stuff about every little thing but I could swear I read that couple of times that rear walls should be well prepared for the incoming bass waves
Old 21st March 2019
  #4
Lives for gear
Depends on GFR and density of the mineral wool used.

Play around with: acousticmodelling.com
Old 21st March 2019
  #5
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Quote:
Originally Posted by NoobInAudio View Post
Although I do have a question... isn't it logical that you want the rear wall to have the "as big as possible" rather than the front one?

English is not my native language, what exactly do you mean "dead space"? and why does your rear wall have "space problems"?

I have no clue about this... I designed my own studio and had tremendous help here to adjust things in order to get a flat sweep test and I had to ask stuff about every little thing but I could swear I read that couple of times that rear walls should be well prepared for the incoming bass waves
What I mean by "dead space" is space that cannot be efficiently utilized for other purposes. I wouldn't want to put gear in those front corners, too small for furniture, no need for lamps... so that makes it "dead space." Other than my desk and monitors, I don't need anything else on my front wall, so the bass traps can use all that dead space.

As far as the back wall, that is not dead space. The deeper the treatment on the back, the smaller my floor gets... the closer my couch moves to my desk... if that makes sense. I've attached an image of the studio layout to help it make sense.
Attached Thumbnails
Predicting the absorption of a corner super chunk bass trap?-img_0323-2.jpg  
Old 21st March 2019
  #6
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Quote:
Originally Posted by JayPee View Post
Depends on GFR and density of the mineral wool used.

Play around with: acousticmodelling.com
Yes, I'm aware. However, AcousticModelling only allows for rectangular prisms... not a triangular prism.
Old 21st March 2019
  #7
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tymish's Avatar
 

Quote:
Originally Posted by logjamparty View Post
What I mean by "dead space" is space that cannot be efficiently utilized for other purposes. I wouldn't want to put gear in those front corners, too small for furniture, no need for lamps... so that makes it "dead space." Other than my desk and monitors, I don't need anything else on my front wall, so the bass traps can use all that dead space.

As far as the back wall, that is not dead space. The deeper the treatment on the back, the smaller my floor gets... the closer my couch moves to my desk... if that makes sense. I've attached an image of the studio layout to help it make sense.
My suggestion for the back and side walls is corner trapping at the wall/ceiling corner. Maybe Some trapping on the back wall itself interspersed with diffusion. You don't lose as much floor space. You get more effective lower bass trapping as well. Diffusion keeps it from becoming too acoustically dead while killing possible slap issues. Effective filled bass traps below 100 Hz have to be incredibly deep.
Old 21st March 2019
  #8
Lives for gear
Quote:
Originally Posted by logjamparty View Post
Yes, I'm aware. However, AcousticModelling only allows for rectangular prisms... not a triangular prism.
Enter the average of the thickness of your SSC.

Last edited by JayPee; 21st March 2019 at 09:00 PM..
Old 21st March 2019
  #9
Deleted 451f99d
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Quote:
Originally Posted by JayPee View Post
Enter the average of the thickness of your SSC.
hmm great idea
Old 21st March 2019
  #10
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Quote:
Originally Posted by JayPee View Post
Enter the average of the thickness of your SSC.
This is one option yes. But, considering the face of the of the absorber is not parallel to the back wall, or perpendicular to the side walls, it seems angle of incidence may become a larger factor. I could be wrong on this. I have taken the average and run those numbers. What I was curious about is if there was something a little more scientific than taking the average.
Old 22nd March 2019
  #11
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Jason Foi's Avatar
 

I'm pretty sure the depth the soundwaves reflection "sees" will be dependant upon angle of incidence, yes, but thats not really important since you are concerned with LF absorbtion and in a smaller room arent dealing with ray acoustics at LF. Use the amroc calculator to see how the modes will align in your room (your vaulted ceiling complicates things) and the see if the depth of the trap will be sufficient to treat the mode as it relates to the trap. It will help with overall decay times no matter what, but weather or not it will help treat a modal null is dependant on location/thickness.
Old 22nd March 2019
  #12
Deleted 451f99d
Guest
Quote:
Originally Posted by Jason Foi View Post
I'm pretty sure the depth the soundwaves reflection "sees" will be dependant upon angle of incidence, yes, but thats not really important since you are concerned with LF absorbtion and in a smaller room arent dealing with ray acoustics at LF. Use the amroc calculator to see how the modes will align in your room (your vaulted ceiling complicates things) and the see if the depth of the trap will be sufficient to treat the mode as it relates to the trap. It will help with overall decay times no matter what, but weather or not it will help treat a modal null is dependant on location/thickness.
thanks for the explanation Jason
Old 22nd March 2019
  #13
Gear Maniac
 

I've got a similar design as you! I built my back wall absorber on casters. The middle part at least. It consists of two gobos 40 cm thick with a airgap of 20 cm. So I lose 60 cm floor space. When needing more space I just push the absorber against the wall. That way I gain 20 cm. Could be an option!
Attached Thumbnails
Predicting the absorption of a corner super chunk bass trap?-bakre-vagg.jpg  
Old 22nd March 2019
  #14
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Quote:
Originally Posted by ostfisk View Post
I built my back wall absorber on casters. The middle part at least. ... When needing more space I just push the absorber against the wall. That way I gain 20 cm.
That's interesting! Have you tested that with REW, to see how the response changes? It would be a very useful set of data here, for demonstrating what that extra 20cm air gap does. If you have a chance, please do REW tests with that, in both positions, and post some results here!

If you don't already know how to do that, here's the procedure:
John Sayers' Recording Studio Design Forum •

View topic - How to use REW to analyze the acoustics of your room...
.

- Stuart -
Old 23rd March 2019
  #15
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Temple of Light's Avatar
 

The mighty "air gap" is pretty much the least documented possibility in acoustics, I was just thinking what various air gaps do, aside from the obvious
increase in low frequency absorption. Is there any known test results for panels with a 4", 6", 8" or 12" air gap?
What frequency do each target, and how much of in increase in sabin's does each mounting create?
I'd love to see some test results however informal they may be...
I would think, the further away from the wall the lower the frequency that would be affected.
Any theory in detail as to how this really works would be welcome too...

YYMV

Light

Temple
Old 23rd March 2019
  #16
Gear Maniac
 

Quote:
Originally Posted by Soundman2020 View Post
That's interesting! Have you tested that with REW, to see how the response changes? It would be a very useful set of data here, for demonstrating what that extra 20cm air gap does. If you have a chance, please do REW tests with that, in both positions, and post some results here!

If you don't already know how to do that, here's the procedure:
John Sayers' Recording Studio Design Forum •

View topic - How to use REW to analyze the acoustics of your room...
.

- Stuart -
I have some old measurements from when I built the gobos. In these measurements only the gobos were filled with rockwool. Not the corners. So only the middle part of the back wall. No slats either, just rockwool and fabric. The rest of the room is just like the picture above. No treatment in the ceiling or side walls or anything. Just the gobos!

Room is 4.25x4.35x2.52 m or 13ft11in x 14ft3in x 8ft3in.
Attached Files
File Type: mdat Gobo test backwall.mdat (12.85 MB, 61 views)
Old 13th August 2020
  #17
Gear Nut
Quote:
Originally Posted by JayPee View Post
Enter the average of the thickness of your SSC.
I was thinking the same to average out the thickness but is this a guess or ?
Old 13th August 2020
  #18
Lives for gear
Quote:
Originally Posted by jazztronaut View Post
I was thinking the same to average out the thickness but is this a guess or ?
It was an advice by the great Avare.

Can't remember where he told this but I'm 100% sure of it.
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