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whats the relationship between air and absorbtion
Old 16th November 2009
  #1
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whats the relationship between air and absorbtion

I'm building some absorption panels above above my mixing position to stop reflections off the ceiling, and i'm trying to determine whether i should use 1" of 703 with a 1.5" airspace (spaced out with a 2x2) or whether i should use 2" of absorption with a 1.5" airspace.

Or maybe i should go all around thicker with say 2.5" airspace and 2" of 703

How important is absorbing lower frequencies at initial reflection points?

My mixing desk is against a wall, how effective would the 4.5" absorber be at trapping bass if it was in the wall/ceiling corner that is in front of me above my desk?

Im fairly new to this but I've been doing tons of research trying to design a good setup to do my final mixes in

Thanks!
Old 16th November 2009
  #2
Gear Guru
Test it

Some recommend only HF (thin) treatment at the first reflection points. e.g. Ceiling and Side Walls. For most small rooms I believe thicker treatment, plus an equal gap is best.
The ceiling to floor and side wall modes can be just as strong as others.
DD
Old 17th November 2009
  #3
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Quote:
Some recommend only HF (thin) treatment at the first reflection points. e.g. Ceiling and Side Walls. For most small rooms I believe thicker treatment, plus an equal gap is best.
What is the reason for only high frequency absorption on reflection points?

I am also making these bass traps for the side walls and part of the ceiling, and mid to high frequency absorbers on the ceiling and walls. I was planning on doing a 1" 703 panel spaced from the walls with 2x2's for my mid to high range absorbers.

So should I use the same 1" 703+2" airspace absorbers for my ceiling reflection points? Or should i go for something beefier that will cover a bigger range of frequencies?

At the moment i have a bunch of 1" panels all over my room and i think it sounds rather "boxy" as there is only HF absorption.
Old 17th November 2009
  #4
Gear Guru
Basics

There are articles on room treatment at RealTraps and GIK. If you prefer DIY go to Studiotips.com. With respecet, there would be little point in pursuing a Q and A on the basics here. For the moment, I would not build those Bass traps until you are sure they are an appropriate choice. There are reasons why RealTraps no longer make them.
DD
Old 17th November 2009
  #5
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Glenn Kuras's Avatar
Quote:
What is the reason for only high frequency absorption on reflection points?
You can use thick absorption to help the low end, but it generally is not the ideal area. But it can't hurt either.
More about early reflection points here.
What Are Early Reflection Points. SPOTLIGHT:Bob Ebeling - Revolution Studio

Quote:
I am also making these bass traps for the side walls and part of the ceiling, and mid to high frequency absorbers on the ceiling and walls. I was planning on doing a 1" 703 panel spaced from the walls with 2x2's for my mid to high range absorbers.
Those are tuned traps which will work, but most smaller rooms get a better benefit from broad band bass traps. Those are 4" or thicker, straddling corners.

Quote:
At the moment i have a bunch of 1" panels all over my room and i think it sounds rather "boxy" as there is only HF absorption.
1" really is not reaching all that low so you still have the mids and low end bouncing around the room. That is the reason for the boxy sound.
Old 17th November 2009
  #6
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Quote:
Originally Posted by a zombie View Post
How important is absorbing lower frequencies at initial reflection points?
Pretty important in a small room.

Frank
Old 18th November 2009
  #7
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I guess I've been a little bit too general with my questions. I've finally got Room Eq Wizard up and running and tested my room at a few different points.

This is my response at my listening position


There is some pretty bad comb filtering in the mid range and the bass responce varies by about 30db between 100hz and 150hz. I am using yamaha msp5's so the really low bass doesn't exist which is fine for my style of mixing.

I have very limited space to spare because i record every thing in this room which is about 16x11.5 with 7'7'' ceilings. This includes acoustic drums, some acoustic guitar, electric guitar, vocals and percussion.

I realize that a drum room and a control room are two very different things acoustically, but I have already tracked most of the drums for my album and am more concerned with having a balanced mixing space.

Judging by my response chart it seems like i need some serious trapping in the 60 to 300 hz range and broadband absorption in across the entire frequency range

I only have 2 wall/ceiling corners and that i can do any type of bass trapping on and they could only be 1ft triangles. I can only spare about 4" max on any of the walls so i figure the panel traps on Ethan's site would be the only way to absorb effectively in my problem frequency range.

If figured i would build an even number of high and low bass traps and then add absorption to all reflection points of the monitors (including the back wall) and also on the ceiling above the drums. I am trying to figure out how deep i should make the absorbers because a want to avoid the boxy and dead sound that i have right now

Quote:
2" thick panels made from rigid fiberglass or rockwool are the most common product used to treat reflection points, but 4" panels are a great option when additional bass trapping is desired.
Since my room is small and there is so much stuff in it the only ideal spaces are ones that aren't occupied already, so wouldnt it make sense to do as much broadband absorption wherever possible and not do any specifically HF absorbtion?

Is 2" of 703 spaced out with 2x2's a decent broadband absorber?
Attached Thumbnails
whats the relationship between air and absorbtion-response.jpg  
Old 18th November 2009
  #8
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it says here that 2" of fiberglass board is .76 at 250hz which would overlap the panel traps. Would the 1.5" of airspace make it even more effective at 250hz or lower?
Old 18th November 2009
  #9
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I also have some pretty bad modal ringing

Attached Thumbnails
whats the relationship between air and absorbtion-spectral-delay.jpg  
Old 18th November 2009
  #10
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I'm new to Room EQ Wizard myself, and I'm still not sure I'm using it properly,
so can't give you much help. But from your graphs I wonder if you have
calibrated your microphone and soundcard before doing the tests ? How
did you manage to get 130+db's ?

Paul P
Old 18th November 2009
  #11
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Comparing my calculated room modes with my response graph i couldn't help but notice these similarities.


I might be mind ****ing this, but would it make sense to build some of the "better bass traps" that focus on the problem frequencies, and then build some thick broadband absorbers to go in the available corners, say 4 inch thick 4'x4' ceiling traps? in the front corners?
Attached Thumbnails
whats the relationship between air and absorbtion-compring-modes.jpg  
Old 18th November 2009
  #12
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You're over thinking this a little. Basically your room just looks like it needs more broad band treatment and bass trapping. I wouldn't add any more 2" panels, additional air space or not. I'd add as many 4" broad band panels and 6" bass traps as you can manage, leaving an appropriate amount of air space behind each (4"-6"). That will smooth the midrange and deal with the modal stuff around 100Hz.

Frank
Old 18th November 2009
  #13
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There are only a few places on the ceiling where i can spare 6". on the walls i can only spare 4" max so thats the reason for the sealed traps, i need to extend down to 80hz without using 8-12" deep traps.
Old 19th November 2009
  #14
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Quote:
Originally Posted by a zombie View Post
There are only a few places on the ceiling where i can spare 6". on the walls i can only spare 4" max so thats the reason for the sealed traps, i need to extend down to 80hz without using 8-12" deep traps.
A properly built 4" trap with 4" of space will get down that low. We have test results on our 244's that show that. A 6" trap with the same amount of air space will do it better of course.

Frank
Old 19th November 2009
  #15
air gap related question

I am also wondering the importance of having an "air gap" and if filling an air gap with more 703 is preferred over leaving the space/air.

What would be more beneficial:

1) A 4" 703 panel in a corner - this yields an approx 12inch air gap to the corner point

Or

2) A 4" 703 panel with an additional 2 foot wide (so it fits) 4" 703 panel behind it - this would narrow the air gap to 8 inches to the corner point

I ask because doing this will cost money. Logic tells me thicker amount of 703 equals better absorption but I see lots of posts about the benefits of an air gap.

For those interested this is what option two would look like sitting in the corner:

NEST™ Corner Mount System - Ultra Sub Bass Traps Ready Acoustics, LLC - Afforadble, Durable, and Stylish Acoustic Products - Bass Traps - DIY! Solutions - Mounts - Insulation [RANCM] - $299.99 : Ready Acoustics!, Hear - Sound - Better

No I am not buying that product but am considering DIYing something similar if it will increase and extend my low end absorption.
Old 19th November 2009
  #16
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Quote:
Originally Posted by aleatoric View Post
I am also wondering the importance of having an "air gap" and if filling an
air gap with more 703 is preferred over leaving the space/air.
I have yet to hear anyone say that, for a given total thickness, it would be
better to have less insulation plus an air gap than to have just insulation filling
the total thickness.

I believe using an air gap let's you save on insulation, but not on total thickness.

Here is some info on the matter : Effect of airspace behind absorbent

(click on "Page 191 »" to expand the view)

Paul P
Old 20th November 2009
  #17
Lives for gear
to just clarify:

2" panels should have 2" airgap
4" panels should have 4" airgap
6" panels should have 6" airgap

is this what you guys are saying?

i made some 6" 705frk panels but only left 2" air gap...is this bad?

ej
Old 20th November 2009
  #18
Quote:
Originally Posted by PaulP View Post
I believe using an air gap let's you save on insulation, but not on total thickness.
Paul P
Interesting, thanks Paul.

I would love to hear more opinions on this if anyone else has got one!
Old 20th November 2009
  #19
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Glenn Kuras's Avatar
Quote:
i made some 6" 705frk panels but only left 2" air gap...is this bad?
No it is not bad, but you could space it up to 6" if you have the room.
Old 20th November 2009
  #20
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Quote:
Originally Posted by ejsongs View Post
to just clarify:

2" panels should have 2" airgap
4" panels should have 4" airgap
6" panels should have 6" airgap

is this what you guys are saying?

i made some 6" 705frk panels but only left 2" air gap...is this bad?
No it is not bad. Actually it is probably near the maximum (others would misrepresent as optimum) depth for low end absorption and flat absorption response with that particular material's charcteristics. Paul wrote it right in the post previus to yours. For more information start at post 23 in this thread. If you want to get into the deep end read this thread:

Interpreting Materials Gas Flow Properties

There is nothing magic about gaps, or the equal gap/material thickness myth.
Old 21st November 2009
  #21
Lives for gear
hey andre,

thank you for your post.

so would you mind telling me would be ideal air gap for:

4" of 703
4" of 705
6" of 703
6" of 705

also would this change if there is frk facing on the front.

lastly you suggesting that if i had layers of 703 panels with air gaps in between that i would perform as well as a panel equal thickness of 703? for example i ve 3 panels of 2" 703...2 of them i have covered and built in 2" air gap on i have not as of yet (this on has frk facing). anyway i stacked them in a corner for now in the following way.

2" frk 703
2" plain 703
2" air gap
2" plain 703
8" total thickness

would this be roughly equal to 8" of 703 in one panel?

thanks in advance.

ej
Old 21st November 2009
  #22
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Here's my work in progress


Now I'm tired
Attached Thumbnails
whats the relationship between air and absorbtion-cimg7144.jpg   whats the relationship between air and absorbtion-cimg7143.jpg  
Old 21st November 2009
  #23
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Quote:
Originally Posted by ejsongs View Post
hey andre,

thank you for your post.

so would you mind telling me would be ideal air gap for:

4" of 703
4" of 705
6" of 703
6" of 705
There is no ideal air gap. It depends on what you have and what you want to do. For 703 I would not use thicker than 4" of materail. Beyond that I would have the appropriate gap up to 8" or so.

I would not use 705 if I had a choice.

Quote:
also would this change if there is frk facing on the front.
No.

[quote]lastly you suggesting that if i had layers of 703 pane
Quote:
ls with air gaps in between that i would perform as well as a panel equal thickness of 703? ej
I jean the gap between the material and teh hard surface. NOT between the 703.


Andre
Old 21st November 2009
  #24
Lives for gear
[QUOTE=avare;4808186]There is no ideal air gap. It depends on what you have and what you want to do. For 703 I would not use thicker than 4" of materail. Beyond that I would have the appropriate gap up to 8" or so.

I would not use 705 if I had a choice.



No.

Quote:
lastly you suggesting that if i had layers of 703 pane

I jean the gap between the material and teh hard surface. NOT between the 703.


Andre
thanks...i think get it.

so what you are saying it that you would use 4" of 703 and then an appropriate air gap to sort of tune the trap to deal with a rage of low frequencies.

how you do predict what the air gap should be? for a specific example i have an issue around 125hz and 140hz...i think because of the dimensions of my room 14x12x8.6 i have modes there...so is there a graph/chart or formula that would say that to dealing with these frequencies and this thickness of 703 which has these gasflow properties ishould make a panel that has this x air gap? how do you know?

or in this specific instance what would you do?

thank you and i am trying to learn as i go.

ej
Old 22nd November 2009
  #25
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Ahhhh

Finally finished the wall framing, now i just have to put on the caulk, 703 and plywood...then start on the ceiling

The extra deep panels with the 1x4 frames are the "deep bass traps" tuned 80hz to 160hz (one octave). The long panels with no crosspieces are the "high bass traps", they are tuned 150hz to 300hz (also about one octave). The rest of the panels are 3.5 inch absorbers (2 inches of 703 with 1.5 inches of airspace).

Time to kick back, I'll post more pics when I start putting the guts in 'em!
Attached Thumbnails
whats the relationship between air and absorbtion-cimg7146.jpg   whats the relationship between air and absorbtion-cimg7145.jpg  
Old 22nd November 2009
  #26
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Quote:
Originally Posted by a zombie View Post
Finally finished the wall framing, now i just have to put on the caulk, 703 and plywood...then start on the ceiling
I was wondering what all the wood was for, but I'd missed the bit about your
deciding to go with panel traps. Sounds very similar to what ElaineDiMasi is
currently building.

I would really like to hear from Ethan on this since he wrote his article around
fifteen years ago and I haven't heard him mention panel absorbers much at all lately.
I'm also very interested in them.

Thanks for sharing your progress with us. Very interesting.

Paul P
Old 22nd November 2009
  #27
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Quote:
Originally Posted by ejsongs View Post
so what you are saying it that you would use 4" of 703 and then an appropriate air gap to sort of tune the trap to deal with a rage of low frequencies.

how you do predict what the air gap should be? for a specific example i have an issue around 125hz and 140hz...i think because of the dimensions of my room 14x12x8.6 i have modes there...so is there a graph/chart or formula that would say that to dealing with these frequencies and this thickness of 703 which has these gasflow properties ishould make a panel that has this x air gap? how do you know?

or in this specific instance what would you do?

j
For what you are describing use 4" of 703 with a 4" gap. The equal values of material and gap is coincidental.

Andre
Old 26th November 2009
  #28
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yay, finally finished puting up traps, absorbers and clouds.

It sounds WAY better in here now. The panel traps seem to be really effective, and i can feel them vibrating as they absorb bass.

Ill post pics and response chart when i get this room back together! heh
Old 26th November 2009
  #29
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Quote:
Originally Posted by a zombie View Post
yay, finally finished puting up traps, absorbers and clouds.

It sounds WAY better in here now. The panel traps seem to be really effective, and i can feel them vibrating as they absorb bass.

Ill post pics and response chart when i get this room back together! heh
Congratulations!

Andre
Old 27th November 2009
  #30
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Quote:
Originally Posted by avare View Post
Congratulations!

Andre
Thanks!
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