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Does it matter how high a fully absorptive ceiling is? Studio Monitors
Old 20th April 2018
  #1
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Does it matter how high a fully absorptive ceiling is?

If you have a thick absorptive ceiling with good absorption down to low frequencies then does it matter how high the rigid boundry behind it is? So let's take a 10' and 9' room with the same 1' absorptive ceiling. Does one have a benefit over the other?
Old 21st April 2018
  #2
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Yeah.... 10' is higher so you have more room volume...
Old 21st April 2018
  #3
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Quote:
Originally Posted by attaboy_jhb View Post
If you have a thick absorptive ceiling with good absorption down to low frequencies then does it matter how high the rigid boundry behind it is? So let's take a 10' and 9' room with the same 1' absorptive ceiling. Does one have a benefit over the other?
well it matter in the sense of drum overheads. Generally you want as much space as possible between OH mics and the ceiling. Although an extra foot may not be noticeable.
Old 21st April 2018
  #4
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Quote:
Originally Posted by Jason Foi View Post
Yeah.... 10' is higher so you have more room volume...
yes but since the ceiling is fully absorptive, what difference does it make? Even if the ceiling is 12' and fully absorptive, what difference does it make?
Old 21st April 2018
  #5
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Quote:
Originally Posted by Cardinal_SINE View Post
well it matter in the sense of drum overheads. Generally you want as much space as possible between OH mics and the ceiling. Although an extra foot may not be noticeable.
Even though the ceiling is absorptive so the reflections above are absorbed?
Old 21st April 2018
  #6
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Quote:
Originally Posted by attaboy_jhb View Post
Even though the ceiling is absorptive so the reflections above are absorbed?
not sure what the question is,
Old 21st April 2018
  #7
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Quote:
Originally Posted by Cardinal_SINE View Post
not sure what the question is,
You said that "you want as much space as possible between OH mics and the ceiling"

So I wanted to know if you think that this is the case even with a fully absorptive ceiling? The reflections above will be absorbed so what difference does it make how high above you it is? This is the question in the OP:

Does it matter how high a fully absorptive ceiling is?
Old 21st April 2018
  #8
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Quote:
Originally Posted by attaboy_jhb View Post
You said that "you want as much space as possible between OH mics and the ceiling"

So I wanted to know if you think that this is the case even with a fully absorptive ceiling? The reflections above will be absorbed so what difference does it make how high above you it is? This is the question in the OP:

Does it matter how high a fully absorptive ceiling is?
it's definitely going to sound different than a high ceiling. You can get good results with your setup though
Old 21st April 2018
  #9
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Quote:
Originally Posted by Cardinal_SINE View Post
it's definitely going to sound different than a high ceiling. You can get good results with your setup though
Ok, but why? The sound goes up into the trap, gets absorbed and doesn't come back down to the mic so what is the difference theoretically?
Old 21st April 2018
  #10
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You keep saying fully absorbant, but at what frequencies? 300mm of absorption is not "fully absorbant".
Old 22nd April 2018
  #11
What DPower said. 1' of bass trapping is not nearly thick enough for the frequencies that might cause modal issues between the ceiling and floor. I've worked in anechoic chambers with 6' cones on all six surfaces (chicken wire floor) that we're still only reliable down to maybe 40 or 50 Hz. We were testing smaller loudspeakers, so it was fine that. We went outside in an open field for lower frequencies.
Old 22nd April 2018
  #12
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Quote:
Originally Posted by DPower View Post
You keep saying fully absorbant, but at what frequencies? 300mm of absorption is not "fully absorbant".
ok how about 500mm? Obviously the really low frequencies are not going to be tamed by an absorber no matter how thick it is but a 500mm trap is pretty much as "fully absorbent" as you are going to get.
Old 22nd April 2018
  #13
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Quote:
Originally Posted by Jeremiah Sheets View Post
What DPower said. 1' of bass trapping is not nearly thick enough for the frequencies that might cause modal issues between the ceiling and floor. I've worked in anechoic chambers with 6' cones on all six surfaces (chicken wire floor) that we're still only reliable down to maybe 40 or 50 Hz. We were testing smaller loudspeakers, so it was fine that. We went outside in an open field for lower frequencies.
1' of bass trapping will absorb effectively down to around 60Hz but for this discussion let's say a 2' bass trap. So the question is

Does it matter how high a 2' fully absorptive ceiling is?
Old 22nd April 2018
  #14
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Full absorption us pretty much defined as requiring quarter lambda. DD
Old 22nd April 2018
  #15
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Also easy to overlook that NRC or reflection coefficient data, as far as I understand, is measured relative to a wave source that is essentially perpendicular to the material. In this context those figures aren't always relevent to real world application because they don't take into account diffractions from wave sources that hit the surface at more obtuse/accute angles...

If you are putting a mic 1-3 feet away from an absorber, you need to really test the material and the scenario to know that treble reflections/diffractions aren't happening.

I found this out when trying to clean up ER's from my desk, pyramid foam, rated at sufficient NRC to do the job at the relevent frequencies actually made the ER's worse. It seems the sound was diffracting off the pyramids...

Long story short various measurements that you might think are showing 100% absorption don't always take the real world into account.

Also consider that the more dead a space is, the more problematic any remaining specular reflections are...

IMO for these and other real-world scenarios (lower Schroeder frequency etc) the larger volume room is always better provided the larger option doesn't move the room into a really bad room ratio (cube etc).
Old 22nd April 2018
  #16
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Quote:
Originally Posted by attaboy_jhb View Post
If you have a thick absorptive ceiling with good absorption down to low frequencies then does it matter how high the rigid boundry behind it is? So let's take a 10' and 9' room with the same 1' absorptive ceiling. Does one have a benefit over the other?
I think it might be advantageous to think of this question in the inverse of the way in which it is asked here:

The LOWER the rigid boundary of the ceiling, the more absorptive it should be.
.
Old 22nd April 2018
  #17
Quote:
Originally Posted by attaboy_jhb View Post
1' of bass trapping will absorb effectively down to around 60Hz but for this discussion let's say a 2' bass trap. So the question is

Does it matter how high a 2' fully absorptive ceiling is?
Where did you learn this information? The wavelength of 60 cycles is nearly 19 feet. If you employ a quarter-wavelength rule to determine absorption you get to nearly 5' required. Thats assuming you are using material that has a proper coefficient at that frequency. Ok so let's say you have 2' of material. It still isn't enough. You're now at roughly 140 Hz. Want to fully absorb down to 35 Hz? We're talking about a 32' wavelength meaning absorption with proper material at roughly 8' thick. I mentioned something to this effect on the anechoic chamber response.
If you allow some room between the wall and the material you can get away with substantially less, admittedly, but you aren't getting there at 2'.

I'm other words, if you have 15' ceilings you could easily make it work, but then again you wouldn't be having these modal issues.
Old 22nd April 2018
  #18
It should be added that you'll end up with a pretty dead room at frequencies ABOVE the target frequency.
Better to find the locations causing the modal issues and use trapping at those spots - as much as you can - as it's been done for years. Or get higher ceilings to move the trouble frequencies way down.
Old 22nd April 2018
  #19
I'll just answer your original question:

No, it does not matter. If you have a truly fully absorptive ceiling it does not matter how high it is as long as you can work in it. It will be very acoustically dead, however. Height would make a difference if you have reflections off of other walls and wish to bring more life back into the room. A higher ceiling allows more surface area on those walls.
Old 22nd April 2018
  #20
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Quote:
Originally Posted by Jeremiah Sheets View Post
Where did you learn this information? The wavelength of 60 cycles is nearly 19 feet. If you employ a quarter-wavelength rule to determine absorption you get to nearly 5' required. Thats assuming you are using material that has a proper coefficient at that frequency. Ok so let's say you have 2' of material. It still isn't enough. You're now at roughly 140 Hz. Want to fully absorb down to 35 Hz? We're talking about a 32' wavelength meaning absorption with proper material at roughly 8' thick. I mentioned something to this effect on the anechoic chamber response.
If you allow some room between the wall and the material you can get away with substantially less, admittedly, but you aren't getting there at 2'.

I'm other words, if you have 15' ceilings you could easily make it work, but then again you wouldn't be having these modal issues.
This quarter wavelength rule is not really true. Also to answer your question where I got the information... Here is one source (see image attached for a 500mm absorber)

Porous Absorber Calculator

also, I don't really think it is necessary absorbing down to 35Hz.
Attached Thumbnails
Does it matter how high a fully absorptive ceiling is?-screen-shot-2018-04-22-20.33.50.jpg  
Old 22nd April 2018
  #21
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Quote:
Originally Posted by Jeremiah Sheets View Post
It should be added that you'll end up with a pretty dead room at frequencies ABOVE the target frequency.
Better to find the locations causing the modal issues and use trapping at those spots - as much as you can - as it's been done for years. Or get higher ceilings to move the trouble frequencies way down.
I read a post here on GS by Ethan Winer that inspired this post said who said that an absorptive ceiling is essentially an infinitely high ceiling. I guess you will disagree with that then since you seem to think that it won't stop low frequencies. With that point of view you may as well say that you have to have high ceilings to get the low end right and that it is not possible with treatment... especially if we are going with the 1/4 wavelength rule.
Old 22nd April 2018
  #22
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Quote:
Originally Posted by Jeremiah Sheets View Post
It will be very acoustically dead, however.
Unless you have very high ceilings (the actual minimum height I am not sure of but I can;t see anything less than 12' away as being beneficial), you don't want reflections between the floor and ceiling so it should be "dead"
Old 22nd April 2018
  #23
The quarter-wavelength rule is as true as it is defined. Also, your question asked specifically if it matters how high a fully absorbed ceiling is. If you are not worried about absorption at 35 Hz, then yes it does matter how high the ceiling is. If you fully absorbing (which requires the thicknesses mentioned) at all frequencies that effect your listening environment, then it does not matter.
So if you don't want to absorb down to 35Hz, you still need a large enough room to push the room modes below those frequencies.
Old 22nd April 2018
  #24
Quote:
Originally Posted by attaboy_jhb View Post
Unless you have very high ceilings (the actual height is arguable), you don't want reflections between the floor and ceiling so it should be "dead"
It sounds like you've already come to an answer that satisfies you. I'll step aside then.
Old 22nd April 2018
  #25
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Quote:
Originally Posted by RyanC View Post
Also easy to overlook that NRC or reflection coefficient data, as far as I understand, is measured relative to a wave source that is essentially perpendicular to the material. In this context those figures aren't always relevent to real world application because they don't take into account diffractions from wave sources that hit the surface at more obtuse/accute angles...
You can select normal or random incidence

Porous Absorber Calculator
Old 22nd April 2018
  #26
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Quote:
Originally Posted by Jeremiah Sheets View Post
The quarter-wavelength rule is as true as it is defined. Also, your question asked specifically if it matters how high a fully absorbed ceiling is. If you are not worried about absorption at 35 Hz, then yes it does matter how high the ceiling is. If you fully absorbing (which requires the thicknesses mentioned) at all frequencies that effect your listening environment, then it does not matter.
So if you don't want to absorb down to 35Hz, you still need a large enough room to push the room modes below those frequencies.
more data?
Attached Thumbnails
Does it matter how high a fully absorptive ceiling is?-screen-shot-2018-04-22-20.46.59.jpg  
Old 22nd April 2018
  #27
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Quote:
Originally Posted by Jeremiah Sheets View Post
Or get higher ceilings to move the trouble frequencies way down.
But the low ones are the ones that are hard to treat!
Old 22nd April 2018
  #28
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No ceiling, sky visible, is most fully absorbing. 1/4 Wavelength is next best. Then there is reality. Is the question theoretical, hypothetical, or real? DD
Old 23rd April 2018
  #29
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Quote:
Originally Posted by DanDan View Post
No ceiling, sky visible, is most fully absorbing. 1/4 Wavelength is next best. Then there is reality. Is the question theoretical, hypothetical, or real? DD
Ok but no ceiling is not possible so 1/4 wavelength is a must for those who want full absorption right?

Then how can ceiling heights of anything less than 14' be acceptable since the lowest frequencies will require over 6' of treatment?
Old 23rd April 2018
  #30
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what about a 9' ceiling?

I am currently with a 10' ceiling but I need to do soundproofing so I will be left with around 9' in total. This thread is not very encouraging. Is there no treatment that I can have in the ceiling to stop modal problems? I don't want the treated ceiling to be lower than 7'5' so I only have 1.5' to work with. Is this good enough?
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