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do bass traps and ceiling clouds need rigid back? Bass Traps
Old 29th March 2010
  #1
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do bass traps and ceiling clouds need rigid back?

I am building a number of basstraps and broadband panels... I was planning on building them all the same... 4" of mineral wool. The same standard 2x4 panels are going to be used for everything from corner traps to ceiling cloud to wall panels.

I have come up with a completely different way of building the traps using supplies from home depot where only the edges are bound, and there is nothing but mineral wool to be seen from all sides except for the edges. It is just rigid enough to work, extremely lightweight for ceiling clouds, etc... but it has me wondering one thing...

should I place a board of some sort or some type of material along the back side for best bass absorption?

For instance, I am suspending a few inches down from ceiling for cloud. Does it matter that there is no rigid back to the absorbers? Shoud I create one?
Old 29th March 2010
  #2


The ridgid back will do little for bass absorbtion. It helps if you ever want to take them down and use them as GOBOs, though.



-tINY

Old 29th March 2010
  #3
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Quote:
Originally Posted by CallMeAl View Post

For instance, I am suspending a few inches down from ceiling for cloud. Does it matter that there is no rigid back to the absorbers?
Using a rigid back is the same as mounting the panel flush to the wall. A gap is a good thing as we hit the wave "coming and going" so to speak.... Once when it passes through and then again when it is bouncing back from the wall behind it. Placing a back on the panel eliminates the benefit of a gap and limits the effectiveness of the panel. I would vote no back in most cases.
Old 30th March 2010
  #4


Actually, low frequencies tend to pass right through thin (1/2" or less) pannels.



-tINY

Old 30th March 2010
  #5
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Quote:
should I place a board of some sort or some type of material along the back side for best bass absorption?

For instance, I am suspending a few inches down from ceiling for cloud. Does it matter that there is no rigid back to the absorbers? Shoud I create one?
It is always best to keep the back of the panel open to increase the low end absorption.
Old 30th March 2010
  #6
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What about for a cloud though, where the material may be too thin to actually absorb everything, if you were to hang the cloud at an angle, then sound that does hit the back board of the trap and come back is redirected, determined by the angle at which you hang the cloud, (or first reflection side panels for that matter).

Just curious, as it may be a good compromise for those who may not have the room for 4-6" thick traps.

Though I suppose if you don't have room for trap thickness, you likely don't have room for trap angling.

I'm getting really good at talking myself out of my own ideas
Old 30th March 2010
  #7
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Quote:
Originally Posted by [email protected] View Post
What about for a cloud though, where the material may be too thin to actually absorb everything, if you were to hang the cloud at an angle, then sound that does hit the back board of the trap and come back is redirected, determined by the angle at which you hang the cloud, (or first reflection side panels for that matter).

Just curious, as it may be a good compromise for those who may not have the room for 4-6" thick traps.

Though I suppose if you don't have room for trap thickness, you likely don't have room for trap angling.

I'm getting really good at talking myself out of my own ideas
a 2" trap that is spaced 2" off the ceiling will absorb pretty much everything that would be a problem in that area.
Old 30th March 2010
  #8
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if spaced off the ceiling I would say opened back is FAR better, the reflections off the ceiling can hit the back and get absorbed as well...
Old 30th March 2010
  #9
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ok... thx.

I thought as much except for all the talk about frk.

I hadn't planned on making panels any different whether used for corner traps, broadband panels for point of first reflection...


I definitely will not have a membrane (frk) facing outward in this tiny room... but should I maybe add a membrane to the back of the panels used in the corners only?

Also... trying to get the most bang for the buck here... ceiling is a big area, and it's rather expensive doing 4" treatment for whole ceiling... I was planning on 4" with roughly 4" gap... how big of a difference will it be if I just do 2" on ceiling and make sure to use 4" corner traps wherever possible?
Old 30th March 2010
  #10
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If it was me I would treat 40-50% of the ceiling, depending on other things. In the sweet spot area..
Old 30th March 2010
  #11
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You Yanks just love skinny fibre-glass panels and foam wedges ......
they haven't got a hope of going low enough.
How can you call them "bass traps" ?
Old 30th March 2010
  #12
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Well, two of the traps going up are floor to ceiling in corners with 2 foot diagonal (biggest I can fit)... and I will see what I can do about filling in behind them for more of a superchunk... the rest are all 4" mineral wool.

My biggest concern with ceiling is actually lows... not early reflections. If I only cared about that, I could just do 2" on a few points and be done with it, but I have a small, square 10'7" room with a carpeted floor. Lots of lows from my hr824's, and lows are going right through carpet, and creating standing waves from ceiling, so I was trying to do best possible to trap lows with ceiling treatment as well... as many highs are already killed by carpet.

Also, room will be used for vocal tracking, so trying to minimize reflections for that purpose as well.

attached pic of my plans if it helps... jpeg from sketchup. blue boxes are standard 2x4 foot 4" thick panels... reddish purple color are same material, but odd sizes.
Attached Thumbnails
do bass traps and ceiling clouds need rigid back?-autosave_studio-sketchup-2x4-only.jpg  
Old 30th March 2010
  #13
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if you really want to control the bass in your room by your method the depth of the fibre-glass would need to be about 1 metre (over 3 feet) !!
I suspect that you don't have this kind of space to loose so I would build several helmholtz tuned to the problem frequencies. This is the professional way to do it, ditch the guess work, tune it properly.
Old 30th March 2010
  #14
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ok, but for now... need to get rest of treatment up anyway, so...

should I put frk type backing on corner traps?

Is my ceiling treatment good, or could it be improved?

I still have some bare areas in room, so considering just doing 2" for ceiling, and covering everything in room with 2"... then added 4" traps along all corner edges... which I could afford to d if I don't do 4" for whole ceiling.

If I leave largee bare areas in ceiling, won't I still have big standing waves in those areas?
Old 30th March 2010
  #15
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if you like the idea of working in a padded cell then cover all surfaces with 2 inch or 4 inch !!!
personally, I prefer rooms with life in them so I wouldn't worry about untreated areas. I wouldn't be in a hurry to cover everything in fibre-glass, rooms need careful planning to work properly.
Old 30th March 2010
  #16
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I would agree... in anything other than my tiny square box... seriously small and seriously problematic.

I would certainly prefer "live" room... but all life in this room seems to sound bad, frankly.
Old 30th March 2010
  #17
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Morebass,

Every few months or so, someone comes along and proclaims the inefficiencies of broadband traps.

Suggestions are made in regards to tuned traps.

While I agree on effectiveness, you must admit that there's a lot to the designing of such a beast. Not to mention that we are in most cases discussing rooms of less than 1000 cu. ft. Get 3-4 bodies in a room that small and your center frequency for design is off. In terms of reflections in such "bedrooms", most surfaces are going to need to be treated, as a 20msec. "usable" reflection is hard to come by in a room that's about 10' deep. Broadband traps kill multiple birds with just the one, inexpensive, and easy to implement stone.

Occasionally there's a thread where the OP is interested in the road less traveled, and willing to put in the hours & energy necessary to get there. These are great opportunities for some serious learning. If you plan to come in here and dismiss the tried and true, then I suggest you clear your calendar, and put your time where your mouth is. It's very easy to decree that "absorption isn't the way", but if you have the time and knowledge to come here and design complete room systems for free... more power to you.

For the record, I don't remember anyone ever suggesting foam.

-John
Old 30th March 2010
  #18
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Quote:
Originally Posted by [email protected] View Post
Morebass,

Every few months or so, someone comes along and proclaims the inefficiencies of broadband traps.

Suggestions are made in regards to tuned traps.

While I agree on effectiveness, you must admit that there's a lot to the designing of such a beast. Not to mention that we are in most cases discussing rooms of less than 1000 cu. ft. Get 3-4 bodies in a room that small and your center frequency for design is off. In terms of reflections in such "bedrooms", most surfaces are going to need to be treated, as a 20msec. "usable" reflection is hard to come by in a room that's about 10' deep. Broadband traps kill multiple birds with just the one, inexpensive, and easy to implement stone.

Occasionally there's a thread where the OP is interested in the road less traveled, and willing to put in the hours & energy necessary to get there. These are great opportunities for some serious learning. If you plan to come in here and dismiss the tried and true, then I suggest you clear your calendar, and put your time where your mouth is. It's very easy to decree that "absorption isn't the way", but if you have the time and knowledge to come here and design complete room systems for free... more power to you.

For the record, I don't remember anyone ever suggesting foam.

-John
And that's where I'm coming from. I actually don't mind putting time or effort in at all, but it's not gonna change the fact that I'm in a 10 foot 7 inch square room with an 8 foot ceiling. This room is DESTROYING my mixes. I have given up using anything but headphones until I can get treatment up. I realize it won't be perfectly flat, but in the case of a room where I can barely fit 3 people after the gear, it does seem best to kill everything... then maybe see if I need to do something from there. This is also not just a control room, but will be used to cut vocals and percussion, and I just don't see a benefit of having too many live surfaces in such cramped quarters.

I'd love to move into a bigger mix room and have a different type of discussion, but it's not going to happen this year. I will do what I can to kill lows... including superchunking 2 corners floor to ceiling if budget permits.
Old 30th March 2010
  #19
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OK, point taken Dykstraster......
however you know I'm right. 100mm of Fibre-glass just isn't going to get you in the ball park.
If you all want your rooms to look & sound the same then go ahead with your usual methods. Or you can try & think outside the box and take a different approach.

Oh and, for the record, I only have 30 + years experience working in this field.... so what do I know.
Old 30th March 2010
  #20
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Quote:
Originally Posted by morebass View Post
OK, point taken Dykstraster......
however you know I'm right. 100mm of Fibre-glass just isn't going to get you in the ball park.
If you all want your rooms to look & sound the same then go ahead with your usual methods. Or you can try & think outside the box and take a different approach.

Oh and, for the record, I only have 30 + years experience working in this field.... so what do I know.

Awesome. I truly hope to hear more from you in the future.

Thinking outside the box will get the uninformed nowhere. In terms of acoustics, outside the box thinking often means mattresses. There's specific knowledge needed to implement the types of devices you describe... and it's very much inside a well sealed box of physics. I've been doing my best to comprehend it, and I feel as though after a few years of research, I'm getting somewhere.

Personally, I would never expect someone with the knowledge necessary to design for specifics to simply had it out... and that's what I was trying to say... I'm in no way questioning your credentials.
Old 30th March 2010
  #21
Gear Guru
FRK

I am afraid I must disagree with several posters above. I believe FRK on the back of Cloud panels is very beneficial. I have two reasons for this.
1 FRK on the front of panels is known to enhance LF absorption.
Since the back of the panel is only a couple of inches away, why would the FRK not enhance LF absorption there also? A couple of inches is a tiny tiny fraction of the wavelengths here.
2 I had quite a few panels with FRK on the back in my room, as RFZ and Cloud
I believed that the FRK was unnecessary, and possibly detrimental. I carefully and with great difficulty removed it and reassembled the Traps. AAAARRRGH.
I measured noticeably worse peaks and dips in the LF response immediately.

DD
Old 30th March 2010
  #22
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Quote:
Originally Posted by morebass View Post
OK, point taken Dykstraster......
however you know I'm right. 100mm of Fibre-glass just isn't going to get you in the ball park.
If you all want your rooms to look & sound the same then go ahead with your usual methods. Or you can try & think outside the box and take a different approach.

Oh and, for the record, I only have 30 + years experience working in this field.... so what do I know.

Tuned traps are nice but most smaller rooms have problems throughout the frequency range and broad band can tackle that. I invite you to look at our lab reports to see that broad band bass trapping can do a GREAT job on the low end.
Link to reports of our 244 and Monster trap
GIK Acoustic Panels are tested and certified.
Old 30th March 2010
  #23
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Quote:
Originally Posted by DanDan View Post
I am afraid I must disagree with several posters above. I believe FRK on the back of Cloud panels is very beneficial. I have two reasons for this.
1 FRK on the front of panels is known to enhance LF absorption.
Since the back of the panel is only a couple of inches away, why would the FRK not enhance LF absorption there also? A couple of inches is a tiny tiny fraction of the wavelengths here.
2 I had quite a few panels with FRK on the back in my room, as RFZ and Cloud
I believed that the FRK was unnecessary, and possibly detrimental. I carefully and with great difficulty removed it and reassembled the Traps. AAAARRRGH.
I measured noticeably worse peaks and dips in the LF response immediately.

DD
I don't disagree with you Dan, but I would want to see lab reports on that before recommending it. I will say that you are not out of line to do it your way though.
Old 31st March 2010
  #24
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Quote:
Originally Posted by [email protected] View Post
What about for a cloud though, where the material may be too thin to actually absorb everything, if you were to hang the cloud at an angle, then sound that does hit the back board of the trap and come back is redirected, determined by the angle at which you hang the cloud, (or first reflection side panels for that matter).

This was actually my plan... I somehow missed your post earlier. If u look at jpeg I attached above, it shows angled ceiling panels... and I was thinking same thing... a bit of redirection... though I was planning on using 4inch thick panels and spacing of 2inches to 6inches as they angle from the ceiling.

I don't necessarily know that it's helping anything, but it certainly seems on the surface to make sense.
Old 31st March 2010
  #25
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Lab

Hi Glenn, I don't have Lab tests of course. But unfortunately I have a before and after in the same room. Not done rigorously, but a very clear result.
Worse LF anomalies. On top of that a little theorising....
Surely HF will be absorbed by 3 inches of 705 or whatever. LF, say from 500 Hz down will pass right through the 3 inches. It will vibrate the damped FRK, similarly as it does when the FRK is in front. There will be some absorption. The remaining (most of the) LF will continue to the boundary, bounce back and get hit again by the damped FRK. All good, and no down side that I can see. I can't theorise a way around this. Ideas welcome here! Plus of course, to me pain, I found this to be measureably true. I had to replace the modified traps.

Al, see above, angled panels may reflect below 500Hz back at an angle, ish. This may be of some benefit. The destructive comb filtering, a la Lupo and SAC, could well be more significant in a broadband sense than we are generally allowing.
Thus, you may be right. But I would have those angles redirect away from the listener spot, not towards.
DD
Old 31st March 2010
  #26
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Quote:
Originally Posted by morebass View Post
if you really want to control the bass in your room by your method the depth of the fibre-glass would need to be about 1 metre (over 3 feet) !!
I suspect that you don't have this kind of space to loose so I would build several helmholtz tuned to the problem frequencies. This is the professional way to do it, ditch the guess work, tune it properly.
I've been hunting down all I can find on Helmholtz resonators and so far that's
been very little. I have several books with the various formulas and there are
calculators on the net. One thing that is always missing from the formulas
and calculators is what size and how many resonators you need for a given
application.

There are very few examples of real-world implementations with measurement
data that shows how effective they are.

Given the above I don't think many people could justify the effort needed to
use Helmholtz resonators. They'd have to set up a lab and build countless
prototypes until they got one that not only was tuned to the proper frequency
but was also powerful enough to do the job. Then they'd have to repeat
this for each mode they wanted to deal with.

If you have a source for recipe-like information on designing, building, installing
and measuring Helmholtz resonators I'd truly love to know about it.

Lately I've been reading about using multiple subs to treat the low frequency
modes and that looks quite promising.

Paul P
Old 31st March 2010
  #27
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Glen

the test results for your product prove my point perfectly .....
not really a lot of help below 100hz.
If you want to combat standing waves below that you need to take a different approach.
Old 31st March 2010
  #28
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Quote:
Originally Posted by morebass View Post
Glen

the test results for your product prove my point perfectly .....
not really a lot of help below 100hz.
If you want to combat standing waves below that you need to take a different approach.
Look again. I don't disagree that tuned can be helpful but the 244, monster and tri trap do a great job below 100hz. As does products made by Real Traps which has the same kind of testing. Look at corner mount on the monster trap.



I would say that it is kicking some BUTT below 100hz. heh

Edit: Just to clarify though we do also build tuned trapping in our custom shop when a customer wants/needs them, so I am not against them if it is a good fit for the room.
Old 31st March 2010
  #29
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Going to pickup 60 2foot x 4 foot x 4 inch sheets of rockwool and then go try some ideas from lowes for framing...


anyone got a take on the angled ceiling panels shown in jpeg above?
Old 31st March 2010
  #30
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Quote:
Originally Posted by CallMeAl View Post
Going to pickup 60 2foot x 4 foot x 4 inch sheets of rockwool and then go try some ideas from lowes for framing...


anyone got a take on the angled ceiling panels shown in jpeg above?
I like it.

I don't know that at that thickness, a rigid back would redirect much. Personally, I'd want it breathable so the gapping will better effect your vertical mode.

[EDIT] you may just want to leave a bit of an overall air gap and hang them without overlap. I'm just thinking you're setting yourself up for a lot of hanging logistical headaches, and if you don't get the angle the same on all of the traps, it may end up looking hap-hazard.
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