#1920029 - 04/01/08 10:35 AM
Light weight absorber panels
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Ale Cimadoro
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Registered: 04/01/08
Posts: 6
Loc: Waltham, MA, USA
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Ethan,
I am working on the acoustic treatment of my home studio/practice room.
I play string bass and I use the room pretty much for practicing, but some
times I sketch some things out using my Presonus Firepod, Mac, Cubase, M-Audio 61es controller, String Bass (on Shure KSM 32)and Garritan Jazz and Big Band software.
It is a small room (W: 10', L: 11', H: 8.5') and I am doing the best I can to have the acoustics of the room under control.
My question is about the framing of the absorber panels:
I will make the absorbers and bass traps myself using 2" thick Owens Corning 705 FSK. I read in your paper "Acoustic Treatment and Design for Recording Studios and Listening Rooms" that it will be best if I space the panel 2" from the wall.
Does this means that I need to make the frame (a) 4" thick or can I make (b) 2" thick frame and then use 2" spacers to attached to the wall?
Would I have the same acoustical results in ehter case?
Option (a) will make heavier panels compared to option (b).
Also, is there any light-weight alternative to wooden frames (e.g: steel studs)?
Regards,
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#1920277 - 04/01/08 06:12 PM
Re: Light weight absorber panels
[Re: Ale Cimadoro]
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dogster
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Posts: 17
Loc: Sydney, Australia
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Hi Ale
I have been researching this lately so will attempt to answer (please someone correct me if I'm wrong !).
For bass absorbers (that is, not panel traps), you will get best performance by placing them diagonally across the room corners with the FSK facing into the room. 24" has been recommended as a suitable width, but as with any bass absorber, bigger is better. You will get just as much bass trapping if you place your bass absorbers diagonally across the ceiling-wall corners, or even better, do all corners in the room (or at least as many as you can).
For wall- or ceiling-mounted mid/high absorbers, again you can use aluminium or whatever for the framing, and it only needs to match the thickness of your fibreglass... 2" fibreglass, 2" framing. For mid-high frequency absorption you want to have the FSK facing towards the wall (otherwise it will reflect high frequencies back into the room somewhat) with at least some air gap between the absorber and the wall. Here it is a case of more is better - a 2" gap will give better performance than none, 4" is better than 2". 16" is better again but not practical for small rooms. If it's at all possible use 4" thickness of fibreglass. If doubling up 2 layers of 2" material, then only one should have the FSK backing.
Whether you use wood or metal for your frames, you will get even more performance if you drill large holes or slots in the sides so that the absorption material is exposed along the edges. Presumably you will be covering the fibreglass in some sort of breathable cloth ?
However, if you are talking about making panel traps, then they need to be fully enclosed or sealed airtight against the wall or ceiling. My understanding is they would be less effective if you use a lightweight material for the frames. Hope this helps...
Which leads me to ask a question myself, for those in the know, can 1" MDF (or even 3/4" MDF) be substituted for 1" hardwood for the frames of panel traps ? What about 1" pine ?
Cheers, Stewart.
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#1920724 - 04/02/08 12:19 PM
Re: Light weight absorber panels
[Re: dogster]
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geedee
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If doubling up 2 layers of 2" material, then only one should have the FSK backing.
I have a little question there if I may stewart, I'm using rockwool panels for my aborbers (2x 2" thick panels for each aborber)
I don't know what 'FSK' means...does it refer to the foil backing found on the fiberglass sheets? The rockwool panels I'm using don't have a foil backing, but have more of a very thin netting on the back to keep it together.
I haven't taken the backing off either of the rockwool slabs when assembling the aborbers, but do you think i should remove the backing on one of them as you recommended there with the fiberglass sheets? Bare in mind, this backing on the rockwool sheets is very thin, i doubt that they would reflect a great deal but perhaps you know something more about it?
Cheers
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#1920792 - 04/02/08 01:31 PM
Re: Light weight absorber panels
[Re: dogster]
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Ale Cimadoro
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Registered: 04/01/08
Posts: 6
Loc: Waltham, MA, USA
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Thank you Stewart for your reply.
Acoustic treatment is all new to me; I just read a couple of acoustic tratment books and at this point I have more questions than answers. So I appologize if some of my questions do not make any sense.
Presumably you will be covering the fibreglass in some sort of breathable cloth ?
Yes, I will be covering the panels and bass traps with cloth.
However, if you are talking about making panel traps, then they need to be fully enclosed or sealed airtight against the wall or ceiling.
If I do not understand wrong, to have a 2" thick fibergalss panel traps air-tight, I have to make a 2" thick frame and then attached flat to the wall with no air gaps in between? Don't I need at least a 2" air gap between the wall and the back of the panel trap?
My understanding is they would be less effective if you use a lightweight material for the frames.
Does this mean that a lightweight steel sutd frame is less effective to trap bass frequencies than a wooden one?
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#1920918 - 04/02/08 04:44 PM
Re: Light weight absorber panels
[Re: geedee]
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dogster
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Loc: Sydney, Australia
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Hi Geedee
FSK = Foil / Scrim / Kraft, it's a thin laminated material used in construction to (I think) draft- and water-proof buildings. What you have described doesn't sound like this stuff, and if the netting is thin and breathable it will make very little difference to the performance of the rockwool. I would be inclined to leave it on as I suspect it will make handling and securing the rockwool easier.
While surfing the internet for acoustic treatment info you will also see references to FRK, which is Foil Reinforced Kraft.
For the purposes of acoustic treatment FRK and FSK do pretty much the same thing, apparently.
Cheers,
Stewart.
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#1920954 - 04/02/08 06:13 PM
Re: Light weight absorber panels
[Re: Ale Cimadoro]
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dogster
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Hi Ale,
I just want to make sure we're talking about the same thing here. I think of a panel trap as an enclosed device, where the wall or ceiling provides the backing, as in this article:-
http://www.ethanwiner.com/basstrap.html
The panel traps described in that article use 1" fibreglass (you could use rockwool) and an air gap is part of the design:-
http://www.ethanwiner.com/BTPlans.gif
Note the difference between the Deep-Bass trap and the High-Bass trap is only the depth of the sides, and therefore the amount of air gap between the front of the panel and the back (in this case the wall).
The Mid/High Absorber in the above plans has the fibreglass spaced away from the wall because the side panels are 3" wide. I wouldn't call the Mid/High absorber a panel trap, as it doesn't have the resonating front panel. It would work just as well if it had a 1" side panel and was spaced 2" from the wall, and lightweight steel would work just fine in this application. You could even just cover the rigid rockwool in cloth and dangle that vertically from the ceiling close to the wall, so that there's a 2" gap behind it (although it may sag and end up looking awful).
So if you are talking about making absorbers, rather than panel traps, then you can use whatever you prefer for the frames. 2" rockwool with a 2" gap seems to be a good compromise between performance and space requirements.
But of you are talking about making panel traps like the Deep-Bass and High-Bass ones above, I'm afraid I don't know whether lightweight steel can be substituted for the wood framing. I'm guessing you'd need a certain amount of mass in the sidewalls to make a panel trap effective.
Your thoughts Ethan ?
S.
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#1921864 - 04/04/08 11:09 AM
Re: Light weight absorber panels
[Re: dogster]
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Ale Cimadoro
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Registered: 04/01/08
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Loc: Waltham, MA, USA
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Stewart,
Thank you very much for the explanation; now I can see the difference very clearly. The article and the drawings are great to understand the design/construction.
Thanks again,
Ale.
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#1923550 - 04/07/08 09:05 PM
Re: Light weight absorber panels
[Re: Ale Cimadoro]
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Speaker Boy
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Registered: 02/04/08
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Loc: Santa Barbara, California
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For panel bass traps you cannot easily substitute lightweight steel for the wooded framing. Pine or MDF would work fine. With a room that small Ale shouldn't be using panels bass traps. It doesn't look like Ale is trying to build panel traps.
For Mid/High absorbers you would be better off buying 705 without the FSK backing. Since it is cheaper without it.
Here is a link to a site using corner bead for the framing.
http://www.radford.edu/~shelm/acoustics/bass-traps.html
Jeff
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#1925460 - 04/11/08 10:25 AM
Re: Light weight absorber panels
[Re: Speaker Boy]
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Ale Cimadoro
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Jeff Thank you for your response, but I am a bit confused about this:
With a room that small Ale shouldn't be using panels bass traps.
Jeff
Why shhouldn't I use pannel bass traps?
I use this room primarily to practice (Upright Bass). So the goal here is to have a room tuned for Upright Bass playing and may be some Upright Bass solo recording. I will not use this room for mixing. I know that it is a small room (nothing I can do about it) and I also know that small-rooms/Upright-Bass is not a good combination either.
I have a peak of reberveration/volume at 51hz; this is somewhere between low G and open A (it gets pretty annoying when bowing low G, G#, A). That's why I think that I should have the bass freq under control. So I thought that it will help to use 3 deep bass traps, 3 high bass traps, 2 mid/high absorbers and 2 corner bass traps. Am I on the right track?
A very well known Grammy Awarded engineer told me that since the room is small, I should kill pretty much everything.
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#1925476 - 04/11/08 10:37 AM
Re: Light weight absorber panels
[Re: Ale Cimadoro]
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Ethan Winer
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Registered: 06/12/00
Posts: 5227
Loc: New Milford, CT, USA
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A very well known Grammy Awarded engineer told me that since the room is small, I should kill pretty much everything.
I agree with that. But when a room is very small you'll generally do better with lots of fiberglass traps rather than tuned traps. Even though the fundamental for those low notes on a bass are down around 51 Hz, there's usually more energy at the second harmonic. I suggest you record yourself playing those low notes, then load the file into Sound Forge or equivalent and see if 51 Hz is really the culprit or if it's an octave higher.
--Ethan
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#1925582 - 04/11/08 03:22 PM
Re: Light weight absorber panels
[Re: Ethan Winer]
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Ale Cimadoro
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Registered: 04/01/08
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Loc: Waltham, MA, USA
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Ethan,
[quote=Ethan Winer
But when a room is very small you'll generally do better with lots of fiberglass traps rather than tuned traps.
[/quote]
Are the fiberglass traps you suggest here just rigid fiberglass enclosed by a wooden frame spaced from the wall? (e.g.: 2" fiberglass mounted on a 2x4 frame)
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#1925633 - 04/11/08 06:51 PM
Re: Light weight absorber panels
[Re: Ale Cimadoro]
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Speaker Boy
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Registered: 02/04/08
Posts: 54
Loc: Santa Barbara, California
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Are the fiberglass traps you suggest here just rigid fiberglass enclosed by a wooden frame spaced from the wall? (e.g.: 2" fiberglass mounted on a 2x4 frame)
Yes, but you want to use at least 4" thick fiberglass across the corners. You dont need a frame. A frame just makes the panel easier to mount and you can put the cloth on tighter. You actually get more absorption without a frame.
If you want to you can mount the rigid fiberglass across the corners and then put cloth in front. Here is an example
http://picasaweb.google.com/sauceelectrico/20070505CornerTrapsYCloud/photo#5068310909411450434
In this post http://forums.musicplayer.com/ubbthreads.php/ubb/showflat/Number/1713054/page/6#Post1713054 Alejo asks questions about tuned sealed panels versus fiberglass panels. Several of the big guns answer his questions quite well.
Jeff
Edited by speaker_boy (04/11/08 06:56 PM)
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#1925802 - 04/12/08 08:13 AM
Re: Light weight absorber panels
[Re: Speaker Boy]
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Ethan Winer
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Yes, but you want to use at least 4" thick fiberglass across the corners. You dont need a frame.
Exactly.
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#1933242 - 04/27/08 03:50 PM
Re: Light weight absorber panels
[Re: Ethan Winer]
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Ale Cimadoro
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Registered: 04/01/08
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Loc: Waltham, MA, USA
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Guys,
Thank you guys very much for your input; I build 6 absorber panels.
I just put 4 in the corners and two on the side of theroom and the problem has been solved.
I have a pack of 6 4'x2'x2" Owen Corning 705 FSK in it original packing that I am not going to use. If anyone is interested, please contact me off the list at Info@CimaJazz.com.
Ale.
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