Control Room ceiling "acoustic hangers/bass trapping&qu

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Control Room ceiling "acoustic hangers/bass trapping&qu

Postby Sen » Sat Aug 21, 2004 1:27 am

Hello Eric, Scott and others.
I'm really enjoying the forum so far and learning quite a bit of new stuff...thank you all for that :)
I'm in the construction stages of my studio building. The outer shell has been built (230mm cement brick walls) and I'm fine tuning my studio and control room designs at the moment, before I start with the inside construction.
My control room will be 5.22 m long, 4.5 m wide and the wall height is 3.6 m with cathedral ceilings peaking at 5.3 m. Now, I would like to construct my control room ceiling so that it starts at about 3.4 m at the front and slopes up towards the back of the room (@ approx 12 degrees). In the space between my cathedral ceiling and the control room (false/light) ceiling I will be installing lots of acoustic hangers trying to create a large bass trap there. I was planning to construct the ceiling in the first part of the CR of light materials (10-15mm MDF?) and the rear part of the room (starting just after the mix position) would just have cloth over a light frame representing the ceiling. Now is this good idea? Should I go with MDF light ceiling all the way to the rear leaving vents in it for the sound to get into the hangers and get trapped..or perhaps go with the cloth all the way, even in the front of the room?
I hope you understand what I mean, and if you would like to see a picture I could do that as well as I have a couple of shots of the finished shell inside.
Just let me know.
Thank you so much in advance for your help.
:)
Sen
Kind regards

Senad
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Postby Scott R. Foster » Sat Aug 21, 2004 6:19 am

Pics???

Hell Yeah!

As to acoustic hangers, I gather they can work well if properly tweaked.

Sounds compicated to me. I would look at that cathedral ceiling vault as a giant room corner just begging for a giant SCA. So simple, so cheap [just like me].

Good Luck!
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Postby Sen » Sat Aug 21, 2004 7:38 am

Mr Foster,
Thank you so much! I'm attaching a picture of the "control room part" of the building looking from the "studio part" of the building.
If I'm not wrong (just did a search on this) :) SCA stands for Supertips Corner Absorber ..right?? How is it made? :oops: How would I incorporate them into those vaulted spaces? :(

Thank you so much again!
cheers
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Kind regards

Senad
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Postby Eric.Desart » Sat Aug 21, 2004 9:43 am

Hello Sen,

I had seen them before.
http://johnlsayers.com/phpBB2/viewtopic ... 4999#14999

I'm not used to use those hangers.
Spoke once before about them.
I once compared them with traditional wool at a cavity applications for bas trapping purposes.
I should have to find old archives back for those hangers.

I still find it a bit strange why they work that well.
However the advantage was in favor of the wool on a cavity principle.

One however should be really carefull with those hangers. If they are far away from a reflecting backing (your ceiling) and those distances between them become relative large, they start working as baffle applications as you can see on the Sonex site.

Now typical for baffle applications is that they become BAD for low frequency absorption.
They start acting as absorption in a diffuse field, loosing the relationship with the controled reflection of waves against reflective boundaries.

Rougly one could say that a freehanging mineral wood board must be double as thick as the same board against a wall in order to show the same low frequent absorption.

Now, one can state: hé but this aren't baffels, because there is a reflective core in the center (wood, metal, whatever).
On my playing with baffels doc you see 2 times 2 measurements, one with and one without center core.
http://www.acoustics-noise.com/AFBsite1 ... affles.doc
This does not improve low frequent absorption as often is wrongly suggested.
You can also see that baffels as such are the worst way one can use absorption material for low frequent absorption.

What I'm saying is that the reason hangers work is more complicated, and is more related to the way they are positioned versus one another and de reflective boundaries than the hangers in itself.
Since this relationship is almost nowhere mathematically defined, I find it risky once you deviate from the proven exactly copied applications.

But the John Sayers site is more specialized in this type of application.
For me personally, I once left this approach (after studying it), and should need to completely refresh it to explain it better (for me personally it became mainly interesting as theory for the theory and curiosity, not anymore as practical application).

I want to say that this was and is still standard for many designers. So practice proofs that it works. But as you know judging a studio is often very subjective.

I assume Scott's suggestion for the huge SCA becomes more a suspended ceiling, with thick boards. I'm not sure anymore in how far those corner reasonings apply with those size ratios.
Also one should be careful with wool at a distance which becomes too large, since than the boards will start acting as in a free field (frequency dependent).
This means if one lowers a suspended ceiling, as such enlarging the cavity, the reasoning that low frequency absorption will continue to improve is wrong.
Once the diffuse field (reflections from multiple directions) become dominant or important versus the controled reflection behavior of the single reflective boundary, such boards start acting again as boards acting in a free field.

One must compensate that by thickening the boards (or putting a fluffier = cheaper) thick layer on top.

As a general rule: material free in space becomes less effective in the low frequencies, when it looses his relationship with the controlled reflection patterns in the vincinity of a reflective boundary.
The often heard approach that free hanging material can be striked by waves from different directions as such enlarging the useful absorption surface, which in its turn should relate in increased absorption is very questionable, and only valid when the edge effect (diffraction) becomes defining, which is not the case when freehanging objects are used in arrays.
Reflections can be compared with mirror sources. They exist always, whether the material hangs free in space or against a wall.

If that should not be the case, then a relative thin ceiling suspended at about ear height in a room (forget nodes antinodes here) should be superior in the low frequencies.
I can assure you it isn't, such an application will show a very poor low frequent behavior.

If the ceiling only must be functional, the cheapest manner to handle this is hanging a suspended ceiling profile system 600 x 600 mm = ca 2' x 2', putting additional wool on top, in which you can hang absorption tiles (making complete ceiling a bass trap), and substitute whereever needed, for reflection or diffusion, other tiles of whatever reflective or semi reflective board.

You can even hang diffusers in them.
Such an approach allows you to play with the tuning of the studio afterwards.
The advantage of reflective tiles is that they also act as diffuser (depending on sizes covered area), without or with limited effect on diminishing the bass trapping properties.
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Postby Sen » Sat Aug 21, 2004 10:28 am

Mr. Desart, thank you very much for your reply. :)
I actually had to read your post twice to get it sunk into my head a little (sorry I'm not very smart at this :( ) but I think you gave me a good reason to think about using these hangers. Thank you!
As you mentioned, it would certainly be very hard to work out the exact relation in the space between the hangers and the reflective surface (ceiling) and between the hangers them selves, so that one could come up with the right low freq. absorption formula.
Now..
Eric.Desart wrote:Also one should be careful with wool at a distance which becomes too large, since than the boards will start acting as in a free field (frequency dependent).
This means if one lowers a suspended ceiling, as such enlarging the cavity, the reasoning that low frequency absorption will continue to improve is wrong.
.


Eric, are there any general guidelines as to when this distance would start becoming unfavorable at certain frequencies for a given thickness and density of an absorbent material?

Now typical for baffle applications is that they become BAD for low frequency absorption.
They start acting as absorption in a diffuse field, loosing the relationship with the controled reflection of waves against reflective boundaries.
What I'm saying is that the reason hangers work is more complicated, and is more related to the way they are positioned versus one another and de reflective boundaries than the hangers in itself.



So I'm guessing that one would be better off using all these absorbent materials for hangers if they simply randomly hung some solid, reflective boards (on their own) and absorption boards (on their own) so that you would get many "little baffles" in front of (or at the back of) many "little walls"!!? Or am I far off the track?? :mrgreen:

So Scott, the suggested SCA would just be thick absorptive clouds or....??

Thank you all very much for your time and effort!
Kind regards

Senad
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Postby Eric.Desart » Sat Aug 21, 2004 11:33 am

Sen wrote:.....Mr. Desart, ......

........Eric, are there any general guidelines as to when this distance would start becoming unfavorable at certain frequencies for a given thickness and density of an absorbent material? ......

...........So I'm guessing that one would be better off using all these absorbent materials for hangers if they simply randomly hung some solid, reflective boards (on their own) and absorption boards (on their own) so that you would get many "little baffles" in front of (or at the back of) many "little walls"!!? Or am I far off the track?? :mrgreen:

So Scott, the suggested SCA would just be thick absorptive clouds or....??

1) :P Sen, I'm Eric, Desart is a brand name (lots of them). Desart is used in formal circumstances and in informal circumstances mainly when I did something wrong :twisted:

2) I have no specific rule, in this sense that it depends on the sound field itself. In a diffuse field highly reverberant this property will become much faster dominant than an absorption material in front of a free outside wall, where this single reflection path remains dominant.
And it's one of those things which is difficult to test, since you're searching for very low frequencies (too low in the reverb room).
But we can notice this phenomenon in real live projects, where sometimes large cavities are used since one wants to use the empty space for technical things (ventilation, ducting etc).
A fun example: I once (long ago) was confronted with a ceiling added to improve the extremely high reverb/echo in a sport hall with ca 14000 seats and atlethics track in the center.
A really large good absorptive ceiling was hung at large distance of the ceiling to avoid the supporting steel structure and to flatten the center of the hall..
It was as if they were forgotten (matter of speech) to do anything, since the mid, mainly high frequent absorption of those 25 mm tiles was significantly masked by the air absorption of this huge (really huge) sport hall. It really absorbed as 1/2" absorbant against a wall, but in such a huge volume air absorption is very defining already.(speech intelligibility afterwards was about as bad after as before).

In your case I should double the thickness of the wool in the center of the room to 8-10" and to the edges if you come close to the ceiling 2" to 4" (depending on net height below ceiling, I should preffer 4" using the bihedral edges of the ceiling maximal) This musn't be nice gradual.
My simple reasoning is that saving cheap wool is a false manner of saving money. And exactly investigating it cost a multiple of energy and time of just buying and mounting it.

3) The little walls: I'm sure you can find more things to keep me busy with. There are numerous effects (all frequency related), none of them worth discussing here and little sense in practice. Why should you want to absorb sound at a little walls? Is it to safe the main wall behind it for bad times? :wink:

You can of course work with Scott's clouds: It's an alternative suspended ceiling more as individual isles.
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Postby Sen » Sat Aug 21, 2004 11:55 am

Eric.Desart wrote:1) :P Sen, I'm Eric, Desart is a brand name (lots of them). Desart is used in formal circumstances and in informal circumstances mainly when I did something wrong :twisted:



:mrgreen: Ok , understood Mr. Desart (informally)...Just Kidding

3) The little walls: I'm sure you can find more things to keep me busy with. There are numerous effects (all frequency related), none of them worth discussing here and little sense in practice. Why should you want to absorb sound at a little walls? Is it to safe the main wall behind it for bad times?


Well, I probably wouldn't do it with the "little walls".. :D ..I was just trying to illustrate the way I understood your explanation of the behaviour of those things in a given space...but of course....we still have the main walls :D ...
....for this MAYBE :bang

You are a great help Eric...as always...
thank you so much.

cheers
Kind regards

Senad
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Postby Scott R. Foster » Sat Aug 21, 2004 2:20 pm

Sen:

See... complicated... I warned ya.

:D

What goes between and on the joists? Thermal insulation covered by a thick layer of gypsum board I assume - am I close?

If so, here's what my first thoughts -as follows:

1) Finish off the ceiling to match you TL needs;

2) Room volume = good [higher modal density - etcetera] so installing a flat ceiling at wall height will take a large volume away from the room. Reducing volume = bad. Don't do that - snat! Instead move higher up into the ceiling vault and build a frame parallel to the floor at the apex of the ceiling's vault large enough to accommodate mineral wool absorptive panels 4 feet wide. If you like you could use 2x4 ceiling tiles run long ways from the two legs of the apex in a standard drop ceiling grid, or you could fabricate a light wooden frame and drop 703 panels into the frame. You could go more then 4' wide, but Eric suggest a diminishing return - your call - but 4' seems pretty good to me - 6' or even 8' wide wouldn't scare me off though - particularly if you think you need it based on your overall treatment plan.

Something like this:

Image

I like the standard ceiling tile idea because it will result in a neat finish with no extra trouble, but 6" 703 would be a great start acoustically and a 54" bolt of cloth and staples would be a petty easy way to cover your work. If you go with a wooden frame and 703 with a cloth cover [or equivalent - rockwool?], just cover your staple lines with strips of painted wood and you'd get a nice framed look.

3) As you install the ceiling tiles / mineral fiber panels fill the gap above each with a miner fiber "stuffing". Something like 701 might work... or a pyramid stack of extra dense flavored roll insulation.

When you are done you have a 4' to 8' wide SCA with stuffing running the length of the room - Woot! But you have also left the greater part of the ceiling vault's acoustic volume in your room.

The sections of the ceiling left open could have flat absorbent panels interspersed with polys, or even light fixtures covered with polys made of transparent material [Plexiglas?] like Eric used at Galaxy [got pics Eric?]... maybe panels for the front and rear of the room, and a row of hanging lights with polys hung below the lights for the rest?

Good Luck!
SRF
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Postby Sen » Sat Aug 21, 2004 3:01 pm

Scott R. Foster wrote:Sen:

See... complicated... I warned ya.

:D


Hi Scott,
yeah it has been since I started building :mrgreen:

What goes between and on the joists? Thermal insulation covered by a thick layer of gypsum board I assume - am I close?


Yeah pretty close. At the moment there's only thermal/foil insulation and cement roof tiles on top of the joists (rafters) so I haven't really got a leaf of mass there. So, between the joists (which are 200mm wide or deep down looking from the top :) ) I'll be putting first a couple of layers of drywall (could put an additional layer of a different material) in a "sandwich" with differing thicknesses between the layers (all together probably a 50mm leaf of mass). Then I was planning on putting RC onto the joists (perpendicular to them) and stuffing the rockwool between the joists on top of the RC. what's a good density BTW? 3 pcf?
And then hang a double or triple layer of wallboard (and something else..MDF?) onto the RC, adjusting the spacing of the RC to accomodate the total weight of the attached layers. So basically not much of the room volume would be lost, as I'm following the joists with the ceiling. :)

The sections of the ceiling left open could have flat absorbent panels interspersed with polys, or even light fixtures covered with polys made of transparent material [Plexiglas?] like Eric used at Galaxy [got pics Eric?]... maybe panels for the front and rear of the room, and a row of hanging lights with polys hung below the lights for the rest?


Yess! Please Eric if you could find some pics. I visited the Galaxy site, but it seems to have changed and there's no more good pics that were on there... :(

Scott thanks again for the help and the useful illustration..thats great..!
cheers
Kind regards

Senad
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Postby Eric.Desart » Sat Aug 21, 2004 4:36 pm

Scott, Sen,

In fact I never took pictures myself, and at the time I'm not sure they used digital cameras. I know they have lots of them but I should ask.
At the time I never was on the net (better I didn't knew the net).
Indeed I saw myself recent that the site changed.
I see Wilfried (the owner) tomorrow (indeed on Sunday - studio people don't know week from weekend, day from night), will ask for some more pictures.

Below one picture: It looks as if the diffusers are durty (not sure, can be a light effect) but they are clear transparent.
They are spanned together with thin cables and special minor clamps at the top edges (size 4' x 8').
In the room itself from beneath one can very well see the ceiling through them (but is black painted).

This hall, including diffusers is modelled with ray-tracing, but additionally fine-tuned afterwards.

I saw now that GALAXY is on the cover of the most recent MIX-Magazine of Aug. 2004.
http://mixonline.com/mag/audio_galaxy_studios/
This guy on the picture is this Ronald Prent I recently referred to (the guy with the incredible hearing).

Also saw that they made a virtual instrument from their Steinway D Grand Piano in the picture.
http://www.soundsonline.com/sophtml/det ... sku=BS-384

QUESTION:
Scott do you call this POLY's or NOT ???????????
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Postby Sen » Sat Aug 21, 2004 11:30 pm

Hi Eric,

Yeah, i think I've seen this pic on the web site, but everytime I look at that hall my jaw just drops :mrgreen:
So Eric, are the windows to the left of the picture the mentioned 11 cm glass??
If so, do you remember how they put them in place, what kind of crane, how did they hold them up?? Those would have a bit of weight in 'em hey :)
Eric, If you could get some pics from Wilfried that would be great!!

Thanks so much
Have a great Sunday :)
Kind regards

Senad
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Postby avare » Sat Aug 21, 2004 11:59 pm

I seem to recall someone once askiing on another website about the relationship of the two designers of the acoustics for Galaxy rebuilds.

Please note the lines in the lower left corner of the image.

Andre
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Postby Eric.Desart » Sun Aug 22, 2004 7:00 am

Sen,

Those thick window panes are between the control rooms. It should be impossible for whatever factory in Europe to produce those outside Windows in those sizes in this thickness.
In fact: In Galaxy the window sizes were reverse designed in function of measures of the heaviest panes which could be produced and handled, which is +/- 1 metric ton a pane.
I remember about everything, and the rest I can find back, and NO I don't give this design free.
Those details are of no importance in home studio groups.

Avare,

I admit you have an elegant manner of formulating your own question marks :lol:

How Galaxy chooses to publish their studios is up to them.
The text on the picture represents the relationship in function of Galaxy, where Main stands for 90 to 95%, and the recent Mastering for 100%.
The overall acoustic responsibility was mine from the very beginning of the project until as it exists now.
This does not include whatever electronics (I don't know *** about) but building, room and mechanical acoustics.
My relationship with Prof. G. Vermeir is hardly stuff for newsgroups, but has always been good.

Such a project, at the boundaries of what's physically possible, and where hardly any analogies are published is a very interesting study object for any university.
Several measurement techniques were applied and compared there, where I was honored with the co-operation of Prof. Vermeir and his Acoustics lab.
We measured down to 0 dB levels, to assure suitable dynamic ranges, needing measurement equipment incl. microphone with a noise floor of -2dB (unheard of in the audio world)

E.g.: It maybe sound as just another number but measuring accurate Rw/music/dB(A) transmission loss values exceeding 100 dB (STC ca 103 dB) in 1/3 octave analysis from 50 Hz (and lower but with question marks) and up is much easier said than done.
Note that Galaxy exceeds the TL values of official accredited labs. It should be impossible to measure the TL value of those CR windows in a lab, since then, even when it should be mechanical possible to mount them (which isn't), I should measure the TL value of the lab itself, not the windows.
The NR or dB level of the ventilation at full capacity stays below or in the worst case equals the noise floor of the best audio microphones.

And, to correct Ethan's wishfull thinking (there aren't poorer people than those needing to degrade others to confirm their own pseudo qualities):
I NEVER was or acted as assistant of a Prof., but as R&D acoustician, was managing director of the Belgian establishment of one of the top European hi-tech industrial acoustic companies (with establishments outside Europe as well). And industrial does not only relate to technical applications, but also acoustic measurement facilities, environmental, building and room acoustics.
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Postby Sen » Sun Aug 22, 2004 7:39 am

Eric.Desart wrote:Sen,

Those thick window panes are between the control rooms. It should be impossible for whatever factory in Europe to produce those outside Windows in those sizes in this thickness.
In fact: In Galaxy the window sizes were reverse designed in function of measures of the heaviest panes which could be produced and handled, which is +/- 1 metric ton a pane.
I remember about everything, and the rest I can find back, and NO I don't give this design free.
Those details are of no importance in home studio groups.
.


Oh no, no Eric. Not for one second did I think of getting any designs out of you or contemplating installing anything like those windows in my studio :) .
The question was just pure curiousity.
I already greatly appreciate your help and contributions on the News groups, and am always happy with what ever knowledge I can absorb from your posts and those with similar knowledge and experience as yours (probably not many :D )
Thank you again so much.

BTW, you guys (Eric and Scott) have talked me out of those hangers :) . I had problems figuring out how to hang them anyway, so it's a bit of a relief. And after reading a few posts on those "chunks", SCAs and other stuff, I think they'll turn out being pretty effective. ...well I hope anyway

P.S. Eric, any better pics of those "pollies" from Galaxy :mrgreen:
Kind regards

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Postby Scott R. Foster » Sun Aug 22, 2004 1:32 pm

Eric:

Sure looks like a poly to me... I can't imagaine those panels bending in a true circular curve given your description of how they were made.
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Re: Control Room ceiling "acoustic hangers/bass trapping&qu

Postby Boutter » Mon Jun 28, 2010 10:01 pm

Hello Everybody,

i am going to construct my studio and here is the design. This is entirely my own design so am not sure as how well it will work.so please let me know about its accuracy.

The exciting feature about this design is that the back wall opens in a cavity which is 3.5' to 4 feet wide.The Cavity in the back wall as well as ceiling is full of acoustic hangers. The Design also incorporates Quadratic Residue Diffusers on the ceiling and side walls, Slat resonators and Acoustic reflector on the back wall and obviously bass trapping in the corners.The front wall is essentially curved.Based on my research done on internet i have decided to angle side walls from 4 - 8 degrees.The ceiling is slanted between the angles 8 - 15 degrees.

The height of the ceiling varies form 9 feet in the front to 14 feet at the back.

I am not very much Sure about the floor (wooden vs concrete...???)

The dimensions of the untreated room are 14' (Height) 17' (Width) and 19.75' (Length) in conformity with the Room Ratio 1:1.21:1.41 and the room measures 9' (Height) 14' (Width) 17'(Height) after the angled walls and false ceiling.

*I am going for close Monitoring.

#I am looking forward for Ethan Winer from Real Traps to add some suggestions.

Thanks.
Boutter
 

Re: Control Room ceiling "acoustic hangers/bass trapping&qu

Postby Scott R. Foster » Mon Jun 28, 2010 10:56 pm

good luck!
SRF
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Re: Control Room ceiling "acoustic hangers/bass trapping&qu

Postby J.F.Oros » Mon Jun 28, 2010 11:58 pm

A policeman patrolling a dark alley one night sees a drunk guy, who was leaning on a light pole and kept looking at the ground around it.
"What are you doing here Sir ?"
"Errr...*hic*...i've lost my keys somewhere along this alley.."
"Oh?? So why are you searching them here under this pole ?"
"Errr...*hic*...'coz here's more light...*hic*..."
:mrgreen: :mrgreen: :mrgreen:
... studiOTipper ...
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Re: Control Room ceiling "acoustic hangers/bass trapping&qu

Postby Scott R. Foster » Tue Jun 29, 2010 4:45 am

8O
SRF
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