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Author Topic: Meeting hall sound absorption  (Read 3347 times)

garret

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Meeting hall sound absorption
« on: April 11, 2008, 01:17:24 pm »

Greetings, folks.  I've volunteered myself again.   Embarassed  Laughing  I'm helping a local church deal with a noisy meeting hall.  The space has so many reflective surfaces, it's almost impossible to carry on a conversation in there even if you only have two dozen people present.  When you fill it to capacity (200 or so), it's downright painful.

They have a modest budget ($3000-5000), which should be enough to do the job, but probably isn't enough to pay for an acoustics consultant from Chicago or St Louis to travel here and come up with a plan (there's no one local).

I figure they just need some rigid fiberglass panels, wrapped in fireproof fabric, on the ceiling.  But I could use help figuring out exactly how much of the ceiling to cover, what materials to use, and how to attach the panels.

Here are some photos:
http://www.worksongs.net/photos/2008-03-UU/

And some basics about the room:

-- The room is 50 feet by 40 feet, with 12 foot ceilings.  

-- The floor is hard, shiny, linoleum.  For maintenance reasons, they don't want to carpet the floor, although I'm sure that would help the noise problems.

-- They'd like to maintain the aesthetics as much as possible...

-- The ceiling is painted hardwood.   It's a beautiful old space, with the big beams and the woodwork... but there are no absorptive surfaces whatsoever.

-- One side of the room is bay windows, the other is open to a hallway... on the other two sides about a third of the wall surface is doorways, and the other 2/3 is plaster walls, bulletin boards, etc.     It would be hard to find a place for sound treatment on the walls...

-- The ceiling is divided into six or seven bays by big exposed beams.  In each bay there are two hanging pendant lights, with surface mounted electric wiring (in conduit.)  

--  Big ventilation ducts run along the long sides of the room, at the ceiling level.    


Some questions...

1) Do you agree that adding some fiberglass panels on the ceiling is the most cost-effective solution?  They are also considering acoustic tiling.. but the surface mounted wiring makes that tricky... they'd have to put in drop ceiling which would look awful.  They were also considering acoustic paints, but I figure those would be of marginal effectiveness.

2) How much of the ceiling surface area should be covered?  I don't want to deaden the room too much, but I figure it would still be a lively room even if they covered the whole ceiling, what with the floor being so reflective.

3) Is it okay to mount DIY fabric wrapped rigid fiberglass panels on a ceiling?  I don't want to have fiberglass fibers or dust fall out... I've only used that kind of panel on walls where it seems to be fine.  Would it be better to use rockwool or another non-fiberglass product?  Or an encapsulated commercial product designed for ceiling use?

4) If panels are the thing.. how would you go about making them and mounting them on the ceiling?  Or is there a commercial product you would recommend?

Thanks for the help!
-Garret
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Steve Hudson

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Re: Meeting hall sound absorption
« Reply #1 on: April 11, 2008, 03:34:35 pm »

You could hang 4'x2' fabric-wrapped 703 "clouds" using eye hooks and washers with short lengths of chain to suspend them to the ceiling. I did this in my last two tracking rooms. They can hang 4"-6" off the ceiling and improve their efficiency. Stagger them as you must because of the configuration of the beams and light fixtures. The only way to know "how many?" is to install a bunch and see how the room responds.
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garret

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Re: Meeting hall sound absorption
« Reply #2 on: April 11, 2008, 05:14:41 pm »

Thanks, Steve... how thick do you think we should go with for the clouds? 1", 2", 4"?

My guess is that it would be better to cover more of the ceiling with less thickness, than less of the ceiling with more thickness.   But the easiest first thing to treat is the middle section of each bay, betweent the pendant lights.

I suppose we could add treatment to the outside later if the room needs more..

You can see what I mean in this shot:
http://www.worksongs.net/photos/2008-03-UU/slides/IMG_5730.h tml

Or do you you think we should alternate bays to start?  Treat each bay completely, side wall to side wall, then skip a bay and do the next?

I found these just now... they look nice and very easy to install.
http://www.acousticalsolutions.com/products/banners/alphasor b_banners.asp

-G
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avare

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Re: Meeting hall sound absorption
« Reply #3 on: April 11, 2008, 09:05:23 pm »

Your room is 2,000 ft^2.  The bags you linked are over $6.00 per square foot.  That $12,000 just for the bags.

Another alternative is making frames, covering them pretty material and suspending those.

Distribute the panels or bags evenly under the ceiling.

If the absorbers are not against the ceiling, then 2" will fine.

Work on your budget.  Call local suppliers of materials and determine what you can afford.

Andre
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garret

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Re: Meeting hall sound absorption
« Reply #4 on: April 11, 2008, 09:45:59 pm »

avare wrote on Fri, 11 April 2008 20:05

Your room is 2,000 ft^2.  The bags you linked are over $6.00 per square foot.  That $12,000 just for the bags.

Andre


Yikes.. good point.. I hadn't noticed the price.. just the convenience of not needing a frame to mount.

The budget can go higher for the right product... perhaps double.  I need to go make some measurements this weekend... see what we're really talking about.

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gullfo

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Re: Meeting hall sound absorption
« Reply #5 on: April 15, 2008, 12:49:45 am »

i would take a slightly different approach. i'd use 2'x8'x1/4" finished plywood polys with open backs, lined with some 1" cotton batts (avoid fibers), hung down 1 or 2' from the ceiling on chain and hooks, and alternate those with some ceiling mounted absorbers  - simple wood frames with 4" rigid insulation attached with eye bolts and hooks, hanging down 1-4" from the ceiling. on windows and/or walls, i'd hang some heavy folded drapes. on another two walls create some absorption using 2x4 or 2x6 over some rigid insulation covered with cloth.

these should break up the space acoustically, and preserve a lot of energy. if you need to add more absorption you can do that. i think its easier on a tight budget to  work your way up in terms of cost and effort than to try to cover everything and find out you need to remove some...

here's the idea on paper (so to speak).

http://img293.imageshack.us/img293/2952/garrettchurchrf0.th.jpg
http://img166.imageshack.us/img166/9148/garrettchurchrenderdn8.th.jpg
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avare

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Re: Meeting hall sound absorption
« Reply #6 on: April 15, 2008, 12:49:36 pm »

Excellent ideas Glenn.  The thing that drove my recommendation was the budget.  Both of us, and all the regulars here know that $5k could be spent on acoustics for a personal studio.  Your rendering indicates 18 absorbers.  That is about $280 per unit, ignoring the diffusors.  Very realistic if done by oneself.  About right if paying for labour.  We do not know if the labour is by members of the church, or being paid for.

Why the diffusors for a common area?

I find it ironic that with all the projects on the web we have been involved with, that the greatest interaction is on a non studio environment.

Andre
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garret

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Re: Meeting hall sound absorption
« Reply #7 on: April 15, 2008, 03:43:52 pm »

Thanks for the ideas, everyone.   I know this is a low brow situation for a high end forum...  I appreciate your input.

The church will probably have the work done by a local carpenter who has built and installed acoustic treatment panels before (for the Gene Siskel theater in Chicago, among other projects...)  He's not an acoustician, however, so I'm trying to help out a bit.

I'm intrigued by how much diffusion you have in your design, Glen.  This is a very loud room.... ugly sounding too, with tons of flutter echo.  (The ceiling is flat, the floor is hard and shiny, and the walls are square.  Oh, and the bay windows at one end reflect a lot of high end...)  So I can see how diffusion would help to make it a better space, particularly for music events.  

The room is painfully loud when it's at capacity (200 people or so).  I forgot to bring my db meter over the other day, but I'll go back this weekend.   I did a few test recordings, comparing the ambient noise with no one in the room, with two dozen people, and with 100 or so people.  

I've attached the spectral comparison... the bottom line is the ambient baseline, the middle is w/ two dozen people, and the top line is the crowded state.

Somewhere on the net, I found a rule-of-thumb for how much absorption to add to a room... you take the cubic volume of the room in feet, and multiply by 0.03 or 0.04 and you get the sq footage of absorptive material to add.

That works out to 600-800 sq. ft for this room.   I found an insulation supplier in Chicago who can sell us the material at a decent price, and wood for frames and fabric (guilford of maine) is affordable... so it looks doable in the budget if we get some volunteer labor from church members.

An option we are considering is to hang three large panels in each bay... 4 x 8 foot, 2' thick fiberglass with frames + fabric covers.    That would be 96 sq feet of absorption per bay.  The bays are 40 feet by 7 feet wide, so we're talking about covering 35% of the ceiling.

I'm sure it would be better to distribute small panels on the ceiling evenly throughout the room... but I'd think the labor to build and install 90 panels would be significant.   Making 21 larger panels should be more manageable.

A second area we are thinking of treating is the "pockets" at the end of each bay, along the wall.  I think you can see what I mean in this picture...
 http://www.worksongs.net/photos/2008-03-UU/slides/IMG_5732.h tml

Those pockets (between the hvac duct and the ceiling) are 2 ft high by 7ft wide by 2ft deep... and run the perimeter of the room.   I'd expect adding some material there would do some good, and be aesthetically invisible.

Curtains are also in the long-term plans.. but they are a lot harder to get approved by the church committees... too many color choices!   With acoustic treatments we can just go with a neutral that blends in with the walls/ceiling, and avoid the arguments. Smile

-Garret
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gullfo

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Re: Meeting hall sound absorption
« Reply #8 on: April 16, 2008, 10:01:46 am »

the backs of the diffusers would be absorptive in addition to the inter-spaced porous absorbers. the diffusers would help prevent that weird voice getting sucked out of the room effect of a highly absorptive ceiling (which looks to be closer to 12' than 16'). plus any meetings where you have speakers on one end, the room energy will still be good but smoother. that said, the big absorbers should be ok, i don't know if the pockets will be much more use once the big absorbers are in place. the lateral reflections between walls needs to be solved so i'd push the idea on drapes - maybe hung behind on the posts instead of the walls.
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garret

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Re: Meeting hall sound absorption
« Reply #9 on: April 16, 2008, 10:13:13 am »

gullfo wrote on Wed, 16 April 2008 09:01

... ceiling (which looks to be closer to 12' than 16').


You're right... good eyes.

Someone had told me 16ft, but I measured it myself and it's only 11 1/2...
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avare

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Re: Meeting hall sound absorption
« Reply #10 on: April 16, 2008, 01:49:18 pm »

So what is your budget?

Economically,
Andre
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jimmyjazz

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Re: Meeting hall sound absorption
« Reply #11 on: April 16, 2008, 01:54:53 pm »

avare wrote on Wed, 16 April 2008 13:49

So what is your budget?


Original post:

Quote:

They have a modest budget ($3000-5000)

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avare

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Re: Meeting hall sound absorption
« Reply #12 on: April 18, 2008, 01:48:05 am »

jimmyjazz wrote on Wed, 16 April 2008 13:54

avare wrote on Wed, 16 April 2008 13:49

So what is your budget?


Original post:

Quote:

They have a modest budget ($3000-5000)




In the fifth post in this thread, after I pointed out the cost of just the bags to fully cover the the ceiling, it was written:

Quote:

Yikes.. good point.. I hadn't noticed the price.. just the convenience of not needing a frame to mount.

The budget can go higher for the right product... perhaps double. I need to go make some measurements this weekend... see what we're really talking about.


So, after the first reality check, my question.


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garret

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Re: Meeting hall sound absorption
« Reply #13 on: April 18, 2008, 11:31:11 am »

I checked with the church budget committee, and it looks like $5k is it for this phase.   So I guess we'll split this up and plan some things now that can fit in the budget, and some for the future when more money is available.

I'm thinking we treat the ceiling now for sure.  

Then either do the wall pockets, or add curtains in various places... Curtains are a headache to get approved because of color choices, but they might do more good than treating those wall pockets...hmm.

Thanks again for your help.

I'm just so glad I could give them some solutions other than cheap wall-to-wall carpet, popcorn paint, and drop ceilings... That's the kind of stuff they were considering before I nosed into the planning meetings. Smile  Oh, and hanging up old quilts.  Flammable, mismatched, donated quilts, stapled to the ceiling.. ugh... Smile

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rankus

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Re: Meeting hall sound absorption
« Reply #14 on: April 18, 2008, 06:22:06 pm »



What about some simple hanging cloth banners?  

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