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Reducing Room Reverberation


Woodog
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Hello all!

I use a couple pairs of my speakers (Cornwalls Heresys) as a PA for my church.

We recently built a new building - and, as usual, no thought to acoustics was given until they found the room too lively.

I wasn't asked to be a part of the planning, but I did get wind of what was currently going on with 'fixing' the sound.

What do you think of this plan of attack outlined in the emails below. I personally would love to see tapestrys and carpets instead of acoustic panels (boring).

All help and advice appreciated. We don't have the funds to do what they are considering doing, and I feel they will hate the look.

I know this place knows audio! Help!!

and many thanks....

Forrest

the email:

HI guys and gal,

The bit of homework that I’ve done so far on acoustic panels.

Given our space in the social hall- 45’ x 50’ x 10 or 12’ ceilings, Tile
floor, dry wall ceilings and walls, with some glass. Here’s what I’m
finding with some consistency.



An acoustic panel 2’x 4’x 2” covered in a hemp/jute material with sound
dampening filling, runs about $60 per panel. An on-line analysis of
these features by ATS Acoustics suggests a minimum of 57 panels and 86
would be on the high end. This would run somewhere around $3,600 with
shipping.




Speaking with a representative of Audio-Mute Corp. suggests a lower
expenditure. They state for this size room you would need 15-20% wall
coverage with acoustic panels. Approx. 40 panels would be equal to that
amount with a similar price tag. With shipping an approximate cost would
be $3,000.



Another member's suggested company (Acoustimac) has the same size panels for
$49.95. (The $25 panel noted in the e-mail is much smaller.) The
minimum number of panels suggested for the space is 50, $2,500 prior to
shipping.




I considered the idea of building our own but I’m not sure would could
make ones that pass a fire inspection. Acoustic panel are made to be
flame resistant.



There are such things as ceiling baffles, but I’d personally hate to see
stuff hanging from the ceiling. As it is, the mounts for these acoustic
panels will make the space pretty unusable for hanging an art show.
Each panel requires a hooking system (a flange) mounted permanently into
the drywall. We could remove the panel but the flange would be
displayed. The two inch thickness and relative thin panel (24” wide)
means that only very small works could be hung, for fear of snagging the
jute covers.




I forwarded the following attachments to my committee but haven’t had any feedback yet.

Something to chew on.


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If you want to make your own there is a product from a Canadian company (Home Depot usually carries it) called Roxul. Its a mineral rock fiber and meets very substantial fire resistance ~ several thousand degrees ~ you can put a torch on it and it won't burn. Obviously most coverings you might apply around it won't be as fire resistant. This stuff usually comes in rolls. They also have an even denser version Roxul RHT80 which is a little more like rigid insulation. It's made of the same material, just more compressed and denser.

There's probably someone in your church that can help make some kind of wood frame surrounds to make them look nicer and provide something hang them from.

Other than that, all I can say is that a few thousand dollars to tame the reverberation of a room that size is well worth it as long as your not looking to make the room acoustically correct for something like musical performances ~ concert hall type stuff.

Keep in mind that most carpeting and especially tapestries are not all that thick nor dense so they may not absorb as much as you think they will. And acoustical curtains are also not inexpensive.

Another alternative would be to hang drywall or masonite panels on the walls at various angles. The masonite panels could also be curved to help diffuse the sound. What you'd be trying to accomplish is basically to make the walls non-parallel so that sound reflects in different directions as it bounces off the walls.

Take a look at my thread in the Architectural section of the Forum or even my avatar in the upper left corner with a pic of my room to get an idea of what I'm talking about.

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Forrest,

Have a look at this site. Their prices seem reasonable and they will do panels covered with fabrics of your choice.

http://www.atsacoustics.com/panels

Bruce

Bruce, I think those were on the list Forrest presented, but they are nicely appointed and lots of flexibility in how you can order the product. I notice they are using the Roxul mineral (rock) wool as well.

This is one of those situations where an "ounce of prevention is worth a pound of cure".

Forrest, maybe you could start out with a smaller quantity of smaller panels and distribute them more widely. The individual panels will be more effective over a wider area by doing that. Then, if you need more, it might be easier to convince the powers that be to ante up for more at a later date after they see the results.

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Excellent info Artto and Marvel!

I think the entire committee is looking at this thread now! [:P]

I also think using curtains might have a good effect. I also think that having 100 or so folks sitting in upholstered chairs would calm the sound more than they realize.

The current 'sanctuary space' (as a Unitarian, can I use the word sanctuary?) anyway, I LOVE that space as there are no parallel surfaces and the acoustic is just 'wet enough' so that singing is wonderfully enhanced.

I also know it's easier to reduce reverberation than to add it - except by electronic means.

thanks again!

Forrest

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What is the goal, intelligible speech, or music, or?

Any kind of material a couple inches from the wall will make a huge difference, but to meet code you may need to buy code approved items even if they have no functional advantages.

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Forrest--

The church needs to hire an acoustical consultant. There are known criteria and known methods of calculating how much of what materials/products should be installed to meet the criteria. Any vendor's first job is to sell products and services, not figure out the lowest-cost way to solve your problem. Contact an acoustics professor at a nearby university that offers engineering degrees and ask for a recommendation. Maybe the prof can do the work or recommend someone local that can help.

Good luck!

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... no thought to acoustics was given ...

I wasn't asked to be a part of the planning

So typical. Here is an old story, but a good one. A medium sized
church in San Francisco had essentially parallel stone/concrete walls
that were way too live. To cure this, they put in walls within the
walls with widely spaced studs and sheet rock with an acoustically
absorbent covering. Much of the bass produced by their pipe organ
disappeared. Oops. They considered filling the gap between the old
walls and the new ones with sand to make the new walls more rigid, but
San Francisco is earthquake country, and the vision of the parishioners
buried neck deep -- or worse -- in sand was disturbing. I heard that
they finally solved the problem, but I didn't hear how. They may have
had to remove the inner walls. Oh, well .. it's only time and money.

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Forrest, I would recommend getting four to six larger portable panels that are decorated/covered with murals or symbols that are sympathetic to your church's central tenets. You can even get two sided murals, so your parishioners don't get bored with the same views every time. Build frames of nice oak or walnut finish, and go to town on the above rockfill. These give you the best of all worlds - portable, flexible, non permanent, and visually attractive. I have done this and they work out quite well, and make for an inviting space.

I would even go out and make two of them slide in pockets for large photos of your worshipers, especially the kids. No one will ever complain about these!

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