Building an Orchestra Shell

[GBtimex]

Audio guys/gals

I have a idea that I wanted some feedback/WTF are you doing, on.

You see my theatre is wonderful for dance, bands and stage shows. What it's god awful for is orchestra and unamplified sound.

We currently do not have any shells and the space is so **** big (128' x 52' x 66' 8") that the sound goes strait up and not toward the audience at all.

New shells are bit out of our price range so I am looking to do the following:

Build our own.

What I am thinking of building is flats with a hard wood or surface on them to surround the musicians and are at least 12ft tall.

Then taking flats of various lengths and flying them on 2 different line sets. This will make a ceiling and force the sound down and out. I will be able to control the angle and the height easily.

My carps assure me this is possible, my riggers can make it safe and my lighting guys will get over their problems at some point.

My question to the audio guys is:

Is this worth doing?

Will this help my sound problems?

Is there anything you all know that would be helpful in this situation?


I am a humble TD who knows very little of the audio world. Can anyone help me out a bit?

Thanks,

GBTimex

 

[Footer]

It can make things worse if done wrong. You run the risk of wasting a lot of time and money on something that does very little.

Before you go building, I would get someone in to analyze your space. With that, they can give you information about where best to put hard surfaces, what materials to use, and how the surfaces should tie in with the space. Give a call to a local engineering university and see if anyone wants a good capstone project...

 

[GBtimex]

I am on a campus but I have had a terrible time working with engineering departments. They are very busy and often scoff at my suggested projects (I asked them to come up with a way to improve my orchestra pit). If not a engineer who do I get in contact with?

GBTimex

 

[Call911]

Where are you located? Contact some local universities or high schools. They might have an old sound shell they're looking to get rid of. I'm in the Chicago area and have had a sound shell sitting on my dock for 10 years looking for a good home...

 

[FMEng]

This is pretty elementary stuff for any competent acoustical engineer. I know of one, excellent acoustical firm in your area. This is a little out of their specialty, so if they aren't interested they could perhaps recommend another firm in the Dallas area.
RBDG [Home]

The key to good shells is stiff mass. In other words, make them out of heavy, rigid material. Think well braced 3/4" plywood or high density fiber board. The weight is why the better shells I've seen are panel sections on wheels, not something to be flown. The mass is what makes them effective for low frequencies. Bass energy tends to pass through light materials like plastic or composites, and you want a reflector.

 

[museav]

This is pretty elementary stuff for any competent acoustical engineer. I know of one, excellent acoustical firm in your area. This is a little out of their specialty, so if they aren't interested they could perhaps recommend another firm in the Dallas area.
RBDG [Home]

Russ is a great acoustician and fun to work with, although their focus is on studios I'm sure they could do a great job. There are a number of other good acousticians in the area as well such as Kinsella Marsh Group Home Page and WJHW - HOME. And there are also a large number of good acoustical consulting firms in the Austin and Houston areas. It may also be practical for firms located some distance away to be able to help, especially as you are near a major airport.

As to building flats yourself, one consideration is that acoustical shells are usually not comprised of flat, reflective surfaces but rather of shaped, diffusive surfaces. And those surfaces ideally affect all relevant frequencies, which in the case of vocals can go down to 80Hz or so for bass vocalists while for orchestra double bass, harp and contrabassoon may have as low as 30-40Hz fundamentals while overtones of piccolo, violins and some other instruments go to the upper range of human hearing. You can also get into much more detailed acoustics aspects such as the timing and density of the reflections received by the musicians as a result of the shell, the effectiveness in coupling the performance space to the audience chamber and so on. Many shells are installed without consideration of such details and work more than acceptably, however the risk as Footer noted is that a poorly designed or applied shell could inadvertently cause other problems, especially for the performers.

A practical consideration is that a significant amount of design effort and development goes into developing systems for safely and effectively moving and storing the shell elements and this is an area where there can be differences between different shell options. Also consider that you have to make sure you are properly addressing stability of the wall elements, attachment points for the ceiling elements and so on, DIY would seem to mean your assuming liability for any related issues. And if anything was permanently attached then you might have to address issues related to it being considered permanent construction.

 

[Chris Chapman]

Acoustic Shell Construction?

When my facility was built in '98, they ran out of money on the acoustic shell, so we only have 3 ceiling shell pieces that fly in. We have been using soft goods on the upstage side of the shell, but the conversation come up about building an upstage wall unit that matches the ceiling pieces.

I'm playing around with different concepts for it, and basically I'm planning on standard wall framing on caster bases. My only question comes into skinning the walls. Since the main issues is sound reflection, do I need more than just luan? I was thinking of 1/4" or 1/2" OSB as a substrate on the frame, and then skinning with luan and staining to match the existing pieces.

For acoustic reflection do I need to think of more? Weight is starting to get to be a concern, due to these wall sections needing to be 12-14' tall. See attached concept elevation and chime in.

The Yellow Jacket is the school mascot, but is going to be nixed from the final design. Primary implementation would be for Band and Orchestra concerts and some choir concerts.

 

[Footer]

Re: Acoustic Shell Construction?

You are really opening up the same can of worms that we talked about earlier in this thread.

This is my total "arm chair" acoustics advice that probably sounds more right than is right:
The only advice I would give you is to not go with OSB/luan. Both of those are pretty "airy/soft" material. If I were to build a flat wall that I wanted to reflect sound, I would probably go with some type of 7 1/2" ply plywood with a cabinet grade top ply. Do you intend to fly this wall or roll it?

 

[derekleffew]

Re: Acoustic Shell Construction?

... about building an upstage wall unit that matches the ceiling pieces. ...
My only question comes into skinning the walls. Since the main issues is sound reflection, do I need more than just luan? I was thinking of 1/4" or 1/2" OSB as a substrate on the frame, and then skinning with luan and staining to match the existing pieces. ...

So how are the ceiling pieces made of? One would think a starting place would be to construct the wall exactly the same as the overhead. Although there may be acoustic considerations that would render that line of thought invalid.

I've never seen an installed shell that was lightweight and thin. Most are (or at least seem to be) ridiculously heavy. Wall units are often moved with air casters, and/or permanently hinged/affixed to the building structure.

 

[gafftapegreenia]

and my lighting guys will get over their problems at some point.

Gee, thanks.

 

[marmer]

Yeah. What Footer said. Luaun is a waste of time, it's acoustically not much better than canvas. You need lots of mass, stiffness, and possibly a surface contour. I completely agree with the recommendation to go with an acoustician.

 

[Chris Chapman]

Re: Acoustic Shell Construction?

So how are the ceiling pieces made of? One would think a starting place would be to construct the wall exactly the same as the overhead. Although there may be acoustic considerations that would render that line of thought invalid.

I've never seen an installed shell that was lightweight and thin. Most are (or at least seem to be) ridiculously heavy. Wall units are often moved with air casters, and/or permanently hinged/affixed to the building structure.

The flying pieces are steel framed, but are foam core. I can't identify what the skin is on them but the "show" side is a wood veneer, and the back side seams to be masonite. SECOA did the install. Each shell is counterweight to a full arbor, coming in at around a ton and a half. But that includes rigging for tilting, and raceways for power.

I'm watching the load so I don't need to go to aircasters. Wood frame, OSB lid, styro layer, masonite layer and then luan kicks my weight up over the construction limits I'm dealing with. I wish steel was an option for me, but it's not. The SECOA wall sections had powered bases for movement, and came in at $35K for SL, SR and US wall units.

For an upstage wall how critical is that weight for acoustic reflection?

 

[Chris Chapman]

Re: Acoustic Shell Construction?

You are really opening up the same can of worms that we talked about earlier in this thread.

This is my total "arm chair" acoustics advice that probably sounds more right than is right:
The only advice I would give you is to not go with OSB/luan. Both of those are pretty "airy/soft" material. If I were to build a flat wall that I wanted to reflect sound, I would probably go with some type of 7 1/2" ply plywood with a cabinet grade top ply. Do you intend to fly this wall or roll it?

It can be an interesting can of worms to try to puzzle through though.

Built in casters on each unit. No flying on this piece for maximum flexibility. For smaller groups I would fly in the 2 downstage ceiling shells + back wall, and for larger groups add the 3rd ceiling shell plus back wall. Funny thing is we never use our 3rd ceiling piece, because when it's deployed it breaks the line of our furthest US lineset and I have nothing to mask our US storage space

 

[DuckJordan]

Re: Acoustic Shell Construction?

Chris without the weight, and the contour your acoustical shell will do little more than what your curtains are doing.There is a reason acoustical shell is big dumb and heavy. Ours are about 2-3 inches thick High density engineered foam with a steal structure running along. They are mounted on leveling posts and are moved with a big 4 post 4 caster per post hydraulic lift.

 

[Chris Chapman]

Re: Acoustic Shell Construction?

Thanks for all of the good input folks. One of the questions here, is how is this build different than some commercial products? We "used" to have a Wenger TravelMaster shell that was used for one year in my venue. Our facilities people conveniently "lost" it. Don't ask. The Wenger Travelmaster is made out of ABS Plastic and tube steel for framing. How is that any better than the build options what we're discussing here? Plus it looks like a scenic piece from 60's Star Trek.

If we go with a frame, a hard back, a filled foam core, and then a hard lid, isn't that a better solution than ABS Plastic?
I didn't mention that with wall pieces on caster frames, we would be able to shape the back wall so it isn't a pure, straight surface, but would have an arc across the space.

 

[josh88]

Re: Acoustic Shell Construction?

Part of the advantage are those ridged surfaces every other panel, and thinking of my shell even the non ridged sections form a slight pyramid in the middle so that the edges slope and redirect sound back out more effectively. Something flat doesn't do that a well. Think of this, (and this is why you'd want to use a harder wood) ABS is pretty solid, it's not a porous material, wood has pores and with softer wood there is more and they are more open. Hard woods are more densely packed so it better mimics the plastic consistency. So the harder and denser material you can get the more reflection you get, and that's where the plastic is a stronger choice than wood.

 

[marmer]

Re: Acoustic Shell Construction?

The light weight ABS plastic will definitely reflect high frequencies outward. It will have little to no effect on midrange to low frequencies because it has so little mass. That's not necessarily a bad thing, depending on what you need it for. It will help with intelligibility for spoken content and vocal music. It may help with clarity and brilliance for instrumental music, especially if the space seems "muddy" without a shell. If your space swallows low frequencies or sounds "thin", it probably won't help with that very much.

 

[museav]

Re: Acoustic Shell Construction?

An important distinction here is between reflection and diffusion. Simple reflection is like a mirror, sound hits a surface at some angle (the angle of incidence) and reflects off the surface at anequal angle (the angle of reflection). Any change in level is due to absorption by or transmission through the reflecting material.

With diffusive surfaces the sound hitting a surface at some angle is instead reflected off at multiple different angles. And since the energy is spread over the multiple reflections, there is some associated loss in level for any indivdual reflection along with any absorptive and transmissive losses.

Diffuse reflections are often desirable for music and vocal performance spaces, especially lateral reflections arriving within a limited time of the direct sound. Those reflections can be what provide ensemble for performers and warmth and presence for listeners. And that is why better acoustical shells often incorporate diffusive rather than solely reflective surfaces.

 

[marmer]

Re: Acoustic Shell Construction?

Yes. What Brad said about diffusion. Diffusion can also help offset flutter echo caused by hard parallel surfaces facing each other.

 

[BillESC]

Re: Acoustic Shell Construction?

Why are you trying to reinvent the wheel? By the time you purchase the materials, invest the labor, correct mistakes, your invention will probably not come in any cheaper than off the shelf items. Another consideration is how much space will your creation take up when not being used?