Treating a room for Orchestra Rehearsals

[ozmorphasis]

Hi,

At the school where I teach, we are looking to turn a room that is 41' x49' with ceilings that are 16' high into a rehearsal space appropriate for full orchestra rehearsals. The floor is linoleum, and aside from some cut out doorways that are always open, the walls are bare.

The acoustics are a bit too live at the moment with some nasty flutter echo because of the parallel walls. I would like to build some 2'x4' panels to absorb some of the reflections. My question is what material to use if I want to do this on the cheap. I know that OC703 is the common fave, but I was wondering if there are cheaper and more commonly available (at Home depot, etc) materials that are suitable for this, keeping in mind that they are not meant to be bass traps, but more for flutter echo.

Thanks for your advice!

O

[avare]

For flutter echo in that size space, I would recommend diffusion and splaying walls, or angled surface treatments. As far as cheap absorbent material, how deep are you making the absorbers? I recommend 4" minimum. Safe n Sound by Roxul is the best bang for buck in my part of the woods. Look for equivalent material. That is ~2.5lb/ft3 3.5" thick mineral wool.

Andre

[PaulP]

Originally Posted by ozmorphasis

At the school where I teach, we are looking to turn a room that is 41' x49' with ceilings that are 16' high into a rehearsal space appropriate for full orchestra rehearsals. The floor is linoleum, and aside from some cut out doorways that are always open, the walls are bare.

Personally I would hire an expert for something that big. You could end up with
a fantastic sounding space that would be appreciated for years and years.
And with a professional the result will be guaranteed. I somehow doubt you'll
be able to acquire the necessary experience in any kind of short time period.
Full orchestras can put out an awful lot of energy and no amount of thin
panels will take care of that.

To save some money you could maybe hire the design then do the work yourself.

Paul P

[ozmorphasis]

Originally Posted by avare

For flutter echo in that size space, I would recommend diffusion and splaying walls, or angled surface treatments. As far as cheap absorbent material, how deep are you making the absorbers? I recommend 4" minimum. Safe n Sound by Roxul is the best bang for buck in my part of the woods. Look for equivalent material. That is ~2.5lb/ft3 3.5" thick mineral wool.

Andre

Thanks for the info Andre. The only really affordable diffusion solution that I have found would be the DIY poly-cyllindrical types made of bent plywood. Do you think this would be a reasonable solution for this room:

Poly Diffuser - Help Please

[ozmorphasis]

Originally Posted by PaulP

Personally I would hire an expert for something that big. You could end up with
a fantastic sounding space that would be appreciated for years and years.
And with a professional the result will be guaranteed. I somehow doubt you'll
be able to acquire the necessary experience in any kind of short time period.
Full orchestras can put out an awful lot of energy and no amount of thin
panels will take care of that.

To save some money you could maybe hire the design then do the work yourself.

Paul P

What you are saying makes perfect sense. It is, however, not cheap, and the powers that be are looking at this as an "alternative" use space, not an actual venue. So, it's been tough getting any real budget approved for this.

[avare]

Originally Posted by ozmorphasis

Thanks for the info Andre. The only really affordable diffusion solution that I have found would be the DIY poly-cyllindrical types made of bent plywood.

So you have a budget already? You did not state that in your first post. What amount (surface area) of treatment did you calculate you need when establishihg your budget? Or are you assuming without facts?
Angled sheets of plywood/gypsum/MDF making triangles with the surfaces at least 12° from the wall would do the job.

What is the ceiling finish? Once you have the walls treated, reflections from the ceiling/floor will become unmasked.

Andre

[ozmorphasis]

Originally Posted by avare

So you have a budget already? You did not state that in your first post. What amount (surface area) of treatment did you calculate you need when establishihg your budget? Or are you assuming without facts?
Angled sheets of plywood/gypsum/MDF making triangles with the surfaces at least 12° from the wall would do the job.

What is the ceiling finish? Once you have the walls treated, reflections from the ceiling/floor will become unmasked.

Andre

No, I don't have a specific budget yet. It's more like this:

Me: We need to improve the acoustics of this room if we want to have meaningful orchestra rehearsals in here. It costs $XXX to have an acoustic consultant come and assess the situation.

School Director: Ok, but we can't spend that much.

Me: Ok, with some DIY tweaks, perhaps we can make it usable. It will cost some money, but nothing outrageous.

Director: Ok, let's try to keep it under a thousand if possible.

Me: Ok, I'll do some research.


So, that's where I'm at in terms of budget. No, I have not done the math to see exactly what we need because I have a hard time predicting how much absorption would be needed to make it useful for rehearsals.

I'm open to the idea of splaying walls, diffusion panels, etc. However, I'm still not clear to what degree I should use diffusion vs absorption. The room is simply too live at the moment, and with all of the parallel walls, the flutter is an obvious problem that needs addressing. Beyond that, I want to tame it some without killing it.

Lastly, it's a student cafeteria, and so I also have to keep that in mind in terms of treating walls (it must be relatively kid proof, safe, etc).

Here are some pics. The ceiling has 1.5' x 1.5' tiles, but I don't know exactly what the acoustic properties of these tiles are. I will try to find out asap.

A friend of mine took some measurement of reverb time (T30) across the following frequencies.

Freq--------------31.5 63 125 250 500 1000 2000 4000 8000 16000

Café T30 (sec) 0.98 0.85 1.03 0.97 0.95 1.05 1.14 1.11 0.83 0.58

Thanks again for taking the time, and more over, for putting up with the amateur level of knowledge.

O

[avare]

We are starting to get somewhere. Trying get things in order, the issues are:

flutter echoes,
and too live a room.

The financial situation is one of an arbitrary $1,000 budget.

Is this correct? Are there any other significant factors to be aware of?

Note, and this is not meant in a hostile manner, but if you were dealing with a paid consultant, you would have been paying their hourly fee for them to ask you and get this information.

Coming back to the issues, is the room reverb too live, or is it that the flutter echoes are unnacceptable and so dominant? The reason I ask is that for a ~32,000 ft3 room, an RT60 of around 1.0 s is in the preferred range.

Do not be concerned about the absorption of the ceiling in detail. Looking at he pictuers, I can not make out if teh celing is absortive or reflective. I think it is absorptive. Confirmation please. What is important is the net effect, which we have. BTW, good thinking having the RT60 measured!

Do you have a school shop available for building things?

On the question of coverage, At least 5-10% of the walls to control the flutter echo.

Andre

[tINY]

Quick though:

Where to those tables and benches end up when the rehearsal is happening? I'm thinking that standing them up along the walls at a bit of an angle could help a lot...



-tINY

[avare]

Originally Posted by tINY

Where to those tables and benches end up when the rehearsal is happening? I'm thinking that standing them up along the walls at a bit of an angle could help a lot...

Great thinking! +1

Andre

[ozmorphasis]

Originally Posted by tINY

Quick though:

Where to those tables and benches end up when the rehearsal is happening? I'm thinking that standing them up along the walls at a bit of an angle could help a lot...



-tINY

Yes, that is definitely an option! Thanks for the suggestion.

[ozmorphasis]

Originally Posted by avare

We are starting to get somewhere. Trying get things in order, the issues are:

flutter echoes,
and too live a room.

The financial situation is one of an arbitrary $1,000 budget.

Is this correct? Are there any other significant factors to be aware of?

Note, and this is not meant in a hostile manner, but if you were dealing with a paid consultant, you would have been paying their hourly fee for them to ask you and get this information.

Coming back to the issues, is the room reverb too live, or is it that the flutter echoes are unnacceptable and so dominant? The reason I ask is that for a ~32,000 ft3 room, an RT60 of around 1.0 s is in the preferred range.

Do not be concerned about the absorption of the ceiling in detail. Looking at he pictuers, I can not make out if teh celing is absortive or reflective. I think it is absorptive. Confirmation please. What is important is the net effect, which we have. BTW, good thinking having the RT60 measured!

Do you have a school shop available for building things?

On the question of coverage, At least 5-10% of the walls to control the flutter echo.

Andre

Andre, I'm still trying to figure out what the ceiling tiles are. In any case, yes, we definitely have the facility to make treatment on site, as well as the labor.

You are right about the 1 sec of rt60. It is indeed not too wet, and probably much more important to control flutter rather than getting carried away with absorption.

The rt60 was taken by a friend/acquaintance who works for a national level consulting firm. He did it for free with equipment he borrowed from work. However, he has since become very busy (marriage, buying a home, travelling, etc) an is not really available much these days. Meanwhile, the orchestra that want to use the space is itching to get in, thus my desire to press forward quickly.

The budget is indeed arbitrary, and if I make a compelling case in terms of the benefits of treating the room for other performances/uses, then I'm sure I can squeeze some more money out of the school, however, not much more most likely.

Andre, aside from the benches being stood up at angles, what would building diffusion look like otherwise? Especially if we want it to look elegant enough to use for the ocassional recital in addition to the orchestra rehearsals?

Some of the walls are plain enough to allow for splaying panels to be added, but some of them have enough inconsistencies in the structure to require smaller individual panels to be built.

Thanks again for your thoughts!
O