Fixing the sound of my kid's Cafe-Gym-Atorium

gafftaper

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My kids go to a small school with your classic small gym that get's used for lunch, music recitals, and P.E. The room's probably 40' wide x100' long x25' high. It has concrete walls with a ring of glass windows way up at the top. The ceiling is fairly flat, with a slight arch... probably 3 or 4 feet rise to the centerline. It has that old ceiling tile that was installed in every classroom in the 60's (remember killing time in math class trying to count all the holes?). Nice hardwood floors. The hard surface reflections in this room seem to go on forever!

There is a single cone speaker that must be 40 years old at one end with a barely functional amp to match. Most of the time they use the portable system which consists of a small speaker (Brand unknown) about the size of a Macke 350 which is powered by an all in one mixer/amp box (brand unknown). I think the only mic the own are Shure pg 48's... which they use for everything from solos to long distance choir mics. There is a LOT wrong with this system.

The principle just told me she has about $1500 to spend. My thoughts are as follow:

1) I don't have enough money to even scratch the surface of the speaker, amp, dsp, mixer problem. I really want to do a good full installation... which is probably going to cost $7500-$10k to do it right. There are several parents who are contractors who I could team up with to do this project labor free. There is also a movement underway for a big capital improvement drive and this could be part of that project in a few years.

2) I could address the microphone problem with this money, but I question if this improvement would even be noticed with the rest of the problems. I'm not sure that it's wise to throw my money after better mics when the system sucks and the reflections are so bad.

3) I could buy a lot of heavy weight velour and have a team of moms make monstrous "banners" to hang on as much of that wall surface as possible. This would make an immediate impact on the reflection issues and make both the existing system and the future system sound better.

Do banners seem the wisest move to you acoustics gurus?

Anyone have a better idea how to spend this pot of money?

EDIT: Footer sent me a link to http://www.acousticalsolutions.com pointing out several cool products. These look great but doing the math I can cover 1000 square feet of wall surface with 20 oz velour with my $1500. With the cheapest product on that site (4'x8'x2" PVC pannels filled with fiberglass) I can only cover 480 square feet at my budget. What are your thoughts on the effectiveness of 1000 sq feet of velour vs. 300-500 sq feet of a professionally designed acoustic tile product? Is quality or quantity more important?
 
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Are you sure altering the acoustics takes priority over replacing equipment? I have worked in many rooms similar to what you describe and, while not the most ideal space, it can work just fine. Can you give us more specifics on exactly what problem(s) you're trying to fix? If the sound coming out of the speakers is garbage then putting up acoustical panels will not be a solution. If you do go the afoustic treatment route, of course make sure you're looking at FR or IFR fabrics.

Also, PG48's aren't the best but they'll certainly work.
 
For a number of reasons, I typically look at some combination of wall and ceiling treatments for such spaces. The ceiling treatment is often a spray-on, hanging baffles, catenary or 'wave' baffles or some combination of these. The wall treatment is often something like one of these, http://www.kineticsnoise.com/interiors/pdf/sportsboardconform.pdf, http://www.kineticsnoise.com/interiors/pdf/ksp.pdf or http://www.kineticsnoise.com/interiors/pdf/knp.pdf.

While wall fabrics may help the acoustical performance is going to be dependent on a number of things such as the fabric itself, the fullness and the spacing off the wall. That performance is typically difficult to predict, one reason I generally stay with manufactured materials is having known known acoustical performance data upon which to base any analyses. Of course durability and fire resistance are also considerations for any potential treatment. However, you already noted the reality that $1,500 is not going to get you that much area of that type of wall or ceiling treatment.

Another factor can be how any acoustical treatments actually affect the sound system. Putting acoustical absorption higher on the side walls may reduce the general reverberance of the space but will it do anything for any potentially problematic discrete reflections to the listeners? What is fairly common in similar situations is to 'deaden' down the space only to then start noticing specific reflections and echoes that were previously masked by the general reverberance. A slap back echo off the rear wall may have been just one of many arrivals at a listener, get rid of some of those but not the slap back and it may start becoming more apparent. So the issue becomes not just what materials you use but where they are located.

I'd also be careful of the existing ceiling, chances are it is not an issue but your reference to 1960's acoustical tile reminded me that acoustical ceiling tiles containing asbestos were once common, if the existing tiles do contain asbestos and you start doing anything with the ceiling that disturbs those tiles then you may get into needing to address asbestos abatement. That can quickly kill a budget. On the other hand, it can also sometimes justify the cost to do something to replacing the tile out of some other budget and in that process allow you to do something that may be more acoustically effective.
 
Are you sure altering the acoustics takes priority over replacing equipment? I have worked in many rooms similar to what you describe and, while not the most ideal space, it can work just fine. Can you give us more specifics on exactly what problem(s) you're trying to fix? If the sound coming out of the speakers is garbage then putting up acoustical panels will not be a solution. If you do go the afoustic treatment route, of course make sure you're looking at FR or IFR fabrics.

Also, PG48's aren't the best but they'll certainly work.

My feeling is the acoustics takes priority because I can't really fix any other issue for $1500, but I can at least begin to address acoustics. But again that's why I posted this here to get other opinions.

I'm not sure how I can be more specific. The built in system is toast. The existing portable system might be okay if the acoustics could be fixed. It's not spectacular but it's a functional little setup that would sound okay in a dead room. We definitely need some microphone upgrades, most notably we need some choral mics for those music recitals. Using two pg 48's to try to pickup a group of 25 kindergarten kids singing is just a joke. As I said I can use this $1500 to fix the mic problems however I'm not convinced it will make a difference if we can't get the reflections under control.

Clearly it's a chicken or the egg scenario.
 
My kids go to a small school with your classic small gym that get's used for ...

Anyone have a better idea how to spend this pot of money? ...
Send your kids to a different school? :rolleyes:

"A multi purpose space is a no purpose space." --George Izenour, (NOT!)

"Wow, this school IS nice; their gym and auditorium are two different rooms!"--Lisa Simpson
 
Don’t worry Derek, the first thing I did was pull in some favors to move the spring musical to the nearest real theater.
 
Maybe you might try to do some repairs on the amps and speakers? With 1500USD, you certainly couldn't buy quality new equipment, but you might be able to get some repairs done on the old stuff to get it back into working condition.

For that price, you might even be able to purchase the start of some decent used stuff if that might help, assuming that Washington schools are allowed to.

But I'm just a HS Student, so take anything I say with a grain of salt.
 
Can you be more specific about what is wrong with the existing system? I'm no expert, but it might not be that difficult to repair the current system. What kind of amp do they have? Just to be sure, have you checked the basics, such as connections and settings? I've had situations where folks have messed with settings that caused what seemed like serious issues. Once someone turned on a low pass filter on the main output of our system. I've also had people mess with the equalizer.
Pictures of the current setup might help as well.

If the existing equipment is indeed faulty and repair is not practical, you could look at used equipment. I work in both tech and in the business office at my school, and we don't have any problem buying used equipment. Schools and states vary, of course, so check to be sure. I've been able to get decent results with very inexpensive, older equipment when budget was a hindrance. For instance, we can show movies with stereo sound in our auditorium thanks to a pair of monitor speakers and an old Realistic stereo amp I bought at a resale shop.

I know what ceiling you have because we have that in some of our classrooms (I also used to count the holes!). Ours is metal so there is no asbestos risk. However, asbestos might not be lurking too far away given the building's age.

-Nelson
 
Here's a quick summary of the acoustical properties of some drapery options and how they compare to some other materials, Theatrical Curtains and Acoustics. One important thing to note is the absorption at lower frequencies that are still relevant to speech and especially how that compares to materials such as 1" thick rock wool.
 
Is this school a Seattle Public School? Because if it is the asbestos should have already been inspected and a plan of action (or at least control) should have been formed for the building. Somewhere in the building there should be (at least from past experiences with SPS schools) a binder with Asbestos some thing plan on it. That should detail where the asbestos is, and what measures have been put in place to control or to remove it.


If you are in SPS I also have a contact at the central office that can supply ALL building plans for each school building. He is a great resource as I try and redo my space. I also might be able to suggest some places where you can get speakers/amps for free (or for very little) from the district.

PM if you want to get his info/other information on the district....
 
Do banners seem the wisest move to you acoustics gurus?

Anyone have a better idea how to spend this pot of money?

EDIT: Is quality or quantity more important?

[FONT=&quot]Hi Gaff. I am Chris - I have worked in sound and video for about 27 years, and have been involved in large scale events for the last 15 years. I do both live sound, and media system installation. Frequently - when we are in a big room with parallel walls - and mainly when there is a large flat back wall - we will rent a large curtain and hang it near the back wall. It really helps calm down the high frequency issue a lot. In your case - a typical "gymnatorium" - the high frequencies can wreak havoc on speech intelligibility. [/FONT]

Banners will help some. But as the site you mentioned states - thicker insulation provides better results.

Can your contractor team help build acoustic panels? In my experience - 2" or 3" rigid fiberglass panels are the most common solution. You can buy the rigid fiberglass- cut them to 2'x4' or 4'x4', frame them with 3/4", and cover them with muslin. Put as many of those as possible between 8' up and the windows, and you will get a lot of benefit.

If you want to upgrade the mics - SM58s are only $100 each. Not the best for choir - but 4 of 'em will do a children's choir. It is the universal mic for a reason.

Quantity vs. Quality...... Hmmm. If you get enough thick curtain coverage - it will help - especially if you can get 2x or more area coverage than with sound panels. It only needs to come down to about 7' or 8' off the ground to give decent results.

I'm not an acoustician - just an experienced sound guy. I would personally get 4 SM58s, and figure out how to get $1100 worth of something on the walls. (google this: corning 703 - find the cheap imitation) If you use the panels - nail something to the wall that sticks into the panel and holds it while the liquid nails sets. But you have a lot of wall to cover.

Just my .02
 
My feeling is the acoustics takes priority ... SNIP...
We definitely need some microphone upgrades, most notably we need some choral mics for those music recitals. Using two pg 48's to try to pickup a group of 25 kindergarten kids singing is just a joke. As I said I can use this $1500 to fix the mic problems however I'm not convinced it will make a difference if we can't get the reflections under control.
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As has been discussed in many threads, area micing a group is fraught with difficulties at the best of times. You're fighting an up hill battle already in a not ideal acoustical space, with a system that appears to be outdated, failing, & poorly designed for the purpose.

To be blunt;New microphones in this situation will be a waste of money. Fix the problem with both the sound system & use some acoustic treatment first.

Acoustic panels while potentially solving the acoustics, are again probably a waste of money, especially in a room that is also used as a gymnasium. You want to have something that is hardy & durable that you're not going to mind if it gets hit with a basketball or volleyball...or loose shoe.. Curtains of some sort will be more likely to be visually appealing, as well as durable, and at a pinch can be taken down. Acoustic panels are unlikely to survive rough treatment, and if the room gets painted by someone with no knowledge of the function of the panels, will probably devalue their efficiency by painting them.

In this case it sounds like the basic sound system & speakers are what you should go for with the money, but also push the curtains, which could potentially come from either volunteers or ask a nearby facility/theatre if they have any old ones lying about. Here we've gifted old drapes to other smaller venues in the past.

Cheers,
Ric
 
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"A multi purpose space is a no purpose space." --George Izenour, (NOT!)

My favorite comment on Izenour went something like, "Izenour was a genius architect, if only he hadn't hated the theatre".
 
New microphones would be pointless, like giving a guy with broken legs a new pair of shoes and expecting him to run a five minute mile.

Treat the room acoustics. I just did an analysis of a "gymatorium" a few weeks ago of the space as it is now, and then again after the school had rented some pipe and heavy drape to define the "stage", and along the back wall behind the audience, as well as a few panels on the side walls. The difference was astounding and the data reflected the improvement we heard.

The school has now budgeted about $2500 for new drape and acoustic tiles. I kind of shot myself in the ass on this one though, as they decided to go with purchasing drape instead of a new sound system from me :)

If you've got the time to fiddle with it, you can download a demo of Smaart and take some IR measurments, save the WAV's and run them through Smaart Acoustic Tools (also a free demo) and generate some numbers for the space.
 
Acoustic panels while potentially solving the acoustics, are again probably a waste of money, especially in a room that is also used as a gymnasium. You want to have something that is hardy & durable that you're not going to mind if it gets hit with a basketball or volleyball...or loose shoe.. Curtains of some sort will be more likely to be visually appealing, as well as durable, and at a pinch can be taken down. Acoustic panels are unlikely to survive rough treatment, and if the room gets painted by someone with no knowledge of the function of the panels, will probably devalue their efficiency by painting them.
Look at some of the products I linked, they make acoustical panels for just such applications and they're more durable and acoustically effective than drape, I've even used some in industrial and military spaces as well as prisons. Acoustical panels can also be mounted in a removable fashion if desired, I've worked on several gymnatoriums and black box theatres where we used wall treatments that could be moved to most effectively support different room configurations.

One of the factors that is often overlooked in quick analyses and site measurements is the effect of the audience. The absorption an audience, and air in very large spaces, represents can be quite significant An audience also provides diffusion, which in turn also increases the effective absorption. An example of the potential impact can be seen if looking at classical Reverberation Time based on the overall absorption in the space. An empty room may have X total amount of absorption while with an audience that may increase to 2X. So say you add another X amount of absorption, then for the empty room the total absorption would double and the reverb time halve, but for the room with people that same added absorption is just a 50% increase and the RT drops by just one third. The point is that the improvement one gains in areas such as general reverberance is typically going to seem more significant with the room empty than it will be with people in the room, which is the situation that really matters.

A corollary to this is that the same 'diminishing returns' effect applies to any treatments added. If you start with X absorption and add X additional absorption you then have 2X. But getting that same difference again would then require adding an additional 2X of absorption and 4X the next time and so on. In terms of general reverberation control you basically get the most 'bang for the buck' with the first bit of absorption added and each subsequent similar amount will have increasingly diminishing impact. That's why the most cost effective approach is often to first add absorption where it can provide the greatest benefit in aspects other than just general reverberance, that way you may be able to get the greatest benefit with the least material.

I'll also add that one common challenge is addressing slap back and other discrete specular reflections, flutter echo, room modes, etc. without also making a room too 'dead' or 'boomy'. Many times it is not just about adding large amounts of absorption but rather adding smaller amounts wisely and/or using treatments other than absorption.
 
Look at some of the products I linked, they make acoustical panels for just such applications and they're more durable and acoustically effective than drape, I've even used some in industrial and military spaces as well as prisons. Acoustical panels can also be mounted in a removable fashion if desired, I've worked on several gymnatoriums and black box theatres where we used wall treatments that could be moved to most effectively support different room configurations.

Fair call Brad. I may have been a bit blunt in what I was trying to say. :oops:

My point was more aimed at the low maintenance, low budget style of gymntoriums I've seen, and the type of care & maintenance they're given versus the cost of decent acoustic treatment. I was envisaging either foam style studio absorption, or dense, heavy rockwool stuffed panels, and the likelyhood of them being damaged by general Gym use. I wasn't aware that there were acoustic treatments that would suit that application !

Cheers,
Ric
 
[FONT=&quot]Can your contractor team help build acoustic panels? In my experience - 2" or 3" rigid fiberglass panels are the most common solution. You can buy the rigid fiberglass- cut them to 2'x4' or 4'x4', frame them with 3/4", and cover them with muslin. Put as many of those as possible between 8' up and the windows, and you will get a lot of benefit.

This is something I hadn't considered. We've litterally got an army of contractors and roofers who are happy to build stuff for free. I bet we could knock out dozens of them in a Saturday afternoon. Has anyone built them with positive results?
 
Tectum is one example of a durable sound absorber - you've probably seen it before as it is quite common. Here is a picture.

It's made of wood and is very tough.
 
This is something I hadn't considered. We've litterally got an army of contractors and roofers who are happy to build stuff for free. I bet we could knock out dozens of them in a Saturday afternoon. Has anyone built them with positive results?
DIY acoustical panels are pretty common and can be quite effective, however this really gets into the "doing something" versus "trying to achieve a goal" aspect. The acoustical performance of the panels is going to depend on many factors and details and since there is no testing of the panels to establish the resulting acoustical performance or characteristics, then you can't really account for any specific results. Basically, DIY acoustical panels will likely help, however the results would be very difficult to predict and thus they are not a practical approach to try to achieve any particular improvement or goal. Similar issues also apply to aspects such as flame spread and smoke created as even if the components are all properly rated, the panel assembly may not be tested and rated as an assembly or in that specific application.

I do have to say that having the panels starting at 8' A.F.F. would typically not be the most efficient application of them especially with ground stacked or pole mounted speakers. What will likely happen is that the overall reverberance of the room would probably decrease but the panels would be too high to impact on anything directly affecting the listeners or the speaker-to-listener paths. This is always a challenge in gym type spaces but wall panels are usually going to be most effective if applied where they directly impact the listeners, which typically means primarily at ear height and slightly above that.

If you try DIY panels there are some common tricks. For example, putting a panel on sleepers can increase the effective depth of the panel, for example a 1" thick panel mounted on 2x4 sleepers to create a 1-1/2" airspace behind the panel may acoustically perform more like a 2" thick acoustical panel. Or that being able to easily to breathe through or blow smoke through the covering fabric can help determine if the fabric is 'acoustically transparent' and thus won't negatively impact the acoustical performance of the core behind it.

I also wanted to address baffles and banners since they are a very common treatment in gym type spaces. There are several reasons for that with an important one being that both sides can be exposed to the space thus doubling the effective surface area. And since they are hanging in the space rather than mounted to reflective surfaces, they can also help break up as well as absorb sound. And since they are usually some distance from the people, the finish materials are often more utilitarian (and cheaper). However, with hanging treatments one does have to be very careful of the potential impact on lighting, HVAC and especially sprinkler systems.

Related story but some years ago part of my work included audio and acoustical consulting services for a client that built a large number of multi-purpose spaces. Apparently they mounted a number of competing 'impact resistant', fabric wrapped acoustical wall panels in an existing space and let a bunch of kids loose on them with basketballs, volleyballs, etc. and found that panels with a denser face material such as a perforated metal or plastic or a denser fiberglass board layer under the fabric fared best as they not only resisted damage from balls but also limited damage from sharper objects such as corners on chairs or table carts.
 

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