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Author Topic: Distributed Sound In High School Gym  (Read 9231 times)

Daniel James

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Distributed Sound In High School Gym
« on: February 01, 2006, 12:09:51 pm »

Hi, I'm a first timer on this forum.  I'm a teacher at a large school In Edmonton, but have also done some SR work/mixing for our live production company (family owned).

I'm trying to get a good system for my school, and have many ideas already.  Recently though, i brought in a 'consultant', and he suggested that we use distributed sound instead of one or two sources.  He wants me to basically get the electronics/mixer that i want, but run it through the existing PA speakers in the ceiling. I just have a hard time buying in, and believing that this will work well.

The kinds of production i'll be doing will range from school celebrations/mass (catholic school), pep rally's, band/choir performances (our stage is in the gym), drama performances, and hopefully some student bands and musicians in talent shows.

Please, i really need some suggestions/info.

Thanx

Danielr
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Oldaudioguy

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Re: Distributed Sound In High School Gym
« Reply #1 on: February 01, 2006, 04:02:23 pm »

A distributed system in a gymnasium is only appropriate when the room reverberation time is low, and that is usually only the case when there is acoustical treatment on one or more large surface in the gym.
Distributed systems exacerbate the reverb issue because the distance (and delay) between the speakers add to the reverb time.
A central cluster is always the best way to go because it creates a single sound source.  Choose speakers and amplifiers that will produce enough level to overcome the loudest audience noise (should be at least10-15dB SPL higher than max audience noise).  Central clusters must be carefully designed and implemented to ensure minimum comb filtering and other undesirable interaction.
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Duane Massey

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Re: Distributed Sound In High School Gym
« Reply #2 on: February 01, 2006, 07:39:22 pm »

Personal opinion alert!!

Distributed systems only work well when there is no signifigant live sound being run thru the system, ie: a live band. Unless the system has mulitple zones delayed properly from one specific location the delay between the live source and the speakers can be atrocious.
I also believe that it is desirable to have the sound source coming from the same general area as the visual performance.
And there's always the issues of frequency response and potential SPL. Unless the existing system is unusually potent I would be surprised to find that it sounded acceptable for live music or singing.
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Duane Massey
Houston, Texas, USA

Brad Weber

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Re: Distributed Sound In High School Gym
« Reply #3 on: February 02, 2006, 10:34:06 am »

Actually distributed systems are a common solution to address more reverberant environments.  They reduce the speaker to listener distance and help place more of the listeners in the direct field of a source.  A properly configured distributed system can often provide more even coverage and get the sound direct to the listeners with less room interaction than a cluster type system.

The delay issue raised is valid, however look at the events you mentioned.  You potentially have sources at the middle of the floor (pep rally), spread over a larger area (concert), at one end or the other (mass, graduation, etc.) and at the side (announcer during a game).  So where is "the" source?  With this range of events and potential source locations a single point cluster system would also have source delay issues, in some cases potentially worse than an undelayed distributed system.

As far as live sound, the same multiple source issue can also  impact gain before feedback.  Anywhere you might have a source, you likely have an open mic.  If you properly zone a distributed speaker system you can adjust the level for, or even turn off, each zone to fit the event and thus likely increase the potential gain of the system.  You can also turn down or off speakers in areas that may not require coverage (maybe the visitor's stands during a pep rally) reducing the extraneous acoustic energy introduced into the room.

Fidelity can also be an issue, but you might be surprised by the sound quality and levels you can get from a properly designed distributed system using high quality ceiling speakers.  And distributed system aren't limited to using small ceiling speakers, I've done distributed systems with full range 2 and 3 way boxes as well.

I have been involved in numerous very successful gymnasium and even arena sound systems that used some form of distributed system.  There are lots of "tricks" (using essentially a scaled down large arena distributed array/cluster system with compact full range speakers, properly zoning the speakers, using a matrix DSP and programmed presets in conjunction with the zoned speakers to provide various delay and processing configurations for typical events, etc.) that can make distributed system very effective in these situations.  I'm not saying that a distributed speaker system is always the best solution, but certainly do not discount it out of hand.  
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Brad Weber
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Daniel James

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Re: Distributed Sound In High School Gym
« Reply #4 on: February 02, 2006, 10:54:42 am »

I had a hunch this would be the case.  I know that our exising PA system in the gymnasium isn't outstanding.  And it is quite a large gymansium, with room for ample audience on either side of our b-ball court.

We actually ahve 2 existing systems.  One that is purely set up for announcements (the distributed sound system that i've questioned tying into), and another designed for sporting events, as they are common at our school.  We are considering a third system that will be used purely for a set up on the stage.  School band/choir, rock bands, ceremonies, etc.  I think i'll push to not have the distributed sound.  

Thank you
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Daniel James

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Re: Distributed Sound In High School Gym
« Reply #5 on: February 02, 2006, 10:57:30 am »

We definately will not be able to zone the PA system on our budget, and as i mentioned, our speakers are not high quality.  They're quite old, possibly original.

Based on what you're telling me, It seems like if there was the budget distributed sound might be an option, but i'll be leaning against it for now.
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Brad Weber

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Re: Distributed Sound In High School Gym
« Reply #6 on: February 02, 2006, 01:00:16 pm »

The primary intent of my initial response was not to indicate that one approach is inherently better or more costly than the other, but rather to simply suggest that you do not just reject or investigate any one approach, instead look at your specific requirements and see which system fits best.  I have designed systems for several private schools that had essentially the very same description that you had expressed and where they were quite happy with the results, so I also wanted to counter what appeared to be some misunderstandings that were expressed and that likely resulted from experiences with poorly designed and/or installed distributed systems or unfamiliarity with this particular application.

Whether distributed or cluster, the budget will affect either speaker system approach and neither is inherently more expensive than the other.  If zoned distributed systems were inherently more expensive (or of lesser value) they probably wouldn't be in just about every restaurant, convention center, casino, etc.  I have designed distributed systems such as I described for several public and private high schools without budget problems.  I have also used more traditional cluster and PA horn systems, it all depended on the particular space and that project's requirements.

Remember that you do not have a typical stage scenario, with the variety of events you indicate you expect to support you will almost certainly have times when you have live mics placed in areas that are in the coverage of the speaker system for other events (the speaker coverage requirement is driven by the system performance requirements and should be the same no matter what speaker system is used, although how you can adjust that coverage might vary).  In addition you have a fairly large and live room.  So a Gymnasium is a very different environment than most performance facilities, please don't assume that what works or doesn't work in those venues would necessarily give the same results here.

One major problem in most gym type spaces are the large, flat, parallel walls.  If you do not acoustically treat these walls then you definitely need to minimize the sound hitting them in order to avoid echoes, comb filtering, reduced intelligibility, etc.  This can often be difficult to do, both covering all the audience while at the same time minimizing the sound hitting the walls.  It can be done, but the speaker system must be properly selected and designed, not always an inexpensive solution with any approach.

Another issue is simply the physical constraints of the space.  It sounds like you are working in an existing facility and you need to see what practical limitations may exist.  Are there any problems with hanging the weight of a central cluster from the existing structure?  Are there only certain locations where this load could be supported?  Does the structure itself allow you to place a central cluster in an appropriate location?  Do backboards in either the raised or lowered positions or other building elements potentially block the sound from possible speaker locations?  How much power is available and can it be supplemented if required?  Is there a center scoreboard and if so does it present a problem or a potential speaker mounting point?  What equipment space is available?  And many more issues that must be considered in an existing space.

All of these aspects must be accounted for before deciding which speaker system is appropriate.  Making a determination without considering these type of issues can lead to major problems down the line.

One thing I recommend considering as you are modifying the system to support a variety of events is whether you require or desire an ALS (assistive listening) system.  If you do not have already have such a system you may want to look into this.  Many athletic venues avoid ALS by offering that during games the scoreboard provides the same critical information as the sound system, but this will not hold true if you add events such as pep rallys, commencement and concerts.  You may be exempt from needing to provide ALS as a compliance issue, but I suggest that you verify what requirements for ALS apply if you install a new system and consider the possible public relations value of providing an ALS system even if not required.

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Brad Weber
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Duane Massey

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Re: Distributed Sound In High School Gym
« Reply #7 on: February 02, 2006, 02:58:13 pm »

Perhaps I mis-understood Daniel's post, but I was assuming that the performances were mostly going to be on the stage. If that is the case, I would still stay away from the existing 70v system UNLESS it is a multi-zoned system that can be time-aligned to the stage. I suspect that this is not the case.
    70v systems are very useful in the proper application, both in terms of cost and performance, but a well-designed distributed system that has enough horsepower and frequency response is not that common in school gymnasiums, especially older buildings.
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Duane Massey
Houston, Texas, USA

Daniel James

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Re: Distributed Sound In High School Gym
« Reply #8 on: February 02, 2006, 03:27:22 pm »

I appreciate you taking the time to explain these things to me.  We're actually not considering a centre cluster.  Our gym roof is not tall enough, and it doesn't meet our needs.  I am not trying to set up a system for sporing events.  We have an existing system for that.  We are simply installing an additional system for events from the stage.

I have used my personal system and have rented other systems to run celebrations in our gym from the stage.  I usually set it up just like you would most venues, speakers on either front-side of the stage, and a 2nd array on a delay halfway down the gym.  We find this works well, and were ready to install it until a consultant (hired by our superintendent of schools) suggested we use distributed sound.  The consultant did not appear to be that knowledgable, and I dont' think he quite understood our needs, which Is why I'm on this forum getting help from generous people like yourself.

Thank you,

Daniel
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Daniel James

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Re: Distributed Sound In High School Gym
« Reply #9 on: February 02, 2006, 03:30:25 pm »

Also,

The only reason why a non-distributed system would be less expensive for us is that our existing distributed speakers are not zoned, nor do i believe they would be sufficient.  It would have to be upgraded, at a significant instally cost.  A pair of speakers sitting on the wall either side of stage is pretty inexpensive to install.

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