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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => SR Forum Archives => Installed Sound/Contracting FUD Forum Archive => Topic started by: Daniel James on February 01, 2006, 12:09:51 PM
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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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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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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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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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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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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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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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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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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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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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about that 70 V system. I understand why there is a need for that higher potential difference on a school's PA system. THis must mean that there is a solenoid at each speaker? Is there a standard 8 ohm or 4 ohm driver at each of those speaker boxes, and if this is the case, could I essentially just have those drivers swapped out for a higher quality one?
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Yes, there is a transformer (not a solenoid) on each loudspeaker in a 70V system.
You certainly could replace the loudspeakers with higher quality devices. But chances are that the quality of the transformers, themselves, in your existing system would limit the frequency response and power handling of the new loudspeakers. Better to replace the existing loudspeakers with better devices that also have better transformers. Tannoy, EAW, JBL and a few others make very good 70V loudspeakers.
You need to also look at the power amplifier and determine whether it provides enough power and has a decent output transformer. You could replace this with a more appropriate amp that may or may not need an output transformer.
Less of a concern is the cable from amp to loudspeaker to loudspeaker. But it may be a concern and therefore needs to be evaluated.
Finally; as is the case with any type or configuration of loudspeakers, you need to provide equalization (plus high-pass filter, alignment delay and limiting) and have the system measured and optimized in order to achieve the best response.
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We're actually gonna go up there in a couple of weeks to evaluate the equipment, i just need to wait until i have time and I can bring a lift in (it's busy teaching full time AND trying to do the extra-curricular stuff).
I didnt' even consider the quality of the transformer..that's a good point I'll look into. Chances are, they are of poor quality.
It just seems like it may be easier to install a couple of speakers at the front, and rear fill, then trying to make what's already there work. I hate retro-fitting.
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The existing speakers are part of the original school paging/intercom system, correct? I would be surprised if the transformers were tapped higher than 5 watts, or if the speakers themselves could handle more than ten watts each. Those speakers are definitely not designed for anything but voice paging.
At the head end, the line(s) terminate in switchbank "ports" that are also limited in the wattage they can handle, usually between 12 and 30 watts per switch.
If you break the lines to add a local amp, you may run into a code issue: The school's paging system may be required to take priority over local systems in the event of a building emergency. (a.k.a. "Take-over")
IMO it would be much better to install a separate system for your concert events (distributed or not) than to try and make the school's voice-only paging system serve two masters.
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thank you for the insight. This was my biggest concern with the distributed system proposed by the consultant: that he wanted to use the exising pa system. You're right, they're 8 W each. The consultant claimed this would be plenty. This was my largest concern.
The fact that the exising PA needs to take priority during an emergency is the reality, another one of my major concerns. I don't want announcements coming over my system.
Thank you again,
Many of you have been very helpful in reminding me of major concerns as well as explaining new things to me
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As stated earlier, a distrubted system in a gym only works if the room is fairly "dry"-most are not.
The problem with simply doing a center cluster or exploded clusters is using a speaker that does not have enough pattern control to a low enough freq. That means big horns. Often times small speakers are used-because of budget-and they just spray everywhere.
My current favorite approach for a limited budget is to use the Atlas Ap series of outdoor horns. they have a 15" and a 1" and have a fairly large horn and are "basketball proof". They have a decent amount of low end and do require a fair bit of "radical" eq to get them to behave, but can work fairly well.
A little trick here when doing the system setup. After you have the system slignment to as flat as you want-do a RT60 frequency dependent test and find the major (hopefully there is only 1 that really sticks out) cause of the Reverb. Yes this will change with bodies in there, but you have to start somewhere. Then put a notch in the response at that point-how wide and how deep depends on your RT60 measurements. This will help to keep from energizing the room so much at that freq. Music does not sound quite as good, but intelligability is often quite higher.
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Another option to consider is the widely-used Community R-series, including the R1 and R2 series speakers. The R2 uses two 12" woofers and is similar in design to Community's T-Class touring array systems. My high school had a suspended scoreboard in the middle of the room, above which would have been the perfect place to install a center cluster. Is there any reason your school can't just put together a decent, loud portable system and then move it into the room whenever it's needed?
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Your gym sounds a lot like the gym in indy I did a couple years ago.
I have 8 passive JBL AE 4212/95 series speakers independently hooked into the eight outputs of the DBX 482 (no controls on the front for kids to screw with the settings) obviously amps in between Crown CTS series 9 mounted in a rack up on the stage.
There are three of the JBL AE speakers on each side of the basketball court evenly spaced facing the bleachers. The other two are L/R of the stage at the end of the court shooting down the court.
Every speaker has a custom mounting bracket that allows it to rotate 360dg. by taking a genie lift and turning it. You can also adjust the tilt.
The DBX 482 is in a rack with a cd player and a little mackie mackie mounted on the wall in the gym that feed input 1 of the DBX.
All the sport teams have their own preset in the DBX. They know how to turn the system on and get to their asigned preset. i.e: basketball preset 1, volleyball preset 2 etc.... Each preset is designed specificly for that event and has been time aligned. Basketball has music and speach that needs to be loud to get over the crowd. Wrestling isn't that big so only the center speakers on each side are turned on and the two shooting down the court.
You cannot set the mutes for each preset but you can turn off the routing to certain speakers in the gui software for the DBX.
For Musicals and speacial events the speakers are turned creating a distributed delay system for the gym. The Drama department has their own mixer and FOH gear that gets patched into the system through a snake routed from the back of the gym to the stage. There is an xlr input jack on the side of the gym rack that feeds input 2 of the DBX which goes into effect when they hit their preset. Normally they have the gym for awhile and it only takes 10 minutes to turn all the speakers. I trained the theatre teacher on how to do this.
It works really well and handles music seamlesly. There are even subs that can roll out and hook into the system ( just a different preset on the DBX where two speakers are turned off to make room for the subs.)
Overall it's a great system for their application which is a Catholic High School that does everything from sports, plays, mass etc... in the gym. I have never really seen another like it.
Good luck....