# More power ?



## whaleboat (Dec 15, 2009)

Recently , a 57 piece orchestra performed along with a 180 member choir at the auditorium where I work . Everybody was on stage in a huge mass , as opposed to the orchestra being in the pit . The choir was mic'ed and it all sounded good , but I was really at my limit , if the orchestra had played any louder I wouldn't have been able to bring up the choir without everything distorting and falling apart . I'm running a mono mix to three rows of cieling mounted speakers in the house , first row FOH , second row about a third of the way towards the back of the house , third row about two thirds back . Each row of speakers has three speakers running off of an amp that provides something like 475 watts into a 4 ohm load and 325 into an 8 ohm load . I have the right and left speakers running off one channel of the amp and the center speaker running off the other channel , and the amp is paralleled . The speakers are rated at 250 watts RMS with a good sensitivity rating , 99db if I recall correctly . My question is this , if I were to go to larger speakers , say 500 watts RMS , and the amps to run them , would I gain more headroom ?


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## gpforet (Dec 15, 2009)

How are you micing the choir and how close to feedback were you? Seriously, if you were withing 3db of feedback more power won't help.


whaleboat said:


> Recently , a 57 piece orchestra performed along with a 180 member choir at the auditorium where I work . Everybody was on stage in a huge mass , as opposed to the orchestra being in the pit . The choir was mic'ed and it all sounded good , but I was really at my limit , if the orchestra had played any louder I wouldn't have been able to bring up the choir without everything distorting and falling apart . I'm running a mono mix to three rows of cieling mounted speakers in the house , first row FOH , second row about a third of the way towards the back of the house , third row about two thirds back . Each row of speakers has three speakers running off of an amp that provides something like 475 watts into a 4 ohm load and 325 into an 8 ohm load . I have the right and left speakers running off one channel of the amp and the center speaker running off the other channel , and the amp is paralleled . The speakers are rated at 250 watts RMS with a good sensitivity rating , 99db if I recall correctly . My question is this , if I were to go to larger speakers , say 500 watts RMS , and the amps to run them , would I gain more headroom ?


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## Studio (Dec 15, 2009)

Were you using 1 or 2 mics for the choir or did each member get a mic, also if you need more power see if your school has portable speakers for events in large rooms. My school has three sets of these Stagepas 500 and they would be great if we ever need more speakers in our theater(which really needs more) or our auditorium.


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## epimetheus (Dec 15, 2009)

Studio said:


> Were you using 1 or 2 mics for the choir or did each member get a mic, also if you need more power see if your school has portable speakers for events in large rooms. My school has three sets of these Stagepas 500 and they would be great if we ever need more speakers in our theater(which really needs more) or our auditorium.



I seriously doubt each member got a mic, the OP did say an 180 member choir...

I second what gpforet asked. Where would the distortion you were getting close to come from? Were you close to clipping at the board inputs, board outputs, amp inputs, or just overloading the speakers themselves?

From your description of your setup, you've got 3 dual channel amps, one for each row of speakers. Each amp paralleled (bridged or just inputs paralleled?), with 2 speakers (left and right) on one channel and the center speaker on the other. The critical speaker value that I didn't see was the speaker impedance. If each speaker is 8 ohms, you've got a little more speaker capability than you do amp power on your outside channels, and vice versa on your inside channels. If the speakers are 4 ohms, then you need to know the amp power rating at 2 ohm output impedance, if it can even drive that.


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## Studio (Dec 15, 2009)

180 thats a lot of people maybe I should pay more attention. I ment did he just have a few hanging mics or mics on stands, or more mics closer to the chorus. He could have been picking up the instruments also. Also are there sound clouds in the space, if the choir was near the back of the stage then sound clouds could have helped also.


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## mixmaster (Dec 15, 2009)

Another big question that hasn't been asked yet, were you comfortable with the overall level? IF you got bigger speakers and the correct amps to drive them, would you be able to use the extra power? or would the resulting overall level be to loud? Let's say you are at 100db already. Wouuld you really want the ability to go to 110 db for a chior/orchestra concert? If that's the case the orchestra needs to play quieter. OTOH if you could only get to 75 db, you may indeed need more rig.

How often do you need more volume? If this is the only time that you find yourself needing the extra boost, is it financially worth while to drop the money on new racks-n-stacks? Or would the money be better spent on better mics or something? OTOH if you are regularly running out of headroom on the system, it may be time to upgrade.

Either way, I would look at more than just the power figure. Chose your speakers based on the speaker output ratings (efficiency and max spl) that you need to cover your venue at the loudest you want to get (plus some headroom) and then get whatever amps are appropriate to drive them. 
Matt


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## whaleboat (Dec 15, 2009)

I had a very small amount of headroom I don't know how close to feedback I was in db , but it wasn't far . if I pushed it from -5 to 0 on the mains fader I bet I would have got a heck of a squeel . By distortion I mean the voices start sounding high and words that are supposed to end crisply kind of keep carrying on and everything starts running together in kind of a ringy blur . my set-up is on a rather small stage with the Wenger ceiling clouds and wall towers forming an aluminum box open at one end . I set up four tier Wenger choir risers in a horseshoe shape inside the box . I have eleven hanging choir mics , seven across the front at a decent heigth intended to pick up the second tier of vocalists and four across the back intended to pick up the fourth tier best . By the way , I've had choir concerts without the aluminum box and have had no problem with headroom . The orchestra sits in the space left inside the horseshoe , with the percussion section pretty much rubbing up against the bottom tier of vocalists . All the speakers are Renkus-Heinz 12 inch , 8 ohm .


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## rwhealey (Dec 15, 2009)

I wouldn't rely on wattage alone to measure how loud a speaker gets. A Source 4 is 575 watt, but it doesn't make a lot of noise...

You might also want to mess around with mic placement. I have very rarely gotten enough sound from hanging chior mics. 

How big is the space you're covering? I know a single 12 probably wouldn't be enough for the space I used to work in.


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## whaleboat (Dec 15, 2009)

No problem with clipping anywhere in the system , The house is 75 feet x 75 feet , has 1,000 seats , and was during that concert , a full house .


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## museav (Dec 15, 2009)

whaleboat said:


> I'm running a mono mix to three rows of cieling mounted speakers in the house , first row FOH , second row about a third of the way towards the back of the house , third row about two thirds back . Each row of speakers has three speakers running off of an amp that provides something like 475 watts into a 4 ohm load and 325 into an 8 ohm load . I have the right and left speakers running off one channel of the amp and the center speaker running off the other channel , and the amp is paralleled . The speakers are rated at 250 watts RMS with a good sensitivity rating , 99db if I recall correctly .


Let's see if I get this. Three rows of speakers from front to back. Each row has three speakers across, the left and right speakers are in parallel off one channel of an amp with the center speaker off the other channel with the amp run in parallel mode. On the stage you have eleven hanging choir mics, seven across in one row and four across in another. We don't know the mic, speaker or amp models, how high the speakers and mics are mounted, how the speakers and mics are oriented or aimed, what the speaker coverage is like, etc.



whaleboat said:


> My question is this , if I were to go to larger speakers , say 500 watts RMS , and the amps to run them , would I gain more headroom ?


Maybe or maybe not, it depends on several things from the speaker sensitivity to the resulting coverage. However, probably more important is that it is likely irrelevant to your problem as headroom and gain before feedback are two different and unrelated aspects of the system. The anomalies in the sound you note sound like you were starting to ring, which is right on the edge of feedback, thus it sounds like your problem is gain before feedback rather than clipping or headroom.


A few general thoughts. How big is the stage or more specifically, the shell? Where are the hanging choir mics relative to the singers? Seven mics across seems like a lot unless it is a very large stage or the mics are very close to the singers. Have you applied the 3:1 rule ( see http://www.sennheiserusa.com/media/pdfFiles/ChoirMikingTip_HOW.pdf and http://www.sennheiserusa.com/media/pdfFiles/ChoirMikingTip_HOW.pdf)? 

What kind of mics are they and how are they aimed? If the mics are hyper or super cardioid then their pattern probably includes a back lobe and it is not unusual for that lobe to end up pointing right at the speakers. In some cases you may have to do some counterintuitive things like aim the mic not to maximize the pickup of the singers but rather to minimize the pickup of the speakers.

How are the speakers mounted and what are they? Is the floor or ceiling sloped? Are the speakers aimed straight down or tilted to be aimed further back in the house? How much does the first row of speakers impact the stage? Given the size of the orchestra and choir and the natural sound they provide, could you simply turn down the front row of speakers?

Do you have any system processing such as EQ for the speakers? Has any of that been optimized or adjusted to try to improve the potential gain before feedback?


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## hsaunier (Dec 16, 2009)

One source of the clarity issue could be more of a delay problem. That many speakers spread over the house would be a nightmare to try to aline. Where is your mix position? If you are at the rear of the room and there has been no delay placed on any of the signals hitting all of those speaker you will be hearing the sound from the stage 4 different times. spkr row 3--- spkr row 2--- spkr row 1--- and finaly the accoustic sound itself will arrive last. Sounds like distortion to me regardless of the SPL.


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## mixmaster (Dec 16, 2009)

whaleboat said:


> I had a very small amount of headroom I don't know how close to feedback I was in db , but it wasn't far . if I pushed it from -5 to 0 on the mains fader I bet I would have got a heck of a squeel . By distortion I mean the voices start sounding high and words that are supposed to end crisply kind of keep carrying on and everything starts running together in kind of a ringy blur . my set-up is on a rather small stage with the Wenger ceiling clouds and wall towers forming an aluminum box open at one end . I set up four tier Wenger choir risers in a horseshoe shape inside the box . I have eleven hanging choir mics , seven across the front at a decent heigth intended to pick up the second tier of vocalists and four across the back intended to pick up the fourth tier best . By the way , I've had choir concerts without the aluminum box and have had no problem with headroom . The orchestra sits in the space left inside the horseshoe , with the percussion section pretty much rubbing up against the bottom tier of vocalists . All the speakers are Renkus-Heinz 12 inch , 8 ohm .



Based on this, it sounds like you have a gain-before-feedback issue. This is different than a system headroom issue. You can add speakers and amps and power till you run out of money or places to put them and you won't fix your problem. Actually, making thing louder may make the problem worse. Here's a couple things to think about.
You mention that you've done choir shows without the shell before and not had problems. Why add the shell this time. It's possible that the shell could be focusing sound from the house into the mics. Or it's possible that the shell is capturing some sound from the orchestra, which is then bleeding into the mics, which makes the choir harder to hear, so the mics get turned up, so they pick up more orchestra, and things spiral up from there.
I use hanging mics for our swing choir concerts and use 3 on a 28 foot stage. 11 mics in a small stage when the sound is confined by a shell seem like a lot of mics. Remember the 3 to 1 rule. Have you tried fewer mics? This may be a time when less is more. One thing I would try, next time you find yourself in this situation, is to run up right to the edge of feedback, and cue up each mic individually into your headphones. The feedback will probably be more obvious on some mics than others. Turn those mics off and see what effect, if any, that makes on the "good" sound. You may turn them off and find out that you don't need that many mics, and can weed out the troublesome ones.
Sometimes the band (or orchestra as the case may be) is just too loud. I fight this problem with our Jazz Choir concerts that sing in front of a live 5 piece jazz ensemble every year. If the band is louder than the max gain before feedback, sometimes the band has to turn down. You can't defy the laws of physics.
Most of the issues above are things you can look at without a lot of extra gear. If you don't have one, a good eq can help, and if there's no delays to align the 3 rows of speakers, that's not helping your intelligibility issues either. But I would look to placement and acoustic issues before I start throwing money and new gear at the problem. 
MAtt


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## gpforet (Dec 16, 2009)

Sounds like your room was beginning to load-up on standing waves. Making it louder will make it worse.

If I'd have to guess I'd say it time for acoustic treatment of the space. 

Set up SMAART and run some program thru the system and start turning it up. If it's the room, then you'll see the transform getting worse as levels increase. Even more simple, just listen to the rig with music and see at what level you lose articulation. My quess it's going to be at around the same level (SPL wise) as where you began to lose articulation with your choir.


whaleboat said:


> I had a very small amount of headroom I don't know how close to feedback I was in db , but it wasn't far . if I pushed it from -5 to 0 on the mains fader I bet I would have got a heck of a squeel . By distortion I mean the voices start sounding high and words that are supposed to end crisply kind of keep carrying on and everything starts running together in kind of a ringy blur . my set-up is on a rather small stage with the Wenger ceiling clouds and wall towers forming an aluminum box open at one end . I set up four tier Wenger choir risers in a horseshoe shape inside the box . I have eleven hanging choir mics , seven across the front at a decent heigth intended to pick up the second tier of vocalists and four across the back intended to pick up the fourth tier best . By the way , I've had choir concerts without the aluminum box and have had no problem with headroom . The orchestra sits in the space left inside the horseshoe , with the percussion section pretty much rubbing up against the bottom tier of vocalists . All the speakers are Renkus-Heinz 12 inch , 8 ohm .


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## gpforet (Dec 16, 2009)

It does when dropped from from trim height into a hardwood surfaced stage. Sadly, I know from experience when a lift-line failed.....


rwhealey said:


> I wouldn't rely on wattage alone to measure how loud a speaker gets. A Source 4 is 575 watt, but it doesn't make a lot of noise...


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## whaleboat (Dec 16, 2009)

Thanks , as always the people at controlbooth have been helpful and informative .


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## museav (Dec 17, 2009)

gpforet said:


> Sounds like your room was beginning to load-up on standing waves. Making it louder will make it worse.
> 
> If I'd have to guess I'd say it time for acoustic treatment of the space.
> 
> Set up SMAART and run some program thru the system and start turning it up. If it's the room, then you'll see the transform getting worse as levels increase.


Standing waves are location specific, move the mic a bit and you can get a very different response, in fact not a bad way to establish if an anomaly may be a result of a standing wave or specific surface reflection. Standing waves also tend to be low frequency phenomena in larger rooms, large rooms tend to be reverberant rather than modal controlled. So unless the feedback is occurring primarily at low frequencies, which could also be related to the speakers and mics being less directional at lower frequencies, and changes if you move the measurement mic a foot or two, then you might want to first look elsewhere. Also, if you use program material for the source then it has to have content at the frequencies that relate to any standing wave problems, a transfer function let's you see what happens to the original signal but there has to be relevant content in the original signal for it to have any meaning.


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## gpforet (Dec 17, 2009)

I agree with you Brad. For me, lack of articulation is my first indication that I'm getting a lot of reflection. I didn't mean to imply that the only acoustic component loading the room was low freq. and I do suspect that he's got quite a bit of reflection happening. My main intend was to suggest that the room may have been the culprit to lack of clarity as SPL increased.

Do modes grow in size with increased SPL? 


museav said:


> Standing waves are location specific, move the mic a bit and you can get a very different response, in fact not a bad way to establish if an anomaly may be a result of a standing wave or specific surface reflection. Standing waves also tend to be low frequency phenomena in larger rooms, large rooms tend to be reverberant rather than modal controlled. So unless the feedback is occurring primarily at low frequencies, which could also be related to the speakers and mics being less directional at lower frequencies, and changes if you move the measurement mic a foot or two, then you might want to first look elsewhere. Also, if you use program material for the source then it has to have content at the frequencies that relate to any standing wave problems, a transfer function let's you see what happens to the original signal but there has to be relevant content in the original signal for it to have any meaning.


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## gpforet (Dec 17, 2009)

Oh, I wasn't referring to feedback at all, strickly the audio blurring he experienced.


gpforet said:


> I agree with you Brad. For me, lack of articulation is my first indication that I'm getting a lot of reflection. I didn't mean to imply that the only acoustic component loading the room was low freq. and I do suspect that he's got quite a bit of reflection happening. My main intend was to suggest that the room may have been the culprit to lack of clarity as SPL increased.
> 
> Do modes grow in size with increased SPL?


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## museav (Dec 17, 2009)

gpforet said:


> I agree with you Brad. For me, lack of articulation is my first indication that I'm getting a lot of reflection. I didn't mean to imply that the only acoustic component loading the room was low freq. and I do suspect that he's got quite a bit of reflection happening. My main intend was to suggest that the room may have been the culprit to lack of clarity as SPL increased.


I actually meant to include a comment that I agree that the room can definitely be a factor but forgot to do so. Sorry!

I also made an assumption that I did not make clear. As I noted, room modes in larger spaces are typically a low frequency phenomena. They might affect bass, kick drums, timpani, bassoons, etc. but typically aren't as much of a concern for choir due to both the frequency content and that a choir represents multiple sources distributed over a large area. So I assumed them to be a less likely problem due to the choir application.


gpforet said:


> Do modes grow in size with increased SPL?


If all else remains the same, the peak amplitudes of standing waves resulting from room modes will also grow in amplitude as the source increases in amplitude. The zero points still stay zero.


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## gpforet (Dec 18, 2009)

Thanks for the info....looks like I may need to spend a little time in study hall.


museav said:


> I actually meant to include a comment that I agree that the room can definitely be a factor but forgot to do so. Sorry!
> 
> I also made an assumption that I did not make clear. As I noted, room modes in larger spaces are typically a low frequency phenomena. They might affect bass, kick drums, timpani, bassoons, etc. but typically aren't as much of a concern for choir due to both the frequency content and that a choir represents multiple sources distributed over a large area. So I assumed them to be a less likely problem due to the choir application.
> 
> ...


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## FMEng (Dec 19, 2009)

I agree with Mixmaster, this is a gain before feedback problem. He uses the description as a "ringy blur." That sounds like a system on the edge of feedback. Ringing is the classic sound of a system that is unstable and just going into feedback. This theory is also supported by the fact that he did not have the problem before reflective surfaces were added to the stage setup. If it is feedback, no amount of additional speaker output will improve matters. At that point, you need to reduce the amount of gain until things clean up.

Remember that for every doubling of microphones, the amount of gain before feedback is reduced by 3 dB. This could be a case of where fewer microphones might be better, as long as you can achieve a balance between choir sections. You need not try to pick up all of the singers, just the strongest from each section of tenors, altos, bass, etc. Try reducing the number of choir mics. I would try not to use more than eight on the choir itself.

Don't forget that as the mics get further from the singers, the level falls off (the inverse square law). Moving the mics closer will allow you to make them louder, but will tend to focus in on fewer voices. It's a compromise.
Internet Sound Institute - Microphones: Techniques for Choirs

Once you get levels to where the system stays clean, if the choir/orchestra balance is not good, then the director needs to work with the musicians to correct it. Trying to "fix" the system to compete with a 57 piece orchestra would be expensive folly, but the orchestra could easily play -3 dB softer or simply reduce the number of musicians in it.

Besides, I have to ask why 180 voice choir should need micing at all, unless the venue is absolutely huge or acoustically horrible?


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## David Ashton (Dec 20, 2009)

Two points, with many microphones they will cancel each other in places crating a combing effect.Second,your gain structure is possibly the most important factor in utilizing the power you have, and I rarely see gain structure set correctly.
http://www.gain.pe.kr/spboard/board.cgi?id=audio&action=download&gul=14


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## FMEng (Dec 20, 2009)

David Ashton said:


> Two points, with many microphones they will cancel each other in places crating a combing effect.Second,your gain structure is possibly the most important factor in utilizing the power you have, and I rarely see gain structure set correctly.
> http://www.gain.pe.kr/spboard/board.cgi?id=audio&action=download&gul=14



Comb filtering is what the three to one spacing rule is intended to avoid. It works very well.


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