Sound Reinforcement in a Small Theater

[AsherSB]

I work at a small (~100 seat) Children's theater. The space isn't particularly large, but we still use mics over the stage (4 Rode NTG-1s) that go to speakers at the back (2 Gemini RS-408s). Right now the system is out of commission, and I'm redoing it. The mics previously pointed in from the side of the stage, but I think that mounting them facing forward would cut out feed back issues that we have had in the past. We need to make the kids on stage as loud as we can, but right now all our efforts are plagued by high feed back, any thoughts on a more workable solution?

Notes:
-The ceiling is around 7ish feet from the stage floor, and 9ish feet from the house floor.
-the front of the stage is probably around 20-25 feet from the back speakers.
-We have $200, at most $300 to spend on our efforts.

I will post pictures of the space, accurate measurements, and the sound board we will be using as soon as I can tomorrow.

(We open in less then a week, and my window for ordering closes soon, so time is of the essence.)

Thanks!

 

[Lextech]

So are you saying that your speakers are facing the stage from the back of the room?

 

[dbaxter]

I think the point Lextech was trying to make is never have your speakers behind your mics. Mics > Speakers > Audience path will reduce your feedback problem.

 

[jkowtko]

It sounds like the speakers are behind the audience. If so, that is both prone to feedback and disorienting to the audience. I suggest the first thing you do is to place the speakers in front of the audience flanking the stage. If you can afford to get a third small speaker, hook up a center speaker as a center fill and place it on the floor just in front of the stage facing the audience. The combination of the three speakers will give you a good wall of sound reinforcement for the actors on stage, and it will also pull the sound stage into the center of the stage area. I use a center fill in this way for my middle school concerts and it works very well. You may be able to find an Anchor AN-1000X used for under $100 ... They are great speakers (I have 3 of them).

 

[FMEng]

In addition to speaker placement, the NTG-1 has a very poor pattern for this kind of use. It picks up a lot from the rear. Specs show its tail is only down -7 dB. Something like a Crown PCC-160 or Bartlett Mic C would work better.

 

[jkowtko]

As far as mics go ... you are using rather bulky shotgun mics. If you can find smaller mics to hang from the ceiling and point 45 degrees upstage, or even just strsight downward, hanging them at about 8 foot spacing will allow you to pick up a lot of the kids voices at moderate volume and have good feedback control.

At our school, for the kids choir I use four Beheringer C2s on boom stands, positioning the mics about 8 feet apart, 7-8 feet off the ground, and pointed downward at a 45 degree angle towards the risers. I actually only use two channels for this as I have the mics paired up with XLR Y-connectors. It works great, and the kids sound great through the PA. The choir is on the left side of the gym and my left PA speaker (Mackie SRM450) is only 8-10 feet from leftmost mic. And I still get plenty of GBF.

In the case with kids, increasing the number of mics may help. If you can mount or hang them from the ceiling, put four across the front 1-2 feet behind the front of the stage, space them 8 feet apart, and then four more if you can in a line about 8 feet upstage from there. It will end up looking like a corporate conference room but you should be able to pick up the kids comfortably enough to get their voices into the room (with your stage-flanking speakers and center fill.

Just so you are clear, the goal with this type of sound reinforcement is to pull out the voices just enough so the audience can hear them. This will not sound like a rock musical

 

[AsherSB]

I forgot to mention that we have another RS-408 as a center speaker, and to clarity the back of theater speakers face in towards the audience from the sides. I know the NTGs are far from ideal, but they're what we have. We also have 4 15 inch mains, also Gemini, that are also used for stage monitors. I will have more info soon.

 

[jkowtko]

Wow these are tiny speakers ... basically monitors. My immeidate thought is to place them on the stage L, C, R positions facing the audience. If you want to hang or stand the L and R speakers up higher, maybe 6-7 feet off the ground, on the sides of the stage opening, that would raise the sound field a bit. You want these speakers to sugment the natural voices coming from the kids mouths -- not compete with it. so they should be in the same general location as the actors themselves.

If you can send a pic of the stage front area showing the front lip of the stage, the stage ceiling, and a bit of the walls on each side, I could annotate and send back my suggestions on where to place speakers and mics.

Thanks. John

 

[AsherSB]

Update: We just ordered 4 C2s, planning to hang them over the stage. Two of the NTG-1s have been repositioned to face the stage. We will be using a Presounus StudoLive 16.0.2, acting as a stand in for our 16.4.2. I know that the RS-408s are small, but their output is enough for our size, and pictures of the theater are attached (It's much cleaner for shows, but we are still installing the set for our next show.)

 

[jkowtko]

Interesting little space. I wonder if the reflections off the walls and ceiling are hurting you.

Here's a pic showing me first thoughts on where to place things. You'll probably have to play with locations a bit until you find something that works best.

* First, remove that speaker hanging from the ceiling on the right side of the room. This space is too small to require a rear fill, and that just looks like it owuld mess up the sound
* My first guess for L and R positions are wall-mounted where I have the red ovals. Since you already have one speaker wall-mounted I figure you could do both of them and free up some floor space from that tripod stand. If you want to use two tripod stands thats' okay ... just position these two speakers symetrically in the room. angle them in only slightly as you have done with the left speaker ... the right one looks like it's at too much of an angle, but that's probably because you have it mounted so far back into the room. If you can hang aheavy curtain cloth on the wall approx where the thin blue squares are it will help to cut reflections off of the wall and keep the sound as clean as possible.
* I positioned the center speaker on the first step. If the kids are going to use that step, then put the speaker on the floor. Keep it upright, not laying down, so the dispersion angles are correct and it will lessen the chance of feedback. I generally run the center speaker at a lower volume than the main LR speakers. The net effect of the three speakers is that wherever you are in the room you should be able to hear the actors equally. To test the speaker setup, play some of your favorite music on medium volume and walk around the room. It should sound about the same no matter where you are.
* Guesswork again on the mics, but that's about a 8 foot spacing. Since you have a lot of lighting hanging down, I suggest hang the mics as low as you can get without the kids knocking them around. I drew in three rows of mics, but I don't know if the rear section of the stage is going to be used.

Overall I would start out with the goal of low sound reinforcement, getting to head the kids clearly from the rear of the room, but without trying to blast them.

If the grand piano is going to stay there and be used for the performances, that is going to be a problem. I suggest you get an electronic keyboard and pump the music through the main speakers. That will give you much more control to blaance the instruments vs vocals.

So, anyway, that's how I would start with this space not knowing how it sounds.

-- John

 

[damjamkato]

At our school, for the kids choir I use four Beheringer C2s on boom stands, positioning the mics about 8 feet apart, 7-8 feet off the ground, and pointed downward at a 45 degree angle towards the risers. I actually only use two channels for this as I have the mics paired up with XLR Y-connectors.l

I just want to quickly point out that this is not a good practice to get in the habit of. Y-Cables are okay for splitting a signal, but not for combining two discrete sources.

 

[jkowtko]

I just want to quickly point out that this is not a good practice to get in the habit of. Y-Cables are okay for splitting a signal, but not for combining two discrete sources.

Yes that's the theory. However I've been doing this for 6 years now, I record in 24-bit wav format, and have never noticed an issue with those channels.

Maybe it's just the C2s that work properly in a Y.

 

[damjamkato]

Yes that's the theory. However I've been doing this for 6 years now, I record in 24-bit wav format, and have never noticed an issue with those channels.

Maybe it's just the C2s that work properly in a Y.

Sure, you'll still pass audio, however equipment damage could still happen in long term. Here is a good explanation of why it isn't the proper way of combining two signals.

 

[jkowtko]

The document talks about mixing powered outputs, which I agree is a no-no ... a more extreme example would be Y-ing two power cords together and the plugging both sides into the wall output ... wouldnt' want be around when someone tries that!

I am talking about unpowered microphones, which provide a small voltage fluctutation based on a (phantom) power voltage being supplied by their common power supply (at the mic preamp XLR input). The only real "danger" I would be concerned about is the signal from the two sources not combining nicely resulting in poor quality sound from that channel. However I am not seeing any of that.

 

[TimmyP1955]

Mics that are combined directly are driving a much lower impedance load than is intended (as each is driving the output impedance of the other). As such, performance will suffer to some degree. Phantom voltage may also be reduced owing to the extra load of the second mic.

 

[jkowtko]

All I can say is -- try it. If you don't like it, then take out the Y and use more input channels. But if it sounds fine, then you can save on the use of input channels. Those mics are pretty much all picking up the same audio anyway, just at different volumes depending on where the source is.

 

[DuckJordan]

Saying I've been doing it for 6 years and haven't had a problem with it is like saying "I've been rigging with hemp rope from Home Depot, and haven't had a problem". Doing any sort of Passive Y on microphone, DMX, or speaker lines, while may not cause issues right away, are likely destroying microphones. Suggesting to have the OP Y the microphones together when there was nothing said about Mic inputs being a problem is frankly unhelpful. I do believe that his best option is to get a bit better shotgun mics hung from the ceiling angled 45* outwards from center as well as roughly a 20* down angle.

Speaker postion isn't Ideal but doesn't look to be causing the issues. Feedback is as much Mic placement as it is amplification. Get the mics closer to the source means you can get more volume out of the amplification stage before getting feedback.

 

[jkowtko]

I am just telling you my experience. I am an engineer, trained to be skeptical, and this is one of those things I am not skeptical about. Cheap rope to hang heavy objects above people's heads I would be more concerned about ... but not this.

Again, these audio sources are not powered. Check out this web page that describes what a basic condenser mic is inside:

http://www.mediacollege.com/audio/microphones/condenser.html

and check out this web page that discusses what happens when you connect two capacitors in parallel.

http://farside.ph.utexas.edu/teaching/302l/lectures/node46.html

In my opinion, not a whole lot going on here. The worst I would expect is the combination of the two discharge voltages of the capacitors not syncing perfectly, which would translate into signal interference and thus poor sound quality. I am not worried about the discharge voltage of two mics vs one exceeding the phantom power voltage range and somehow zapping my sound console. Look at the range of phantom power --

http://www.tangible-technology.com/power/Phantom_Power_connect.html

So while I will back off from making a recommendation, I will tell you that this was some of the information I researched, and some of my thought process when deciding to do this. I am also working with Behringer C2's at $50/pair, so not a lot of valuable equipment at stake. But I would probably Y my CAD M179s without hesitation. If you live in the SF Bay Area and would like to drop by to see the next time I do a concert (which will be in May), I would be happy to let you check out my setup.

Again, I would not do this with a powered source, which includes battery powered mics.

 

[robartsd]

Saying I've been doing it for 6 years and haven't had a problem with it is like saying "I've been rigging with hemp rope from Home Depot, and haven't had a problem".

I have to say risking life safety is not equal to possibly damaging expensive equipment. (But thanks for bringing up potential problems with the passive Y.)

 

[FMEng]

Again, these audio sources are not powered. Check out this web page that describes what a basic condenser mic is inside:

http://www.mediacollege.com/audio/microphones/condenser.html

and check out this web page that discusses what happens when you connect two capacitors in parallel.

http://farside.ph.utexas.edu/teaching/302l/lectures/node46.html

In my opinion, not a whole lot going on here. The worst I would expect is the combination of the two discharge voltages of the capacitors not syncing perfectly, which would translate into signal interference and thus poor sound quality. I am not worried about the discharge voltage of two mics vs one exceeding the phantom power voltage range and somehow zapping my sound console. Look at the range of phantom power --

This presents a misunderstanding of how condenser mics work. The charged plates of the mic element produce a voltage source of extremely high impedance. Therefore, every condenser mic has some type of internal pre-amplifier to buffer and boost the signal to drive the cable and mixer preamp. The internal preamp is what the manufacturer is referring to when they describe tube or FET stages in their mic.

Connecting two mics together with a Y cord won't harm anything, but the results are likely to be less than stellar. Most likely, there will be a gentle, low frequency roll off at 6 dB/octave, because the output stage is capacitively coupled, and it would be loaded down by the output impedance of the other mic. At what frequency the roll off starts is anyone's guess without knowing internal component values. It could be surprisingly high.

This could be done better by using a pair of resistors in both branches of the Y cord. Metal film resistors of around 330 ohms should work. Put them in series with pins 2 and 3 inside the female connectors.