I run into this situation all the time with elementary and middle school age musicals.  I design and tech-direct about 10 shows at this age level each year.  It can be problematic...

It's very tricky to mix the lead actors on Body Mics with the chorus on Floor Mics.  Your sound operator needs to have his hands on the faders at all times and "play the sound board like a piano", as I say.  Because he needs to fade the offending mic as soon as in starts to hum, NOT after it already starts to whine! 

I often tell my sound crew that, "I WOULD RATHER HEAR NO MIC AT ALL THAN HEAR FEEDBACK".   So they should be prepared at all times to kill that offending mic, (or even kill the Masters if necessary - in a worst-case panic situation).  Yes, cutting off a microphone mid-song is bad...but having the "suspension of disbelief" smashed by screeching feedback is even worse!  Besides, an actor should be able to PROJECT.  Yes, our little kids might have small lungs and no stage experience, but a sound system is only intended for about 20% ENHANCEMENT of acoustical voices - for clarity sake - not for delivering 100% of the singing.   Hey, this is theatre, after all, not radio! 

So if little kids are incapable of projecting their voices in a standard proscenium theatre without the crutch of technology, then hey, maybe we need to re-think the mission statement of our youth theatre programs.  Maybe kids aren't ready to fill a big hall.  Maybe our "kiddie shows" should be staged in a Studio Theatre or other small "Found Spaces".  This is an issue that I deal with for 10 kid shows a year around here.  Just last month I reluctantly gave-in to a Director's demand to put my $850.00 Sennheiser/Countrymen earset mics on all 8 kids in a 4th grade production of "Grinch, the Musical"!   None of the mics got broken.  Whew!

So anyway, back to your particular floor mic situation.  I use the same Crown PCC area mics that you do, I bet.  But you must remember that each mic will pick up about a 20' wide area, so don't place them too close together or you'll get echoing, phasing or feedback.  My proscenium arch is 40' wide, so I put one floor mic mid-SL and one mid-SR, at the lip of the pit.  That way, my sound operator, (who is also a young kid), can bring up his right mic for a stage-left scene or his left mic for a stage-right scene.  We only bring up both floor mics if the entire cast is singing a big number.   And even then, you have to remember that the leads have all their body mics operating as well.   So there is some finesse involved here.  By the way, I usually don't place a floor mic center-stage on the apron because, generally, directors will put their lead actors center - and leads already wear lots of wireless mics. 

Technically, the way that a Floor Microphone works is that it uses the actual wood boards in your stage floor as it's own "pick-up membrane".  This is good, because it picks up a lot of "bounce" from the voices of our short little kids.  But, the drawback is that your sound crew has to watch out for too much stomping near the mics during dance numbers.  Another precaution is to keep kids from stepping on the floor mic itself - or it's wires.  Because a condenser mic uses Phantom Power, and when you step on the plug, the electrical connection will pop very loudly...once again shattering the suspension of disbelief...or some eardrums!  Another pitfall of floor mics is that they inevitably pick up "bleed-over" from your pit orchestra.  So don't mount them too close to the edge of the pit...or if you must, then install some kind of "back shield" as a sound barricade. 

Traditionally, floor mics and body mics are really only needed for musicals - to overcome the powerful pit orchestra.  If you are doing a straight play, you shouldn't need them.  Although sometimes I'll put a single floor mic center for a Shakespeare play in order to get a tad more verbal clarity, (and to send voices into my radio Headphones for the Hearing Impaired).

My main advice for a good show is to take the time in pre-production to write up a very detailed SOUND CUE SHEET for your crew and a WIRELESS MIC ASSIGNMENT SHEET for your actors. 

1)  The Board Operator, who has both ears open to hear what the audience is hearing.  Yes, he can use the Headphones to monitor mic levels from time to time, but he should NEVER wear the Intercom Headsets.  This background chatter will just distract him!  (I have his assistant wear the  Intercom Headsets; see below).    The Operator should be sharp and on the ball at all times...riding the levels and anticipating the next entrances.   He needs to anticipate every entrance so he won't "clip" the first two words of every line!  (Argh! That's a major pet peeve of mine!)  And like I said, he should "play the mixer like a piano" to eliminate the problems before the audience ever knows...and before that dreaded feedback ever happens.    

With these 3 dedicated techies on the ball, you should have a clean show.  Although, I must admit, for most elementary and middle school musicals, I do hire a local sound dude to sit behind the sound crew.   He gives critical over-the-shoulder coaching...at least during the Tech Rehearsal, First Dress with Orchestra, and maybe Opening Night.  Having this professional technician sitting up there at the Board frees me up to "put out fires" on stage with sloppy set changes, dangerous fly cues, and complicated light cues.  He's worth the money.

And if you want to read up on sound or teach it, then the best book by far I have found is this. In fact this was the textbook used in the sound course I took at the local community college a few years ago.

Well, sorry to drone on so long.  I hope some of this helps.  Sorry if I sounded to "preachy" about these sound issues.  (KEEP IN MIND THAT I AM NOT A SOUND EXPERT).  I just had to learn a lot of this stuff the hard way!  

Break a Leg...(not an eardrum!)     -Dana

 

You can also use feedback exterminator and again they are cheap or you could be daring and set up your EQ. The more bands, the better. One the the common problems is input gain so if you get that right, a lot of your problems will be minimised

 

John

 

Very true IMO singers and actors have become more and more spoiled and dependent on mics to do all the work for them.  But that's just me as a lighting guy and actor with a huge set of lungs on him, talking.  "Sing out Louise!"