Brad is right on in his quote below. We need to educate sound people about the differences in gain-before-feedback of headworn mics vs. floor mics, just based on the difference in mic'ing distance.
We've found that many schools and churches who do theater cannot afford headworn wireless mics, and the sound operators cannot deal with them effectively. So floor mics are a
practical compromise. The laws of physics (such as the PAG/NAG equations) dictate the
gain before
feedback of any particular mic/
speaker system, and these laws suggest various ways to get the reproduced sound as loud as possible given the mic'ing distance of floor mics.
Some ways to optimize the gain-before-feedback of floor mics are:
* Place the loudspeakers closer to the audience than to the microphones. To do that, some schools rent
portable PA speakers on stands, and sometimes delay the speakers' signals so that the precedence
effect localizes the sound on
stage.
* If a
speaker must be used over the center of the
stage, try to use a
line array to reduce the sound radiation down toward the microphones.
* Reduce the number of open microphones (NOM) - turn up only one mic at a time when possible. The more mics that are on, the poorer the clarity and
gain before
feedback.
* Another way to reduce the NOM is to use one
amplifier channel and
loudspeaker per
microphone. Place the speakers close together.
* Use a
graphic equalizer, or automatic
feedback suppressor, to notch out frequencies that feed back.
* Place the mics as close to the actors as is practicable. If this creates the problem of the mics being stepped on, use a TM-125C mic which has a permanently attached cable, and no tiny TA3F
connector to break.
* Use highly directional mics, such as half-cardioids or half-supercardioids.
* Most important, teach the actors to project! The mics need something to
pick up.
-- Bruce Bartlett, Bartlett Microphones
Which seems to indicate that it may be the application of the mics, not the mics themselves, that is the problem. Boundary mics still have the same factors of
pattern,
inverse square law, phasing between mics,
etc. that all mics have. Go from a mic being 6" away from a performer's mouth to being 10' away and that's up to 26dB of
gain lost regardless of the mic. Push a mic from being back on
stage out to the front
edge or
stage apron and you are probably pushing it more into the
house sound
system coverage and into the mic's
pattern, thus more losses in
gain before
feedback.
What you often get with mics mounted 2' to 3' above the
stage is
combfiltering due to reflections off the
stage.