You're going to have to adjust the gain on the receivers of each wireless set. Remember that there are limits to the distance the receiver can be from the transmitter, and that police bands and other kinds of radio transmitters can interfere with reception. Also, you will probably have much fewer problems with distortion and artifacts if you use a better quality mixer.
Wireless mics create problems all of their own. They have to be hidden on the talent so their frequency response is curtailed by the clothing worn by the talent (mostly loss of high end) and consistant pickup is more difficult as they turn their heads back and forth.
Boom mics are a much better option for most situations. The problem with boom mics is not the mics themselves but which boom mic is used in a given situation (short shotgun vs. long shotgun, polar patterns, etc.) and the person handling the boom. It's a serio-comic mantra in the industry that boom handlers have the arms of gorillas. They must hold the boom over their heads (and other often uncomfortable positions) for hours on end without creating any noise. They also need to be able to adjust the aim the mic from actor to actor for maximum pick-up, also without creating any noise, while they run alongside horses and cars, balance on trailers, etc.
The advent of the new digital field recorders is beginning to provide more options to the location sound team. Light weight field recorders of four tracks and more are beginning to come onto the market at reasonable prices (reasonable being under $10k). This allows for the running of the boom, a couple of lavs and another mic hidden on the set.
Here goes Uncle Bob jumping up on his soap box again.......
Sound for film and video is an art form, just like cinematography, lighting, scriptwriting, editing, set design, painting, composing, dancing, singing, playing the piano, etc. Yes, location sound is a very technical exercise, but doing it well is a true art form. A lot has been said about the rancor between the location sound and post sound people, but anyone who is good at either will tell you that the respect for well done work is mutual on both sides. Most of the time I want to smack the producer and/or director because they didn't allocate enough funds for the location sound or ignored it completely. Then they come to me and my fellow audio post engineers and want us to fix the unfixable. Yes, you can turn feces into diamonds, but it takes a couple of million years.
People will watch mediocre visuals if the sound is good, but if the sound grates on their ears it doesn't matter how good the visuals are. I have only recently started going out to movies again rather than buying or renting them because a new local theatre has great sound - big, full, powerful, clean but not abrasive or overly loud. I have been to theatres where people have walked out because the sound was overly loud or the theatre was not properly "tuned" for the film being shown. Yes, every film comes with a reel to optimize the theatre for the picture and sound, but many theatre owners haven't balanced their systems since it was set up for the first film shown after the system was installed. It'$ ju$t too expen$ive to pay the technician for a couple of hour$ when the film$ change over; and this when they are losing audiences to home theatres, high prices and their own ineptitude.
Anyway, I'll get off of my soap box now. Thank you for at least thinking about sound before you shoot.
