Now we can actually hang mics on actors. This requires at least passing attention, and perhaps coordination, with costumes, make-up, and wigs. My personal philosophy is that we are never going to be able to hide the fact that we are re-enforcing their voices; I don't try to hide the microphones, but I do try to keep them from being distracting.
First, the transmitter. The transmitter is about the size of a pack of cigarettes. Most take a pair of double-A batteries, and most batteries can safely get you through two performances. I can not underline how important it is to track and monitor the battery usage. Make an iron-clad routine of checking and replacing batteries; every mic needs to be checked before every show. It is NOT fun to have the batteries die when an actor is already on stage.
This means batteries are not a small cost. Multiply, say, 16 channels of wireless by two batteries each by five weeks of performance by five performances a week and you've got several hundred bucks worth of batteries.
The modern rechargeables -- the nickle-metal hydride stuff -- now work in most mics (the older batteries did not put out sufficient voltage). There is a bit of a start-up cost for them, and you have to be even more methodical to make sure they get back in the chargers after every performance.
Most theaters have constructed a belt for the mic pack; this is a wide belt of elastic with velcro fasteners and a pouch to hold the actual transmitter. Usually costumes will build and track them. My preference is to treat the belt as part of the costume; one the actor has found one that fits, it stays with their costume and is washed with their costume. Other theaters, it becomes part of the job of the Mic Wrangler to hang up belts to dry, and to put the mics in them before each performance.
The placement of the belt depends on the costume and the physical needs. Many women hang it low, so it doesn't obscure the natural waist. Actors that have to sit down a lot and do other physical actions place them higher, with the belt wrapping around their upper abdomen. Some need to place it as high as the small of the back, for which you can make a special "child-carrier" style mic belt. For some roles involving a great deal of tumbling and rolling about, a placement under one arm, like a shoulder holstered pistol, will work better.
And then you will have a show like Gypsy, or a role like "Princess Tiger-Lily" where there isn't enough clothing to hide the mic belt. For a recent Peter Pan we consulted with wardrobe and modified her bra so she could carry the transmitter there. For a production of Cabaret I made a mic bag from black taffetta with a thinner belt so when the actress disrobed it just looked like part of her garter belt. Another option is, strange as it may sound, to place the transmitter in the actresses' wig. Now you understand why I mentioned you may need to coordinate with wardrobe and wigs!
And while we are talking naked people... Before the transmitter goes into the pouch, it goes into a condom. Actors sweat, and water is never a good mix with electronics. (A warning; some actors have latex allergies. Actors, it seems, have LOTS of allergies. It is not easy to feed them!) This means someone has the unenviable task of shopping for extra-saver packs of extra-large, unlubricated condoms. Which when they are in the same order with double-A batteries and surgical tape and alcohol prep pads (very nice to have to wipe the oil from an actor's face before taping on a mic) can get you some very strange looks indeed.
Since a lot of people seem to be hitting this old entry, I'm updating with some new comments. Just worked with mic-in-wig on, of all shows, "The Drowsy Chaperone." JANET has backless dresses and lots and lots of quick-changes. And wore a wig for the role. So what we did; she french-braids her natural hair up on her head and pins that. We double-condom the mic pack and stuff most of the extra mic cable inside the condoms. She puts it on top of her head and pinned the wig cap over hair and pack, pulling the element out just enough to bobby-pin it near her hairline. The wig goes on top of that and look, ma, no wires.
Many wireless mics come packaged for lecture use; with the intention of clipping the element to tie or lapel or shirt collar. This does not work well for theater. Besides the fact that as the actor's head moves, the sound level will go up and down (they are moving in relation to the mic), placement on the upper chest puts the mic in the shadow of their chin. You end up with a hollow, displeasing sound.
The most natural sound is, for most people, from a mic placed high on their forehead, just peeping out from behind their hair. Many wigs make this an obvious choice -- and the element can be clipped into the wig cap itself. However, many theatrical shows are period dramas, and far too many involve hats (as well as other headgear and wigs that do NOT support having a microphone under them).
I just finished Shrek, Jr. with a grade-school cast. Because of innumerable mic changes and the general skill level of the children the company choses to use lapel positions for everyone. I was able to push a few microphones on to caps, ears, and otherwise out of chin shadow, but there was still significant volume changes and handling noise. I ran bus compression at near limiter levels and extremely fast attack, and rolled off the bottom up above 200 Hz and that tamed the handling noise a little -- at least to where it didn't deafen everyone when it happened.
This is why my fall-back position is ear. At the basics, the element is positioned on the cheekbone just forward of the actor's sideburns. The cord runs over the top of their ear, behind the ear, then is tucked up along the hairline to the back of their head...at which point it descends into their shirt. It is secured here by surgical tape; one piece just behind the element itself, one piece behind the ear, and one at the nape of the neck (for actresses with longer hair, C7 or the seventh cervical vertebrae is the default.) For an actress with a low-cut dress, the usual is to tape down her spine. Remember when placing the tape at the back of the head to have the actor turn away from you; you want to leave just enough slack to permit full and comfortable head movement without pulling the tape off!
(Nexcare flexible tape is the top choice for theaters...just like Goo Gone is the secret potion for cleaning tape residue OFF the mic cords.)
The clip will still need a little tape to re-enforce it. But for most actors it is more comfortable and often more secure. However, it is also more visible, and less flexible.
Because, just like everywhere else in sound, it is all about location, location, location. An inch below the cheekbone and the sound will be heavy and thick (you pick up more resonance through the cheek). Point too high and it will be nasal, get too close to the mouth and you'll hear lip noise and possibly even breath pops. And if the actor is going to use a phone, lie on the ground, or (as is usually the case!) sing a duet, you need to plan and try to get the mic to the opposite side.
As said above, many wireless sets are packaged for presenters, and thus you'll have some black soup can of an element that was designed to clip to a lapel. There really isn't much you can do to hide it. Also, the typical elements packaged with a wireless range greatly in quality. The Shure SM84/86 are not bad sounding, although they are giant soup cans that are difficult to tape to an actor's face. The Shure SM93 is the cheapest element they make, and the smallest, so of course everyone buys it. It is fragile, however, and sounds like crap. Sennheiser's otherwise lovely EW series come out of the box with a black golf ball...but at least the golf ball sounds decent.
Although there are other good elements out there, and you will hear lots of arguments about the pros and cons (especially when you get into the high end), the wireless equivalent of the SM57 is Countryman's B3. The element is match-head size, the cord robust, it is available in six colors that at least get you closer to matching skin tone and hiding the mic, it sounds great -- and it costs only about twice what you spend on a '93. Given how much longer it lasts (and you can actually clean them, too, in alcohol) the savings are obvious.
Getting towards the higher end, four hundred bucks will get you a Countryman E6, which is their version of the "Madonna-mic." Unlike the latter, the B6 is pin-head thin, with a whisker of a wire boom. From forty feet away it is completely invisible.
Now, you can actually paint cords to try to hide the mics better. Painting down is better than painting up; lighter colors look like a scar, but darker colors will look like a shadow, and be more invisible. I use Deco-color paint markers myself. They aren't easy to apply, and tape residue gets more gummy on top of them, but they don't seem to hurt the mic, they last for a while without coming off on clothing or anything, and you can clean it off with Goo Gone.
I suppose I should have also mentioned the "Halo" rig, which is a scheme using a thin elastic to secure a microphone at the hairline. I've never built one myself, though; I've always clipped to a wig cap, used hair clips, or taped to the forehead. As I said; my philosophy is that we can't hide that we are using them, so I don't try to make them completely invisible. I just try to make them not distracting...I really don't want to make the cast look like they were replaced by Secret Service agents.
The Basics of Mic'ing a Cast IV