I hear it all the time: “I just want to use a lapel mic. Those other mics are too big, and I can’t be bothered to stay in one place.” Sometimes, people just kinda miss the point.
Lapel mics work in television and on stage because of the size of the room. A TV studio may be 30 x 50 feet, with a 20 foot ceiling and plenty of acoustical treatment. A lecture hall will be similar. By the time sound reflections make their way back to the mic, they are diminished to the point that they are insignificant.
A typical radio studio, or home-office studio, may be only 8 x 10 feet with a 7 foot ceiling. Reflections come back to the mic’s position very quickly, with enough audio energy to be a niusance. This is part of the reason we speak so close to the mic… well, ego figures into it, but that’s another subject. Basically the equation is: more “me” equals less “room.”
The radio studio will have some amount of acoustical treatment (foam on the walls, maybe something on the ceiling). A home-office studio likely has nothing but hard, parallel walls, and hard furniture. Even up close to the mic, you sound like you’re talking in a tunnel.
Yes, a mic processor with gating can help to some extent. But the gate is only active when the talking stops. During speech, the reflections are clearly heard, and contribute to an indistinct and unclear sound.
Small rooms are a big challenge. Ideally, you would speak in a padded cell (think of a voice-over booth… nothing but foam everywhere). But since most of us would like more flexibility in the decor, we make compromises.
Do as much acoustical treatment as reasonable. Use a mic with a narrow pickup pattern. Consider a dynamic mic for its reduced sensitivity. Keep the mic close to the subject. Use a downward expander to reduce the background sound when the subject isn’t speaking.
In an acoustically perfect room, you would be free to use any type of mic you like. In the real world, things are different.