There are essentially four types of microphones, each with a different pickup pattern. Cardiod microphones are perhaps the most commonly used by speakers. These microphones pick up what's in front of them, not what's behind. Since they don't pick up as much sound from onstage speakers or monitors, they tend to prevent feedback. Omnidirectional microphones pick up sounds from all directions. If several people are singing and sharing a mike, for example, you'll need an omnidirectional microphone. Shotgun microphones are good at picking up sound at a distance (think sporting events); bidirectional microphones pick up sound from two sound sources, excluding all other sounds.
For a reasonable price, hotels and conference centers often can provide a sound system that's absolutely fine — despite what an audiovisual rental company might want you to believe. But the only way to know is to test the system with your own ears during a site inspection. Walk around the room as someone speaks through the mike. Is the sound clear? Is there a technical person on-site to help you with any problems? This is also the time to test the soundproofing between rooms, especially those with partitioned walls.
Work an audio technician into the budget (or find an expert volunteer) for all but the most basic microphone setups. If you plan to have more than one microphone, an audience of more than a few hundred people, microphones placed in the audience, or several speakers, it's critical to have a specialist on hand.
Your meeting — and your reputation — cannot afford to have trouble with the microphones. If you can manage to budget for backup equipment, do it. No one but you will notice the extra little gooseneck microphone on the lectern, but everyone will notice if the sound goes out.
Lavalier, or lapel, microphones should be clipped to the speaker's clothing four to six inches below the chin. If you get clothing noise, one trick is to put an overhand knot just below the microphone, with the loop about the size of a 50-cent piece. This will cancel out clothing noise below the knot.
Sources: Merriam-Webster Online, www.m-w.com; United Visual, www.unitedvisual.com; The Writing Works, www.thewritingworks.com; Audio Visual Innovations, http://rental.aviinc.com/support/presentation-tips.asp; Financial & Insurance Meetings, “Can You Hear Me in the Back?”