Reply: I'm assuming that the voices in the room are not amplified with a PA system.

Ceiling mics

Ceiling mics are generally not recommended because they are far from the participants, resulting in a muddy sound. But if table mics are not an option, ceiling mics may be your only choice.

Suppose a room is 30 feet x 55 feet and 8 feet high. The area populated by the meeting participants would be maybe 20 feet x 45 feet.

To achieve equal volume pickup of everyone, the mics should be spaced twice the mic-to-mouth distance. So if the mics are 4 feet above the participants' mouths, the mics should be 8 feet apart. You'd need about 8 mics to cover all the participants. PZM-10 microphones are low-cost and easy to install in the ceiling.    PZM mics

If the ceiling is more than 8 feet high, consider using hanging mics such as the Crown CM-30 or CM-31. That way the mics can be closer to the participants. The CM-30 has an electronics module with screw terminals in the ceiling. The CM-31 has an XLR connector.    CM mics

Be sure to plug the mics into an automated (gated) mixer so that only one mic is on at a time. This greatly increases clarity.

A popular automatic mixer is the Shure SCM810:

Table mics

If the mics can be on the conference table, you can use one of these Crown mic models. Place each mic arm's-length from each participant, or arms-length between every two people.

PCC-170: Supercardioid, best quality.

PCC-170SW: PCC-170 with on-off switch.

PCC-130: Cardioid.

PCC-130SW: PCC-130 with on-off switch.              PCC mics

The Mini Boundary mics below are about 1 inch diameter:

MB-1: Plugs into a metal cup in the table. Use with MB-100 or MB-200 interface.

MB-2: Plugs into a phone jack in the table. Use with MB-100 or MB-200 interface.

MB-3: Installs in the table, has an XLR connector.

MB-4: The mic and its cable lie on the table. Has an XLR connector.

MB-4E: Mini boundary mic. Connects to an MB-100 or MB-200 interface which accepts up to 4 mics.    MB mics

If table noise is excessive, or the mics are often covered up by papers and notebooks, consider using Crown CM-30 or CM-31 hanging mics, each mic arm's length from every two people.

Or use Crown LM-201 or LM-300A lectern mics.           LM mics

Blackberry devices will cause interference in the mic signal. Please see this link: