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Boundary Microphones: Sonic Problem Solvers for Your House of Worship


Imagine a microphone that is nearly invisible, yet can provide clear and natural sound over your sound system. That's a boundary microphone, or surface-mounted mic. It lies on the floor or on a table and picks up sound from there.

Some examples are the Crown PZM series, Crown PCC-160, Bartlett TM-125, Astatic 901R, Audio-Technica U851R, Shure MX391, and AKG C 547 BL, C 680 BL, and C 400 BL.

How can a microphone sound good on the floor? Basically, boundary mics are designed to solve the following problem: Sound reflections off the floor or table top interfere with the direct sound from people or musical instruments, sometimes causing a "filtered" or "hollow" sound quality. Boundary mics remove the sonic effect of surface reflections, so the resulting sound is natural -- more like a real person or instrument.

As another benefit, surface-mounted mics are low-profile -- no mic stands to clutter the stage, no booms to adjust.

Boundary mics can have an omnidirectional (all-around) pickup pattern like the Crown PZM series, or a unidirectional pattern such as cardioid or supercardioid. Uni boundary mics tend to pick up less feedback, room acoustics and background noise than omni types.

A boundary mic should be placed on a large surface to have adequate bass response. Such a mic on a small pulpit can sound thin (weak in the bass). Boundary mics sound best on a floor or large table top.

Some applications for surface-mounted microphones are:

  • Choir
  • Altar table
  • Drama
  • Small musical ensembles or recitals
  • Let's go over each application.

    A choir can be picked up well with miniature mics hung a few feet in front of the singers and over their heads. But it's easier to place a few boundary mics on the floor in front of the choir. Use one microphone in the center of every 20-30 foot span of singers. A choir of 30 to 45 voices should need only two or three mics.

    Altar table
    Place a boundary mic on the table aiming at the people speaking. It will clearly pick up speech.

    Drama sound reinforcement
    Many houses of worship put on plays or musicals. One-to-three supercardioid boundary mics on the stage floor ("floor mics") can amplify the actors' voices. Place the mics about 1 foot from the front edge of the stage. To reduce feedback, mount the loudspeakers close to the audience and far from the mics.


    How many mics do you need?

    20’ stage: 1 mic center stage.
    25-30’ stage: 2 mics 12 to 15 feet apart.
    35-40’ stage: 3 mics 15 feet apart.
    45-50’ stage: 3 mics 17 feet apart.

    Floor microphones tend not to pick up floor thumps or vibrations. They do pick up footsteps, but so do your ears -- you expect to hear walking sounds when the actors are walking.

    Recording small musical ensembles or recitals
    A boundary mic (or a pair for stereo) on the stage floor can make high-quality recordings of a piano soloist, singer, singer/guitarist, string quartet, and so on. A cardioid boundary microphone designed specifically for recording is the Bartlett TM-125HP.

    I hope these suggestions offer some alternatives to stand-mounted mics. Give boundary microphones a try -- you may be delighted with the results.

    Bruce Bartlett

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