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Technical introduction

Microphones often must be placed near hard reflective surfaces. Two si-

tuations where this occurs are (Fig. 1) picking up/recording a drama or opera

with microphones near the stage floor, (Fig. 2) picking up/recording partici-

pants at a conference with microphones on desk stands on the conference

table or (Fig. 3) recording a piano with the mics near the open lid, or recording

an instrument surrounded by reflective baffles.

In these situations, sound travels from the sound source to the microphone via

two paths: directly from the source to the microphone, and reflected off the

surface (Fig. 1). Note that the reflected sound travels a longer distance than

the direct sound, so the reflected sound is delayed relative to the direct sound.

When the direct and delayed sounds combine at the microphone diaphragm,

this results in phase cancellations of various frequencies. A series of peaks

and dips is created in the net frequency response. This is called a comb-filter

effect. It colors the tone quality and gives an unnatural sound.

To solve this problem, we need to shorten the delay of the reflected sound so

that it arrives at the mic at the same time as the direct sound.

THE PZM

SOLUTION

In a PZM

, the diaphragm can be placed as close to the surface as desired.

Then the direct and reflected waves arrive at the microphone at the same

time, in phase (Fig. 3). This eliminates phase cancellations and results in a

smooth frequency response. The diaphragm is mounted in the “pressure

zone” just above the plate, a region where the direct and reflected waves are

effectively in-phase. This special microphone was designed to be used on

surfaces such as floors, walls, tables, or even piano lids. It includes a minia-

ture omnidirectional condensermic capsule, which is mounted face-down next

to a soundreflecting plate. The microphone diaphragm is parallel with and very

close to the reflecting surface.

THE PCC

SOLUTION

In the Phase Coherent Cardioid or PCC

Solution, the microphone diaphragm is

small enough so that any phase cancellations are above the audible range (Fig.

2). This results in a wide, smooth frequency response free of phase interference.

Unlike the PZM

which uses an omnidirectional mic capsule facing down, the

PCC

uses a supercardioid mic capsule facing horizontally across the surface.

Its directional polar pattern improves gain-before-feedback, reduces unwanted

room noise and acoustics, and rejects sound from the rear. Figure 4 shows the

difference in construction and polar patterns of the PZM

and PCC

Tech Made Simple

Fig.1 Fig.2

Fig.3 Fig.4

application guide

Microphone

Conferences and courtrooms

Suppose you need to reinforce

speech at a conference table

or in Courtrooms. You’ll use

several microphones fed into

a mixer (either standard or

automatic mixer). If you use

a standard mixer, each user

needs to manually switch his

or her mic on or off. Choose one of these switchable microphone models:

PCC

-130SW or PCC

-170SW. The switches of these microphones can be configu-

red to work three ways: On/Off the switch, Momentary on and Momentary off.

The PCC

-170SWO additionally provides remote sensing of switch closure. This mic

can be used e.g. with a video camera switcher. When somebody turns on his mic, the

camera aiming at that person is switched on. If you want to use an automatic mixer,

one of these non switch mic will do a perfect job: PCC

-130, PCC

-170, MB-3 or

MB-4. Typical placement for each microphone is at arm’s length from the user. Place

one microphone in front of each person or one between every two people.

For teleconferencing applications, see tips for Distance Learning and Teleconferencing

on the next page.

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