Handbook for Sound Engineers

Microphones 521

16.5.3 Polarity

Microphone polarity, or phase as it is often called, is
important especially when multiple microphones are
used. When they are in polarity they add to each other
rather than have canceling effects. If multiple micro-
phones are used and one is out of polarity, it will cause
comb filters, reducing quality and stereo enhancement.
The EIA standard RS-221.A, October 1979, states
“Polarity of a microphone or a microphone transducer
element refers to in-phase or out-of-phase condition of
voltage developed at its terminals with respect to the
sound pressure of a sound wave causing the voltage.”
Note: Exact in-phase relationship can be taken to
mean that the voltage is coincident with the phase of the
sound pressure wave causing the voltage. In practical
microphones, this perfect relationship may not always
be obtainable.
The positive or in-phase terminal is that terminal that
has a positive potential and a phase angle less than 90°
with respect to a positive sound pressure at the front of
the diaphragm.
When connected to a three-pin XLR connector as per
EIA standard RS-297, the polarity shall be as follows:

• Out-of-phase—terminal 3 (black).


• In-phase—terminal 2 (red or any color other than
  black).


• Ground—terminal 1 (shield).

Fig. 16-63 shows the proper polarity for three-pin
and five-pin XLR connectors and for three-pin and
five-pin DIN connectors.
A simple method of determining microphone
polarity is as follows:
If two microphones have the same frequency
response and sensitivity and are placed next to each
other and connected to the same mixer, the output will
double if both are used. However, if they are out of
polarity with each other, the total output will be down
40–50 dB from the output of only one microphone.
The microphones to be tested for proper polarity are
placed alongside each other and connected to their

respective mixer inputs. With a single acoustic source

into the microphones (pink noise is a good source), one

mixer volume control is adjusted for a normal output

level as indicated on a VU meter. Note the volume

control setting and turn it off. Make the same adjust-

ment for the second microphone, and note the setting of

this volume control. Now open both controls to these

settings. If the microphones are out of polarity, the

quality of reproduction will be distorted, and there will

be a distinct drop in level. Reversing the electrical

connections to one microphone will bring them into

polarity, making the quality about the same as one

microphone operating and the output level higher.

If the microphones are of the bidirectional type, one

may be turned 180° to bring it into polarity and later

corrected electrically. If the microphones are of the

directional type, only the output or cable connections

can be reversed. After polarizing a bidirectional micro-

phone, the rear should be marked with a white stripe for

future reference.

16.5.4 Balanced or Unbalanced

Microphones can be connected either balanced or

unbalanced. All professional installations use a

balanced system for the following reasons:

• Reduced pickup of hum.

Figure 16-62. Typical semiprofessional, hi-fi microphone to
preamplifier wiring.

Microphone Preamplifier

Microphone Black

Shield 1/4 phone plug

Figure 16-63. Microphone connector polarity.

2

3

1 5

4

3

2

1

3-contact XLR:

1 - Ground

2 - Audio (In-phase)

3 - Audio (Return)

1 - Ground

2 - Audio (In-phase)

3 - Audio (Return)

4 - Audio (In phase)

5 - Audio (Return)

A. XLR connectors.

3

2

1

2

3 4

5

3-contact DIN:

1 - Audio (In phase)

2 - Ground

3 - Audio (Return)

5-contact DIN:

1 - Ground

2 - Left (Return)

3 - Right (Return)

4 - Left (In-phase)

5 - Right (In-phase)

B. DIN connectors.

1

5-contact XLR:

} Channel 1

} Channel 2