Handbook for Sound Engineers

Microphones 533

phone to the source distance requires an increase in the

gain of the amplifying system to produce the same

output level. This is accompanied by a decrease in SNR

and an increase in environmental noises including

reverberation and background noise to where the indi-

rect sound may equal the direct sound. The wanted

signal then deteriorates to where it is unusable. Distance

limitations can be overcome by increasing the sensi-

tivity of the microphone, and the effect of reverberation

and noise pickup can be lessened by increasing the

directivity of the pattern. The interference tube micro-

phone has these two desirable qualities.

The DPA 4017 is a supercardioid shotgun micro-

phone. It is 8.3 in (210 mm) long and weighs 2.5 oz

(71 g), making it useful on booms, Fig. 16-92. The polar

pattern is shown in Fig. 16-93.

The difference between interference tube micro-

phones and standard microphones lies in the method of

pickup.

An interference tube is mounted over the diaphragm

and is schematically drawn in Fig. 16-94.

The microphone consists of four parts as shown in

the schematic:

1. Interference tube with one frontal and several
   lateral inlets covered with fabric or other damping
   material.

Figure 16-88. Neumann U-87 microphone. Courtesy
Neumann USA.

Figure 16-89. Neumann U-89 microphone. Courtesy

Neumann USA.

Figure 16-90. Circuit of the Neumann U-87 condenser

microphone with electrically switchable direction

characteristic. Courtesy Neumann USA.

60 V to +60 V

1G 7

8 0

A

DC B

E

+

60 V 0 V +60 V

+

0 V

+60V

1G 7

G

D

1G 7 S

C