Handbook for Sound Engineers

536 Chapter 16

allowing the high frequencies to enter the tube only near

the diaphragm. This makes the tube look shorter at high

frequencies, Eq. 16-27.

While a cardioid microphone may be capable of

picking up satisfactorily at 3 ft (1 m), a cardioid in-line

may reach 6–9 ft (1.8–2.7 m), and a super in-line may

reach as far as 40 ft (12 m) and be used for picking up a

group of persons in a crowd from the roof of a nearby

building, following a horse around a race track, picking

up a band in a parade, and picking up other hard-to-get

sounds from a distance.

There are precautions that should be followed when

using interference tube microphones. Because they

obtain directivity by cancellation, frequency response

and phase are not as smooth as omnidirectional micro-

phones. Also, since low frequencies become omnidirec-

tional, the frequency response drops rapidly below

200 Hz, which helps control directivity.

It should not be assumed that no sound will be

picked up outside the pickup cone. As the microphone

is rotated from an on-axis position to a 180° off-axis

position, there will be a progressive drop in level.

Sounds originating at angles of 90° to 180° off-axis will

cancel by 20 dB or more; however, the amount of

cancellation depends on the level and distance of the

microphone from the sound source. As an example, if

Figure 16-97. Characteristic of a supercardioid microphone
(MKH 60). Courtesy Sennheiser Electronic Corporation.

Figure 16-98. Shure SM89 condenser shotgun micro-
phone. Courtesy Shure Incorporated.

Figure 16-99. Polar response of a 0.5 m long shotgun

microphone. Courtesy Shure Incorporated.

0 o

180 o

250 Hz

500 Hz

1000 Hz

6300 Hz

10000 Hz

10 dB

20 dB

30 dB

2500 Hz