Microphones 501This configuration is used for three reasons. By
using a multiple arrangement of entry holes around the
circumference of the microphone case into the
low-frequency system, optimum front response and
polar performance can be maintained, even though most
of the entries may be accidentally covered when the
microphone is handheld or stand mounted. The micro-
phone has good proximity performance because the
low-frequency entry ports are far from the diaphragm
(4.75 inches) as well as the high-frequency entry having
very little proximity influence at low frequencies. The
two-entry configuration has a cardioid polar response
pattern that provides a wide front working angle as well
as excellent noise rejection and feedback control.16.2.3.1.5 Multiple-Entry Cardioid MicrophonesThe Electro-Voice RE20 Continuously Variable-D
microphone, Fig. 16-26, is an example of multiple-entry
microphones. Multiple-entry microphones have many
rear entrance ports. They can be constructed as single
ports, all at a different distance from the diaphragm, or
as a single continuous opening port. Each entrance is
tuned to a different band of frequencies, the port closest
to the diaphragm being tuned to the high frequencies,
and the port farthest from the diaphragm being tuned to
the low-frequency band. The greatest advantage of this
arrangement is reduced-proximity effect because of the
large distance between the source and the rear entry
low-frequency port and mechanical crossovers are not
as sharp and can be more precise for the frequencies in
question.As in many cardioid microphones, the RE20 has a
low-frequency roll-off switch to reduce the proximity
effect when close micing. Fig. 16-27 shows the wiringFigure 16-24. Shure Beta 57 dynamic microphone.
Courtesy Shure Incorporated.Figure 16-25. Sennheiser MD441 three-entry cardioid
microphone. Courtesy Sennheiser Electronic Corporation.Figure 16-26. Electro-Voice RE20 multiple-entry (variable-D
cardioid microphone). Courtesy Telex Electro-Voice.