BRUEL & KJAER 4131 - 1 Description; General Description of the Equipment

1. Description
General Description of the Equipment.
A complete microphone consists of a microphone cartridge and a cathode
follower for impedance conversion, allowing long cables and relatively low
input impedance amplifiers to be used between the microphone and the
measuring instrument. The microphone cartridge is screwed onto the housing
of the cathode follower by means of an adaptor making a small, rugged unit.
Fig. 1.1.
Cable
Fig. 1.1. Quarter-inch microphone with outer dimensions in mm
(1 mm = o.03937 inch).
The microphone may be directly connected to the different B & K measuring
instruments which are provided with a "Condenser Microphone" input socket
fitting the microphone connecting plug. Stabilized plate and heater voltages
for the cathode follower and polarization voltage for the cartridge are avail-
able on this seven-pin socket. The microphones may also be used with
other equipment when operated from a Microphone Power Supply Type 2801
which provides the necessary voltages in the same conditions as the B & K
measuring instruments (see Accessories).
For free-field and room-acoustic measurements, the microphones should be
placed remote from the measuring instruments, since these would often
disturb the sound field because of their non-negligible dimensions. Different
types of microphone stands and extension cables are available for this
purpose, see Accessories. The length of cable, however, has a significant
influence on the response above 40 kHz as will be seen in the description of
the cathode follower.
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