7
LI0010 – 1 October 2015
Driving a Microphone as Sound Source
The 14AA Electrostatic actuator amplifier can be used for driving a microphone as a precision
sound source, for example for frequency calibration of an an Ear Simulator. When used as a sound
source in accordance with the guidelines laid out in IEC 60318, the sensitivity of the transmitter
microphone can be assumed to be identical to its response as a receiver.
A signal generator is connected to the input BNC connector of the 14AA and the output is con-
nected to a transmitter adapter.
Two transmitter adapters are avialable for 1/2” and 1/4” microphones respectively:
•
1/2” microphone:
Transmitter adapter RA0067 and BNC-BNC cable AA0032.
•
1/4” microphone:
Transmitter adapter RA0086 and BNC-Microdot cable AA0073-05.
If the microphone is an externally polarized microphone like the G.R.A.S. 40BP 1/4” Pressure
Microphone, the RA0086 should be connected to the
AC 200 VDC
. If the microphone
is a prepolarized microphone like the G.R.A.S. 40BD 1⁄4” Pressure Microphone, the RA0086
should be connected to the
AC Output
.
Important.
Short cable lenghts (0.5 m) between 14AA and the transmitter adapter must be
used. Longer cables will impair the high-frequency performance. For further information, see
“Technical Specifications” on page 9.
An example of the electrical connections needed for a frequency calibration of an ear simulator is
shown in Fig. 8. For a detailed information about how to calibrate an RA0045 Ear Simulator, refer to
the documentation for the RA0045 and the recommendations of IEC 60318.
Actuator Supply
14AA
Po we r
G.R.A.S.
Actuator Supply
Type 14AA
AC Output
AC Output
+800VD C
AC Output
On
GND
AC Input
Overload
Equipment for frequency calibration of an ear simulator
Max. 1Vrms
080013
+200 VDC
Ext. pol. microphone
Prepol. microphone
To analyzer from preamplifier
From signal generator
Computer with hardware
and software for signal
generation and signal analysis
RA0086
Transmitter adapter
RA0052
Test Jig
¼
”T
ransmi
tte
rAdapte
r
RA
0
08
6
G.R.A.S
.
Sound source,
e.g 40BP microphone
DUT, e.g.
RA0045 Ear Simulator
Signal generation and analysis
Fig. 8.
A setup for frequency calibration of an IEC60318-4 Ear Simulator.
