G.R.A.S. AL0010 User manual

G. R . A . S .
Sound & Vibration
Skovlytoften 33, 2840 Holte, Denmark Tel. [phone] Fax [phone]
Instruction Manual
Actuator Calibration Stand
Type AL0010

Revision 02 11 2004
Actuator Calibration Stand Type AL0010

Actuator Calibration Stand Type AL0010 - Page 2
G.R.A.S. Sound & Vibration
Actuator Calibration Stand Type AL0010
Actuator Calibration Stand Type AL0010

Actuator Calibration Stand Type AL0010 - Page 3
G.R.A.S. Sound & Vibration
Introduction
The Actuator Calibration Stand Type AL0010 (Fig. 1) provides a convenient platform for testing
condenser microphones. It has a xture with a grub screw for holding a -inch preamplier
securely in place as well as recesses and a column for safely parking electro-static actuators
and microphone protection grids when not in use (see Fig. 2).
Microphone Set-ups
Fig. 2 and Fig. 3 show respectively the set-ups for -inch and 1-inch microphones. Note the
adapter in Fig. 3 for mounting a 1-inch microphone on a -inch preamplier.
Additional Equipment
Fig. 5 shows what additional equipment can be supplied by G.R.A.S. Sound & Vibration and
Fig 6 shows a block diagram of a possible set up with all additional equipment.
The following is a list of all required additional equipment:
1) Power supply for the  inch preamplier,
e.g. the G.R.A.S. Power Module Type 12AK shown in Fig. 5
2) Actuator supply for electro-static actuators
e.g. the G.R.A.S. Actuator Supply Type 14AA shown in Fig. 5
Fig. 1 Actuator Calibration Stand Type
AL0010
LEMO plug of
preamplier to
Power Module (e.g.
Type 12AK)
To Actuator Supply
Type 14AA
Socket for plug on
electro-static actuator
-inch preamplier
(e.g. Type 26AK)
Grub screw for
securing the
preamplier

Actuator Calibration Stand Type AL0010 - Page 4
G.R.A.S. Sound & Vibration
Fig. 2 Showing places for parking electro-static actuators and microphone
protection grids and the grub screw for securing the preamplier
3) Signal generator capable of generating logarithmically swept tones within the frequency
range of interest. This signal is fed to the actuator supply.
4) Measurement amplier.
This receives, via the Type 12AK, the signal picked up by the microphone and measures
the response of the microphone to the swept tone.
Items 3 and 4 could be combined in the same unit, e.g. a computer tted with suitable hardware
and software for A/D and D/A conversions in order to simulate both a signal generator and
measurement amplier.
Test Procedure
General
The basic stages in the test procedure are:
1) Setting up the microphone on the AL0010, see Fig. 3 or Fig. 4.
2) Applying a signal via the actuator supply to the electro-static actuator and measuring the
output from the microphone.
The following deals in more detail with each stage of the test procedure.
Plug
Place plug in hole provided before
parking the -inch electro-static
actuator here
Recesses for parking elec-
tro-static actuators and micro-
phone protection grids

Actuator Calibration Stand Type AL0010 - Page 5
G.R.A.S. Sound & Vibration
Setting up
Note: the terms generator and measurement amplier refer to a set up which simultaneously
provides the test signal to the electro-static actuator and measures the signal picked up by
the microphone.
Proceed as follows:
1) Power Module Type 12AK
 Connect the free end of the preamplier cable to the LEMO Input socket.
 Connect, via a suitable cable, the BNC Output to the input of the measuring amplier.
 Select Lin. or Direct.
2) Actuator Supply Type 14AA
 Connect the thin lead (with banana plug) from the AL0010 to the socket marked
+ 800 V DC.
 Connect the output from the signal generator to the BNC socket marked AC Input.
3) Adjust the signal output level as required.
Applying a Swept Signal and Measuring the Output from the Microphone
The following describes a typical procedure for applying the swept signal.
It is assumed that the generator and measuring amplier work to produce constant-condence
results (i.e. maintaining a constant β T product) in real time throughout the frequency range of
interest and make the measurement data available graphically and numerically.
With everything set up as described above, proceed as follows:
a) set the generator to oscillator mode
b) set the measuring amplier to at response
c) initiate a constant-level logarithmic sweep on the generator.
The measuring amplier will follow the response of the microphone throughout the sweep
and record and display the results accordingly.
Curves showing the upper and lower tolerance levels for the frequency range of interest could
be superimposed on the graphical display.

Actuator Calibration Stand Type AL0010 - Page 6
G.R.A.S. Sound & Vibration
Fig. 3 Set-up for calibrating the frequency response of a -inch condenser microphone
-inch Electro-static Actuator
RA0014
-inch condenser microphone
without protection grid
Remove protec-
tion grid
Parking places for -inch
Actuator when not in use
-inch preamplier
From the -inch
Electro-static Actuator
RA0014

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G.R.A.S. Sound & Vibration
Fig. 4 Set-up for calibrating the frequency response of a 1-inch condenser microphone
1-inch Electro-static Actuator
RA0015
1-inch condenser microphone
without protection grid
Remove protec-
tion grid
Adapter
RA0017
Parking places for 1-inch
Actuator when not in use
-inch preamplier
From the 1-inch
Electro-static Actuator
RA0015

Actuator Calibration Stand Type AL0010 - Page 8
G.R.A.S. Sound & Vibration
Fig. 5 Showing AL0010 in a set up with Power Module Type 12AK and Actuator Supply Type 14AA
Type 14AAType 12AK

Actuator Calibration Stand Type AL0010 - Page 9
G.R.A.S. Sound & Vibration
Fig. 6 Block diagram of a complete set-up for making tests
Response signal from test micro- phone to measuring amplier
From signal generator to AC Input
Actuator Supply Type 14AA
To AL0010 from AC Output + 800 V DC (via thin lead of AL0010) AL0010 set up for testing a -inch micro- phone (see Fig. 3)
Power Module Type 12AK
Computer with hardware and software for simulating:  a signal generator capable
of generating logarithmi- cally swept tones
 a measuring amplier
From preamplier to Input