GRAS 48LA User manual

LI0273 – 2 November 2020
Instruction Manual
GRAS 48LA and 48LX-1 UTP
Level and Frequency Calibration

Instruction Manual 48LA and 48LX-1 – Level and frequency calibration | 2
Revision History
Revision Date Description
1 2 November 2020 First edition
Copyright Notice
© 2020 GRAS Sound & Vibration
http://www.grasacoustics.com
Any technical documentation that is made available by GRAS is the copyrighted work of GRAS
and is owned by GRAS.
The content in this document is subject to change without notice. GRAS Sound & Vibration is not
liable or responsible for any errors or inaccuracies that may appear in this document.
Trademarks
Any product names mentioned in this document may be trademarks or registered trademarks of
their respective companies and are hereby acknowledged.
Do not touch the diaphragm

Instruction Manual 48LA and 48LX-1 – Level and frequency calibration | 3
Contents
Introduction ......................................................................................................................4
Sensitivity Calibration ..........................................................................................................................5
Frequency Calibration ..........................................................................................................................6
Warranty, Service and Repair......................................................................................... 7
Warranty, Service and Repairs............................................................................................................ 7

Instruction Manual 48LA and 48LX-1 – Level and frequency calibration | 4
Introduction
Proper calibration requires the use of dedicated calibration equipment in a controlled environ-
ment, i.e. a laboratory or similar. For this purpose, we have developed two dedicated adapters
• RA4801 Adapter for sensitivity calibration of 48LA/48LX-1.
• RA4802 Actuator for frequency calibration of 48LA/48LX-1.
The RA4801 can be used with a pistonphone such as the GRAS 42AP Intelligent Pistonphone or
the GRAS 42AA Pistonphone.
The RA4802 is an electrostatic actuator for frequency calibration, integrated in a stand with a
mechanism for holding and locking the microphone during calibration.
The RA4802 requires connection to a proper supply and signal source. For this purpose, we rec-
ommend microphone calibration system, such as the GRAS 90CA Microphone Calibration System
which oers all the hardware and software required for proper laboratory calibration.
For further information, visit www.grasacoustics.com/90CA

Instruction Manual 48LA and 48LX-1 – Level and frequency calibration | 5
Sensitivity Calibration
Before calibration, the microphone must be connected to the analyzer to warm up. About three
minutes are required.
Neck for pistonphone
with ½"collar
Lever for holding and
releasing the microphone
Fig. 1. Mounting a UTP microphone in the RA4801 Adapter for sensitivity calibration of 48LA/48LX-1.
1. Insert the neck into the pistonphone's collar and tighten the collar.
2. While holding the pistonphone-adapter assembly at the top with one hand, insert the micro-
phone into the slot, with the backside turned upwards.
3. Turn the lever to lock the microphone.
4. Turn on the pistonphone.
Correction Factor (Pistonphone)
Frequency Correction Factor Accuracy
250 Hz 0 dB ± 0.2 dB
Calibration with the 42AG Multifunction Sound Calibrator
The procedure for using a 42AG is the same as described for a pistonphone.
Correction Factors
Frequency Correction Factor Accuracy
250 Hz -0.3 dB ± 0.2 dB
1 kHz -1.0 dB ± 0.2 dB

Instruction Manual 48LA and 48LX-1 – Level and frequency calibration | 6
Frequency Calibration
For frequency calibration, a setup like the one shown in Fig. 2 is needed, we recommend a com-
plete microphone calibration system like the GRAS 90CA Microphone Calibration System.
Power
G.R.A.S.
Actuator Supply
Type 14AA
AC Output
+200VDC
AC Output
Max. 1Vrms
+800VDC
AC Output
On
GND
AC Input
Overload
Signal generator 14AA Actuator Supply RA4802 Actuator Analyzer
48LA/LX-1
Fig. 2. Block diagram of a setup for frequency calibration
Procedure
When the calibration system and microphone are connected, proceed as described below.
Lever for holding
and releasing the
microphone
Electrostatic actuator
Slot for
microphone
Microphone
locked in place,
ready for
calibration
Fig. 3. The RA4802 Actuator for frequency calibration of 48LA/48LX-1.
1. With the RA4802 in the open position, place the microphone with the diaphragm facing
upwards in the slot as shown above.
2. Turn the lever to lock the microphone in place.
You are now ready to perform the calibration.

Instruction Manual 48LA and 48LX-1 – Level and frequency calibration | 7
Warranty, Service and Repair
Warranty, Service and Repairs
GRAS products are made of components from our proven standard portfolio and are all manu-
factured of high-quality material and branded parts that were chosen and processed to ensure
life-long stability and robustness.
The warranty does not cover products that are damaged due to negligent use, an incorrect power
supply, or an incorrect connection to the equipment.
Further information about warranty and our repair service can be found at
www.grasacoustics.com/repair-center
WEEE directive:
2002/96/EC
CE marking directive:
93/68/EEC
Manufactured to conform with:
RoHS directive:
2002/95/EC
GRAS Sound & Vibration continually strives to improve the quality of our products for our
customers; therefore, the specications and accessories are subject to change.