GRAS RA4803 User manual

LI0272 – 16 November 2020
Instruction Manual
GRAS 48LX-4 and 48LX-8 UTP Line Arrays
Level and Frequency Calibration

Instruction Manual 48LX-4 and 48LX-8 Line-Arrays | 2
Revision History
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Revision Date Description
1 16 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 48LX-4 and 48LX-8 Line-Arrays | 3
Contents
Introduction ......................................................................................................................4
RA4803 Sensitivity and Frequency Calibration Kit for 48LX-4 and 48LX-8 ......4
Adapter for Calibration of UTP Line Arrays .....................................................................................4
Pistonphone Calibration Adapter and Electrostatic Actuator....................................................4
Mounting the Line Array Calibration Adapter ............................................................ 5
Frequency Calibration.....................................................................................................8
Accessories ....................................................................................................................... 9
Warranty, Service and Repair.........................................................................................9
Warranty...................................................................................................................................................9
Service and Repairs ..............................................................................................................................9

Instruction Manual 48LX-4 and 48LX-8 Line-Arrays | 4
Introduction
Proper calibration of the line array requires that each microphone is calibrated separately in a
controlled environment. For this purpose, the RA4803 calibration kit must be used. The contents
of this kit are described below.
RA4803 Sensitivity and Frequency Calibration Kit for 48LX-4 and 48LX-8
The RA403 Calibration Kit consists of the following items:
Adapter for Calibration of UTP Line Arrays
This adapter is used both for level and frequency calibration. It is mounted on the UTP line array
and serves as a receiver for the adapter for level calibration and the actuator for frequency cali-
bration. It can easily be released and glided from one microphone to the next. When mounted over
a microphone and its rubber fairing, a well-dened volume for the calibration is created.
Pistonphone Calibration Adapter and Electrostatic Actuator
The pistonphone calibration adapter consists of two pieces, the upper piece ts in the piston-
phone while the lower piece has an inner thread for securing the assembly on the pistonphone
and an outer bayonet-type ange which screws into the receptor ange of the line array adapter,
see Fig. 1, Fig. 4, and Fig. 5. The electrostatic actuator is designed to simply rest on the line array
adapter. A stop and three distance legs make proper alignment easy.
Slot for UTP line array
Electrostatic Actuator
Pistonphone Calibration Adapter
Nut with bajonet
type outer ange
Top piece with neck for
pistonphone Assembled adapter
Shoulder and backstop for
mounting on top of the line array
calibration adapter
UTP Line Array Calibration Adapter
Stops
Bajonet-type ange and recess for securing
pistonphone calibration adapter
Finger screws for securing the
adapter over the microphones
Opening for the
calibration signal
Fig. 1. The RA4803 Sensitivity and Frequency calibration kit for 48LX-4/48LX-8.

Instruction Manual 48LX-4 and 48LX-8 Line-Arrays | 5
Mounting the Line Array Calibration Adapter
The calibration adapter for the line array consists of two parts held together with two nger
screws. When assembled, but not fully tightened, the line array can be pushed into the slot, and
can easily be moved and xated over the microphone to be calibrated.
When the nger screws are loosened about one full turn, the opening for the array is wide enough
for this. The cavity for the calibration must be centered over the diaphragm of the microphone.
This need not be very accurate, a visual estimate of correct centering is sucient.
When the two nger screws are
loosened (about one full turn),
the line array can be glided into
the adpater.
Fig. 2. Showing how the line array slides into the line array calibration adapter.
When mounting the adapter, it is important that it seals evenly on the rubber fairing to ensure a
closed cavity for the calibration. In the gure below the orange dotted lines indicate where the
adapter must establish a seal. Therefore you should push down the adapter in the middle while
tightening the screws to avoid that more pressure is applied to one side than the other. The
adapter has four stops that help to obtain an even seal.
The yellow dots show
where the adapter
seals onto the fairing.
When sealed onto the fairing, this cavity
constitutes part of the volume for the calibration.
The two ngerscrews
must be tightened
(approximately) evenly.
Fig. 3. Showing how the adapter seals over the rubber fairings.