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
Any feedback or questions about this document are welcome at [email protected].
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.

Instruction Manual 48LX-4 and 48LX-8 Line-Arrays | 6
Procedure
1. Ensure that the two nger screws are suciently loose for the strip to move smoothly in the
slot. If the adapter is closed, about one full turn will suce.
2. Push the strip into the slot until the diaphragm of the microphone to be calibrated is located in
the center of the calibration opening.
3. Place one or two ngers close to the center of the upper part and press it downwards.
4. While doing this, tighten the two screws until you feel the upper part hitting the stops.
It is important that the screws are tightened fairly evenly so that the upper part does not tilt, as
this could mean that the volume will not be tight. The four stops shown in Fig. 1 prevent that you
damage the rubber fairing by overtightening the screws. Finger force is sucient, but do tighten
enough to obtain a proper sealing of the calibration volume.
Level Calibration
For level calibration with a pistonphone, a two-piece pistonphone adapter is used. This adapter
is push-tted in the pistonphone and secured with a nut that ts into the line array calibration
adapter.
Procedure
1. Unscrew and remove the collar and rst o-ring.
2. Push the top piece of the adapter into the pistonphone as far as it will go.
3. Screw on the nut and tighten it.
Remove the collar from
the pistonphone
Push the adapter into
the pistonphone
Secure it with the nut
Fig. 4. Inserting the pistonphone adapter into the pistonphone.

Instruction Manual 48LX-4 and 48LX-8 Line-Arrays | 7
4. Push the pistonphone down into the line array adapter.
5. Turn the pistonphone about 1/8 to 1/4 turn until the bayonet mechanism takes hold of the
pistonphone.
When this is done, the pistonphone will be kept upright by the grip exerted by the bayonet
mechanism, and you are now ready to calibrate.
6. Turn on the pistonphone.
Turn the pistonphone about 1/8
turn until the bayonet mechanism
secures the pistonphone.
Push the pistonphone
with the adapter down
into the cavity.
Fig. 5. Inserting the pistonphone with its adapter into the line array adapter.
Correction factor
Frequency Correction Factor Accuracy
250 Hz 0 dB ± 0.2 dB

Instruction Manual 48LX-4 and 48LX-8 Line-Arrays | 8
Frequency Calibration
For frequency calibration, a setup like the one shown in Fig. 6 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 Electrostatic
Actuator Amplier
Line array in
calibration adapter
Electrostatic
actuator
Analyzer
Microphone
response
Calibration
signal
Fig. 6. Connection diagram for frequency calibration.
The electrostatic actuator is easy to mount, you simply place it on top of the adapter as shown in
Fig. 7 below. It must be placed in the middle between the two nger screws. When this is the case
and the backstop rests against the adapter, the actuator will be located over the center of the
hole. Three distance legs at the front ensure that the actuator will rest on the sensor and that the
distance to the diaphragm is correct.
Diaphragm centered
in hole
Electrostatic actuator
When the electrostatic actuator is placed
over the hole, a back rest and spacers help to
obtain correct alignment
Spacers
(not visible)
Back rest
Fig. 7. Placing the electrostatic actuator onto the line array calibration adapter.
Procedure
1. Place the electrostatic actuator over the hole in the line array adapter.
2. Ensure that it is centered between the nger screws and that the backstop rests against the
adapter as shown in Fig. 7 above.
You are now ready to calibrate.

Instruction Manual 48LX-4 and 48LX-8 Line-Arrays | 9
Accessories
42AP Intelligent Pistonphone
42AA Pistonphone
14AA Electrostatic Actuator Amplier
Warranty, Service and Repair
Warranty
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.
The length of the warranty period can be found at grasacoustics.com/repair-center/warranty.
Service and Repairs
All repairs are made at GRAS International Service Center located in Denmark. Our Service
Center is equipped with the newest test equipment and staed with dedicated and highly skilled
engineers. Upon request, we make cost estimates based on xed repair categories. If a product
covered by warranty is sent for service, it is repaired free of charge, unless the damage is the
result of negligent use or other violations of the warranty. All repairs are delivered with a service
report, as well as an updated calibration chart.
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.