GRAS 48LA User manual

LI0271 – 2 November 2020
Instruction Manual
GRAS 48LA and 48LX-1 UTP Microphones
Mounting and In-Situ Verication

Instruction Manual 
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 
Contents
Introduction ......................................................................................................................4
Mounting............................................................................................................................4
Mounting with Hard Fairing.................................................................................................................5
Mounting with Soft Fairing..................................................................................................................6
Mounting without Fairing .................................................................................................................... 7
Mounting with Hard Fairing and top-mounted Tape..................................................................... 7
Verication ........................................................................................................................8
............................................................................................................8
The Adapter.............................................................................................................................................8
Procedure................................................................................................................................................9
Sensitivity Calibration with 42AG Multifunction Sound Calibrator.........................................10
Ordering Information .....................................................................................................11
..................................................................................................................................11
Mounting Accessories .........................................................................................................................11
Warranty, Service and Repair....................................................................................... 12
Warranty, Service and Repairs.......................................................................................................... 12

Instruction Manual 
Introduction
Our primary design goal with the UTP microphones has been to create a very thin microphone

But ease of use when preparing for measurements has also been a primary design goal. This is


Mounting
Mounting the 48LA and 48LX-1 microphones is fairly straightforward. Four mounting methods are

Mounting with Hard Fairing
This mounting method can be used on plain structures. The hard
fairing can be used as a mechanical docking station which allows
for easy insertion and removal. The fairing has an aerodynamical
design with angle of 7.5 degrees and a height of 1 mm.
See page 5.
Flip
Flip
Mounting with Soft Fairing
The soft fairing can be used for mounting on slightly curved sur-
faces. The microphone and fairing is secured with top-mounted
masking tape. The soft fairing has an angle of 6.5 degrees and a
height of 1 mm.
See page 6.
Mounting using Tape Only
Using one of the fairings has the advantage of introducing a


the microphone can be mounted directly using only the masking
tape.
See page 7.
Mounting with Hard Fairing and Top Tape
This method can be used to further smoothen a mounting with
the hard fairing.
See page 7.

Instruction Manual 
Mounting with Hard Fairing
The fairing for 48LA and 48LX-1 is made from hard plastic. It has a recess for holding the micro-
phone. Once mounted, the fairing can be used as a dock in which the microphone can be inserted

While mounted in the fairing, a tap keeps the microphone locked in its position.
Double-sided
adhesive tape
Hole for safe
removal of the
microphone
Small tap that locks the
microphone
Enlarged view showing the
shoulder on the microphone
and the recess in the fairing
Fig. 1. The fairing is designed to be used as a dock in which the microphone can be inserted and removed.
1. Clean the surface where the fairing will be mounted.
2. 
structure.
 
Important. When removing the microphone, use a small tool to pull it out. Do NOT pull at the
cable as this will damage the connection.
Push into the recess
Pre-mounted fairingDouble sided tape
Pull with the tip of
a small screwdriver,
tweezer or similar
InsertionMounting Removal
Fig. 2. The microphone is pushed into the fairing. When pushed all the way, it will be locked in the fairing.

Instruction Manual 
Mounting with Soft Fairing
The soft fairing comes mounted on a precut piece of masking tape for top-mounting of the fairing
and microphone. As shown below, the sticky side of the masking tape must point upwards when
mounting microphone and cable in the fairing.
1. Clean the surface where the fairing will be mounted.
2. With the sticky side upwards, remove the protective tape from the masking tape.
 Push the microphone down into the fairing.
4. Press the cable gently onto the tape.
When the microphone has been placed in the fairing, microphone and cable will be secured by the
adhesive tape.
Flip
Flip
Protective liner Sticky side of tape

Underside of
fairing
Hole for
diaphragm
Fig. 3. Showing the pre mounted soft fairing with and without the protective liner.
5. Turn over the assembly so that the sticky side points downwards. You can now mount it onto
the test object.
Flip
Flip
Test structure
Cable attached
to the tape
Sticky side
Topside
Flip
Flip
Fig. 4. Showing how to mount 48LA/LX-1 and the soft fairing onto a test structure.

Instruction Manual 
Mounting without Fairing
The masking tape can also be used for top-mounting of the microphone without any of the fair-
ings. The following procedure is recommended:
1. Clean the surface where the tape will be mounted.
2. Secure the microphone to the structure with a small piece of tape.
 With the protective layer removed, place the top tape over the microphone as shown below.
4. 
Test structure
Tape for holding the
microphone during
mounting

Overlay Tape
Fig. 5. Mounting the microphone using tape only.
Mounting with Hard Fairing and top-mounted Tape
The hard fairing has an aerodynamical design with an angle of 7.5 degrees. However, if you want
to further optimize the mounting, top-tape can be used to smoothen the mounting even more
as shown below. This method can be used to secure the cable, smoothen the surface and make
the mounting more resilient. The illustration below assumes that the fairing and microphone have
already been mounted as shown in Figure 2.
Important. When mounting and removing the tape, make sure that the cable and its connection
to the microphone is not subjected to strain.
Test structure
Microphone mounted
using the method shown


Fig. 6. Optional top-mounted tape for smoothened mounting of fairing and cable.

Instruction Manual 
Verication
In-Situ Sensitivity Verication

-
ing the microphone.
Proper calibration of sensitivity and frequency is covered by a separate manual.
The Adapter

The adapter has three main features.
• 
• It has a soft cushion similar to those found on circum-aural headphones. It creates a closed
cavity over the microphone to be calibrated.
• 

Top view Side view
1” collar
Soft cushionSpacers

Soft cushionSpacers
Fig. 7. The RA4800 adapter/eld verication set for level calibration.

Instruction Manual 
Procedure
Important. 

sensitivity.
G.R.A.S. 42AG
dB Hz Met
dB Hz Met
G.R.A.S. 42AG
dB Hz Met
dB Hz Met
Fig. 8. In-situ verication using 42AG and RA4800.
Place the calibrator over the microphone and press it down until stopped by the four distance
spacers. You must keep it still in this position during the calibration.
When you have turned on the calibrator and pressed it down over the microphone, you must keep
it there until the reading on the analyzer is stable.
-
cation can be done quite quickly.
Correction Factors
Frequency Correction Factor Accuracy
250 Hz -0.8 dB ± 0.2 dB
1 kHz  ± 0.2 dB
Refer to the manual for 42AG for further information about how to operate the calibrator.

Instruction Manual 
Sensitivity Calibration with 42AG Multifunction Sound Calibrator

48LA/48LX-1 can be used in combination with the 42AG Multifunction Sound Calibrator
Important. Before calibration, the microphone must be connected to the analyzer to warm up to
obtain stable polarization, and consequently, stable sensitivity. About three minutes are required.
Neck for pistonphone with
½"collar
Lever for holding and
releasing the microphone
Fig. 9. Mounting a UTP microphone in the RA4801 Adapter for sensitivity calibration of 48LA/48LX-1.
1. Insert the neck into the 42AG's collar and tighten the collar.
2. Place the 42AG upright on a table.
 While holding the calibrator-adapter assembly at the top with one hand, insert the microphone
into the slot with the backside turned upwards, as shown in Fig. 9.
4. Turn the lever to lock the microphone.
5. 
minutes.
6. Turn on the calibrator.
7. 
Correction Factors
Frequency Correction Factor Accuracy
250 Hz  ± 0.2 dB
1 kHz -1 dB ± 0.2 dB
Refer to the manual for 42AG for further information about how to operate the calibrator.