G.R.A.S. 43BA Series, 43BA-1, 43BA-2, 43BA-3 Instruction Manual
www.gras.dk
LI0105 – 11 December 2013
Instruction Manual
43BA ¼” 0.4cc High-frequency Coupler Kit
43BA-1 ¼” 0.4cc High-frequency Coupler Kit
43BA-2 ¼” 0.4cc CCP High-frequency Coupler Kit
43BA-3 ¼” 0.4cc CCP High-frequency Coupler Kit, High Sensitivity
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Revision History
Any feedback or questions about this document are welcome at gras@gras.dk.
Revision Date Description
1 11 December 2013 First publication
Copyright Notice
© 2013 G.R.A.S. Sound & Vibration A/S
www.gras.dk
Trademarks
Product names mentioned in this document may be trademarks or registered trademarks of their
respective companies and are hereby acknowledged.
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Contents
Introduction and Description ............................................................ 4
Design ...................................................................................................... 4
Performance .............................................................................................. 5
Delivered Items ............................................................................. 7
Assembling the Coupler .................................................................. 9
Mounting and Dismounting the Microphone ...................................... 10
Calibration ................................................................................. 10
Ordering Information .................................................................... 11
Specifications and Warranty .......................................................... 13
Specifications .......................................................................................... 13
Calibration ............................................................................................... 14
Service and Repairs .................................................................................. 14
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Introduction and Description
The G.R.A.S. 43BA is a ¼” 0.4cc High-Frequency coupler made for and with the hearing aid
industry. Compared to the reference 2cc coupler it has a smaller volume and a ¼” microphone.
It retains the advantages of the 2cc coupler, but adds the capability of delivering differentiated
and precise data up to 16 kHz because of the combination of the smaller volume and the ¼”
microphone.
The 0.4cc coupler body fits all G.R.A.S. ½” 2cc standard ear mould and tube adapters.
Therefore, the 0.4cc coupler can be used for the same type of tests as the traditional 2cc coupler,
but with the added benefit of a wider frequency range. It is designed for repetitive use and is
equally suited for research, quality assurance and production test applications.
Design
The coupler housing is dimensioned to accomodate the ear mould and tube adapters normally
used with the 2cc coupler, but the inner volume is only 0.4cc.
Its 0.4cc volume is a well defined cylinder where the diaphragm of the microphone is flush with
the bottom of the cylinder. The cylinder is machined to within ±2% of the nominal 0.4cc volume.
The exact volume of each individual coupler is stated in the accompanying calibration chart. The
performance of the 0.4cc coupler can therefore be accurately simulated, and it can easily be a
part of a complete simulation model.
The microphone-preamplifier set is kept firmly in position by a very precise locking mechanism,
which automatically centers and locks the microphone at the same time, eliminating the risk
of measurement errors caused by incorrect positioning of the microphone. An O-ring ensures a
tight sealing of the microphone. The microphone can easily be removed for sensitivity calibration
without the use of tools.
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Performance
An important benefit of the small volume and the ¼” microphone is the fact that the resonance
frequency at 30 kHz is so high that it does not interfere with measurements in the audible
frequency range. Therefore it can be used for measurements up to 16 kHz, one octave higher
than achievable with the reference 2cc coupler.
Because of the small volume, the measured sound level from the coupler is about 13.5 dB higher
than with the 2cc coupler. This effect raises the measured signal with respect to the noise floor
and thus improves the signal-to-noise ratio. This difference of signal levels is shown in Fig. 1.
Therefore, the signal-to-noise ratio obtainable with the 0.4cc coupler and a ¼” microphone with a
sensitivity of about 1.5mV/Pa is almost as good as that of a 2cc coupler using a ½” microphone
with a sensitivity of 12.5mV/Pa. The 43BA-1 has a sensitivity of 1.5 mV/Pa and the noise floor
is 39dB(A), the 43BA-2 has a sensitivity of 1.45 mV and the noise floor 44dB(A).
When used with a high-sensitivity microphone (18 mV/Pa), the 0.4cc is very close to the 2cc
coupler in this respect. With the 43BA-3 high sensitivity version, the noise floor is 25dB(A).
Refer to page 13 for more information about the 43BA’s specifications.
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100 1000 10000
Magnitude [dB re 20 uPa]
Frequency [Hz]
Typical Frequency Response
With G.R.A.S. 1/4" pressure microphone as receiver @ 1Vrms input signal
0.4cc coupler response
2cc coupler response
Fig. 1. 0.4cc coupler compared to the reference 2cc coupler, with a ¼” microphone used as receiver.
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