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.
