Calibration Of The Mouth Simulator - BRUEL & KJAER HF HATS 5128 User Manual

6 High-frequency Head and Torso Simulator (HF HATS) Type 5128 – User Manual
The mouth simulator is equipped with a protection circuit to prevent damage to the unit,
CAUTION:
and even though this protection circuit is present, there may be a risk of damaging the
mouth simulator by excessive input voltage. Should the protection circuit be activated
(due to a high voltage input), turn down the input level and wait until the protection circuit
deactivates. The mouth simulator will be ready again after approximately 30 s.
An input signal is applied to the mouth simulator via the BNC connector marked 'Mouth', see
Fig.2.2.
Any type of input signal can be used, ranging from a pure sine wave to a real voice signal (for
example, ITU-T Rec. P.501).
Fig.2.2 HF HATS connector panel: (1) for configurations with a mouth simulator only, (2) for configurations with left
and right ear simulators only, (3) for configurations with left and right ear simulators and a mouth simulator
2.3

Calibration of the Mouth Simulator

The method of calibrating the mouth simulator depends on the application for which it is to be
used. For example, the standards IEEE 269 and ITU-T Rec. P.51 for measurements on telephone
equipment demand that measurements refer to the MRP, 25 mm in front of the equivalent lip
plane. Therefore, the output sound pressure level should be measured at this position during
calibration procedure.
For calibration at the MRP, Type 5128 has a microphone holder which positions a 1/4
microphone with preamplifier (for example, Brüel & Kjær Type 4944) at the MRP (see Fig.2.3). The
diaphragm of the microphone should be positioned at the level of the centre of the mouth. This
holder can also be used to hold a 1/4 microphone at the opening of the mouth simulator orifice
in order to monitor the sound pressure at this location.