BRUEL & KJAER 4128-C - 1.6 Calibration of the Ear Simulator

CHAPTER 1
Operation
13
WARNING: Be careful not to ruin the fine thread in the preamplifier or the angle adaptor.
Do not use any force and make sure that the threads in the two pieces engage properly
before you screw in the preamplifier (check that the preamplifier body can be moved slight-
ly in all directions before screwing it fully in). Do not over-tighten.
8) Fit the microphone cable onto the microphone preamplifier (see Fig.1.5.6).
9) If the head has been split you must reassemble it by reversing the dismantling procedure
given later in this chapter (see “Splitting the Head” on page 14.).
10) Fit the pinna simulator onto the head.
The mounting procedure is the same for right and left ears.
1.6 Calibration of the Ear Simulator
Disassembly of the head or the ear simulator is not required for calibration, only the silicone
rubber moulding of the outer ear (the pinna simulator) needs to be removed. Calibrate the
measurement chain using either Pistonphone Type 4228 or Sound Calibrator Type 4231. Type
4228 supplies a stable, accurate signal at 250 Hz (±1%) and gives a calibration accuracy of
±0.15dB. The signal supplied by Type 4231 is at 1kHz (± 1.5%), and calibration accuracy is
±0.3dB.
To calibrate:
1) Remove the pinna simulator by sliding it towards the front of the head and then pulling the
back of it outwards away from the head.
2) Push calibration adaptor UA-1546 (see Fig.1.1.10) firmly into the ear canal.
3) Fit the calibrator onto the adaptor. Ensure that it is pushed firmly over the end of the adaptor.
4) Switch the calibrator on.
5) Adjust the sensitivity of the measuring instrument(s) to display the correct sound pressure
level, as indicated in Table 1.1. The procedure for doing this should be described in the
instruction manual for the equipment concerned.
Table 1.1
The actual sound pressure
level at the microphone
diaphragm when using
Calibrator Type 4228 or
4231 with Calibration
Adaptor UA-1546
Calibrator Adaptor
Corrected Output
Level (SPL)
Pistonphone
Type 4228
UA-1546
a
and
DP-0776
b
a. Supplied with Head and Torso Simulator Type 4128-C
b. Supplied with Pistonphone Type 4228
Stated SPL +
L
p
– 0.8dB
c
c. “Stated SPL” is the sound pressure level stated on the calibration chart (BC0195) of Type 4228. The nominal SPL of
Type 4228 is 124dB
“L
p
” is the correction for the ambient pressure, which can be read directly from Correction Barometer UZ-0004 supplied
with Type 4228
Sound Calibrator
Type 4231
UA-1546 97.1dB