11
The Basic Principles of 90CA: Microphone Calibration in Four Easy Steps
The 90CA Microphone Calibration System was designed to eliminate the risk of operator
errors during calibration. The workflow is simple and straight-forward with its four steps as
shown in the following figure.
Fig. 5.
The four steps of calibration with the 90CA
Microphone Registration
is the first step. You enter the test conditions (meteorological
data) and microphone parameters (sensitivity, frequency response, tolerances, etc.) into
the system. The system has a database that already contains calibration information
for G.R.A.S. microphones (sensitivity, frequency response, tolerances, and so on). This
database can easily be extended to contain the same type of details about microphones
from other manufacturers.
Level Calibration
uses the pistonphone and an insert-voltage preamplifier to determine
the open-circuit sensitivity of the microphone capsule at 250 Hz @114 dB.
Frequency Calibration
is performed after the level calibration to determine the fre-
quency response using an electrostatic actuator.
The
Calibration Certificate
is a file that contains all the results for the level and the
frequency calibration. The layout, data used, text, and logo for the certificate can be
customized. The file can be saved as a PDF file.
Ambient Conditions for the Calibration
Ambient noise: < 65 dB
Temperature: 20 - 25° C
Relative Humidity: 30 – 70 %
Microphone
Registration
Level
Calibration
Frequency
Calibration
Calibration
Certi
fi
cate