BRUEL & KJAER 4188 - The Calibration Chart

Chapter 2 — Prepolarized Free-field
1
/
2
" Microphone Type 4188
Introduction
Falcon™ Range of Microphone Products
Microphone Handbook
BE1374– 12
2
−
3
2.1.2 The Calibration Chart
Each microphone is supplied with an individual calibration chart (see Fig.2.2)
which gives the microphone’s open-circuit pressure sensitivity together with the
typical capacitance and free-field and random-incidence frequency responses
*
. When
these are combined with the microphone’s typical data supplied in this chapter, the
individual microphone’s response under various conditions can be determined.
Open-circuit Sensitivity
The stated open-circuit pressure sensitivity is valid at the reference frequency
(1000Hz) for random-incidence and pressure-field conditions. The free-field sensitiv-
ity at the reference frequency (1000Hz) is 0.11dB higher than the pressure sensi-
tivity.
Ambient Conditions
The ambient conditions are measured continuously during calibration at the factory.
The calibration results obtained at the measured environmental calibration condi-
tions are corrected to the stated reference ambient conditions (23°C, 101.325kPa
and 50%RH).
Frequency Responses
Two typical frequency responses are shown on the calibration chart. Both are nor-
malized to 0dB at the reference frequency (1000Hz).
The left-hand curve on the rear side of the calibration chart is the open-circuit 0°-
incidence free-field response for the microphone without the supplied Random Inci-
dence Corrector DZ9566.
*Random-incidence response with supplied Random Incidence Corrector DZ9566.
Fig.2.2 Microphone calibration chart (front and back)
Brüel & Kjær
Caution: Static electricity discharge directly on the centre terminal may damage the prepolarization of the
cartridge. Therefore, ensure that the housing of the cartridge makes contact before the centre terminal.

Sensitivity: The loaded sensitivity is typically 0.05dB lower than the sensitivity stated. The random-field
sensitivity is the same as the pressure sensitivity. The free-field sensitivity at 1000Hz is 0.15dB higher
than the pressure sensitivity.

Free-field calibration with Sound Level Calibrators at 1000Hz: Adjust the Sound Level Meter, or other
measurement equipment, to indicate 0.15dB lower SPL than the actual SPL produced by the calibrator.

The two grooves means “prepolarized”, i.e. 0V external polarization voltage.

Refer to the 4188 Product Data for further information. See also rear side.
Prepolarized Condenser Microphone Cartridge Type 4188 

Serial No.:

Open-circuit Pressure Sensitivity at 1013 hPa 23˚C and 50% RH:

dB re 1 V/Pa or mV/Pa

Frequency: 1000Hz Capacitance: 12pF (typical)

Polarization Voltage (external): 0V

Date: Signature: .......................................
B
K
7/6-'89
BC0211-11
930776e
-3
-2
-1
0
1
2
3
12 51020 50 100 200 500 1k 2k 5k 10k 20k
Typical random-field response with random incidence corrector
Frequency response satisfies ANSI S 1.4–1984 Type 1
-3
-2
-1
0
1
2
3
12 51020 50 100 200 500 1k 2k 5k 10k 20k
Typical free-field response for 0˚ incidence
without random incidence corrector
Tol.
Tol.
Tol.
Tol.
Frequency response satisfies IEC 651 Type 1
1. July 1993
–30.2
1740259
30.9
N.G.