BRUEL & KJAER 4188 - Frequency Response

Chapter 2 — Prepolarized Free-field
1
/
2
" Microphone Type 4188
Frequency Response
Falcon™ Range of Microphone Products
Microphone Handbook
BE1374– 12
2
−
5
With Microphone Preamplifier Type 2639: G = –0.15dB
With
1
/
2
" Microphone Preamplifier Type 2669: G = –0.30dB
Example
Loaded sensitivity of typical microphone with
1
/
2
" Microphone Preamplifier Type
2669:
S
C
= –29.8 + (–0.30) = –30.1dB
2.2.3 K-factor
Some types of Brüel&Kjær instruments use the K-factor (correction factor) or the
K
O
-factor (open-circuit correction factor) for calibration.
(2.2)
(2.3)
Example
Correction factor for typical microphone with
1
/
2
" Microphone Preamplifier Type
2669:
K = –26 – (–30.1) = +4.1dB
Open-circuit correction factor for typical microphone with
1
/
2
" Microphone Preampli-
fier Type 2669:
K
O
= –26 – (–29.8) = +3.8dB
2.3 Frequency Response
2.3.1 General
In acoustic measurements, there are three types of sound field:
●
Free field
●
Pressure field
●
Diffuse field
The microphone is optimized to have a flat frequency response in one of these
sound fields. This response is called the optimized response. A microphone’s re-
sponse in a diffuse field is equivalent to its random-incidence response.
K
26
–
S
C
–=
K
O
26
–
S
O
–=