BRUEL & KJAER 2206 - Output Socket; Frequency Response; Influence of Reflections; Directional Characteristics

3.7.2. Output Socket
This is a standard microsocket accepting B & K cables with microplugs (e.g. AO 0037).
Tape recorders or level recorders can hence be connected when noise signals need to be
recorded
for later evaluation. The load impedance should be at least 5 kO. Output vol-
tage for full scale deflection on the meter is approx 2,5 V RMS. Maximum peak value
1 0 V. Typical signal to noise ratios at the output socket are shown in Table 3.1.
3.7.3. Frequency Response
A typical free-field frequency response for microphone Type 4148 at 0° incidence is
shown in Fig. 3. 5. This curve is for the microphone mounted on a preamplifier (261 9)
with a diameter equal to that of the microphone cartridge. A similar curve is supplied in
the calibration chart which accompanies each microphone, and is the free field response
of that particular microphone. Reflection of sound causes diffraction effects to be noticed
when the reflecting surfaces are close to the microphone.
Meaauring Obj.
dE d
160
31 15
Free Field Response
Pressure Response
4 ~'
1~ 5
Roc. No.:
Date:
Sign
.: 0 0
0
10 20
Hz 50 100 200 500 1000 2000 5000 10000 20000 40000 D A 8 C l1n.
<P 1124 Muhiply Frequency Scole by :
Zorol- __ Frequency (Hzl (1112121121 A 8 C U'690651'
Fig. 3.5. Typical free-field response of 4148
3.7.4. Influence of Reflections
If. pure tones, narrow band noise, or highly directional sound is being measured, it may
be desirable to separate the microphone and meter with extension cable AO 0063 so
that the microphone is away from the influence of reflections from the observer.
3.7.5. Directional Characteristics
The microphone is of the omnidirectional type, with typical directional characteristics as
shown in Fig. 3.6. The random incidence response, representing the frequency response
to a diffuse field, is normally calculated conventionally at frequencies of 250, 500,
1000, 2000, 4000, 8000 and 12.500 Hz, according to the formula
where K
1
,
K
2
· · · K
7
are constants (see IEC Recommendation 1 79) and
S
0
,
S
30
· · ·
S
180
are the sensitivities (m V per N/m ) at 0°, 30° · · · 180°
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