BRUEL & KJAER 2240 - Diffuse-field Frequency Responses; Directional Response; Self-generated Noise

CHAPTER 4
Specifications
17
4.6.2 Diffuse-field Frequency Responses
The deviation from the ideal frequency weighted Diffuse-field frequency responses (also called ran-
dom-incidence frequency responses) with A or C frequency weighting are provided in Fig.4.2. Table
A.3 in Appendix A provides the Microphone Diffuse-field 0° Response, the Random Incidence Corrector
DZ-9566 Influence, the frequency weighted Electrical Responses, the overall frequency weighted
Acoustical Responses, and the Expanded Uncertainties of Measurement.
The Diffuse-field body influence of Sound Level Meter Type 2240 is so small that the diffuse-field
frequency responses is only influenced by the Microphone Type 4188 and the Random Incidence
Corrector DZ-9566.
Fig.4.2 Diffuse-field deviation from ideal A- or C-weighted frequency responses, for Sound Level Meter Type 2240,
with Microphone Type 4188 and Random Incidence Corrector DZ-9566
4.7 Directional Response
This section gives directional responses for plane, progressive, sinusoidal sound waves normalised to
the response in the reference direction.
4.8 Self-generated Noise
Self-generated noise is given for the most sensitive level range and for nominal microphone open-
circuit sensitivity.
10 100 1000 10000 100000
Hz
-4
-2
0
2
4
dB
070016
Table 4.1
Directional re-
ponse (equivalent
to reduced IEC
61672-1 limits)
Maximum absolute difference in displayed sound levels at any
two sound-incidence angles within ±θ degrees from the
reference direction (dB)
Frequency (kHz) θ = 30° θ = 90° θ = 150°
0.25 to 1 1.0 1.5 2.0
>1 to 2 1.0 2.0 4.0
>2 to 4 1.5 4.0 6.0
>4 to 8 2.5 7.0 10.0
>8 to 12.5 4.0 10.0 14.0