Instruction Manual

Sound Level Meter Types 2245 – Instruction Manual Page 44 of 110
4.6 Frequency Responses
The frequency responses are given in tabular form in Appendix A and in graphical form
in this section.
The specifications for the Lin response defined in IEC 60651 are equivalent to those
given here for the Z-weighting.
The acoustical frequency response depends on the sound field, the microphone, the
used microphone accessories and the electrical frequency response. To improve the
quality of the measurement, the sound level meter compensates for the sound field,
the microphone and the used microphone accessories by changing the electrical
frequency response.
This means that it is very important that parameters on menus reflect the desired
configuration. The important menus are:
 Measurement settings > Input
 Measurement settings > Broadband parameters and
 Measurement settings > Spectrum parameters
Limit curves are drawn on some of the frequency response graphs in the following
sections. These curves represent the IEC 61672–1:2013 acceptance limits.
The Expanded Uncertainties of Measurement in the tables are the two-sigma limits
maintained in the Brüel & Kjær production for the specific product. This means that the
correct value lies in the range of the measured value plus/minus the Expanded
Uncertainties of Measurement with a probability of 95%.
Please note: This range is not related to the production spread. The range is for a
specific typical unit. The factory acceptance tests at Brüel & Kjær ensure
that the ranges for all units are within the IEC 61672–1 limits.
4.6.1 Electrical Frequency Responses
The uncompensated electrical frequency response for the different frequency
weightings are given in Fig. 4.1 and Table A.1.
The compensated Z-weighted electrical frequency response is given in the “Electrical
Response” column of the appropriate tables of Table A. 2 to Table A. 6 in Appendix A.
The electrical frequency responses in Fig. 4.1 and Table A.1 are valid for introduction of
the electrical signal through the recommended means to substitute the microphone
with an electrical input facility (see section 3.3.2).