HBK 4231, User Manual

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Chapter 3 – Characteristics
13 Sound Calibrator Type 4231
User Manual
3.3 Influence of Load Volume
The calibrator uses a feedback technique to create a very low output
impedance (refer to section 3.7 for a more detailed description). This
minimises the influence of varying acoustic loading and, as a result, the
sound pressure level does not change for different sizes of microphone
(from 1/8

to 1

). This means that you do not need to have the exact
load volume of the coupler and the microphone you are calibrating.
The specified equivalent coupler volume is based on the assumption
that the sound field generated in the coupler is homogeneous. That is,
both the built-in reference microphone and the microphone you are
calibrating are exposed to the same sound pressure level.
3.4 Traceability
Calibration of Sound Calibrator Type 4231 is traceable to both the
Danish Primary Laboratory of Acoustics (DPLA) and the National
Institute of Standards and Technology (NIST), USA.
3.5 Stability
The stability mentioned in the specification consists of two parts:
•
A short-term stability (defined in IEC 60942) – which covers
fluctuation and repeatability
• A long-term stability – based on an analysis and tests of the
electrical circuit/reference microphone
3.6 Recalibration of the Calibrator
Several standards recommend that you should recalibrate your
calibrator at least once a year. This can be done by an authorised HBK
representative or by a recognised standards laboratory or institution.