HD2024
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V1.0
3
CALIBRATION PROCEDURE
The HD2024 can calibrate standard 1/2” (and 1/4” with HD2020MA adapter) micro-
phones compliant with IEC 61094-1 and IEC61094-2.
To calibrate the microphone, insert it deep into the cavity. The O-ring will offer some
resistance.
The calibrator can be held in vertical position or placed on a flat surface.
While measuring, you should move neither the microphone nor the calibrator; make
sure that the worktable doesn’t transmit vibrations.
A small misalignment of the microphone and calibrator axes is allowed.
•
Switch on the calibrator by pressing the ON/OFF key.
•
Calibrate the sound level meter as per the procedure shown in the instrument
manual.
•
Apply the correction to the pressure level depending on the type of microphone
(see the following paragraph).
•
Once calibration is complete, switch off the sound level meter and the calibrator
and remove the microphone from the cavity.
The HD2024 calibrator allows calibrating any sound level meter provided that it is
equipped with a laboratory or working standard 1/2” microphone compliant with IEC
61094-1 and IEC 61094-4 standards.
3.1
C
ORRECTION DEPENDING ON THE TYPE OF MICROPHONE
The calibrator generates a 94 dB sound pressure level referred to 20
μ
Pa. Working
standard 1/2” microphones for sound level meters are manufactured to achieve flat
frequency response in free or diffuse field, i.e. in a field of progressive plane waves
propagating in the same direction as the microphone axis and in a field of sound
waves coming from every direction, respectively. These propagation conditions are
different from those in the calibrator cavity.
In free field, reflections due to the microphone alter the sound level by increasing the
actual high-frequency capsule sensitivity. Microphones optimized for free field meas-
urements exploit this phenomenon to achieve flat frequency response even at very
high frequencies. In these microphones, the sound level increase at 1 kHz corre-
sponds to approximately 0.05 dB ÷ 0.20 dB. Therefore, when you calibrate a free field
microphone, you must take into account for this difference by setting in the sound
level meter a sound level 0.1 dB or 0.2 dB lower than the calibrator nominal one.
Microphones optimized for diffuse field measurements don’t require corrections when
calibrated in a closed cavity at 1 kHz instead.
Summary of Contents for HD2024
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