User manual

Calibration

Applying Correction Values @ M2230

The goal is to measure the sound pressure without the inﬂuence

of the microphone in the air. However, the presence of the mi-

crophone body in the free-ﬁeld environment affects already the

sound pressure level at high frequencies. The measurement mi-

crophone acts at high frequencies like a reﬂector. The sound

pressure increases in front of the microphone capsule mem-

brane. For example, the sound pressure level is 114.0 dB in the

free ﬁeld prior installing the microphone. Now the measurement

microphone is placed into the free ﬁeld. The pressure in front of

the capsule is increased by 0.1 dB at 1 kHz. However, since the

sound without microphone inﬂuence shall be determined, the

free-ﬁeld equalization of the M2230 compensates this effect. The

XL2 Sound Level Meter reads the accurate measured value of

114.0 dB and not 114.1 dB.

If the Class 1 Sound Calibrator is placed on the M2230 measure-

ment microphone, then the pressure conditions applies to the

microphone capsule. The pressure in the volume of the calibrator

matches the pressure on the membrane surface of the micro-

phone. Now the free-ﬁeld equalization and the pressure condi-

tions for the calibration have to be taken into account. Thus, the

XL2 has to be adjusted to a calibration level of 113.9 dB when us-

ing the M2230. This applies for calibrations at reference ambient

conditions and an accurate calibrator output level at the reference

sound pressure level.