Static pressure coefficients of laboratory standard microphones type LS2 and its influence in the free-field sensitivity level calculation

摘要

Static pressure coefficient of a laboratory standard microphone is used to calculate its pressure sensitivity level when transducer is calibrated at environmental conditions different from the reference value.Static pressure coefficient is calculated using a linear regression approach from the pressure sensitivity level estimated by reciprocity calibration at different static pressures, carried out inside a chamber with controlled static pressure.Resulting static pressure coefficients are also used to correct the free-field sensitivity level.CENAM’s free-field reciprocity calibrations are carried out about 81 kPa,and the correction value of the measured free-field sensitivity level with respect to the reference one will be around 0,5 dB near the resonance frequency,with higher values for higher frequencies.Measurements of static pressure coefficient were carried out for LS2 microphones in the range from 81 kPa to 105 kPa.Measurement results are compared with the approaches proposed in literature and software commercially available for reciprocity pressure calibration.The differences found are discussed,and their effect in the measurement uncertainty for the free-field sensitivity level is evaluated.