Scantek Inc  //  Details on Calibration Services 1. Microphones

1. Calibration of Microphones

 

There are several services we put in place to determine the main parameters of the microphones. 
 

1.1 Standard calibration (accredited)
 

  • Open circuit sensitivity measured at 250Hz, using the insert voltage method. 

  • Frequency response measured using the actuator method. Frequency domain: from 63 Hz up 200 kHz or up to the upper specified domain for the tested microphone (whichever is lower). Tests above 100 kHz are not covered by the current accreditation. 

 

The service is applicable for condenser microphones of 1”, ½”, ¼’ diameter, with removable grid, and for pairs microphone/preamplifier. In the latter case, the sensitivity of the ensemble is reported.  
 

1.2 Calibration of reference microphones (A) (accredited)
 

  • Open circuit sensitivity measured at 250Hz and 1 kHz, using the insert voltage method. 

  • Frequency response measured using the actuator method. Frequency domain: from 63 Hz up 200 kHz or up to the upper-specified domain for the tested microphone (whichever is lower). Tests above 100 kHz are not covered by the current accreditation. 
     

The service is applicable for condenser microphones of 1”, ½”, ¼’ diameter, with removable grid, and for pairs microphone/preamplifier. In the latter case, the sensitivity of the ensemble is reported.  
 

This service is offered for microphones used as reference by other laboratories.  
 

1.3 Calibration of reference microphones (B) (accredited)
 

  • Open circuit sensitivity measured at 250Hz using primary standard calibrator, which was calibrated directly by a national laboratory.

  • Pressure response within a frequency domain (open circuit sensitivity) (31.5 Hz to 16 kHz, at center frequencies of the octave band filters) measured by comparison with the primary standard microphone (which was calibrated directly by a national laboratory). 

 

The service is applicable for laboratory standard microphones of ½” diameter (example 40 AU, 4180). The service is also offered for 4134 microphones.  
 

1.4 True free-field response of microphones (accredited)
 

  • Sensitivity measured at 250Hz, and 

  • Free-field response tested with acoustical excitation, by simultaneous comparison with a reference microphone (CDP method ). Frequency domain: 160 Hz to 20 kHz. 

 

This service is applicable for microphones or microphone/preamplifier pairs of ½” and 1” diameter for which the regular actuator method cannot be applied because:
 

  • The actuator will influence the acoustic impedance of the microphone and falsify the results (example: the low-noise measuring systems for which manufacturers recommend only the acoustical method).

  • The microphone grid is not removable. 

  • The corrections between the free-field and the pressure responses are not publicly available.

  • Because the microphones are not a condenser type.  

 

1.5 Measurement of the windscreens insertion loss 
 

The CDP Method  is used to determine the influence of the windscreens in a frequency domain between 160 Hz and 20 kHz. Currently, the service is offered for windscreens of diameters up to 90 mm [3.5”].  

 

1.6 Measurement of the microphones correction factors (accredited)
 

The CDP Method  is used to determine the correction factors between the free field and actuator microphone responses, in a frequency domain from 160 Hz to 20 kHz. 
 

The service is applicable for microphones for which the actuator method can be used. 
 

1.7 Intensity probes or paired microphones
 

The microphones and preamplifiers are each separately tested, and then the match of the characteristics, according to the IEC 1043 standard is checked. Finally the phase match is checked by testing the pressure-intensity residual (PIR) index. For this purpose, either the customer provided or the laboratory reference analyzer is used.