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Microphones and Acoustics

Frequently Asked Questions

Get your most commonly asked acoustics questions answered.

Section I: Definitions and Terminology
Section II: Microphone Recommendations
Section III: Calibration and Testing
Section IV: Specification Clarifications
Section V: Specialty Microphone Applications
Section VI: Maintenance and Handling

If you don’t see the answer to your question, call our 24/7 SensorLineSM 716-684-0001 to speak with an application engineer or visit Ask the Acoustics Experts.

How often should I calibrate my microphone?

How often you calibrate a microphone depends upon a number of factors. It depends on whether it is a single point in the field calibration or a factory full sweep calibration.

There are two common types of calibrations for microphone users. The first is a calibration done at the factory to ensure that the product is meeting specification and working properly. This test will check the sensitivity, first through a reference frequency and then we will test the linearity throughout the whole frequency range. This is done either using a back-to-back reference microphone or using an electrostatic actuator. A few examples of the actuator are shown:





1. The factory sweep calibration with an actuator is the only time the grid cap should ever be removed. How often an end user should perform this type of calibration depends upon the level of risk and end user is willing to tale for inaccurate measurements vs cost of the calibrations along with a number of other factors, including, but not limited to:

  • What is the internal requirement by the end users quality control department? Does the QC department have a standard internal period for all sensors?
  • Are there any standards or legal factors that they must comply with? These should be calibrated more often.
  • How often you use the microphone? A microphone used once every few months and stored properly, may not need to be calibrated as often as one used daily.
  • What is the environment the mic is used in? A mic that is used in rough environments and is exposed to extreme temperatures, or dust and oil and other contamination, should be checked more often than a mic used in a controlled lab environment.
  • Has the mic been dropped or abused? Just dropping a mic can change the sensitivity and put it out of spec and should be checked, first by a single point calibration (detailed below) and if a significant shift in the sensitivity is seen, then it should be checked my the manufacturer before it is required for the next test.




If there is a sufficient quantity of microphones, you might be able to justify the purchase of calibration station for example, Model 9350C is shown below and sold by The Modal Shop. With this a factory style sweep calibration can be performed in house and save both time and money.





2. A single point, in field calibration is a test that is performed with a speakerphone or pistonphone. A few examples of the hand held calibrators are shown below:





The goal is to test the sensitivity at a single point (typically 250 Hz or 1 kHz) to make sure that the microphone is working properly and the sensitivity has not shifted, which would cause erroneous results. This does not check the whole frequency range. The end user assumes that the sweep is still flat as shown in the last factory calibration, if no major changes in sensitivity are shown. The other reason why this single point calibration is performed, is to account for the changes in temperature, humidity and atmospheric pressure, so that you get the most accurate test results. It is highly recommended that this single point calibration be done both before and after every test, because that provides confidence that the microphone was working properly throughout the test.

In summary, the factory calibration is a more elaborate test, that the end user should determine their own calibration cycle depending upon the usage, environment, legal requirements, level of risk, and internal requirements. These are typically done once every 1-2 years, but there is nothing written in stone by the manufacturers of the microphones and up to the discretion of the end user. In contrast a single point verification calibration done in the field is recommended both before and after every test to help ensure the results are valid. This is why every customer and every quote should contain a CAL200 or CAL250 as a recommended accessory.

How often should I calibrate my microphone?

How often you calibrate a microphone depends upon a number of factors. It depends on whether it is a single point in the field calibration or a factory full sweep calibration.

There are two common types of calibrations for microphone users. The first is a calibration done at the factory to ensure that the product is meeting specification and working properly. This test will check the sensitivity, first through a reference frequency and then we will test the linearity throughout the whole frequency range. This is done either using a back-to-back reference microphone or using an electrostatic actuator. A few examples of the actuator are shown:





1. The factory sweep calibration with an actuator is the only time the grid cap should ever be removed. How often an end user should perform this type of calibration depends upon the level of risk and end user is willing to tale for inaccurate measurements vs cost of the calibrations along with a number of other factors, including, but not limited to:

  • What is the internal requirement by the end users quality control department? Does the QC department have a standard internal period for all sensors?
  • Are there any standards or legal factors that they must comply with? These should be calibrated more often.
  • How often you use the microphone? A microphone used once every few months and stored properly, may not need to be calibrated as often as one used daily.
  • What is the environment the mic is used in? A mic that is used in rough environments and is exposed to extreme temperatures, or dust and oil and other contamination, should be checked more often than a mic used in a controlled lab environment.
  • Has the mic been dropped or abused? Just dropping a mic can change the sensitivity and put it out of spec and should be checked, first by a single point calibration (detailed below) and if a significant shift in the sensitivity is seen, then it should be checked my the manufacturer before it is required for the next test.




If there is a sufficient quantity of microphones, you might be able to justify the purchase of calibration station for example, Model 9350C is shown below and sold by The Modal Shop. With this a factory style sweep calibration can be performed in house and save both time and money.





2. A single point, in field calibration is a test that is performed with a speakerphone or pistonphone. A few examples of the hand held calibrators are shown below:





The goal is to test the sensitivity at a single point (typically 250 Hz or 1 kHz) to make sure that the microphone is working properly and the sensitivity has not shifted, which would cause erroneous results. This does not check the whole frequency range. The end user assumes that the sweep is still flat as shown in the last factory calibration, if no major changes in sensitivity are shown. The other reason why this single point calibration is performed, is to account for the changes in temperature, humidity and atmospheric pressure, so that you get the most accurate test results. It is highly recommended that this single point calibration be done both before and after every test, because that provides confidence that the microphone was working properly throughout the test.

In summary, the factory calibration is a more elaborate test, that the end user should determine their own calibration cycle depending upon the usage, environment, legal requirements, level of risk, and internal requirements. These are typically done once every 1-2 years, but there is nothing written in stone by the manufacturers of the microphones and up to the discretion of the end user. In contrast a single point verification calibration done in the field is recommended both before and after every test to help ensure the results are valid. This is why every customer and every quote should contain a CAL200 or CAL250 as a recommended accessory.