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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

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Will you get the same results (at frequencies < 1 kHz) when you use a free-field random incidence or pressure response microphone?

Yes, here is why they provide the same results:

At low frequencies (< 1 kHz) a Free-field, Random Incidence and Pressure response mic all can be used for the same application and produce the same test results.

Below 1 kHz The Free-field, Random Incidence (diffuse Field) and Pressure response microphone will all provide the same results and any can be used in the same application, because the test data output will be the same (within 0.2 db uncertainty of the system.) As the frequency of interest for the test gets higher, the actual sound pressure waves become smaller, causing smaller objects to now have an impact on the the sound field. As the waves approach a similar size to the mic mass, the output between the responses will deviate. As frequencies become higher, it becomes more important to choose the correct sound field, so that you have the most accurate test results. In the below graph you can see how the separation starts to occur after 1 kHz. For example, at 20 kHz a ¼” pressure response microphone will output close to a 6 dB incorrect result, if a pressure response mic is used incorrectly in a Free-Field application. A ½” mic will be out close to 10 dB at 20 kHz due to effects of the larger mass. Below 1 kHz they all exhibit the same test result.

Will you get the same results (at frequencies < 1 kHz) when you use a free-field random incidence or pressure response microphone?

Yes, here is why they provide the same results:

At low frequencies (< 1 kHz) a Free-field, Random Incidence and Pressure response mic all can be used for the same application and produce the same test results.

Below 1 kHz The Free-field, Random Incidence (diffuse Field) and Pressure response microphone will all provide the same results and any can be used in the same application, because the test data output will be the same (within 0.2 db uncertainty of the system.) As the frequency of interest for the test gets higher, the actual sound pressure waves become smaller, causing smaller objects to now have an impact on the the sound field. As the waves approach a similar size to the mic mass, the output between the responses will deviate. As frequencies become higher, it becomes more important to choose the correct sound field, so that you have the most accurate test results. In the below graph you can see how the separation starts to occur after 1 kHz. For example, at 20 kHz a ¼” pressure response microphone will output close to a 6 dB incorrect result, if a pressure response mic is used incorrectly in a Free-Field application. A ½” mic will be out close to 10 dB at 20 kHz due to effects of the larger mass. Below 1 kHz they all exhibit the same test result.