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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.

When performing acoustic measurements in a tube, why is it recommended that the wavelength of sound be bigger than the diameter of the open end of the tube?

For general acoustic applications the reason to have a tube small compared to a wavelength of sound is so that the radial pressure distribution (i.e. the pressure variation along a cross-section of the tube) is relatively constant resulting in plane waves traveling down the length of the tube.  Generally the wavelength needs to at least 10x larger than the diameter of the tube for this approximation to be valid.  The dimensions of the tube depend on the desired accuracy of the measurement...what is being measured, how is it being measured, what is the frequency range of interest, in what environment is it being measured, what are the limitations of the test equipment being used to measure it, etc..