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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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What does the phase specification for a microphone represent and how is it used in acoustics applications?

Phase is the position of a point in time on a waveform cycle, expressed in angular units (e.g. degrees or radians.) For test and measurement microphones and their applications, phase can be reported in absolute phase or relative phase.

Absolute phase is the phase of a sensor relative to an independent standard (e.g. an electrostatic actuator). Absolute phase may be determined by comparing the phase characteristics of two sensors if the phase response of one of those sensors is used as a reference. The response of the reference may be factored out with software or during post-processing of the data to show only the phase characteristics of the unit under test. This would be appropriate if the reference sensor has well established and stable phase characteristics. Absolute phase is used to examine phase characteristics that are intrinsic to the sensor under test, such as resonance frequency.

Relative phase is the difference in phase between two or more sensors. Relative phase is used to determine how well sensors are matched to each other. Phase represents a delay in the response of a sensor to an applied force. If two microphones have different phases, there will be a lag between the responses of the sensors even if they experience the same pressure change at the exact same time.

Consider the sound wave shown in the diagram below (left). A sound wave incident upon the two microphones at an angle will strike the nearest microphone first. The difference in response times between the two microphones (shown on the right) indicates the direction of the sound wave. Any intrinsic phase delay between the two microphones would be added to the phase shift detected in the measurement.

In applications where the direction and speed of sound are important, such as for sound intensity measurements or noise source location, it is critical for the difference in response times of the two sensors to be the result of propagation delay of the sound itself. Phase lag between the sensors creates error in the measurement.

Relative phase specifications are more often provided for array microphones because these microphones are cost effectively designed to be used in configurations where multiple measurements channels are required. Often arrays are used to provide increased directionality for sound source location. Phase is a frequency dependent characteristic, and so phase data is specified and plotted as a function of frequency as shown in the figure below for the 130A23 high amplitude array microphone.

What does the phase specification for a microphone represent and how is it used in acoustics applications?

Phase is the position of a point in time on a waveform cycle, expressed in angular units (e.g. degrees or radians.) For test and measurement microphones and their applications, phase can be reported in absolute phase or relative phase.

Absolute phase is the phase of a sensor relative to an independent standard (e.g. an electrostatic actuator). Absolute phase may be determined by comparing the phase characteristics of two sensors if the phase response of one of those sensors is used as a reference. The response of the reference may be factored out with software or during post-processing of the data to show only the phase characteristics of the unit under test. This would be appropriate if the reference sensor has well established and stable phase characteristics. Absolute phase is used to examine phase characteristics that are intrinsic to the sensor under test, such as resonance frequency.

Relative phase is the difference in phase between two or more sensors. Relative phase is used to determine how well sensors are matched to each other. Phase represents a delay in the response of a sensor to an applied force. If two microphones have different phases, there will be a lag between the responses of the sensors even if they experience the same pressure change at the exact same time.

Consider the sound wave shown in the diagram below (left). A sound wave incident upon the two microphones at an angle will strike the nearest microphone first. The difference in response times between the two microphones (shown on the right) indicates the direction of the sound wave. Any intrinsic phase delay between the two microphones would be added to the phase shift detected in the measurement.

In applications where the direction and speed of sound are important, such as for sound intensity measurements or noise source location, it is critical for the difference in response times of the two sensors to be the result of propagation delay of the sound itself. Phase lag between the sensors creates error in the measurement.

Relative phase specifications are more often provided for array microphones because these microphones are cost effectively designed to be used in configurations where multiple measurements channels are required. Often arrays are used to provide increased directionality for sound source location. Phase is a frequency dependent characteristic, and so phase data is specified and plotted as a function of frequency as shown in the figure below for the 130A23 high amplitude array microphone.