Microphones Sensitivity Explained

Content Summary
Microphone Sensitivity is a core parameter for measuring its sound-to-electricity conversion efficiency, defined as the voltage output of the microphone per unit Sound Pressure (1 Pa, equivalent to 94 dB SPL), with units of millivolts per pascal (mV/Pa), and can also be expressed in Decibels (dBV or dBFS). The higher the sensitivity, the stronger the microphone's ability to capture faint sounds, but it may also amplify ambient noise. This article provides an in-depth analysis of the differences in sensitivity expression between analog microphone (using dBV) and digital microphone (using dBFS), and explores selection strategies for different types of microphone (such as condenser, dynamic, and electret) in various application scenarios. By considering signal-to-noise ratio, system gain, and the actual requirements of the recording environment, this article helps users make more informed and scientifically sound choices when selecting microphone suited to their specific needs.

What is microphone sensitivity?

microphone sensitivity refers to a microphone's ability to convert sound pressure into voltage or digital signals. Generally, the higher the sensitivity, the stronger the signal output by the microphone, meaning that the subsequent amplifier requires less gain.

The output voltage of a microphone per unit Sound Pressure Level. Unit: millivolts per pascal (mv/Pa).

Core Definition and Technical Analysis of microphone Sensitivity

microphone sensitivity (Sensitivity of microphone) is a core parameter for measuring its sound-to-electric conversion efficiency, defined as the open-circuit output voltage of the microphone per unit sound pressure. When a sound pressure of 1 Pascal (Pa) (equivalent to a sound pressure level of 94 dB SPL) acts on the microphone diaphragm, the output voltage value (in millivolts, mV) is the sensitivity, with the standard unit being mV/Pa. This parameter directly reflects the microphone's response capability to sound signals: the higher the sensitivity, the stronger the ability to capture weak sound pressures; conversely, a higher sound pressure is required to produce an effective output. In professional acoustic measurements, recording production, and sound reinforcement systems, sensitivity is one of the key criteria for selection.

In-depth interpretation of sensitivity units: linear and logarithmic notation

Sensitivity is typically expressed in two forms: linear units (mV/Pa) and logarithmic units (dB). Linear units directly reflect the physical proportional relationship between voltage and sound pressure, for example, 10 mV/Pa indicates an output voltage of 10 mV at 1 Pa sound pressure. Logarithmic units are expressed in deciBels (dB), with a reference baseline of 1 V/Pa (0 dB). The calculation formula is: SdB = 20 × log10(SmV/Pa / 1000). For example, converting 10 mV/Pa to logarithmic units: 20 × log(0.01) = -40 dB. Logarithmic representation compresses the numerical range, facilitating engineering comparisons and system gain calculations. The two units can be converted between each other, and professional equipment manuals often list both simultaneously.

Scientific methods and influencing factors for sensitivity measurement

Measurements must be conducted in a controlled acoustic environment such as an anechoic chamber: a standard sound source generates a 1kHz sine wave at 94dB SPL (1Pa), the open-circuit output voltage of the microphone is recorded, and the ratio is calculated to obtain the mV/Pa value. Measurement accuracy is affected by environmental noise, sound source stability, and circuit impedance matching. Sensitivity is not an isolated parameter; its actual performance is strongly correlated with the following factors:

Transducer principle: condenser microphone (including electret microphone) have thin diaphragms and are sensitive to electric fields, resulting in sensitivity values typically ranging from -40 dB to -30 dB (10 to 30 mV/Pa). dynamic microphone, which operate based on electromagnetic induction, have lower sensitivity values (-60 dB to -50 dB, approximately 1 to 3 mV/Pa).

Physical size: Large-diaphragm microphone have a larger sound energy capture area, resulting in higher sensitivity, making them suitable for detailed recording; small-diaphragm microphone are better suited for high-sound-pressure environments.

Circuit design: Electret microphone with built-in JFET amplifiers can enhance output, but it is important to note that fluctuations in supply voltage can significantly alter sensitivity.

Typical correlation between microphone types and sensitivity performance

Condenser microphone (including electret) are preferred for vocal and instrumental recording in studios due to their high sensitivity (-40 dB to -30 dB) and flat frequency response, particularly excelling in capturing weak sound sources. However, high sensitivity also makes them susceptible to wind noise and airflow disturbances, necessitating the use of a windscreen.

Dynamic microphone, with their lower sensitivity (-60 dB to -50 dB), excel in live performances and high-pressure environments: they are less prone to Distortion from large dynamic signals and have a robust, impact-resistant design. For example, vocal microphone at concerts must withstand the high sound pressure generated by the proximity effect.

Aluminum ribbon microphone, though the least sensitive and most fragile, offer superior transient response and are indispensable in specific professional recording scenarios (such as brass instruments).

The dialectical relationship between sensitivity and signal-to-noise ratio (SNR) and application strategies

While high-sensitivity microphone can enhance signal gain, they may also amplify circuit noise and environmental noise, leading to reduced SNR. For example, in a noisy conference room, a -35dB microphone may produce clearer speech output than a -28dB model, as the latter is more prone to picking up background interference such as air conditioning noise.

Professional selection requires balancing scene requirements:

Low-noise environments (recording studios, anechoic chambers): Prioritize high-sensitivity + high-SNR microphone to maximize signal detail reproduction.

High-noise environments (stages, outdoors): microphone with medium to low sensitivity can suppress background noise, and directional designs (such as supercardioid) can further improve the signal-to-noise ratio.

Note: SNR is defined independently of sensitivity and reflects the ratio of the output signal to inherent noise (in dB), while the EIN (equivalent input noise) parameter provides a more intuitive assessment of the microphone's minimum measurable sound pressure level.

microphone sensitivity application strategies in professional fields

microphone sensitivity selection for recording must match the characteristics of the sound source. When recording acoustic instruments like classical guitars, condenser microphone with high sensitivity (e.g., -32 dB) can capture string overtones; however, for electric guitar amplifier pickup, dynamic microphone (e.g., SM58, -54.5 dB) are needed to avoid overload. In close-talking scenarios (such as podcast voiceovers), note that high-sensitivity microphone are prone to “popping” sounds caused by mouth airflow. It is recommended to use a pop filter or select a model with moderate sensitivity (-42 dB to -38 dB).

At the system integration level, sensitivity directly affects preamplifier gain design. For example, a -50dB dynamic microphone requires approximately 10dB more gain than a -40dB condenser microphone. If the mixing console's gain margin is insufficient, it will limit the Dynamic Range. Digital microphone have a uniform sensitivity of -26dBFS (at 94dB SPL), with full scale corresponding to 120dB SPL. Ensure that the rear-end ADC dynamic range is matched.

Detailed Explanation of dBV and dBFS in Analog and Digital microphone

When selecting a microphone, sensitivity is a very critical technical parameter. It helps you assess the microphone's ability to convert sound signals into electrical signals. However, many users are confused by the units of sensitivity, particularly the difference between dBV used for analog microphone and dBFS used for digital microphone.

Analog microphone: Sensitivity Expressed in dBV

For analog microphone, sensitivity is typically expressed in dBV (decibels relative to 1 volt). This unit indicates the voltage output of the microphone under standard test conditions.

For example:  

If an analog condenser microphone has a sensitivity of -40 dBV, it will output approximately 10 millivolts (mV) of voltage at 94 dB SPL.

The closer the value is to 0, the higher the sensitivity; the more negative the value, the lower the sensitivity.  

High-sensitivity analog microphone are suitable for quiet environments such as recording studios and vocal recording;  

low-sensitivity microphone are more suitable for high-sound-pressure environments such as drum kits and guitar amplifiers to prevent overload distortion.

Digital microphone: sensitivity expressed in dBFS

With the development of digital audio devices, digital microphone (such as MEMS microphone) are becoming increasingly common, especially in smart speakers, headphones, and IoT devices. The sensitivity of such microphone is typically expressed in dBFS (decibels relative to full scale).

0 dBFS represents the maximum output value of the digital system, and any sound below this value is represented as a negative number.  

For example, a digital microphone outputs -26 dBFS at 94 dB SPL, meaning its digital signal strength is 26 dB lower than the system's maximum value.  

This representation allows engineers to directly assess the dynamic range of the digital signal without considering the effects of preamplifiers or voltage changes.

Can dBV and dBFS be directly compared?

No. Because they belong to different signal processing stages:  

dBV is a measure of analog signal voltage  

dBFS is a measure of digital signal amplitude  

To make an effective comparison, you must know the ADC (analog-to-digital converter) resolution, bit depth, and whether additional gain adjustment has been applied.  

This is particularly important for professionals involved in hardware design, embedded development, and audio engineering.