How to Measure and Interpret Microphone Sensitivity

Microphone sensitivity is a key specification that affects the performance of a microphone in various recording environments. For individuals who are interested in the technical side of audio equipment, understanding how to measure and interpret microphone sensitivity is essential. In simple terms, microphone sensitivity refers to how efficiently a microphone converts sound pressure into an electrical signal. The higher the sensitivity, the stronger the signal produced by the microphone for a given sound level.

This guide explains the basics of measuring microphone sensitivity and interpreting its values in a practical context.

Measuring Microphone Sensitivity

Microphone sensitivity is typically measured by exposing the microphone to a standardized sound pressure level (SPL) and determining the output signal in response. The standard SPL used for testing is usually 94 dB SPL, which is equivalent to 1 Pascal of sound pressure. In controlled conditions, a 1 kHz tone is used to ensure uniformity in measurements.

To measure microphone sensitivity, the following equipment is commonly required: A sound level calibrator or signal generator, which produces a consistent and precise sound pressure level at a specific frequency, typically 1 kHz; an anechoic chamber or soundproof environment, which eliminates background noise and room reflections that could skew the measurements; an audio interface or sound analyzer that can capture and quantify the electrical output from the microphone.

Once the microphone is placed in front of the calibrator, the sound pressure level is applied. The microphone’s electrical output is measured in millivolts (mV) or decibels relative to 1 Volt (dBV). This output reflects the microphone’s ability to generate an electrical signal from the incoming sound. Higher output levels indicate a more sensitive microphone.

Sensitivity Ratings: dBV and mV

Microphone sensitivity is often expressed in two main formats: decibels relative to 1 Volt (dBV) or millivolts per Pascal (mV/Pa). Understanding these ratings is crucial for interpreting the performance of different microphones.

In the dBV format, sensitivity is usually expressed as a negative value, such as -42 dBV. This indicates the signal level in decibels below 1 Volt. A microphone with a sensitivity of -42 dBV will generate an output signal that is 42 decibels below 1 Volt when exposed to a 94 dB SPL sound source. The smaller the negative number, the more sensitive the microphone is. For example, a microphone rated at -30 dBV is more sensitive than one rated at -40 dBV, as it produces a stronger output signal for the same input sound pressure.

In the mV/Pa format, sensitivity is expressed in millivolts produced for each Pascal of sound pressure. For example, a microphone with a sensitivity of 25 mV/Pa generates 25 millivolts of electrical output for each Pascal of sound pressure applied at 94 dB SPL. In this case, the higher the millivolt value, the more sensitive the microphone. A microphone rated at 25 mV/Pa is more sensitive than one rated at 10 mV/Pa.

Interpreting Sensitivity in Real-world Applications

The sensitivity rating of a microphone affects its performance in different recording scenarios. Higher sensitivity microphones are better suited for capturing quieter or distant sounds, as they produce stronger output signals from weaker sound sources. However, in noisy environments, high sensitivity can lead to the capture of unwanted background noise or distortion when the microphone is exposed to excessively loud sounds.

Conversely, microphones with lower sensitivity are often used in high-SPL environments, such as live concerts or recording loud instruments like drums. These microphones are less likely to overload or distort under high sound pressure levels, but they may require more amplification in quieter settings.

It is also important to consider microphone sensitivity in relation to preamp gain. A high-sensitivity microphone may not require much gain from the preamp, while a low-sensitivity microphone might need significant gain to produce an adequate signal level. This balance between microphone sensitivity and preamp gain can have a direct impact on the overall noise floor and signal quality of your recording.

Standardization and Calibration

Microphone manufacturers typically follow industry standards, such as the International Electrotechnical Commission (IEC) or Audio Engineering Society (AES) guidelines, when measuring and reporting microphone sensitivity. This ensures consistency and comparability between different microphones.

When interpreting sensitivity specifications, it’s essential to note whether the manufacturer provides measurements based on the same conditions and standards. In some cases, measurements may vary slightly due to differences in testing environments, equipment, or calibration methods. Therefore, it’s a good idea to check whether the microphone’s sensitivity is measured at 94 dB SPL with a 1 kHz tone, as this is the standard reference for most sensitivity ratings.

Final Note

Measuring and interpreting microphone sensitivity is an important skill for audio enthusiasts and professionals alike. It provides valuable insight into how efficiently a microphone captures sound and translates it into an electrical signal. Understanding sensitivity values in dBV or mV/Pa formats allows you to make informed decisions about which microphone is best suited for a particular recording situation.

By carefully considering sensitivity in the context of your recording environment, sound source, and preamp settings, you can ensure that your microphone performs optimally, delivering clear and balanced audio output.