Photo by RAWKU5
When using different microphones, some models require less gain than others. In layman’s terms, that means some mics are “hot” or especially “loud” while others are not. In technical terms, this is “sensitivity.” But what does it mean and why does it matter to the sound recordist?
When exposed to the same sound source, different microphone models may produce different output levels. This means some microphones are more sensitive than others. Microphone sensitivity is the measure of the microphone’s ability for converting acoustic pressure into an electric voltage.
The higher the sensitivity, the less pre-amplification required to bring the sound to a useable level on the mixer channel. The less the sensitivity, the greater the pre-amplification required. The mic pre-amp boosts the signal coming into the mixer.
As you may have guessed, things get a bit more complicated from there, since there are various ways to specify sensitivity. However, the measurement of acoustic pressure converted into electric energy is shown in two ways. It can be listed as millivolts (mV) produced per Pascal unit. Or it can also be cited as dBV per Pascal unit. A Pascal unit is the unit for pressure and it’s a constant of 94 dB SPL.
In the United States, sensitivity is specified in relation to a hypothetical microphone, which produces 1 volt, when exposed to a sound pressure of 1 pascal (94 dB SPL). As this hypothetical mic is much “hotter” than any existing microphone, such sensitivity figures are always negative.
This can be confusing, since –40 dB is much “hotter” than –50 dB. However, this measurement method does have an advantage. Users can easily estimate how much gain is required for an average medium-level sound source.
In Europe, sensitivity (or “transfer factor”) is specified in millivolts per pascal (1 pascal is the equivalent of 94 dB SPL). In other words, it’s output voltage per sound pressure.
In a whitepaper on the subject, Neumann said different transducer technologies achieve different sensitivity levels. Typical values for dynamic microphones are 1 to 4 mV/Pa or –60 to –48 dB re 1V/Pa. Ribbon microphones are usually on the lower end of the scale, while some moving coil dynamic mics achieve as much as 3-4 mV.
Condenser microphones usually have much higher sensitivity than dynamic mics. Typical values are 8 to 32 mV/Pa or –42 to –30 dB re 1V/Pa.
So why does sensitivity matter? As a rule of thumb, sensitivity is an important spec for dynamic and ribbon microphones only. For condenser mics, the sensitivity specification is not as important, because any value above about 8 mV/Pa is more than enough for excellent noise performance with just about any preamp.
Some think that high sensitivity can compensate for a mediocre self-noise figure. But Neumann said that’s not true! For noise measurements, gain must be adjusted according to the mic’s sensitivity. The self-noise figure tells the whole story.
However, high sensitivity can be beneficial when working with an entry-level preamp. Low-cost preamps often sound dull and lifeless at high gain settings above 50 dB. A high sensitivity microphone will rarely require that much gain.
Microphone sensitivity becomes an important microphone property which must be considered when picking the right microphone for a specific need. But don’t assume one microphone is more sensitive than another just because of it’s type. Sensitivity is another property that goes towards giving the microphone its unique sound so you can use it to paint the sound texture you want in a specific application.
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