Glossary definition of 'Sensitivity'

(transducers) A measure of how responsive a transducer is to an input stimulus, or how effective it is at transforming one form of energy into another. It is usually defined as the number of output units that are measured for a given input unit and is not the same as efficiency.

For example:

Loudspeakers: (voltage sensitivity) the resulting sound pressure level in dBSPL measured at 1m distance on axis in an anechoic environment when the loudspeaker is driven by an input voltage of 2.83V_RMS (the voltage necessary to produce 1W dissipation in an 8 ohm resistor). IEC 60268-5 defines a method of measuring the sensitivity of a loudspeaker in frequency bands using pink noise.

Sensitivity is invariably frequency dependent so the frequency should be stated or the conditions under which it is measured specified. It should also be noted that this is not the same as efficiency which is a dimensionless ratio resulting when the input and output units are the same - we would need to be able to measure the power entering the system in Watts (electrical) and the power exiting the system in Watts (acoustical) in order to be able to do this. Measuring the electrical input to the system in Watts is fairly easy but measuring the acoustic output power of a loudspeaker is not trivial.

Microphones: (pressure sensitivity) The ratio of the open circuit output voltage of a microphone to the sound pressure to which it is exposed - e.g., 1.9mV/Pa. The conditions under which this is measured are defined in IEC 60268-4.

It is also possible to express this as the sensitivity level L_m in dB. This is the sensitivity relative to 1V/Pa, e.g., L_m = 20Log(M/M_r) where M is the sensitivity of the microphone in V/Pa and M_r is the reference sensitivity of 1V/Pa.