When reading microphone specifications, it is extremely important to understand how to interpret them.
In most cases, the specifications can be measured or calculated in many different ways.
While microphone specifications provide an indication of a microphone’s electro-acoustic performance, they will not give a total appreciation of how it will sound.
Specifications can detail objective information but cannot convey the subjective sonic experience.
For example, a frequency response curve can show how faithfully the microphone will reproduce the incoming pure sinusoidal frequencies, but not how detailed, well dissolved or transparent the result will be.
The deciBel (dB) Scale
The basis for most microphone specifications is the decibel scale. The dB scale is logarithmic and is used because of its equivalence to the way the human ear perceives changes in sound pressure.
Further, the changes in dB are smoother and more understandable than the very large numbers that might occur in pressure scales (Pascal, Newton or Bar). The dB scale states a given pressure in proportion to a reference pressure, mostly 20μPa.
The reference pressure 20μPa is chosen equal to 0 dB. Please note that 0 dB does not mean that there isn¹t any sound; it only states the lower limiting sound pressure level of the average human ear’s ability to detect sounds.
Frequency Response
The frequency response curve illustrates the microphone¹s ability to transform acoustic energy into electric signals, and whether it will do so faithfully or will introduce coloration. Take care not to mistake frequency response for frequency range.
The microphone’s frequency range, will only give a rough indication of which frequency area the microphone will be able to reproduce sound within a given tolerance. The frequency range is sometimes also referred to as bandwidth. (Figure 1)
Multiple Frequency Response Curves
Manufacturers of professional equipment will always provide more than one frequency response curve, as it is essential to see how the microphone will respond to sound coming from different directions and in different acoustic sound fields.
On-Axis Response
The on-axis response demonstrates the microphone’s response to sound coming directly on-axis towards its diaphragm (0 degrees).
Be aware that the on-axis response may be measured from different distances, which may influence the response on directional microphones because of the proximity effect.
