11/01/15

CALCULATING THE DYNAMIC RANGE OF A MICROPHONE

Dynamic range is a key feature of any microphone. This article gives clues as to how to calculate it correctly.
Keywords: Dynamic range, distortion and sound pressure.
Achieved knowledge: You have learned how to assess and calculate the dynamic range of microphones.

Dynamic range is a key feature of any microphone, here are some clues as to how to calculate it correctly.
 

What is dynamic range?

The dynamic range of any kind of professional audio equipment is basically calculated as the difference between the noise floor and the maximum sound pressure level which the microphone can handle (aka. the overload sound pressure).

The noise floor is normally expressed as the equivalent sound pressure level due to inherent noise (meaning: what acoustic sound would produce the same output from the microphone as the output now “created” internally by the microphone itself). This noise is in this case measured rms and A-weighted.

The upper limit, the maximum sound pressure level or overload sound pressure level, is determined by that level where a certain amount of total harmonic distortion appears.
 

Distortion and sound pressure

The manufacturer can choose the amount of distortion at which they want to specify the overload SPL, as long as the THD (total harmonic distortion) is stated. Usually, microphone manufacturers specify the equivalent sound pressure level at 0.5% or 1% THD. At DPA we specify the maximum sound pressure level at 1% THD.
 

Are microphone specifications reliable?

Most manufacturers offer data sheets with THD, noise floor, clipping level, and other key specs. Bear in mind that these specs are only as reliable as the measurement techniques the manufacturer uses, and be especially cautious when comparing mics from different manufacturers.

Some microphone manufacturers specify measurement results that could easily be mistaken for solid data. They measure the noise floor of the total microphone (i.e. capsule and preamplifier), but the figures for distortion and the sound pressure level before clipping occurs are measured without the microphone capsule – the most critical component of the microphone. Only the microphone preamplifier is measured with an equivalent electronic signal.

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