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To be able to choose the microphone that suits your requirements the most, it is important to understand the technical acoustic aspects of the device. One such useful parameter is its dynamic range.
What is the Dynamic Range?
The dynamic range of a microphone is defined as the range between two extremes – the noise floor and the maximum sound pressure level (SPL) at the point where a perceivable total harmonic distortion (THD) occurs. SPL is measured in dB.
The noise floor is measured in rms or dB(A) and is defined as the sound pressure level equivalent to the noise. This is a measure of the amount of sound that would give an output that is similar to the one generated internally by the microphone itself.
How to Assess the Dynamic Range of a Microphone?
The range is normally assessed using the specifications provided by the manufacturer. Typically, the data sheet mentions an SPL at a 0.5% THD, but it is easy to extrapolate the SPL at any THD. This is because the distortion is proportional to the input levels at a rate that doubles the THD with a 6dB increase in input level.
Another important and related specification with dynamic range is the headroom. This is the range from the SPL level (THD = 1%) to the clipping level of the device.
Now for the base noise floor. This is also measured and the information is provided in the data sheet along with the product.
Alas – the pitfalls!
The measurement of these specifications may vary from manufacturer to manufacturer and so does its reliability. Worst still, since the benchmarks may be different, it may be quite a task when you decide to compare one microphone from another. Hence It is extremely important to understand the method used by the manufacturer to measure these values, since the dynamic range will certainly depend on the same.
Understand whether the microphone capsule has been included in specifying the distortion and SPL before clipping. Mostly the practice is to measure these without the capsule. In sharp contrast, the noise floor uses both the preamp and the capsule.
Some of the various techniques in practice include the B&K High Pressure Calibrator for omnidirectional microphones and the tuned tube for the pressure gradient microphone capsule. Both use reference method measurements to compare the performance of the device against a known standard.
In the former, a good-quality known device is used and the calibrator produces very high sound pressure levels of the mic that is fitted into the adapter of the calibrator.
In the latter, a tuned tube is mounted on a loudspeaker to get high sound pressure levels. By adjusting the wavelength of the tube such that the quality of the sound from the loudspeaker is good, one can ascertain the toleration levels.
Read the data sheet carefully and then make an informed assessment of the dynamic range of the microphone.