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Why do microphones sound different?

Microphones are the most inconsistent products in the whole of audio (apart from loudspeakers that is!). But why do they sound different? Isn't there such a thing as the perfect mic?


Firstly, is there such a thing as a perfect microphone? How would we know that it is perfect?

Well, if you could record someone speaking, then play the recording back through a very accurate loudspeaker, probably an electrostatic, then you would have an excellent basic for a comparison test.

Simply compare the sound coming from the loudspeaker, blindfold, with the real live sound of your voice artist.

If you can't tell the difference, then the microphone is as perfect as it needs to be.

If you want to buy a near-perfect microphone, then you might start with DPA products, which are widely regarded as being very accurate.

But this isn't always the sound that we want. Usually we seek to achieve an up-front, 'larger than life' sound, for which imperfect microphones are often more appropriate.

Microphones that do not strive too hard for perfection nearly always sound different to each other. Even seemingly identical samples of the same model can show a difference.

So why do they sound different?

Firstly, the size and shape of the microphone - objects that are larger in size than the wavelength of the sound that strikes them have an effect on that sound. So at higher frequencies, the microphone interacts with the sound field and changes the sound it is trying to pick up.

Second, the grille. Try scratching the grilles of several microphones (gently) and compare the often huge differences in sound. This must be affecting the audio. We will find out by how much at some point in the not-too-distant future when we conduct a grille test. (George Foreman will not be invited.)

Third, the capsule. The capsule is the part of the microphone where the diaphragm is mounted. There are a variety of materials from which the diaphragm itself can be made, and methods of construction differ. This has a significant effect on the sound.

Fourthly, the internal amplifier of capacitor (condenser) microphones. These amplifiers tend to be very simple in design and often do not exhibit the ultimate in accuracy. Every deviation from accuracy affects the sound.

Finally, the transformer. Most professional microphones have a transformer and those that do not have an electronic circuit that mimics the effect of a transformer. Transformers subtly, but often audibly, alter the sound quality.

In summary, we like mics that are accurate and near-perfect. We'd like more of them to be available.

But it's in the differences between imperfect microphones where much of the texture and interest in audio lies. Long may these differences continue and prosper!

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By David Mellor Thursday November 30, 2006

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