The microphone is the front-end of almost all sound engineering activities and, as the interface between real acoustic sound travelling in air and the sound engineering medium of electronics, receives an immense amount of attention. Sometimes one could think that the status of the microphone has been raised to almost mythological proportions. It is useful therefore to put things in their proper perspective: there are a great many microphones available that are of professional quality. Almost any of them can be used in a wide variety of situations to record or broadcast sound to a professional standard. Of course different makes and types of microphones sound different to each other, but the differences don't make or break the end product, at least as far as the listener is concerned.
Now, if you want to talk about something that really will make or break the end product, that is how microphones are used. Two sound engineers using the same microphones will instinctively position and direct them differently and there can be a massive difference in sound quality. Give these two engineers other mics, whose characteristics they are familiar with, and the two sounds achieved will be identifiable according to engineer, and not so much to according to microphone type.
There are two ways we can consider microphones, by construction and by directional properties. Let's look at the different ways a microphone can be made, to start off with.
There are basically three types of microphone in common use: piezoelectric, dynamic and capacitor. The piezoelectric mic, it has to be said, has evolved into a very specialized animal, but it is still commonly found under the bridge of an electro-acoustic guitar so it is worth knowing about.
The piezoelectric effect is where certain crystalline and ceramic materials have the property of generating an electric current when pressure or a bending force is applied. This makes them sensitive to acoustic vibrations and they can produce a voltage in response to sound. Piezo mics (or transducers as they may be called - a transducer is any device that converts one form of energy to another) are high impedance. This means that they can produce voltage but very little current. To compensate for this, a preamplifier has to be placed very close to the transducer. This will usually be inside the body of the electro-acoustic guitar. The preamp will run for ages on a 9 volt alkaline battery, but it is worth remembering that if an electro-acoustic guitar, or other instrument with a piezo transducer, sounds distorted, it is almost certainly the battery that needs replacing, perhaps after a year or more of service.
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