Digital Sound & Music: Concepts, Applications, & Science, Chapter 1, last updated 6/25/2013
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sometimes be provided by a battery. The conductive plates are very thin, and when sound waves
push against them, the distance between the plates changes, varying the charge accordingly and
creating an electrical representation of the sound. Condenser microphones are much more
sensitive than dynamic microphones. Consequently, they seem to pick up much more detail in
the sound, and even barely perceptible background sounds may end up being quite audible in the
recording. This extra sensitivity results in a much better transient response and a much more
uniform frequency response reaching into very high frequencies. Because the transducers in
condenser microphones are simple capacitors and don‟t require a weighty magnet, condenser
microphones can be made quite large without becoming too heavy, or can be made quite small,
allowing them to be easily mounted to small instruments or concealed when visual aesthetics are
a concern. The smaller size also allows them to pick up high frequencies coming from various
angles in a more uniform manner. A disadvantage of the capacitor microphone is that it requires
external power, although this is often easily handled by most interfaces and mixing consoles.
Also, capacitor elements can be quite delicate, and are much more easily damaged by excessive
force or moisture. The features of a condenser microphone often result in a much higher quality
signal, but this comes at a higher price. Top of the line condenser microphones can cost
thousands of dollars.
Electret condenser microphones are a type of condenser microphone in which the back
plate of the capacitor is permanently charged at the factory. This means the microphone does not
require a power supply to function, but it often requires an extra powered preamplifier to boost
the signal to a sufficient voltage. Easy to manufacture and often miniature in size, electret
condenser microphones are used for the vast majority of built-in microphones in phone,
computer, and portable device technologies. While easy and economical to produce, electret
microphones aren‟t necessarily of lower quality. In the field of professional audio they can be
found in lavaliere microphones attached to clothing or concealed for live performance. In these
cases, the small microphones are typically connected to a wireless transmitter with a battery that
powers the preamplifier as well as the RF transmitter circuitry.
Generally speaking, you want to get the microphone as close as possible to the sound
source you want to capture. This improves your signal-to-noise ratio. When getting the
microphone close to the source is not practical such as when you're recording a large choir,
performing group, or conference meeting a type of microphone called a pressure zone
microphone (PZM) can be useful. A PZM, also called a boundary microphone, is usually
made of a small electret condenser microphone attached to a metal plate with the microphone
pointed at the plate rather than the source itself. These microphones work best when attached to a
large reflective surface such as a hard stage floor or large conference table. The operating
principle of the pressure zone is that as a sound wave encounters a large reflective surface, the
pressure at the surface is much higher because it's a combination of the direct and reflected
energy. Essentially this extra pressure results in a captured amplitude boost, a benefit normally
available only by getting the microphone much closer to the sound source. With a PZM, you can
capture a sound at a sufficiently high volume even from a significant distance. This can be quite
useful for video teleconferencing when a large group of people must be at a greater distance to
the microphone, as well as in live performance where microphones are placed at the edge of the
stage. The downside to a PZM is that the physical coupling to the boundary surface means that
other sounds such as foot noise, paper movement, and table bumps are picked up just as well as
the sound you're trying to capture. As a result, signal-to-noise ratio tends to be fairly low. In a
live sound reinforcement situation you can also have acoustic gain problems if you aren‟t careful
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