PZM (microphone)
Encyclopedia
Microphone
A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...
" in which a small omnidirectional condenser mic capsule faces a boundary a few thousandths of an inch away. PZM is a trademark of Crown International
Crown International
Crown International, or Crown Audio, is a manufacturer of audio electronics, and is a subsidiary of Harman International Industries. Today the company is known primarily for its power amplifiers, but has also manufactured microphones, a line of commercial audio products as well as digital audio...
.
The PZM can be used as a piano mic or on hockey
Hockey
Hockey is a family of sports in which two teams play against each other by trying to maneuver a ball or a puck into the opponent's goal using a hockey stick.-Etymology:...
boards for body check sound effects. It is also commonly used to record full room sound by being mounted on a wall.
Development
A conventional microphone placed on, or a few inches above, a hard boundary surface will pick up the desired direct sound as well as delayed sound reflecting off the boundary surface. The direct and delayed reflected sounds will combine at the microphone to create comb filterComb filter
In signal processing, a comb filter adds a delayed version of a signal to itself, causing constructive and destructive interference. The frequency response of a comb filter consists of a series of regularly spaced spikes, giving the appearance of a comb....
ing, with constructive and destructive interference causing peaks and valleys in the frequency response
Frequency response
Frequency response is the quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system. It is a measure of magnitude and phase of the output as a function of frequency, in comparison to the input...
. The delay time of the reflection for most microphones would be in the range of 0.1 to 1 milliseconds, corresponding to cancellation frequencies of a few kilohertz and octave multiples. Since these frequencies are audible, the cancellation effects are also audible and are said to "color" the resulting audio signals. The goal of the PZM design was to avoid this coloration.
By placing the diaphragm of the microphone capsule parallel to and facing the plate boundary provided by the microphone package, the reflected sound delay is reduced, and the resulting comb filter interference frequencies are high enough that they are outside the audible range.
Crown International
Crown International
Crown International, or Crown Audio, is a manufacturer of audio electronics, and is a subsidiary of Harman International Industries. Today the company is known primarily for its power amplifiers, but has also manufactured microphones, a line of commercial audio products as well as digital audio...
owns the trademark on the term "Pressure Zone Microphone" and PZM. However, the patent for the microphone invention expired in 1999.
PZM is the trademark for Crown International's line of omnidirectional boundary microphones. Most other microphone manufacturers offer that generic type of microphone (as shown in their product catalogs).
The Directional Boundary Microphone
A directional boundary microphone is a boundary microphone with a directional polar pattern such as cardioid or supercardioid. One method to create a directional boundary mic is to mount panels (hard surfaces) next to an omnidirectional mic capsule. An example is the Crown PZM-2.5 .Another method to create a directional boundary mic is to use a small-diameter (1 cm or less) directional mic capsule mounted on a boundary surface, with the axis of the microphone parallel with the surface. As shown on manufacturers' datasheets, the mic capsule retains its directionality (cardioid or supercardioid polar pattern) and prevents comb filtering by keeping phase interference above the audible range. Examples are the Crown PCC-160 introduced in January 1985, the Shure SM-91 , and the Bartlett TM-125 .
The predecessor of the directional boundary microphone was a directional microphone placed in an Electrovoice Mic Mouse, a foam block that suspended a conventional microphone horizontally just above a surface. Because conventional microphone diaphragms are relatively large (> 1 cm diameter), phase interference from surface sound reflections caused a rolloff in the high frequencies of a microphone in a Mic Mouse.
Some applications for directional boundary mics are picking up actors' voices onstage in drama or musicals, picking up the footwork of dance troupes, picking up speech at conference tables and boardrooms, and recording small musical ensembles or soloists .