Omnidirectional Microphone Set

This microphone set is a (stereo) pair in an integrated package. It is 
intended for high quality music recording where a pair of omni mics is 
appropriate.


Installation and Hook-Up


The set consists of: 
1) Two microphone capsules, which are detachable

2) The cable and battery box package

Unscrew the four Phillips head screws to open the cover of the battery 
box. Find the two snap battery connectors, and connect a 9 volt 
transistor radio type battery to each. One battery powers one microphone 
channel, so if one goes dead, the other should still work. Place the two 
batteries on their sides, adjacent to each other, in the center well of 
the battery box. They should fit perfectly. Position the wires so they 
don't get pinched in the cover and replace the cover.

Connect the mic capsules to the cables. Note that there is a locking 
button on the female connector which must be pressed to release the mic 
capsule when you remove them. On the other side of the battery box, 
connect the phone plugs to microphone inputs on your tape recorder. When 
you are not using the mics, remove them or they will drain the 
batteries. With ordinary use the batteries should last many months. 

The cables are each about 15 feet long, but should you need a greater 
distance from your mics, you can use professional type microphone 
extension cables that use the same style connectors as the mics. 
Distances up to about a hundred feet should be OK. It is not recommended 
that extensions be added to the phone plugs on the other side of the 
box.

Tips On Use
 
These mics are intended to be used for high quality music recording in a 
manner known in the recording industry as A-B, or spaced omni mic 
placement. The mics are typically spaced apart about 8 feet and 
approximately equidistant from the performer. They should be somewhat 
above the performer. 

The microphones are omnidirectional, that is they pick up sound from ALL 
directions. They do, however, have a brighter sound directly in front, 
on axis. You can use this to your advantage by aiming directly when you 
want a bright sound, and aiming slightly away when you want a smoother 
sound. 

If you use the mics outside, you must put a foam windscreen over the mic 
capsules or the wind will cause a tremendous rumble in the recording. 
Get any generic windscreen such as Radio Shack's, even if it doesn't 
quite fit and must be taped on. 




Some tape recorders have a switch on them called "MIC ATT(enuator)", and 
may have two or more positions such as " 0dB, -10 dB, or -20dB"  This is 
meant to reduce the strength of the microphone signal before the mic 
preamp circuitry in the recorder, and it is not the same as turning down 
the record level controls. Inexperienced recordists, when confronted 
with a very loud program , will just turn down the record level controls 
in order to keep the VU meters out of the red area, and still end up 
with a distorted recording.This is usually NOT the mic overloading, or 
so called tape saturation from too high a record level, but overload of 
the mic preamp circuitry in the recorder. The solution is to attenuate, 
or reduce, the signal   going to the  mic preamp, and this is what this 
switch does.  Therefore, if you are recording a loud program, and you 
find that you can barely turn up the record level control and still get 
too strong a signal in the VU meters, you should attenuate the mic 
signal with the attenuator switch. It is also possible to modify this 
mic set (see the technical section).



Gary Louie
University of Washington School of Music
Box 353450
Seattle, WA 98195
206-543-1218






Technical Section

The mic set uses a 1/4 inch omnidirectional electret capsule made by 
Matsushita/Panasonic (WM-063T, available from Digi-Key Electronics). It 
is set with silicone RTV into the end of a Switchcraft A3M connector. 
Signal is through pin 2, ground is pin 1. Pin 3 and shell are not 
connected. The battery box holds the batteries  which power the electret 
capsules, which have internal FET preamp/impedance converters. A 
capacitor blocks the DC  to the tape recorder, and a resistor network  
attenuates the signal to a nominal microphone level. The entire wiring 
is electrically unbalanced. Source impedance is about 5K ohms, and 
should  work acceptably with any low impedance mic input. Very low 
professional inputs may reduce signal level somewhat, but typical 
consumer mic inputs are about 5 K ohms input impedance and this gives a 
very normal  level. 

Signal level can be modified in the battery box if desired. Changing the 
18K ohm resistor to 30K  or 50K will give about 10 or 20 dB  less 
signal.