Shure 730B User Guide

DATA SHEET

No.

128A

27-02

DATE:

SUBJECT:

MODEL 730B "UNIPLEX" CRYSTAL MICROPHONE

GENERAL:

acteristic of the "Uniplex" allows highly satisfactory operation under adverse conditions of background noise and reverberation where a conventional microphone would be practically useless. (See "Acoustic Considerations" for a discussion of directional characteristics)

The "Uniplex" contains a diaphragm-type element

combined with acoustical networks which cause cancella-

tion of sound pressures for sounds incident from the rear. The crystal is a Grafoil (high capacity) bimorph unit, triple moisture sealed to withstand adverse climatic conditions. Case is pivoted at the rear and may be conveniently pointed in the direction of the desired

sound, or pointed upwards for non-directional horizontal plane pickup.

The microphone is provided with a three-way plug and a 25-foot single conductor shielded cable.

APPLICATIONS:

wide-range uni-directional characteristic of the "Uniplex" creates an easy solution to the feedback problem

in reverberant locations, facilitates orchestral placement, permits best utilization of space in small broadcasting studios, and allows a practically complete ex-

clusion of unwanted noises.

By pivoting the microphone upwards a 360° non-directional horizontal plane characteristic is obtained which is useful for group or round-table pickup (See

"Acoustic Considerations" for information on non-direc-

tional placement).

INSTALLATION:

Convenient cable changing is possible due to the built-in receptacle. A 25-foot single-conductor shielded rubber-jacketed cable is furnished with plug attached. External flexible couplings are unnecessary

since the internal elements of the microphone are substantially isolated from the outer case.

CONNECTIONS: The inner conductor or "hot" lead should

sistance of 5 megohms. Input resistances as low as 1 megohm may be used if necessary but higher values are recommended because of the better low-frequency re-

sponse obtained. The shield or ground should be con-

nected to the chassis. See Fig. A.

If the "Uniplex" is to be used with considerably less than 25-feet of cable, a shunt condenser having 30 mmf capacity for each foot of cable removed should be connected across the terminals at the amplifier, otherwise an increase in high frequency response will result.

Added lengths of connecting cable will be accompanied by a decrease in output level as given in the table below. troduced by the cable, regardless of length.

* (Expressed in db below 1 volt per bar.)

Model 730B is a uni-directional widerange diaphragm type crystal microphone. The true uni-directional "cardioid" char-

detachable

Model 730B is suitable for high-quality public address, broadcasting, recording

and similar applications. The true

Model 730B is equipped with the standard

5/8"-27 thread and may be mounted on any Shure desk, banquet, or floor stand.

be connected to the grid of the first tube in the amplifier across a load re-

There is no frequency discrimination in-

Total Cable Length Cable Terminals

Ft. 50 Ft. 75 Ft.

100

(Standard) -63.0

Ft.

Output Level* at

-67.5

-70.5

-72.5

Most modern high-gain amplifiers have a sufficient

margin of gain to make up for the decrease in output

levels shown in the table. If the amplifier does not

have the necessary gain a preamplifier at the micro-

phone or near the main amplifier, is suggested. Preamplifiers with low impedance output are recommended if the main amplifier system has low impedance transformer or mixer input.

Cable should be of high quality and low capacity. The inner leads should be soldered and Insulated with a good grade of rubber tape. Metal braid sleeve or a serve of fine wire should be soldered between the shields of the cable to complete the shielding. Longer lengths of cables with standard plug attached may be purchased at small cost, and may be used interchangeably with shorter cables.

OPERATION:

Crystal microphones may be seriously damaged if accidently connected to loud speaker or power supply

outlet; carrying high voltage. Check your connections carefully.

The microphone case should not be opened. Our

guarantee is voided by tampering with the mechanism.

Crystal microphones should not be used or kept in

places where the temperature exceeds 125° F. They should not be exposed to the rays of the sun in very hot weather for any considerable length of time - or left in closed automobiles parked in the sun during hot weather, as the temperature inside the automobile may easily build up to over 125° and permanently damage the

crystal.

When used near a radio transmitter, use the minimum length of cable consistent with placement requirements. Careful grounding of the cable shield is advis-

able.

(over)

July, 1945

Model 730B "Uniplex" Crystal Microphone

No polarizing voltage is required for crystal microphones.

Printed In U.S.A.

No.

128A

DATA SHEET

No special precautions beyond ordinary care are necessary in the operation of the “Uniplex” microphones. They will operate efficiently and dependably under all ordinary conditions.

ACOUSTIC CONSIDERATION:

a cardioid of revolution. There is a wide, useful pickup angle at the front of the microphone while the response at the sides is down 6 db from the front response. The rear response in practical cardioid type

microphones is down of the order of 15 db from the

front side response. The Uniplex fulfills these requirements over a broad range of frequencies. The true

unidirectional characteristic of the not be confused with the relatively slight directional

effect at high frequencies only which can be produced

by baffle effects in the conventional pressure micro-

phone.

The result of this unidirectional characteristic

is a complete elimination of acoustic feedback at volume levels which would cause considerable feedback with conventional semidirectional microphones. In practically all cases it is possible to increase loud-speaker

levels when a Uniplex is installed. By directing the

dead side (rear) of the microphone towards the audience or other source of interfering sound, pickup can be concentrated on the desired source. Reverberation energy pickup is decreased approximately two-thirds.

The microphone can be placed close to reflecting sur-

faces without objectionable effects if the rear side of the microphone is toward the reflecting surface. This is particularly valuable In small halls.

It is desirable to experiment with microphone placement and orientation In order to secure the greatest benefits from the unidirectional characteristic.

The expression “cardioid type” response simply means that the horizontal polar characteristic approximates

“Uniplex” should

Voltage Sensitivity:

This is equivalent to 63 db below 1 volt per bar.

Internal Output

Recommended Load

Height, Overall (a)*. . . . 4-3/8

Height, Case (h)* . . . . . 3-1/8

Width (b)*. . . . . . . . .

Thickness (c)*. . . . . . .

Finish. . . . . . . . . . .

Net Weight. . . . . . . . .

Shipping Weight . . . . . .

Code Word . . . . . . . . . RUPEL

List Price. . . . . . . . .

* See Fig. B

Guarantee :

one year from date of shipment from the factory, provided all Instructions are complied with fully. In case of damage, return the microphone to the factory for repairs. case is opened.

License Notice:

SPECIFICATIONS

0.7 millivolts r.m.s. per bar at the end of a 25-foot cable across 1 to 5 megohms at 400 cycles.

Impedance :

Approximately 1 megohm.

1 to 5 megohms.

FIG. B.

3-1/8 3-3/8

Satin Chrome 2-1/4 lbs. 2-1/2 lbs.

$34.00

Each microphone is guaranteed to be free from electrical and mechanical defects for a period of

Our guarantee is voided if the microphone

Shure patent 2,198,424. Other patents allowed. Licensed under patents of the Brush Development Company.

FREQUENCY- CYCLES PER SECOND

TYPICAL FREQUENCY RESPONSE. SHURE MODEL 730B "UNIPLEX" MICROPHONE.