Shure 55S User Guide

SHURE BROTHERS

INCORPORATED

Microphones and Acoustic Devices

225 WEST HURON STREET :: CHICAGO 10, ILLINOIS PHONE Delaware 7-4550 :: CABLE: SHUREMlCRO

DATA SHEET

DATE: MAY, 1951

SUBJECT: Model 55s Multi-Impedance

“Small Unidyne” Dynamic

Microphone.

55s Multi-Impedance "Small Unidyne" Microphone

(Ultra-Cardioid, Unidirectional, Moving-Coil Dynamic)

General: The Model 55s is a small, compact Microphone in which high-fidelity response end excellent directional pattern are achieved. The Ultra-Cardioid unidirectional characteristic of the microphone (obtained by the "Uniphase" principle*) provides highly satisfactory operation under adverse acoustic conditions. It permits placement of the microphone at a distance from the performer 75% greeter than is possible with non-directional (omnidirectional) microphones.

The new "Small Unidyne," Model 55s, embodies all of the advantages found in the world-famous Shure Model 55 Unidyne. Its improvements are notable. The Shure-patented acoustic phaseshift network has been redesigned: the moving-coil system has been revised for high efficiency and extended, smooth, frequency response. Large air-gap clearances, together with a rugged coil construction, provide immunity of the moving system to abnormal atmospheric conditions and severe mechanical shock.

The care is modern in design, with attractive streamlining and grille treatment. Model 55s is smaller than the Model 55, and is therefore ideal for installations where it is desired to keep the microphone size to a minimum and still retain maximum operating efficiency.

A new self-adjusting swivel permits tilting of the head through 80° so that the microphone can be aimed at the source of sound. A built-in cable connector is provided; and a 20 foot, high-quality, two-conductor shielded cable with microphone plug attached is included.

Applications: Model 55s is ideal for high-quality public address, theatre-stage sound systems, and recording applications. Because of its unusual ruggedness and reliability, Model 55s micro-

phone is,	also, recommended for fixed station use in the Police,
Fire, and	Transportation services. For studio broadcasting and T.V.

use, end similar applications where the utmost in quality is desired, Model 556s Broadcast Unidyne is recommended.

The true unidirectional characteristics of the Model 55s provides en easy solution to the feedback problem in reverberant locations, facilitates orchestral placement, permits best utilization of space in

smell	broadcast	studios, and provides practically complete exclu-
sion	of unwanted	noises.

Installation: All microphones have the standard 5/8"-27 thread and may be mounted on any conventional desk, banquet, or floor stand. Physical dimensions are shown in Fig. C. When long lines are used, care should be taken that the cable does not parallel A.C. power lines for long distances to avoid A.C. hum induction.

Model A86A Cable type transformer	permits coupling either a 30-
50 ohm line or 150-250 ohm line to	high impedance input.

The low and medium impedance positions are recommended where long cable lengths are required or under conditions of severe hum disturbances. The permissible line length is practically unlimited, since neither response nor level is appreciably affected by reasonable lengths of line.

The high impedance position on the Model 55s Microphone

may be used with any high gain microphone amplifier or other
amplifier with en input impedance of 100,000 ohms or more (See
Fig. A-3). For best high frequency response in high impedance
the total cable lengths should not exceed 25 feet: longer cable
lengths may be used with some loss of high frequency response.
The additional loss at 5000 cycles is of the order of 2.5 db for en
additional 25 ft. length of cable (50 ft. total) and 6 db for en ad-
ditional	50	ft. length	(75 ft. total). If the Model 55s Microphone
is used	in	the high	impedance position, single conductor shielded

cable may be used to provide additional cable lengths: also, the two-conductor cable furnished with the Microphone may be replaced with single conductor shielded cable, if the microphone is intended to operate directly into high impedance (grid) input only. In this instance, the number one pin and the number two

pin	of the	cable	plug must be shorted together and connected to
the	shield	of the	cable..

The shield, chassis or amplifier ground should be securely connected to a water pipe or similar ground to prevent shock hazard during operation of amplifying system.

Connections: The Model 55s Microphone is of the multi-im- pedance type. Model 55s may be connected directly to a 30-50

ohm line,	a 150-250 ohm line, or high	impedance	input. Selection
of these	impedances is accomplished	by changing	the position of

the switch at the rear of the microphone. The switch positions are marked "L" for low impedance (30-50 ohms), "M" for medium impedance (150-250 ohms), and "H" for high impedance (35,000 ohms).

In the low and medium impedance positions, Model 55s may be connected directly to a standard low or medium impedance input amplifier (Fig. A-1), or into en amplifier with high impedance input (Fig. A-2). In the latter case, Shure Model A86A Cable-

Type Transformer is available for coupling	the low	impedance line
to the amplifier input. The double winding	primary	of the Shure

When used with amplifiers using	the grid	leak type	of bias at
the input tube, it may be desirable	to use a	.01 mfd.	condenser

between the microphone and the input grid circuit.

Operation: The microphone should be placed in its operating position before turning up the volume controls of the amplifier. Jarring or excessive moving of the instrument should be avoided white the system is in operation.

No special precautions beyond ordinary	care are	necessary	in
the operation of the Model 55s Dynamic	microphone. It will op-
erate efficiently end dependably under all	ordinary	conditions	in

hot and cold climates. To retain the full	strength of	the highly
efficient permanent magnet and to maintain	alignment of the struc-
ture, dropping or other severe mechanical shocks should		be avoided.

* P a t e n t e d b y S h u r e B r o t h e r s I n c .
C o p y r i g h t , 1 9 5 1 S h u r e B r o t h e r s . I n c .	(Over)	Printed in U.S.A.

Acoustic Considerations: The front response-frequency characteristic of the Model 55s is shown in Figure B. The smooth, wide-range characteristic is excellent for high-quality reproduction of music and speech.

	“Ultra-Cardioid” describes the	horizontal	polar characteristic of
the	Model 55s. This polar characteristic resembles a cardioid but
is	slightly more directional. There	is a wide,	useful pickup angle

at the front of the microphone, while the response et the sides is down 6 db from the front response. The rear response is down ap-

proximately 15 db.	The Model	55s fulfills	these requirements over
a broad range of	frequencies.	The true	unidirectional character-

istic of the microphone should not be confused with the relatively

slight directional	effect at high frequencies which can be produced
by baffle effects	in the conventional pressure microphone.

Fig. B.

Response-Frequency Characteristic Model 55s Microphone.

The result of this unidirectional characteristic is elimination of acoustic feedback at volume levels which would cause considerable feedback with conventional semidirectional or omnidirectional microphones. In practically all cases it is possible to increase loudspeaker levels when a Unidyne 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 surfaces without objectional effects if the rear side of the microphone is toward the reflecting surface. This is particularly valuable in small broadcast studios. It is desirable to experiment with microphone placement end orientation in order to secure the greatest benefits from the unidirectional characteristic.

					Specifications
1000		C.P.S. Response:
Model	55s		"L"	Position
Open Circuit Voltage Level . . . . . . . . . . . . . . . . . — 87.9										d b *
Loaded			with		50 ohms		. . . . . . . . . . . . . . . . . . . . . — 92.4			d b *
Power Level into 50 ohms . . . . . . . . . . . . . . . . . . . . — 59.4										d b * *
RTMA Microphone Rating GM (Sensitivity) . . . — 153.6										d b * * *
Model	55s		"M"	Position
Open Circuit Voltage Level . . . . . . . . . . . . . . . . . — 81.0										d b *
Loaded with 250 ohms. . . . . . . . . . . . . . . . . . . . . . . — 86.1										d b *
Power Level into 250 ohms . . . . . . . . . . . . . . . . . . — 60.1										d b * *
RTMA Microphone Rating GM (Sensitivity) . . . — 152.8										d b * * *
Model	55s		"H"	Position
Open Circuit Voltage Level. . . . . . . . . . . . . . . . . . — 60.5										d b *
Loaded with 100,000 ohms. . . . . . . . . . . . . . . . . . . — 62.3										d b *
RTMA			Microphone			Rating		GM	(Sensitivity). . . — 157.0	d b * * *
( * )	0	d b	=	1	Volt	Per	Microbar
( * * )	0	d b	=	1	Milliwatt		with	10	Microbars
( * * * )	RTMA Standard					SE-105,		August 1949.

Recommended Load Impedance:

Model 55s	"L" Position	30-50 ohms.
Model 55s	"M" Position 150-250 ohms.
Model 55s	"H" Position	100,000 ohms or more.

			MODEL	55s
Code Word				RUDOT
Net Wt .				3 1/8 lb.
Shipping Weight				4	1/4 lb.
Cable				20 ft. Two-Conductor
Height,	Overall	*		7 3/8"
Height,	Case	*		3	15/16"
Width		*		2	3/16"
Depth				3	1/16"
Finish				Satin Chrome

*See Fig. C.

Guarantee: Each microphone is guaranteed to be free from

electrical and mechanical defects for a	period of one year from
date of shipment from factory, provided	all instructions are com-

plied with fully. In case of damage, return the microphone to the factory for repairs. Our guarantee is voided if the microphone is subjected to accident or abuse or if the case is opened.

MODEL 55s

Architect’s Specification

The microphone shell be a moving coil type microphone with a frequency range of 50 to 15,000 c.p.s. This unit shall have an “Ultra-Cardioid” horizontal polar characteristic. The

cancellation et	the	sides shall be approximately	6	db	and
the cancellation	at	the rear shell be in the order	of	15	db.

The microphone shall be equipped with a three-position impedance change switch for adjusting the microphone rating impedance to 38 ohms, 150 ohms or 40,000 ohms. The microphone rating GM (sensitivity) at 1000 c.p.s. shell be within

± 3 db of the following levels:

"L" Position of switch — 153.6 db "M" Position of switch — 152.8 db "H" Position of switch — 157.0 db RTMA Standard SE-105 August 1949

The microphone shall be provided with a swivel adjustable from 0° to 80° and it shell have a detachable cable connector capable of connection to a two-conductor shielded cable. The microphone will mount on stand having 5/8"- 27 thread. The overall dimensions shell be 7-3/8 ± 1/4 inches in height, 2-3/16 ± 1/8 inches in width, and 3-1/16 ± 1/8 inches in depth.

2 7 A 6 2 . 5 - 5 1 .