Shure 55 data sheet

Page 1

SHURE BROTHERS
INCORPORATED
Microphones and Acousic Devices

225 WEST HURON STREET :: CHICAGO l0, ILLINOIS
PHONE DELAWARE 7-4550 :: CABLE: SHUHEMICRO

DATA SHEET

FEBRUARY, 1951

Model 55 Multi-lmpedance
"Unidyne" Dynamic Microphone.

DATE:

SUBJECT:

55 Multi-Impedance "Unidyne" Microphone
(Super-Cardioid Uni-directional Moving-Coil Dynamic)

General: Model 55 is-a srper cardioid unidirectional
moving coil dynamic microphone providing wide-range
high quality reproduction of sound. The true unidirection-
al characteristic of the "Unidyne", obtained by the "lini-
phase" principle* provides highly satisfactory operation
under advem acoustic conditions where a conventional
microphone would be practically useles. (See "Acoustic
Cons'derations).

The microphone has a specially designed moving
system containing a new type moving-coil element;
operating in conjunction with a high Ilux magnet in the
magnetic circuit providing high etficiency and smooth
peak free response from 40 to 15,000 cycles. The rear
reqaorm is down approximately 15 db due to the "lini-
phase" unidirectional acoustic network.

The case is modem in des'gn with attiactive stream-

lining and grille treatment. The head tilts through an angle
of 90° to permit aiming at the source of sound for best
pickup. A built-in cable connector is provided and a 20
it. d1ielded rubber-jacketed cable with microphone plug
attached is included.
Applications: Model 55 is sritable for high quality
public addres, broadcasting, recording and s'milar appli-
cations. The true unidirectional characteristic of the
"Unidyne" provides an easy solution to the feedback
problem in reverberant: locations, facilitates orchestral
placement. permits best utilization of space in small
broadcast studios, and allows practically complete ex-
clus'on of unwanted noises. The swivel allows the head to
be tilted through an angle of 90° permitting the micro-
phone to be aimed atthe source of sound.

Installations: All microphones have the standard
5/8"-27 thread and may be mounted on any conventional
dedg banquet, or floor stand. \Mien 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.

Connections: The Model 55 Microphone is of the
multi-impedance type. Model 55 may be worked directiy
into a 30-50 ohm line, a 150-250 ohm line, or a high im-
pedance input. Selection of these impedances is accom-
plidted by changing the pos'tion ofthe switch at the rear
of the microphone. The switch pos'tions are marked "I."
for low impedance (30-50 ohms), "M" for medium imped-
ance (150-250 ohms), and "H" for high impedance
(35,000 ohms).

The low and medium impedance positions of the
Model 55 may be fed into a standard low or medium
impedance input amplifier (Fig. A-1), or into an 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 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 pos'tions are recom-
mended where long cable lengths are required or under
conditions of severe hum disturbances. The pennisible

*fitenled by Siure Bothers Inc.
copyright, 1951 Shure Bothers, Inc.

(Over)

line length is practically unlimited, s'nce neither reqmnse
or level is appreciably afiected by reasonable lengths of
line.
The high impedance position on the Model 55
Microphone may be used with any crystal microphone
amplifier or other amplifier with an input impedance of
100,000 ohms or more (See Fig. A-3). For best high
frequency resaonse, the total cable lengths dtould not: ex-
ceed 25 feet; longer cable lengths may be used with
some los of high frequency requonse. The additional loss
at 5000 cycles is of the order of 2.5 db for an additional
25 ft. length of cable (50 ft. total) and 6 db for an
additional 50 ft. length (75 ft. total). If the Model 55
Microphone is used in the high impedance pos'tion, s'ngle
conductor diielded cable may be lmd to provide ad-
ditional cable lengths; also, the two-conductor cable fur-
nidted with the Microphone may be replaced with s'ngle
conductor diielded 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 diorted together and con-
nected to the diield of the cable.

The shield, chasis or amplifier ground should be
securely connected to a water pipe or s'milar ground to
prevent d1ock hazard during operation of amplifying
system.

In circuits using the grid leak type of bias on the
input tube, it may be desirable to use a .01 mfd. or
larger condenEr between the microphone and the input
grid circuit.

Operation: The microphone d1ould be placed in its
operating pos'tion before turning up the volume controls
of the amplifier. Jarring or excefi've moving of the in-
strument mould be avoided while the system is in opera-
tion in orderto prevent the sning-srsmnded microphone
unit from touching the ins'de of the case and producing
undes'rable noises.

No special precautions beyond ordinary care are
neces-ry in the operation of the Model 55 Dynamic
microphone. It will operate efficientiy and dependably
under all ordinary conditions in hot and cold climates. To
retain the fiJll strength of the highly efficient permanent

Printed in U.S.A.

Page 2

magnet and to maintain alignment of the structure,
dropping or other severe mechanical dwcks dwuld be
avoided.

MODEL
55

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FIG. A~l IMPEDANCE iNPUY

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Acoustic Considerations: The expression "super cardioid"
response simply means that the horizontal polar characteristic ap-
proximates a super cardioid. There is a wide, usetul pickup angle
at the front to! the microphone while the response at the sides is
down 5 db irom the iront response. The rear response in practical
super cardioid microphones is down at the order at 15 do from the
trout side response. The "Unidyne" tullills these requirements over
a broad range ol frequencies. The true u ireetional characteristic
ol the "Unidyne" should not be contused with the relatively slight
directional etlecl at high ireouencies only which can be produced
by battle ellects in the conventional pressure microphone.

HO

0

IO

Rosponse- (lb

20

50 100 L000 "1000
Frequency- Cycles per Second l5r°°°
Fig. B. Response-Frequency Characteriflic Model "55" Microphone.

27A31. 2751.

The result oi this unidirectional characteristic is a complete
elimination of acoustic teedback at volume levels which would
cause considerable teedbaclt with conventional semidirectional
microphones. In practically all cases it is possible to increase loud-
speaker levels when a Unidyne is installed. By directing the dead
side (rear) of the microphone towards the audience or other source
oi interiering sound, pickup can be concentrated on the desired
source. Reverheration energy pickup is decreased approximately
iwo-thirds. The microphone can be placed close io retlecting sur-
iaces without objectional eiiecis ii the rear side of the microphone
is toward the reilecting surtace. This is particularly valuable in
small broadcast studios. it is desirable to experiment with micro-
phone placement and orientation in order to secure the greatest
benetits trOm the unidirectional characteristic.

Specifications
1000 C.P.S. Response:

Model 55 "L" position:
Open circuit Voltage Level .. 434.1 db. (')
Loaded With 40 Ohms.. . . . ~90.1 db. (')
Power Level into 40 Ohms... . -56.1 db. (H)
RMA Microphone Rating On (Sensitiv y). 449.3 db. ()

Model 55 "M" Position:
open Circuit Voltage Level. -76.B db. (i
Loaded With 250 Ohms. ...... .. .323 db. ()
Power Level into 250 Ohms. -5s.3 db. (H)
RMA Microphone Rating GM (Sensi Vity).- 443.5 db. (-)

Model 55 "H" Position:

Open Circuit Voltage Level ............ .575 db. (')
Loaded With 100,000 Ohms . .504 db. (I
RMA Microphone Rating GM (Sensi vity). 453.7 db. (I

() 0 db. = 1 Volt Per Dyne Per so. cm.

(I 0 db. = 1 Milliwait with 10 Dynes Per so. cm.

(...) RMA Standard SE-I05 Aug. 1949.

Recommended Load Impedance:
Model 55 "L" Position 30-50 Ohms.

Model 55 "M" Position 150-250 Ohms.

Model 55 "H" Position 100,000 Ohms or More.

MODEL 55

Code Word RUMUL

Net Wt. Less cable 2-3/4 Ibs.
Shipping Weight 4 lbs.

cable 20 it. Two-Conductor
Height. Overall (a) 7'25/32"
Height. Case (h) 4.7/15"

Width lb) 3-3/16"
Thickness (o ) . W16

Finish Satin Chrome
See Fig. C.

Guarantee: Each microphone is guaranteed to be lree trom
electrical and mechanical deiects ior a period oi one year trom
date of shipment irom iactory, provided all instructions are com-
plied with iully. In case oi damage, return the microphone to the
iaciory for repairs. Our guarantee is voided if the microphone
case is opened.

MODEL 55
Arch ects Spec ca

The microphone shall be a dynamic type microphone
with a trequency range of 50 to 15,000 c.p.s. This unit shall
have a superacardioid pattern with nulls located at approxi-
mately ram and 230. The cancellation at the nulls shall be
at least 10 do. over the complete range at audio-irequency.
The microphone shall be equipped with a three-position im-
pedance change switch tor adjusting the microphone rating
impedance to as. 150 or 40,000 ohms. The microphone
rating cvr (sensitivity) at 1000 c.p.s. shall be within a :4
db. oi the lollowing levels:

"L" position of switch 449.3 db.
"M" position of switch 443.5 db.
"H" position oi switch 453.7 db.
RMA Standard SE-105 August 1949.

The microphone shall be provided with a swivel adjust-
able irom 0° to so and it shall have a detachable cable eon-
nector. The microphone will mount on a stand having a 5m"
.27 thread. The overall dimensions shall be 7.25/32 c 1/4
inches in height, 3-3/l6 2 H3 inches in width and 3.9/15 a l/B
inches in thickness.