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Jan. 4, 1949.
w. E'. GILMAN
MAGNETICALLY SHIELDED ELECTRODYNAMIC
2,458,158
SOUND REPRODUCER
3 Sheets-Sheet 1 v
Filed Nov. '25, 1942
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Jan. 4, 1949.
w, E_ GILMAN
2,458,158
MAGNETICALLY SHIELDED ELECTRODYNAMIC
SOUND REPRODUCER
Filed Ngv. 25, 1942
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Patentecl Jan. 4, 1949
' 2,458,158
UNITED STATES PATENT orrlcr.
2,458,158,
MAGNETICALLY smnnnnn srlcptrno
DYNAMIC soUNn BEPRGDUCER
Webster E. Gilman, Maywoed, Ill, assignor to
Per-mo?ux Corporation, Chicago, 111., a corpo
ration of Illinois
Application November 25, 1942, Serial No. 466,903
5. Guitaris-v (c1. ire-115.5)
1
2
This invention relates to transducers and par
complish such shielding through use of the hous
ticularly to transducers of the dynamic type as
contrasted with the magnetic type thereof.
ing not only as a housing but also as a magnetic
In dynamic transducers as heretofore con-.
structed it has :been recognized that in order to
obtain the desired sound transducing capacity
it has been necessary to resort to relatively large
dimensions in the transducers, with the result
that the weight of such transducers has been ex
cessive when compared with the output capaci 10
ties thereof. Where size and weight were deter»
mining and vital factors, it has been customary
to resort to the use of magnetic type transducers,
even though ?delity and range of frequency re
sponse have been sacri?ced through this pro 15
cedure, and accordingly it is an important object
of this invention to enable dynamic transducers
to be employed even where weight and size are
determining factors in the selection of the type
of transducer to be used; and further objects re 20
lated to the foregoing are to enable dynamic
transducers to attain a substantially ?at fre
shield.
In accordance with prior practice it has been
customary to provide an independent diaphragm
support which, after assembly upon the magnetic
yoke, has been used to support and position the
diaphragm and the voice coil. Through the ex
ercise of proper care and skill in the formation
and assembly of the parts it has, of course, been
possible to attain accuracy of relationship of
the parts in such prior transducers, but even
then, the cost and added size resulting from the
use of such prior diaphragm supports have been
objectionable. In view of this it is a further ob
ject of the present invention to enable means
formed integrally with or as a part of an ele
ment of the magnetic circuit of such transducers
to function as a diaphragm support. According
to one aspect of my invention it is a more speci?c
object to enable the diaphragm to be supported by
means formed integrally with the magnetic yoke;
quency response curve and a substantially ?at
and a further object related to the foregoing is
impedance curve over a wide range of frequen
to form the magnetic yoke in a generally cup
cies such as those frequencies utilized in ordi 25 iike form such that the diaphragm may be sup
nary practice and particularly over the range of
ported upon the rim of the cup-like magnetic yoke
frequencies used in conversation; and to enable
while the outer pole piece or pole plate may be
an output capacity to be attained in dynamic
located Within and supported by the cup~like yoke
speakers which is comparable to the output ca~
in spaced relation to the rim thereof.
pacity of other types of transducers of compa 30
A further object of this invention is to sim
rable size and weight.
plify the mounting and location of the outer pole
One factor which has contributed in a large
piece or pole plate in dynamic transducers and
measure to the foregoing disadvantages and lim
a more speci?c object is to accomplish this
itations inherent in prior dynamic speakers has
through the provision of means formed in the
been found to be in the relatively complicated 35 cup-like magnetic yoke in spaced relation to the
manner of construction and assembly of the ele
bottom wall thereof and cooperating with the
ments of the magnetic circuit, and with such prior
separately formed outer pole piece to locate the
constructions the elements of the magnetic cir
same accurately With the relation to the mag
cuit have been enclosed. within a housing which
netic yoke.
has added objectionable size and weight to the
A further object of this invention is to utilize
transducers. A further object of this invention
the outer pole piece or pole plate to support the
is therefore to simplify the construction of the
diaphragm, thereby to eliminate the cost of pro
magnetic circuits of dynamic transducers, and
duction and assembly which has heretofore been
an object related to the foregoing is to accom
involved in the production and assembly of a
plish this simpli?cation in such a manner that 45 separate diaphragm support.
'
an element of the magnetic circuit may func
A further object is to enable a relatively small
tion as the housing of the transducer. Further
permanent magnet to be used in a transducer in
and related objects are to form the magnetic
such a relation that an extremely 'high ?ux den
yoke of a dynamic transducer with an annular
Sity is produced in the magnetic gap of the trans
or circular transverse cross section, to incorpo 50 ducer; and objects related to the foregoing ‘are
rate positioning means in such an annular mag
to enable a transducer to be so constructed that
netic yoke whereby mounting of the outer pole
piece or plate may be readily and accurately ac
complished, to provide a transducer wherein the
operative elements are fully shielded, and to ac
the space within the housing is ef?ciently uti
lized, thereby to produce maximum flux density
in the magnetic gap and to attain this result in
55 relatively small transducers; to so mount the per
2,458,158
3
4
Other and further objects of the present iri-i
manent magnet that the magnet serves as the
inner side of the magnetic gap; and to utilize
vention will be apparent from the following
description and claims and are illustrated in
the accompanying drawings which, by way of
permanent magnets of cylindrical form which
may be economically produced and which serve
the function usually performed by a separate in
illustration, show preferred embodiments and
the principles thereof and what I now consider
to be the best mode in which I have contemplated
ner pole piece.
It has been pointed out hereinbefore that
applying those principles. Other embodiments
dynamic transducers embodying this invention‘
of the invention embodying the same or equiva
may be utilized either as microphones or speakers,
and When a transducer is used as the speaker 10 lent principles may be used and structural
changes may be made as desired by those skilled
or earphone of a headset, many difficulties have
in the art without departing from the present
heretofore been encountered which have ob
invention and the purview of the appended
jectionably increased the cost of production of
claims.
such speakers and have limited the usefulness
In the drawings?
of the speakers. One objection which has been 15
Fig. 1 is a front elevational view of a transducer
found in prior speakers of the dynamic type
embodying the features of Fig. 2 of the inven
has been that in order to utilize such speakers
tion;
or earphones with remotely located receiving
Fig. 2 is a sectional view taken substantially
apparatus it has been necessary to utilize voice
coils having a relatively high ohmic resistance, 20 along the line 2—-2 of Fig. 1;
Fig. 3 is a sectional view taken along the line
and. in order to provide such a high resistance
3-3 of Fig. 2;
it has been necessary to employ numerous layers
.
Fig. 4 is a plan view looking downwardly in
of relatively ?ne wire, with the consequent
difficulties in winding the coils. Accordingly it
,Figs. 1 and 2;
Fig. 5 is a view showing one face of ' the outer
is a further object of this invention to enable 25
pole piece;
'
voice coils having a relatively small ohmic
Fig. 6 is a sectional view of the diaphragm and
resistance to be employed in speakers which
voice coil assembly;
are to be used as parts of a headset, and a
further object related to the foregoing is to
accomplish this result through the incorporation so
of a transformer within and as a part of the
'
~
Fig. 7 is a front elevational view illustrating
another alternative embodiment of the inven
tion;
Fig. 8 is a side elevational view of the trans
ducer shown in Fig. 7;
Fig. 9 is a rear elevational view of the trans-‘
in a practical sense.
Speakers which are adapted for use as parts 35 ducer shown in Fig. '7 ;
Fig. 10 is a cross sectional view taken substan
of a headset are ordinarily arranged for co
tially along the line i0—lll of Fig. '7;
operation with a headband of a particular size
Fig. 11 is a cross sectional-view taken substan
and construction, such headbands being in many
tially along the line ll-ll in Fig. 10;
'
instances provided with a clip assembly at the
Fig. 12 is a fragmental sectional view taken
ends thereof adapted to be snapped into as
along the line l2-l2 of Fig. 11;
sociation with cooperating means provided on
Fig. 13 is a cross sectional view similar to Fig.
the speaker. Such clip assemblies are relative
10 and illustrating an alternative embodiment of
ly well standardized as to their dimensions, but
the invention;
in certain classes of work it has been found that
Fig. 14 is a cross sectional view similar to Fig.
clip assemblies having two different dimensions .
10 and illustrating an alternative embodiment of
are frequently encountered, and as a result it
the invention;
'
has been found that speakers or earphones are
Fig. 15 is a sectional view taken along the line
often unsuitable for use with the headbands which
l5-—l5 of Fig. 14; and
are available. Therefore it is an object of this
Fig. 16 is a sectional view taken along the
invention to enable speakers or earphones to be 50
line |6—I6 of Fig. 15.
readily utilized in connection with clip assem
In the form of the invention illustrated in Figs.
blies of different dimensions, and an object
1 to 6 inclusive of the drawings, the invention is
related to the foregoing is to accomplish this in
embodied in a transducer l0 adapted for use either
a simple and expeditious manner. More specif
ically, it is an object of this invention to utilize 55 as a microphone or as a speaker, this particular
transducer being intended and adapted primarily
a cup-like magnetic yoke which has the side
for use in portable radio broadcasting and receiv
walls thereof so formed as to provide different
ing units so as to avoid duplication of transducers
engaging means of different dimensions where
therein. In accordance with the present inven
by clip assemblies of different sizes may co
operate with either one or the other of such en 60 tion the transducer in has its elements so formed
and related that the magnetic circuit is formed
gaging means.
in part by a cup-like member I I made from a fer
A further object is to simplify the assembly of
rous metal such as steel which constitutes the
the diaphragm and voice coil element so that
magnetic yoke and embodies a bottom wall I2 and
accuracy of interrelation of these elements may
speaker so that the length of the leads from the
speaker to the receiver is rendered immaterial
be readily attained.
‘
A further object is to enable a transducer to
be rendered waterproof in the sense that the
65
an annular side wall l3. Thus the cup-like mag
netic yoke ll may function as a‘housing for the
operative elements of the transducer. The side
wall I3 is tapered from its juncture with the bot
tom wall l2 to a somewhat larger diameter at
the outer end thereof, and the bordering edge of
A further object of this invention is to simplify
the assembly of the cap plate upon the open end 70 the outer end of the annular side wall I3 has an
outwardly projecting annular flange l4 formed
of the speaker housing, and an object related
integrally therewith and parallel to the bottom
to this is to employ interlocking means for
wall 12 to facilitate mounting of the transducer
rotatively relating the cap plate to the housing
III in the unit in which it is to be employed. At
and to employ a simple clamping means to hold
75 a point spaced‘ from the‘rear or bottom wall l2
such interlocking means together.
internal electrical elements cannot be reached
by water or moisture.
and from the ?ange I4, the side wall I3 has an
annular rabbeted groove I8 formed therein to
receive the outer peripheral edge of a soft iron
press nu While such a press ?t in many iri
stances affords the desired‘mechanical and mag
disc I9 which serves as the outer pole piece or
netic connection between the pole piece I9 and
the annular side wall I3 of the magnetic yoke,
pole plate of the transducer, and it will be ob
served that when the pole piece I9 is mounted in
the rabbeted groove I8, the pole piece I 9 is spaced
I prefer to swage the ‘metal of the wall‘ I3 as at
42 in order to ?rmly connect the side wall I3
with the pole piece I9. Such a swaging operation
a substantial distance from the bottom Wall I2
may be conveniently performed along theedges
of the yoke to afford space within which a per
of air relief slots or openings 43 which are formed
manent magnet 26 and a soft iron inner pole 10 ‘in the side Wall I3 intermediate the ?ange I4 and
piece 2! may be disposed. It will also be observed
that when the pole piece I9 is thus mounted it
is spaced from the end ?ange I4, thereby to af
the rabbeted groove I8, and to facilitate this
swaging operation, the edges 43' of the openings
43 are preferably spaced slightly‘ outwardly from
ford space within which a diaphragm 25 may be
the outer face of the pole plate I9. Thus after
disposed.
15 the outer pole piece I9 has been secured per
The permanent magnet 20 is in the present
manently in position within the cup-like magnetic
case frusto-conical in form and has its larger end
yoke II and in the accurately determined loca
seated against the inner face of the bottom wall
tion afforded by the rabbeted groove I8, the pole
I2 of the cup-like magnetic yoke, thereby to es
piece 2! will also be located accurately through
tablish an eflicient magnetic contact with the 20 the action of the locating plate 35. Thus after
magnetic yoke when the magnet 2!! is drawn ?rm
this has been done, the screw 21 may be tightened
ly against the bottom wall I2. The permanent
to produce the desired magnetic connection be
magnet 26 has a recess 26 extending therethrough
tween the pole piece 2| and the wall l2 of the
which may be in the form of a lateral slot or in
magnetic yoke and the opposite ends of the mag
the form of a bore, and a screw 21 is extended 25 net 20;
through a relatively large opening 28A formed in
the bottom wall I2 so as to project through the
recess or bore 26 and into threaded engagement
The diaphragm 25 is preferably provided with
an auxiliary supporting structure operable to
damp the vibratory movement of the diaphragm
with the inner pole piece 2 I. The inner pole piece
and thereby maintain the voice coil 3I in its op
ZI has a relatively wide and thick ?ange 28 formed 30 timum ‘relation to the magnetic gap, and this
on one end of a cylindrical body 29 so that when
end is attained in the transducer of Figs. 1 to 6
the screw 2'! is tightened a relatively large area
through the provision of a ?exible suspension
contact is established between the small end of
member 44 mounted on the outermost face of
the magnet 20 and the ?ange 28 of the inner
the pole plate I9 and engaging the diaphragm
pole piece 2i. The cylindrical portion 29 of the 35 just outwardly of the voice coil structure. Thus
inner pole piece 2I is arranged to extend into a
the suspension member 44 is generally disc-like
central circular opening 30 formed in the outer
in form and is made from a ?exible sheet mate
rial such as paper impregnated with a material
thus an annular magnetic gap is a?orded between
such as a thermo-setting plastic. The suspen
the inner and outer pole pieces, and a voice coil 40 sion member 44 has a central opening therein
structure 3| carried on the diaphragm 25 is ar
de?ned by an integral cylindrical portion 45
ranged to extend into this annular magnetic gap.
which is adapted to surround the voice coil struc
In order to assure accuracy of formation and
ture 3| in spaced relation thereto so that the
pole piece or pole plate I9 centrally thereof, and
dimensions of the magnetic gap, the pole piece
free edge of the cylindrical portion 45 may en
I9 has a locating plate 35 formed from a non 45 gage the inner face of the diaphragm 25. At
magnetic material such as brass and secured in
the other end edge of the cylindrical portion 45
position on the inner face of the pole piece I9
the suspension member extends outtva’rdly‘to af
by rivets 36. The locating plate 35 has an offset
ford a ?exing portion 44’ which preferably in
portion 31 spaced from the plane of that face
cludes a plurality of concentric corrugations, and
of the pole piece I9 upon which it is mounted. 50 at the outer edge an angularly disposed portion
The portion 37 of the locating plate 35 has a
extends'from the portion 44' to merge with an
circular opening 38 formed therein arranged to
outwardly projecting ?at mounting ?ange 46.
snugly embrace the periphery of the cylindrical
The suspension member 44 is mounted on the
portion 29 of the inner pole piece 2|, and in
pole plate I9 with the cylindrical portion 45
practice the openings 30 and 38 formed respec 55 concentric with the annular magnetic gap 30,
tively in the pole plate I9 and the locating mem
and this may be accomplished through the use
ber 35 are simultaneously cut to their ?nal size
of a thermo-plastic adhesive which is applied to
by a suitable trimming tool so as to insure con
the ?ange 46 thereof, and when the suspension
centric location of the two openings 30 and 38.
member is to be secured in position, the ?ange
In the assembly of the transducer ID, the per 60 46 thereof is pressed against the pole plate I9
manent magnet 20 and the inner pole piece 2|
under considerable heat and pressure so that
are ?rst placed in position within the cup-like
the thermo-plastic material bonds the ?ange 45
magnetic yoke II and the screw 21, bearing a
to the pole plate l 9.‘
lock washer iii, is inserted through the opening
After the foregoing assembly operations have
38 in the wall I2 and through the recess or bore
’ been performed, the diaphragm 25 may be placed
25 of the permanent magnet 20 and into threaded
in position and the leads from the voice coil may
engagement with the inner pole piece 2|. The
be connected to the respective terminals #8 and
screw 21 is not tightened at this time, however,
49 which are carried on an insulating'terminal»
for it will be recalled that the locating ring 35 is
plate 50 secured on the outside of the wall I3.
relied upon to accurately position the pole piece 70 It should be observed that while the elements
2i. The outer pole piece or plate I9 is then
of the terminal block might be put in place on
placed in position in the groove I8 with the 10
the wall .13 prior to the assembly of the ele
eating plate 35 engaged with the cylindrical por
, ments of the magnetic circuit, I prefer ‘to do this
tion 29 of the pole piece 2|,‘ and the pole piece
after the pole plate I9 and the suspension 44
I9 is ?xed into the rabbeted groove I 8 with a 75 are in place since by such-‘procedure the outer
8
‘surface of the housing H may be freely used
for centering and supportingpurposes duringas
sembly of these parts. Thus the terminals 48 and
49 are secured on the terminal plate 50 by rivets
5| so that connecting arms 52 of the terminals
48 and 49 project beyond one edge of the ter
member 44 is vented into the relatively large V01?"
ume chamber afforded behind the pole plate 19
by a plurality of openings 51 formed in the pole
plate l9. In some instances the damping of the
diaphragm 25 may be improved by restriction of
the air flow through the openings 61, and this
‘may be accomplished by gluing or otherwise
securing a sheet 68 of fabric across the openings
minal plate; and the terminal plate 50 is posi
tioned on the housing I l with an interposed layer
61 as shown in Figs. 2. 3 and 5.
V
53 of insulating material, and is secured in place
by screws 54 extended through the terminal plate EDI In Figs. ‘7 to 12 of the drawings the invention is
illustrated as embodied in a transducer 10
5|] ‘and threaded into the wall of the housing II.
adapted particularly'for use as a speaker or car
In preparation for its mountingin position in
the housing I i, the diaphragm has a pair of small
metal rivets 55 secured therein as shown in Figs.
1, 2 and 6 and the ends of the voice coil, are
connected thereto, as by solder, and at the same
time ?exible woven lead wires 56 are soldered-to
the respective rivets 55 on the rear face of the
diaphragm 25. The lead wires 56 are extended
loosely and in a radial relation toward the open,-- =.
lugs 43 which are adjacent to the terminal block
50 and are drawn through openings in opposite
ends of a relatively stiff insulating sheet 51 which
phone in'a headset.
In this embodiment of the i
invention a cup-like member ‘ii made from a
ferrous material such as steel affords a housing
for the principal elements of'the speaker and
also serves as a magnetic yoke for the magnetic
circuit. rl‘he housing ‘H is formed as by suitable
stamping and drawing operations to provide a
bottom wall l2 and a generally annular or cylin
drical side wall ‘l3 which is ?anged outwardly at
Mat its outer end. In this embodiment of the
invention the outer pole piece or pole plate 79
is secured by a- rivet 58 on the inner face of,
is mounted on the ?ange ‘M rather than directly
the wall [3 so as to extend at its opposite ends» =
uponthe side wall of the housing, and is secured
in place thereon by rivets 85 extended through
partially across two of the openings 43. The'op
enings in the insulating sheet 51 through which
the lead wires 56 are extended are so positioned
openings appropriately spaced about the ?ange
‘ill and the mounting edge of the pole plate ‘ill.
drop of solder is placedon the wires 56 outside
The pole plate ‘:‘9 is dished inwardly as shown in
Figs. 10 andlZ so that the central portion there
of in which a circular opening 8! is formed is
the cylindrical portion 29 of the inner pole piece
incorporate a foraminous iron or steel plate 89 ‘
ings 43, while the space behind the suspension
plate may be put in position, suitable notches
as to maintain the lead wires out of contact with
the metal of the housing II, and preferably a '
‘spaced inwardly of the housing ‘H, and through
of the insulating sheet 5'! to prevent undue loose
this arrangement space is afforded for the mount
ness of the lead wires between the sheet 51 and
ing of a diaphragm 82 between the pole plate 19
the rivets 55. Short insulating sleeves 69 are
then placed on the extended ends of the wires ~ and a cap plate 83 which closes a substantial
portion'of the open end of the housing H and
56 which are then threaded through outwardly
affords an open central area 85 through which
extending openings in the arms 52 of the termi
sound energy may pass.
nals 48 and 59 and are soldered thereto at 52'
In the assembly of the pole plate 19 and the
on the outer surfaces of the arms‘; The lead
cap plate 83-011 the housing ii, the ?ange ‘M is
wire 56 which is thus connected to the terminal
provided with a plurality of openings Bil’ of a size
48 is extended as at 56' and is soldered to the
adapted to receive the rivets 8B, but such rivets
rivet 58 to afford a ground connection inac
8d are employed only in alternate ones of the
cordance with usual practice.
'
>
-,
openings B??the others of such openings being
The diaphragm 25 and the cylindrical Voice coil
support, in this embodiment of the invention, are 4.5 engaged by projections 85 formed at appropriate
points about the mounting edge of the pole plate
separately formed as shown in Fig. 6, and are
'89. - The projections 36 are provided by what are
secured together by means such as adhesive, and
known as half-punches so that on the opposite
it will be observed that the‘diaphragmv 25.has a
or outer face of the pole plate 79 these half
central opening therein which in the ?nished
transducer is closed by a cap 65 as shown in Figs. 50 punching operations produce sockets Bl which
are arranged to receive complemental projections
2 and 4. When the‘ leads 56 are being-connected
88 formed on the cap plate 83. ‘
.
as just described the diaphragm 25 and the voice
The cap plate Sit is, in accordance with this
coil structure are located loosely in position, and
invention, formed so as to afford an effective
after the connections between the wires 56 and
the terminals 48 and 49 have been completed a 5: magnetic shield for the internal elements of the
speaker ‘to and this is accomplished by molding
plurality of relatively thin shims made from paper
the. cap plate 83 from a plastic material so as to
or like material are placed in position between
through substantially the entire area of the cap
and the inner surface of the voice coil form, there
plate. In the molding operation the openings
60
by to accurately locate and center the voice coil
90 throughout the central area 85 are maintained
structure in the annularmagnetic gap 30; The
free of the plastic material, but throughout the
bordering edge ofthe diaphragm 25 is then se
balance of the area of the plate 89 the plastic
cured in position in a rabbeted annular groove
extends through the openings 90 so as to be inter
formed in the flange‘ l4, and this may be accom
' plished through utilization of a thermo-plastic 65 locked with the plate 89. The outer face of the
plate 89 is preferably covered and concealed by
adhesive, the procedure being the same as that.
the ‘plastic material except in the central area
described hereinbefore in connection :with the
85; and the plastic material is formed to provide
mounting of the suspension member 44. The
clearance sockets ill for the heads of the rivets
shims are then removed and the cap 55 is se.cured in place by adhesive to complete the as 70 8B and to-provide projections 88 for engagement
with the sockets 8'! in the pole plate ‘l9.
sembly of the transducer.I ~
,
- '
1
After the diaphragm 82 has been secured in
In the transducer 10 which is thus provided the
place by adhesive or the like on the outer face of
space between the diaphragm 25 and the ‘sus
the mounting edge of the pole plate '79, the cap
pension member 44 is freely vented by the open
2,458,168
preferably being formed in the edge of the dia
10
and the washer IIlI are shaped to provide a domed
phragm to aiford clearance for the rivet heads
form generally complemental to the internal form
and the projections 88. To secure these parts
of the diaphragm button I I18 and spaced uni
together, a clamping ring 93 is put in position
formly therefrom. The open central area 85 of
with one ?ange 94 engaging the outer face of the
the foraminous plate 89 is also slightly domed as
cap plate 83 and another ?ange 95 is formed at
shown in Fig. 10 to conform with'the shape of
the other edge of the ring, as by spinning, to en
the diaphragm button I08.
gage the rear face of the flange ‘I4. Thus the
The ends of the voice coil, formed by wires I I 9,
housing ‘II is effectually closed and the internal
are preferably led through the diaphragm 82,
elements of the speaker are shielded by the plate 10 near the voice coil form, as shown in Fig. 12, and
‘I9 which is incorporated in the cap plate 83.
on diametrically opposite sides of the form and
These internal elements of the speaker are, of
are led outwardly in generally opposite directions
course, mounted within the housing ‘II prior to
along the forward or outer face of the diaphragm,
the ?nal closure of the housing as aforesaid, and
to points substantially aligned with openings II I
these elements include means cooperating with 15 formed in the pole plate ‘I9. At these points the
the cup-like magnetic yoke afforded by the hous
wires IIO are led back through the diaphragm.
ing II and with the pole plate ‘I9 to afford an
The portions of the wires III) which are thus
annular magnetic gap within which a voice coil
located on the forward or outer face of the dia
structure 96 carried by the diaphragm 82 may
phragm are preferably covered by a water proof
operate.
20 surface coating. The ends of the wires III] are
Thus, as shown in Figs. 10, 11 and 12, a cylin
led through the openings II I where they are
drical permanent magnet 91 is disposed in the
soldered to the free ends of connecting clips M2,
housing ll substantially coaxial therewith, and 2f
the other ends of the clips II2 being secured to
screw 98 is extended through a longitudinal bore
the rear face of the pole plate ‘I9 by rivets H3.
99 in the magnet 91 and into threaded engage 25
The voice coil lead wires III] must, of course,
ment with a stationary nut provided by a plate
be electrically associated with a receiver or other
I80 which is Welded to the bottom wall ‘I2 of the
source of signal current, and this is accomplished
housing. The head of the screw 98 is seated in
by means including a terminal block I I5 mounted
the counterbored central opening of a washer
within the housing II. As shown in Figs. 10 and
[III and the screw is initially left fairly loose 30 11, the terminal block I I5 is molded from insulat
until the proper centered position of the magnet
ing material to include a neck portion I I6 which
97 has been determined. In accordance with the
projects outwardly from the housing ‘II through
present invention as illustrated in Figs. 10, 11
a complemental slot II ‘I formed in the side wall
and 12 the outer end of the magnet 91 is utilized
‘'3 thereof, and a screw IIB extending through
as the central pole piece of the magnetic circuit,
the wall ‘I2 and a bore in the terminal block H5
and hence this end of the magnet extends into
is threaded into one arm of an angle bracket I I ‘I’,
the opening 8I formed in the outer pole piece or
which is in turn held in place by a rivet “8'
pole plate ‘I9. To insure an accurately formed
which passes through the side wall ‘I3 and the
magnetic gap the pole plate ‘I9 has a locating
other arm of the angle bracket. This serves to
plate I93 secured by rivets I04 on the rear face
hold. the terminal block ?rmly in position.
thereof, this locating plate being formed from
The terminal block H5 has two parallel bores’
a non-magnetic material such as brass to afford
or sockets IZEI formed therein and opening out
an offset annular portion I95 arranged to snugly
wardly through the neck portion H6, and. these
embrace the magnet 91. Hence when the pole
sockets are arranged to intersect with and extend
plate '19 is secured in place on the housing ‘H the 45 through metallic sleeves I2I which are molded
locating plate I03 acts to center the magnet 91 in
in the terminal block in spaced and insulated re-_
the opening ill of the pole plate ‘I9, and thus an
lation to each other. The sockets IZE! are of a
accurately formed magnetic gap is afforded.
size adapted to snugly receive metallic connector
The screw 98 may then be tightened to produce
tips of the type conventionally used in radio and
an effective magnetic path between the bottom 50 telephone work, and these tips may be held in
wall of the housing and the adjacent end of the
place by screws I23A which are threaded into the
magnet ill’.
The voice coil structure 96 is preferably formed
with its cylindrical voice coil form molded inte
metal blocks or sleeves I2I and extend into the
sockets I29 and have their heads accessible on
the outside of the back wall ‘I2 of the casing ‘II.<
grally with the flexing portion of the diaphragm 65 The tips of the connecting wires may thus be held
as described in detail in my Patent No. 2,440,439,
issued April 2'7, 1948, and this voice coil form in
in position in the sockets I20 and in electrical
association with the respective metal sleeves I2I;
and to provide for connection of the metal sleeves
I2I to the voice coil, each sleeve I 2! has a metallic
cludes an annular external shoulder IIl‘I facing
away from the diaphragm 82 as to serve as a guide
for locating the voice coil on the form. This 60 ear or clip I23 extending therefrom into an acces
external shoulder I9‘! is formed by offsetting the
sible position within the housing ‘II.
material of the voice coil form, and hence a cor
responding internal shoulder is also formed so as
It has been pointed out hereinbefore that ear
phones or speakers are often used in remote loca
to face toward the diaphragm.
Thus when the
tions with respect to the receiver with which they
screw 93 has been tightened, a diaphragm button 66 are associated, and in the past it has been the
I98 having a cylindrical ?ange I99 thereon may
be mounted in closing relation to the outer end
of the voice coil form merely by inserting the
?ange I 99 into the form until it engages the
internal shoulder, in which position it is secured 70
by means such as adhesive. The diaphragm but
ton I538 in this instance constitutes a part of the
loading portion of the diaphragm structure and
is slightly domed to impart strength thereto.
With this arrangement the head of the screw 98,
practice to employ high resistance voice coils in
such earphones in order to produce a properly
matched impedance in the plate circuit of the
ampli?er. This prior practice has resulted in an
exceedingly high cost and large weight and size
in dynamic speakers, but in accordance with the
present invention these objections are avoided
through the provision ofa transformer I25 in
cluded within the housing ‘II and employed as an
electrical coupling between the metal terminals
2,458,158
ll
12
the respective connector clips H2, there being
insulating sleeves surrounding the intermediate
portions of the wires I28, and the ends thereof,
being connected to their respective clips H2 as
by soldering. The lead wires I29 from the ends
of the primary winding of the transformer I25
are relatively long, and prior to the mounting of
the pole plate '19 in the housing ll, insulating
the high and desirable performance character
istics usually associated with dynamic trans
clucers While materially reducing the weight of
stantially midway between the ledges 13a and the
I21 and. the lead wires l in of the voice coil. Thus,
?ange ‘I4 for cooperation with clip assemblies of
as shown in Figs. 10 and ll, the transformer SE5
a di?erent predetermined dimension or standard.
embodies mounting bracket are which is fixed
Thus the speaker ‘III of this invention may be
upon the pole plate 7419 by a rivet I2? or the like.
The transformer I25 is so disposed on the pole or readily put to use with headbands of two different
standards to thereby facilitate set-up or repair
plate ‘IQ that when the pole plate is put in posi
oi’ radio and like communication systems.
tion in the housing I! the transformer will be
As pointed out hereinbefore, the total weight of
disposed within the housing
a position diamet~
a transducer is ofter a controlling factor in de
rically opposite from the terminal block IE5.
Prior to the mounting of the pole plate ‘IS in the 14.) termining whether or not it is suitable for use
in a particular situation, and while the, embodi
housing the lead wires £28 from the secondary
ments illustrated in Figs. 1 to 12 have maintained
winding of the transformer E25 are connected to
such transducers, an even greater weight
reduction may be attained through the use
of the embodiment of the invention illus
trated in Fig. 1‘3. In this form, the in
_
3 I vention
has
been
embodied
in a transducer
‘III’ which is most of its structural characteristics
sleeves are placed on the wires i253 and the ex
treme ends of the wires I29 are connected by
is ‘similar to the transducer ‘I0 hereinbefore de
soldering to the respective clips E23 of the termi
nals IZ'I. Thus when the assembly of the parts
has been completed the speaker of this invention.
embodies means for matching the impedance of
the receiver with which it is to be used, and hence.
scribed, and in all instances where such corres
pondence exists the same reference numerals
with a prime suf?x have been applied in Fig. 13.
Thus the transducer 10' has a housing ‘II’
which is cup-shaped and is ?anged at its open
end as at ‘I4’. In this form of the invention the
housing ‘II’ also serves as the magnetic yoke of.
the device, and a pole plate 19A is mounted on
the open end of the housing as by rivets 80’. The
pole plate 19A is dished inwardly in the same
general manner as in the transducer ‘I0, thereby
the voice coil may be of a relatively small size and
resistance and the other elements of the speaker.
may be correspondingly reduced in size. Thus:
the present speaker is adapted for use under all
of the conditions encountered in practice. and
particularly Where long leads are to be interposed
-
to locate the central opening 8i’ thereof about
between the receiver and the speaker.
When speakers of the kind shown in Figs. 7 - ‘ one end of the permanent magnet 97’ and in an
to 12 are in use they are ordinarily mounted on
the ends of a headband of conventional construc
inwardly spaced relation to the cap plate 83’. In
this embodiment, however, the pole plate ‘ISA
tion, and such headbands embody clip assemblies
having spaced and resiliently related trunnions
outer edge, as indicated at I33, ‘and gradually
which are adapted to be engaged with aligned
bearing sockets provided on the opposite sides
of the housing of each speaker. Each such clip
assembly is adapted to engage bearing sockets
having a predetermined spacing, and it has been
found in practice that in a particular class of F‘
work there may be two different standards used
in the spacing of the trunnions of the different
headbands encountered. Hence in many in
stances the speakers or' earphones must be
matched with the headbands available, thereby “
causing objectionable delay in setting up or re
pairing a communication system. However, in
accordance with this invention, the casing ‘II
is so formed as to afford two different sets of
bearing sockets spaced different distances apart "
so as to enable different styles or sizes of clip
assemblies to be employed therewith.’ In ac
complishing this desirable result the wall 13 of
the housing ‘II is o?set inwardly at diametrically
is formed so that it is relatively thin near its
increases in thickness toward the central opening
84’. With this arrangement an effective mag
netic path is a?orded from the outer edge or
?ange I34 to the magnetic gap, and yet a sub
stantial reduction in material and in weight is
e?ected. It will be observed that the flange I34
is inthis embodiment. substantially thinner than
the corresponding part‘shown vin Fig. 10, and in
order to maintain the same thickness or size
in the clamping ring 93', a spacer ring I35 of
cardboard or ?ber is positioned about the housing
and against the ?ange l4’.
1
It will be recognized that a substantial portion
of the weight in a transducer such as that to
which this invention pertains is embodied in
the housing, as ‘H’, and in order that the weight
of the housing may be minimized, a relatively ‘
wide and flat. nut I36 is utilized to receive the
end of the screw 98'. The nut I36 has a lug I31
thereon adapted to engage a socket formed by
opposite points to form substantially parallel wall [ill a half-punch I38 in the bottom wall of the
housing, thereby to hold the nut against rotation
sections 1.3’. These wall sections ‘I3’ are dis
as the screw 98' is tightened. The nut I36 is so
posed in symmetrically related positions on ops,
formed as to bear ?rmly against the outer face
posite sides of the opening II"! and the terminal
of the bottom wall ‘I2’ over a wide area, thereby
block H5, and as shown, in Fig. 8, the wall sec
to afford an eihcient magnetic path from the
tions 13’ extend from the bottom wall 12 toward
magnet 91.’ through the Wall, ‘I2’ and to ‘the nut
the flange ‘M for a distance slightly less than
I36, and because of its thickness the nut I35
one-half the distance between the bottom wall
serves to afford ample cross sectional area in the
and the ?ange ‘M. Thus the wall ‘I3 is of cylin
magnetic path near the central axis of the
drical. form between the. ledge ‘113av and the ?ange
‘I4. Av pair of aligned bearing sockets Hill are m housing- The nut I36 is. tapered or rounded to
a thin outer edge, as indicated at I39, but such
formed in the wall sections ‘I3’ substantially cen
taper is gradual so that the nut extends out
trally thereof for cooperation with clip assem~
wardly to point. where the e?ectiv-e cross sectional
blies of one predetermined dimension or stan
area, of the. wall 12. is su?icient. to provide an
dard, while similar aligned bearing sockets I3I
are formed in the areas of the wall 13 sub 78 e?lcient magnetic path.
13
14
With this, arrangement it is in many. instances
possible. to somewhat reduce the Wall; thickness
of the housing 'II', and as a result, the weight of
Ha. A. diaphragm 8.2a of a. generally cone.-~
shaped form has a voice coil structure 96a sup
ported thereon in such position that it may be
centered Within the, magnetic gap a?orded be
the transducer as a whole may be minimized
between. the opening 8| a and the magnet 91a.
The outer edge of the diaphragm 82a is disposed
in abutment with. the outer face of the mounting
?ange ‘I911’, and. a magnetic shield in the form of
a metal plate 8511; has its peripheral edge 85b dis
while maintaining e?icient operation and per-v
formance thereof.
In locations adjacent to magnetically sensitive
apparatus such as magnetic direction ?nding or
indicating equipment. it is. esential thatv stray
magnetic ?elds adjacent to such sensitive apppae.
posed against the outer mounting ?ange portion
of- the diaphragm 82a. The plate 850., the dia
ratus be eliminated or at least minimized. With
the transducers illustrated in Figs. 10 and, 13 it
will be. evident that the housing 'II or 'II'.‘ serves
as the primary path for the magnetic ?ux: so that
phra-gm‘BZa; and the mounting plate 19a. are held
in position on the ?ange 14a of the housing by a
plurality of rivets 80a which are extended
stray magnetic ?elds will be present about such 1.5. through the- several ?anges, and in the present
instance a ?bre gasket I45 is also secured in place
transducers. Where such stray magnetic ?elds
on the rear face of the ?ange 14a by means of
are objectionable as in the above cited instances,
the rivets 80a. After the shield or plate 85a has
the present invention may be embodied in the
been secured in position as just described the
alternative form shown in Figs. 14 to 16 which
retains the general form and size of the trans. 201 outer cap plate 83a; may be placed in position
over the plate 85a, suitable interlocking means
ducers of Figs. 10 and 13;. but is so constructed
being provided so that openings 90a. in the cap
and arranged that stray magnetic ?elds are
plate 83a may be accurately aligned with corre
avoided. Thus the transducer 10a of Figs. 14 to
sponding openings 90b. in the shield plate 85a.
16 has a generally cup-shaped housing 'I.Ia which
is ?anged at ‘Ma at its outer end and is formed 25 After the cap plate 8341 has been placed in posi
tion, it is secured in this position by an annular
with sockets 130a. and I3Ia so as to be adapted
clamping ring’ 93a. In the present instance the
for mounting in clip assemblies of different sizes
shield plate 85a is offset in its central portion as
or designs in the same manner as the transducers
indicated at I41‘, and a sheet of fabric I48 is
of Figs. 10 and 13.
In this alternative form of the invention the 30' secured as by adhesive to the plate 85a in the
space afforded by the offset I41. Through this
housing ‘II (1 serves as a path for conducting the
arrangement the reproduction characteristics of
magnetic flux to the annular magnetic gap of the
the present transducer may be governed to pro
transducer, but in this form of the invention this
duce the desired frequency response character
function of the housing ‘Ila is accomplished. in
such a manner that the. housing acts as a shield
' .
istics.
rather than as a primary part of the magnetic
circuit, and means is provided within the housing
The transducer of Figs. 14 to 16 has a terminal
block I‘I5a which is substantially similar to the
‘I I a to afford a primary magnetic circuit. To this
end a magnetic yoke I40 is formed from a rela
terminal block- shown in Fig. 10 and which is
secured in position by means such as a rivet
“M. In connectingv the terminals I2Ia of the
terminal block to the coil of the voice coil
structure 96, a transformer I25a> is utilized in
substantially the samevmanner as in the embodi
ment- shown in; Fig. 10, and wires I 290. are ex
tively heavy strip of soft iron or other magneti
cally permeable material to afford a bottom mem
ber I4I, two side members I42 disposed at right
angles to the bottom member MI, and a top
member I43 which is provided by bending the
ends of the side members I42 inwardly toward
each other. These ends may be joined together
as by welding, and the two ends joined are
punched to aiiord an opening BIa which forms
the outer side of the magnetic gap. of the trans
ducer, and hence the member I43‘ constitutes the '
outer pole piece in this embodiment of the in
vention. On its inner face the top member I43
‘ tended from the- respective terminalsv I2la to the
opposite terminals of; the primary of the trans
former I25a. The transformer [25a is supported
on the plate 19a by means including rivets IZ‘Ia.
Wires I-28a- are‘ extended from the secondary of
the transformer to rivets I49 which are mounted
by means of- insulatingV-sleeves I50 in the mount
ing plate 19a as shown in- Fig. 14, and wires IIlla
has a locating member I 05a. made from non
are extended from the rivets I49 through the dia
magnetic material and held in place by rivets at
I04a. Thus a permanent magnet 91a of cylin- ‘
phragm 82a and to the opposite ends of the voice
coil in‘ the same manner as in Fig. 12.
It will be.~ observed that the bottom member
drical form may be extended through the. locating '
member I?Ea and into contact with the bottom‘
member I4I of the magnetic yoke. I40, and a
screw 98a extended through an axial bore 99a. in.
the magnet is threaded into the bottom member
I4I to hold the magnet 91a. in position.
[4.1 of the. magnetic yoke I40 is supported out
of contact with the wall- 'Ii2a~ of; the housing, and
a similar vspaced relation‘ is afforded between the
side members I412 and: the side walls of the hous
ing. Since the sockets. I3IJ'a are formed in the
oifsetj portions of the side wall, clearance slots
The magnetic yoke I40 is supported in position
within the housing 'IIa by a mounting- plate 19a
which has a central opening therein somewhat
larger than the opening Bla so that the central’
portion of the plate 19a may be secured tov the
inwardly.‘ projecting bosses, formed in the wall
outer face of the top member I43‘ in a central
relation to the. opening 8Ia, and such a connec
tion is in the present instance afforded by the
clear that any stray’ magnetic ?elds about the
magnetic-yoke I46rwil'l" pass to the walls 12a. or
13a of the housing ‘Ha and will be conducted to
the mounting platev 79a.- and thence to the mem
rivets I04a.
The mounting plate 19a is dished
I52: are formed‘ in; the members I42 so that the
73a. when the sockets time are stamped, do not
contact the side- members I42. Thus it will be
ber‘ M3: which constitutes the outer pole piece
and" de?nes the outer: side of the magnetic gap.
portion 19b is placed against the outer face of the
Hence. the casing; ‘Mary in this, embodiment of‘ the
?ange 14a, the‘ magnetic gap. afforded by the
invention serves asa path‘ for- magnetic ?ux, but
opening 8Ia will be disposed- a substantial dis
tance inwardly of the open endof. thev housing ' since the primary magnetic path afforded by the .
inwardly so that when its outer. ?ange or edge
15
2,468,158
yoke I40 provides the best and most e?ective
path to the magnetic gap, the flux density in the
housing Ha is maintained relatively small at all
times, such flux density in the housing ‘Ila be
ing so small that objectionable stray ?elds out
side the housing are avoided. Where the walls
16
transducer may result at some frequencies. but
in accordance with this invention, such an unde
sired variation is avoided by the provision of
means operable to dissipate the energy of the
air which is thus compressed within the back
chamber.
As shown in Fig. 14, such means‘ are
of the housing are relatively thin as in this em
afforded by providing a ?brous ?ller material in
bodiment of the invention, the bottom Wall 1211
a substantial portion of the back chamber, and
may be strengthened by the formation of an
while this construction may be employed in any
embossed panel 12b therein.
'
10 of the illustrated embodiments, it is herein shown
In securing the desired frequency response in
in but one of such embodiments. Thus, as shown
the transducer the back loading of the dia
in Fig. 14, the rear portion of the housing is
phragm. 82a‘ is preferably reduced through the
?lled with a ?brous material I60 such as kapok or
provision of a plurality of openings 19c in the
wood ?ber. The ?brous material ISO is prefer-~
mounting plate 79a, this arrangement being such 15 ably compressed into blocks of the shaperequired
as to enable substantially the entire interior of
to ?t about the elements of the magnetic circuit
the housing to function as a back chamber.
and the transformer so that the preformed block
Further improvement of the frequency response
of ?brous material may be readily placed in po
is also attained by forming the diaphragm 82a
sition, but if desired the material I60 may be
with an annular bead or corrugation 82b in the 20 packed in place bit by bit while the mounting
outermost portion of the free area of the dia
plate 1% is held in a slightly separated relation
phragm, and with this bead it is found that the
to the open end of the'housing. Where the ma
?exing of the diaphragm isrelatively free under
terial is thus put in place bit by bit it has been
all conditions. The mounting of the textile
found desirable to place a protective'shield of
member I48 between the cap plate and the shield 25 textile fabric across the openings 190, Fig. 16, or
the openings III, Fig. 11, for by such an expedi
85a‘ also contributes to the attainment of the
desired frequency response, for by selection of
ent the ?ller material I60 is maintained out of
the fabric it is possible to eliminate or reduce
contact with the diaphragm at all times. It will
undesirable components of the voice energy.
be understood that for clarity of disclosure, the
It will be evident that the embodiments of this 30 ?brous ?ller material I 60 is shown in but a small
portion of the back chamber in Fig. 14, but in
invention illustrated in Figs. 7 to 16, as thus de
practice the ?ller material is placed in position
scribed, are waterproof in character since the
diaphragms are of waterproof construction and
in all or a substantial portion of the back cham
ber, and is compressed or packed relatively ?rmly
are arranged to cooperate with the housing in
excluding water from the internal electrical ele 35 so as to place a high resistive load on'the back
of the diaphragm and have an efficient dissipat
ments, and in furtherance of this purpose a suit
able lacquer may be applied within the housing
ing action with respect to the energy of the air
as such air is compressed. When the back cham
about the terminal block and at other points
ber has been ?lled to a relatively great extent
where leakage might occur. When, however, the
with wood ?ber it has been found that the pres
transducers are employed for some uses, as for
ent transducers of Figs. 7 to 16 have a frequency
example, in aviation work, it is desirable to pro
response which conforms more closely to the de-‘
vide for equalization of the pressure in the back
sired ?at response curve than any prior trans
chamber, and where this is desirable and where
ducer, and such close conformity has been‘found
absolute protection against moisture is not vital,
this may be accomplished by providing relatively 45 to extend through the range of frequencies from
below one hundred cycles to above four thousand
small pin holes in the diaphragm adjacent to the
cycles. Moreover, it has been found that with
edge thereof.
the transducers of this invention, the variation
Under other circumstances, where the water;
from the normal frequency response which is
proof character of the transducer is to be pre
served. the present invention enables the desired 50 usually experienced at ‘high altitudes is reduced
to a substantial extent, thereby to produce highly
equalization of the pressure in the back cham
improved operation in high altitude aviation uses.
ber to be attained through-means which'pre
Thus these transducers of Figs. '7 to 16 insure
vents entry of water. While such means might
maximum intelligibility of transmission under
be afforded in any of the embodiments shown
in Figs. '7 to 16, it is shown only in Fig. 14 where
all noise conditions, and such intelligibility ma
terially exceeds that attained by prior transduc
an opening I54 is formed in the panel 12b of the
housing and a resilient sheet or membrane I55
of rubber or the like is secured on the inner face
of the bottom wall 12a so as to span the recess
ers.
able variation' in the frequency response. of the
tending into the outer. pole piece and serving as
From the foregoing description it will be evi
dent that the present invention enables dynamic
afforded by the panel. The sheet I55 is secured 60 transducers to attain .the desired transducing ca
pacity while maintaining the size and weight
to the bottom wall 12a by adhesive so as to ex
thereof at the minimum, and hence the trans
clude water from the electrical elements within
the housing, and yet when the pressure within;
ducers of this invention may be utilized where
the housing exceeds that outside the housing, the‘
such considerations are vital factors in deter~
resilient sheet I55 may be stretched into the re-‘ 65 mining what type of transducer is to be'selected.
cess a?orded by the panel 121), thereby to reduce
The use of a cup-shaped housing which also func
the pressure in the back chamber to correspond
tions as a magnetic yoke contributes in a large
with the external air pressure which is applied
measure to the attainment of this desirable re
to the sheet I55 through the opening I54.
sult, and it will be observed in this connection
Where the back chamber is thus completely 70 that the cup-shaped housing affords a magnetic
path of large cross sectional area so as to in
closed or sealed, the air con?ned within the back
crease‘the' effectiveness of the magnet in produc—
chamber is of course compressed as'an'incident
to the operation of the‘diaphragm, and because
ing maximum flux density in the magnetic gap.
Moreover, the use of a cylindrical magnet ex
of the elastic properties of "such air an undesir
v2,458,158
'
17
18
having a bottom‘ wall and a generally annular
side wail,:a mounting plate extended across .the
open end of‘ said housing and secured to the side
Wall of said housing to provide a magnetic path
fromsaid mounting plate to said side Wall, a mag
the .inner pole piece enables the maximum .of
magnetic force to be supplied in a transducer of
‘a lgiven'size. These novel features, of course, en
able maximum magnetic ?ux to be attained at
the magnetic gap to thereby contribute to the
ef?ciency of the transducer as a Whole, and par—
netic yoke formed from magnetically permeable
ticularly it has been found that the high flux
density attained in the magnetic gap of the trans
ducers of this invention enables the voice coil
to be reduced radically insize and resistance to .11 0
thereby correspondingly contribute to the desir
able characteristics of the transducers of this
material to provide a bottom member, side mem
invention. The cup-shaped yoke and housing
employed in the present transducers is so related
to the form and location of the outer pole piece
or pole plate that the yoke may also function as
the primary supporting means for the diaphragm,
and ‘hence the transducers are simpli?ed as to
construction and assembly.
When the present invention is embodied in a
speaker or earphone the arrangement is such
that the cup-shaped housing provides means for
mounting the earphone on. headbands having
different sizes of clip assemblies, and hence the
usefulness of the earphones is greatly increased.
In this embodiment of the invention the e?iciency
of the cup-shaped magnetic yoke is such that the
magnet may be relatively small, and hence the
location of the coupling transformer Within the
housing of the earphone is attained in accordance with this invention Without sacri?ce of com
pactness in the structure asa Whole.
In the illustrated embodiments of the invention
it Will be evident ‘that unusual simplicity of struc
ture and assembly has been attained so that the
transducers may be produced Wi'thgreat economy
of time and material. Moreover, it will beseen
that the construction and arrangement of the
diaphragm and voice coil assembly contributes
materially to the economy of the present con
struction, particularly in the mounting of the
diaphragm button on the diaphragm in the form
shown in Fig. 10, for it Will be clear that the
diaphragm button may be quickly located in its
?nal position merely by insertion of the flange of
the button into the voice coil form until it strikes
the internal shoulder of the form.
Hence, While I have illustrated and described
preferred embodiments of my invention, it is to be
(20 lar magnetic gap, and a ‘diaphragm having a voice
coil ‘structure disposed withinsaid annularmag
netic gap and having "the outer edges of the
diaphragm mounted on the outer edges of said
mounting plate. ,
3. In a transducer, a magnetic yoke formed
from magnetically permeable material to afford a
bottom member, two side member and a top mem
ber .having ‘a central‘ aperture therein, a perma—
nent‘ magnet secured to said bottom member and
extended-into said aperture in said top member to
a?‘ord'ani-annular magnetic gap, a mounting plate
formed from magnetically permeable .material
and secured .to said top member, a cup-like ‘hous
ing formed from magnetically permeable material
735 "andhavin'g said mounting plate secured across
‘the :open 'end ‘thereof to support said magnetic
yoke within said housing in spaced relation to the
Walls'thereof, said ‘mounting plate :being \ secured
‘to said housing at the open end ‘thereof to afford
40 a magnetic path between said plate and said
;.
housing whereby stray magnetic ?ux passing
from said yoke to said housing is transmitted
through said mounting plate to said top member
of said magnetic yoke.
.1.
4. In a transducer, a cup-like housing formed
from magnetically permeable material and
understood that these are capable of Variation '
and modi?cation and I therefore do not wish to
be limited to the precise details set forth, but
desire to avail myself of such changes and altera
tions as fall Within the purview of ‘the following
claims.
I claim:
1. In a transducer, means including a perma
nent magnet and an outer pole piece of magnetic
ally permeable material arranged to cooperate to
de?ne an annular magnetic gap adjacent to one
end of the magnet, a diaphragm having a voice
coil structure disposed in said magnetic gap, a
cup-like housing formed from magnetically per
meable material and disposed about said magnet
in such a relation that said annular magnetic gap
is located inwardly of the open end of said cup
bers and‘ atop member apertured to constitute
said top member as an outer pole piece, said outer
pole piece being permanently secured to said
mounting .rnember ‘to support said magnetic yoke
Within said housingwwith said bottom member
and side members thereof in spaced relation to
said ‘bottom- Wall and sidewall respectively of said
housing, a ‘permanent magnet mounted on said
magnetic yoke With one end of the magnet in ?ux
‘transmitting contact with said bottom member of
the yoke and'vvith the other end disposed Within
said aperture in said pole piece to de?ne an annu
having a bottom Wall and a generally annular
side Wall, a mounting plate extended across the
open end of said housing and secured to the side
wall of said housing to provide a magnetic path
from said mounting plate to said side wall, a
magnetic yoke formed from magnetically perme
able material to provide a bottom member, side
members and a top member apertured to consti
tute said top member as an outer pole piece, said
outer pole piece being permanently secured to
said mounting member to support said magnetic
yoke Within said housing With said bottom mem
ber and side members thereof in spaced relation
to said bottom Wall and side walls of said housing,
a permanent magnet mounted on said magnetic
yoke with one end of the magnet in flux trans
mitting contact with said bottom member of the
yoke and with the other end disposed within said
aperture in said pole piece to de?ne an annular
magnetic gap, a diaphragm having a voice coil
like housing, said pole piece being secured to
said cup-like housing to a?ord .a magnetic path
between the pole piece and the housing, and
structure disposed within said annular magnetic
gap and having the outer edges of the diaphragm
to flow through said housing to said pole piece.
plate of insulating material positioned against
mounted on the outer edges of said mounting
means completing a magnetic circuit from the 70 plate, a shield plate of magnetically permeable
material positioned across and in spaced relation
other end of said magnet to said outer pole piece
to enable at least a portion of the magnetic flux
to the movable parts of said diaphragm, a cap
2. In a transducer, a cup-like housing formed
from
magnetically permeable
material
the outer face of said shield plate, said cap plate
and 75 and said shield plate having a plurality of cor
‘2,458,158
19
20
respondingly positioned perforations therein
locating said cap plate and said shield plate in
through which voice energy may pass into contact
with said diaphragm,means for locating said cap
plate and said shield plate in such a relation that
said perforations are in registry, and means for
such a relation that said perforations are in
registry, a sheet of fabric disposed between said
shield plate and said cap plate, and meansfor
holding said cap plate and said shield plate in
position on said housing.
holding said cap plate and said shield plate in
WEBSTER. E. G'ILMAN.
position on said housing.
5. In a transducer, a magnetic yoke formed
REFERENCES CITED
from magnetically permeable material to a?ord
a bottom member, two side members and a top 10
The following references are of record in the
member having a central aperture therein, a per
?le of this patent:
manent magnet secured to said bottom member
UNITED STATES PATENTS
and extended into said aperture in said top mem
ber to afford an annular magnetic gap, a mount
Number
Name
Date
ing plate formed from magnetically permeable 15
material and secured to said top member, a cup
like housing formed from magnetically permeable
material and having said mounting plate secured
across the open end thereof to support said mag
netic yoke within said housing in spaced relation 20
to the walls thereof, said mounting plate being
secured to said housing {at the open end thereof to
afford a magnetic path between said plate and
said housing whereby stray magnetic flux passing
from said yoke to said housing is transmitted 25
through said mounting plate to said top member
of said magnetic yoke, a diaphragm having a
voice coil structure disposed within said annular
magnetic gap and having the outer edges of the
diaphragm mounted on the outer edges of said 30
mounting plate, a shield plate of magnetically
permeable material positioned across said
diaphragm, a cap plate of insulating material
positioned against the outer face of said shield
plate, said cap plate and said shield plate having 35
a plurality of correspondingly positioned perfora
tions therein through which voice energy may
pass into contact with said diaphragm, means for
966,247
1,115,519
Schwarz __________ __ Aug. 2, 1912
Edwards __________ __ Nov, 3, 1914
1,546,567
Childress ______ __»___ July 21, 1925
1,586,391
1,702,434
1,792,300
1,901,898
Timmons _________ __ May
Hanna ___________ __ Feb.
Hanna ___________ __ Feb.
Clarke ___________ __ Mar.
1,960,449
Midgley __________ __ May 29, 1934
1,961,665
1,987,413
2,010,537
2,020,211
Holly _____________ __ June
Olson _____________ __ Jan.
Emmert ___________ __ Aug.
Quam -1 _________ _>___ Nov.
2,029,282
2,037,185
2,058,555
25,
19,
10,
29,
1926
1929
1931
1933
5, 1934
8, 1935
6, 1935
5, 1935
Serge ____________ __ Jan. 28, 1936
Thuras __________ __ Apr, 14, 1936
Betts, et a1 ________ __ Oct. 27, 1936
2,085,721
Warnke __________ __ June 29, 1937
2,119,272
2,155,474
Engholm __; ______ __ May 31, 1938
Creager __________ __ Apr. 25, 1939
2,162,270
2,180,615
2,202,886
2,216,961
2,293,078
Mott _____________ __ June 13, 1939
Serge ____________ __ Nov. 21, 1939
Abrahams ________ __ June 4, 1940
Samial ____________ __ Oct. 8,1940
Proctor __________ __ Aug. 18, 1942
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