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Патент USA US2131529

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Sept; 27, 1938.
D. SSPENS STEUART
TELEPHONE
'
‘ Filed Jan. 21, 1936
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' 2,131,529
INSTRUMENT
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Sept. 27, 1938.
I
D. s. SPENS STEUART
TELEPHONE
INSTRUMENT
Filed Jan. 21, 1936
11,1.
2,131,529
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4 Sheets-Sheet 2
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‘Sept. 27, 1938. _ v '
D. s. éPENs SH'EUART
I ~
2,131,529
.TELEPHONE INSTRUMENT
Filéd Jan. 21, 1936
4 Sheets-Sheét 3
49.
/I/
Sept. 27, 1938.
D. s. SPENS STEUART
2,131,529‘
TELEPHONE INSTRUMENT
Filed Jan. 21, 1956
4 Sheets-Sheet
2,131,529
Patented Sept. 27, 1938
UNlTED STATES PATENT OFFiCE
2,131,529
TELEPHONE INSTRUBIENT
Douglas Stuart Spens Steuart, Regents “Park,
London, England
-
Application January 21, 1936,,Serial No.’ 60,124
In Great Britain January ,23, 1935
1'7 Claims.
The present invention relates to telephone in-v
struments and has as its main object the provi
sion of a telephone set for use on public and pri
vate telephone systems which will enable a sub
5 scriber using the telephone to write down mes
sages or refer to papers on his desk and general
ly to use the telephone with a minimum of strain
and inconvenience.
According to the main feature of the invention,
10 a telephone set comprises a receiver with limited
range which can only be heard by a user having
his ear in close proximity thereto, a transmitter
arranged to respond to speech produced a con
siderable distance away, e. g. two feet, and means
15 for supporting the receiver at such a distance
from the transmitter and in such a position rela
tive thereto that a user may have the receiver
supported within audible range of his ear while
leaving a clear space between his mouth and the
20 transmitter for the purpose described. With this
arrangement the user has both hands at liberty
so that whilst telephoning he can easily write
and/or refer to papers Whichcan conveniently be
arranged on his desk in front of the mouthpiece
and his head can be comfortably maintained in
positions convenient for speaking, reading and
writing.
’
The receiver is arranged so that the speech pro
duced thereby can only be heard when the ear
30 of the user is within a short distance, e. g. four
inches, from the earpiece, so that the speech is
generally audible only to one person in the room.
There is preferably provided a member which nor
mally supports the earpiece close to the telephone
5 set but is adjustable so as to support the ear
piece at a convenient distanceof up to two feet
in front of the set. ‘ The movement of this mem
ber is preferably arranged to control contacts in
the line circuit of the set.
,
A subsidiary feature of the invention relates to
'
(Cl. 179-100)
junction with the accompanying drawings com
prising Figs. 1-12 in which:
,
Figs. 1, 2 and 3 show respectively a side eleva
tion (partly in section), a plan view and a front
elevation of a telephone desk se ,
'
Fig. 4 shows a detailed View of an anti-side
tone device,
‘
~
Fig. 5 shows another view of the anti-side tone
device with a Bowden wire attachment,
Fig. 6 shows an alternative anti-side tone de
vice using a pneumatic tube,
Fig. 7 shows an alternative form of telephone
desk set in which the dial switch is located in
the centre of the opening to the mouthpiece, ,
Figs. 8 and 9 show an alternative method of
holding the earpiece by means of lazy tongs,
Figs. 10, 11 and 12 show a further modi?ed
construction of telephone desk set.
V
A description will ?rst be given of, the tele
phone desk set shown in Figs. 1, 2 and 3. .
A specially constructed mouthpiece l for col 20
lecting and concentrating sound Waves received
from a distance is arranged so that alternate cy
lindrical elements of its internal surface are sub
stantially parallel to the'axis of the mouthpiece 25
and at 45° thereto.
It is also provided at its ‘ "
opening with two internal- coaxial partitions
which have the same shape as the'corresponding
portion of the internal surface of the mouthpiece.
These partitions are found to increase the sound
concentrating e?ect without introducing distor
tion. For a further description of this type and
modi?ed types of mouthpiece reference should
be made to my co-pending application, Ser. 'No.
52,255, ?led Nov. 29, 1935, Patent No. 2,087,052, 0
issued July 13, 1937.
The mouthpiece is connected by means of .a
sound passage 2 to a carbon granule‘transmitter
3 which is ?tted into a housing 4 of suitable size
and shape which is attached to the remote end 40
a device for overcoming packing of the carbon
of a rectangular base plate l2. A dial switch 5 is
granules of the transmitter, said device being
?tted on the front near end of the base plate be
low the mouthpiece so that the whole forms a
operable at a convenient distance from the trans
mitter so that it may be readily operated by the
subscriber to agitate the carbon granules with a
minimum of effort.
'
A further feature of the invention resides in
the provision of a transmitter located at the rear
of the set and provided with an enlarged mouth
neat, compact and symmetrical desk set. The
receiver 6 is attached by means of a stirrup .1
to a telescopic tube forming the inner member ofv
a set of telescopic tubes slidably mounted within
an outer member_8 ?xed to a rod 9 which is se
curedv through a friction grip member ID to the
piece extending towards the front of the set and
swivel support I l ?tted to the rear of the instru
in which a dial switch is also provided at the
front of the set.
ment casing
The invention will be better understood by ref
55 erence to the following description taken in con
-
I2.
.
.
'
With the desk set in the condition shown in
the drawings, the receiver 6 rests close to the
mouthpiece I and the set is disconnected from the
line by means of the ebonite pin l3 which is se
55
2,131,529
2
cured to the outermost movable tubes and sepa
rates the springs |5 which are inside a portion of
the tube shown in section and are secured to the
rod 9. The line circuit is held open at contacts
l6 and with the receiver in this position the in
dicating member H is located near the “o ” des
It will be readily understood that the telephone
set may be provided with a pair of telescopic
arms similar to that shown arranged so that two
receivers may be applied simultaneously to the
ears; the distance between such receivers is pref in
erably made readily adjustable.
ignation thereby indicating that the set is discon
nected. To take the instrument into use the re
ceiver 5 is pulled forward to extend the telescopic
tubes. When the outermost movable telescopic
tube is extended the ebonite pin I3 is withdrawn
from the springs |5 thereby allowing the contacts
I6 to close and connect the set to the telephone
line. The friction member l0‘ allows the receiver
15
Figs. 4 and 5 show the construction of the anti
side tone device arranged to be operated by the
key 23 of the telephone set shown in Figs. 1, 2
and 3. When the key 29 is depressed it raises
the lever 30 which rotates the bell-crank lever
3| and the lever 32. This latter turns the spindle
33 to which is connected a ?exible strip 34. The
free end of the ?exible strip which is provided
arm to be raised or lowered to a convenient po
sition against the ear of the user-
I
Owing to the use of the enlarged mouthpiece I,
the user can speak at a distance of up to ap
proximately two feet from the mouthpiece and
still be easily heard at the other end of the con
nection. It is found that about 11/2 feet from
the mouthpiece constitutes the most comfortable
distance for dialling and provides convenient
room on the desk in front of the telephone set for
papers, etc.
As the receiver is self-supporting,
both hands are free so that the user can easily
write and/or refer to papers whilst telephoning
with his head comfortably maintained in a con
venient position. When the ‘call is ?nished, the
30 receiver 6 is pushed back into the original posi
with a button preferably of sound-absorbing ma
terial is thus brought into contact with the centre
of the transmitter diaphragm 35, thereby render
ing the transmitter |9 inoperative. It will be ap
preciated that by means of this construction room
noises and side-tone may be completely elimi
nated at_ the will of the user by the operation of
the key 29 convenientlylocated in front of the
instrument. An alternative method of operating
the anti-side tone device is shown in Fig. 5 in
which a Bowden wire 36 is shown connected to ..
the arm 32. When the ?nger press 31 is oper
ated, the Bowden wire 35 draws the arm 32 to the
right and the free end of the ?exible strip 34 is
thereby pressed against the centre of the di
aphragm 35 in the manner previously described. ‘
With this arrangement the side-tone and room
springs |5 thereby opening the line circuit at noises may be controlled at any desired distance
contacts IS. The outermost telescopic tubes are from the set.
Fig. 6 shows a further alternative method of
arranged to telescope more easily than the inner
ones so as to avoid any risk of the set being left operating the anti-side tone device. In this con~
struction a metal tube 48 is inserted under the
connected up due to the receiver not being com
pletely pushed back althoughthis is unlikely as protective grid of the transmitter and is con
the receiver in its forward position is certain to nected by a rubber tube 39 of convenient length
attract attention. If the user prefers to listen to a hollow rubber bulb 38. When the bulb 38
is squeezed the air pressure in?ates a small hol 40
40 with the right car it is only necessary for him low rubberbulb 4| ?tted to theother end of the
to rotate the rod 9 about the swivel support H
and bring the receiver 6 forward to the right of metal tube 40. The bulb 4| is situated near to
the mouthpiece |. If it is required to. re-dial or the centre of the diaphragm35 but does not nor
re-call the operator, the largestrsliding tube only mally touch it. When it is in?ated, however, it 4.5
presses against the diaphragm and completely
45 of the telescopic arm need be closed and this op
prevents the diaphragm responing to oncoming
eration is rendered more convenient by the pro
vision of the milled collar M which is secured to sound-waves.
Fig. 7 shows an alternative form of construction
its near end. An’ indicator I1 is provided to en
able the user to ascertain the position of the of telephone set in which the dial switch 5 is
tion, whereupon the ebonite‘pin l3 engages the
50
switch contacts.
I
a
.
To prevent packing of the carbon granules, a
press key I8 is provided at the front of the set so
that the user by depressing this key causes the
carbon granules to be agitated and thus main
55 tains the transmitter IE3 at its maximum effi
ciency. In response to the depression of the
key Hi, the lever 20 which is pivoted at 2| causes
65
mouthpiece and a sound re?ecting cone 28' is ?t
'ted‘behind the dial switch. The sound waves
are collected by the annular ori?ce surrounding
the dial switch and are then concentrated and
led to the transmitter in the same manner as in ' -
the mouthpiece shown in Fig. 1.
The receiver
the bell-crank lever 22 to rotate in a clockwise
is secured to a device for mechanically support
ing it close to- the ear, e. g. the telescopic tubing
direction; the steel pawl 23 engages the pin 24
shown in Fig. 2.
which is attached to the hammer rod 25 and
causes. the rod 25 to move to the right against
the action of the spring 26. This movement con
tinues until the pawl 23 has. describedga down
ward are sufficient to slip from the pin 24. The
spring 25 then drives the hammer rod 24 back
into its original position, where it strikes the
agitator pin 21 with suf?cient force to disturb
the carbon granules and?eliminate any “pack
ing’f. The agitator pin 21 is designed to enter
a cavity in the transmitter to engage a point
behind the rear electrode so that the blow is. de
livered at the most suitable point. A further key
29 is provided for operating‘ an anti-side tone
device which will be described later with refer
75
mounted in the centre of the opening to the
ence to Figs. 4 and 5.
_
Fig. 8 shows the use of lazy tongs 5| for sup 60
porting an earpiece 49 close to the ear when using
a telephone set of the type described in connec
tion with Figs. 1, 2, 3 and '7. The earpiece 49 is
connected by means of a ?exible sound tube 48 p
to a moving coil receiver 41 which is preferably 65
located in the same casing as the transmitter or
adjacent thereto. The earpiece 49 is supported
in. a clip 5|! ?xed tothe free end of the lazy tongs
5|. When the lazy tongs are closed the rod 52 I
presses on a bell-crank lever 53 which holds
down the switch rod 43 against the tension of
the spiral springs 54. The switch rod 43 in
turn holds open the line contacts in the manner
shown in Fig. 2. When the lazy tongs are ex
tended the bell-crank lever is rotated by the
2,131,529
spring 54, thus allowing the spring 55 to raise the
switch rod 43 to cause the switch contacts to
close in the manner described in connection with
Fig. 2. Alternatively, the earpiece may be taken
from the clip 58 and moved to and from the ear
without necessitating the extension of the lazy
tongs. When the earpiece is taken from the clip
the spring 56 causes the rod 52 to move forward
away from the bell-crank lever 53 thereby causing
the line contacts to operate in the manner previ
ously described. Alternatively, the receiver itself
may be ?tted to the lazy tongs without the use of
the sound tube. It will also be understood that the
lazy tongs arrangement may be replaced by a
r set of telescopic tubes of the type shown in Fig.
2. The moving coil receiver with a diaphragm of
the shape shown is very sensitive so that the
speech produced thereby may be heard at a dis
tance of up to approximately four inches from
the earpiece. It will be appreciated‘ that by 10
cating the receiver inside the casing of the set
it is protected from damage and may therefore
be made more sensitive than if it had to with
stand mechanical shocks.
I claim:
7‘
3
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1. A telephone sub-set assembly comprising in
combination a base, a microphone mounted in
close proximity to said base, a short enlarged,‘
mouthpiece immediately in front of and co-axial '
with said microphone and directed in a certain
direction away from said base, said mouthpiece
being constructed so as to enable sounds uttered
at a distance of 10 to 20 inches away from and in
front of the open end to generate speech currents 10.
of normal strength'with a minimum of distor
tion, a receiver, an extendible and collapsible
support for said receiver secured at one end to
said base in close proximity to said microphone
and normally supporting said receiver alongside
said microphone to form a compact unit when not
in use and extendible to a distance of 12 to 24
inches in a direction parallel with the axial di
rection of said microphone and mouthpiece where
by the person using the instrument may be 20
allowed the free use of both hands and pro
vided with an unrestricted space of 10 to 20
inches between his mouth and the instrument
thereby allowing View and access to a desk and
A further modi?ed construction is shown in > at the same time permitting the location of re
Figs. 10, 11 and 12. In this arrangement the ceiver su?iciently close to his ear to ensure that
mouthpiece la is similar in many respects to the incoming speech sounds are heard exclu
that shown in Fig. 7 but is additionally provided sively by him.
with conical surfaced members 66, 60a arranged
2. A telephone sub-set assembly comprising in
coaxial with the mouthpiece and serving to assist combination a base, a microphone mounted in
in the re?ection and concentration of the sound. close proximity to said ‘base, a short enlarged 30
A fuller description of this feature is also con
mouthpiece immediately in front of and co-axial
tained in my copending application.
with said microphone and directed in a certain
The mouthpiece I has ?tted centrally within direction away from said base, said mouthpiece
35 its ori?ce an automatic dial 6! held in position
being constructed so as to enable sounds uttered
by means of the cylindrical mounting extension at a distance of 10 to 20 inches away from and in 35
62 of the outermost conical member 60. The front of the open end to generate speech cur
inner end of the mouthpiece is connected to a rents of normal strength with a minimum of
carbon granule transmitter 53 and is ?xed to a distortion, a receiver, an extendible and col
40 base 55 by means of a bracket 65. '
lapsible support for said receiver secured at one
A rounded housing 65 is ?tted over the micro
end to said base at a point located substan 40
phone and the associated mechanism to form a tially on the axial line of said microphone and
neat and protected construction. The dial con
mouthpiece and normally supporting said re
nections are carried through the mouthpiece by ceiver alongside said microphone to form a com
means of an insulated tube 57 to a terminal block. . pact unit when not in use and extendible to a dis
The mouthpiece is provided with a suitable dust
protecting screen or the like while the receiver
58 is carried by a telescopic arm 59 of similar
construction to that previouslydescribed with
50 reference to Figs. 1, 2 and 3.
The mechanism for agitating the carbon
granules of the microphone is similar to that
previously described but is in this instance oper
ated by means of a push rod 10 passing through
55 the mouthpiece la. The instrument is mounted
upon a bell box ‘H which is itself mounted upon a
turntable 72.
tance of 12 to 24 inches in a direction parallel
with the axial direction of said microphone and
mouthpiece whereby the person using the instru~
ment may be allowed the free use of both hands
and provided with an unrestricted space of 10
to 20 inches between his mouth and the instru 50
ment thereby allowing View and access to a desk
and at the same time permitting the location of
receiver su?iciently close to his ear to ensure that
the incoming speech sounds are heard exclu~
sively by him.
_
The turntable ‘i2 is carried by a
3. A telephone sub-set assembly comprising in
ball race '53 upon a rubber pad ‘M while a clamping
60 member ‘#5 moved by means of the cam 15 is
adapted to secure the instrument in any desired
position. The cam 16 is carried by a shaft 7?
and in close proximity to said base, a housing
mounted upon said base and surrounding said
provided at either end with operating handles 18.
The telescopic arm 69 carrying the receiver 58
65 is attached to rod 79 by means of a taper fric
ticn clutch which is capable of being locked in
the desired position by a locking nut 86. As in the
previous embodiment the receiver is adapted to be
transferred from one side of the instrument to
>
70 the other as desired.
Although various forms of construction have
been described, it will be understood that these
are given only by way of example and that various
modi?cations and additions may be made with—
75 out departing from the invention.
a
4.5
55
combination a base, a microphone mounted upon
microphone, an enlarged mouthpiece immediately 60
in front of and co-axial with said microphone
and projecting outwardly from said housing, a
receiver, and an extendible and collapsible sup- ‘
port for said receiver secured at one end to said
receiver and at its other end to said base im— 65
m-ediately behind said microphone and said hous—'
ing, said support normally holding said receiver 1
immediately alongside said mouthpiece and hous
ing to form a compact unit when not in use and 70
extendible to a distance of 12 to 24 inches in a
direction parallel to the axial direction of said
mouthpiece and microphone.
.
4i. A telephone sub~set assembly comprising in
combination a base, a microphone secured to said
4
2,131,529
base at a ?xed angle and directed away from said
base, a housing surrounding said microphone and
secured to said base, an enlarged mouthpiece in
support arm secured at one end to an upward ex
front of and co-axial with said microphone per
mitting generation of normal intensity speech
currents by said microphone by speech uttered at
10
tension of said base at a point immediately behind
said microphone and substantially upon the said
axial direction thereof when produced rearwardly
and gimbal means for carrying said receiver upon
the outer end of said telescopic tubular support.
10. A telephone sub-set assembly as claimed in
10 to 20 inches distant from its open end, and an 7 claim 9 in which the support arm is secured to
automatic dial switch located within the open said upward extension of the base by means of
10
end of said mouthpiece.
5. A telephone sub-set assembly comprising in a friction grip permitting rotation about a hori
combination a hollow base containing bell mech
anism, a microphone secured to the upper sur
face of said hollow base, an enlarged mouth
piece secured in front of and co-axial with said
15 microphone, a receiver, and extendible support
ing means secured at one end to said receiver and
at the other end to said upper surface of said hol
low base.
zontal axis and in which the upward extension
is formed as a swivel support rotatable about a
vertical axis.
11. A telephone sub-set assembly comprising
6. A telephone sub-set assembly comprising in
20 combination a base, a microphone secured direct
ly to said base in close proximity thereto, an en
larged mouthpiece in front of and axially aligned
with said microphone and directed at a ?xed
angle away from said base, a receiver and a tele
25 scopic support arm for said receiver secured at
one end to said base by means permitting adjust
ment of the vertical angle of said telescopic sup
in combination a base plate, a microphone having 15
its major sound response axis directed in an up
wardly inclined direction away from the base,
an enlarged mouthpiece in front of and co-axial
with said microphone axis, a receiver, an ex
tendible support arm consisting of an outer tubu 20
lar member connected at one end to said base
at a point immediately behind said microphone,
and a plurality of nested movable tubes disposed
within said outer tubular member, a circuit mak
ing and breaking device carried by said outer 25
tubular member, the outermost of said nested
movable tubes having means for operating said
port and also the movement bodily of said tele
scopic arm and said receiver from one side of
the microphone to the other.
'1. A telephone sub-set assembly comprising in
combination a base member for sup-porting the
whole assembly without securing means upon a
horizontal surface, a microphone secured upon
circuit making and breaking device by sliding
movement within said outer tubular member so
as to cause the disconnection of the instrument 30
from the line when said outermost movable tube
is in its fully nested position and the innermost
nested tube being connected by a hinged stirrup
member to the said receiver.
12. A telephone sub-set assembly as claimed 35
the
upper
surface
of
said
base
member,
an
en
35
in claim 11, in which the outermost nested mov
larged mouthpiece in front of and co-axial with able tube is provided with a manual grip member
said microphone and arranged with its open end whereby the said nested member may be moved
directed in an upwardly inclined direction away to control the line switching directly and not
from said base member, a receiver and extendible through the intermediary of the other nested 40
40 means for supporting said receiver at a distance
from said base member and microphone in a members.
13. A sub-set assembly for use in automatic
direction substantially the same as that of the telephone systems comprising a base plate, a
open end of the mouthpiece, said supporting microphone secured to said base plate, an en
means being secured to said base at a point imme
larged sound collecting mouthpiece in front of 45
said microphone for increasing the response dis
45 diately behind said microphone so that said ex
tendible means may be arranged to locate the re
tance thereof, a dial switch located in the enlarged
ceiver carried thereby at any point along a path
open end of said mouthpiece and a sound reflect
close to and parallel with the direction of the ing member disposed immediately behind said
open end of said mouthpiece and allows of the
50
switch within the mouthpiece.
compact location of the receiver close alongside dial
14. A telephone sub-set assembly comprising
50 the microphone and mouthpiece in the out of use
position of the instrument.
8. A telephone sub-set assembly comprising in
combination a base member, a microphone se
155 cured to the uppersurface of said base member,
an enlarged mouthpiece for extending the sound
response distance of said microphone said mouth
piece having its open end directed in an upwardly
inclined direction away from said base, a receiver
60 and an extendible and collapsible supporting‘
means secured at one end to said base member
at a point behind said mouthpiece and substan
tially in alignment with the direction of the open
end of the mouthpiece so as to enable the re
65 ceiver to be located at any point along a path
adjacent to and parallel with the said mouthpiece
direction up to a distance within the extended
response distance of said microphone.
9. A telephone sub-set assembly comprising a
base, a microphone secured thereon with its axial
and major sound response direction upwardly in
. in combination a base, a microphone mounted in
close proximity to said base, a mouthpiece am
pli?er for said microphone having a passage
therethrough with alternate surface portions 55
thereof disposed parallel to the direction of said
passage and inclined at 45° thereto for collect
ing sounds at its open end and transmitting them
in intensi?ed form with the minimum of dis
tortion to the transmitter so as to enable sounds 60
uttered at a distance of 10 to- 20" away from and
in front of the open end to generate speech cur
rents of normal strength with a minimum of dis
tortion, a receiver, an extendible and collapsible
support for said receiver secured at one end to 65
said base in close proximity to said microphone
and normally supporting said receiver alongside
said microphone to form a compact unit when
not in use and extendible to a distance of 12 to 24
inches in a direction parallel with the axial di 70
rection of said microphone and mouthpiece
whereby the person using the instrument may
clined away from said base, a mouthpiece hav
be allowed the free use of both hands and pro
ing an enlarged open frontal end arranged in' vided with an unrestricted space of 10 to 20
front of and co-axial with said axial direction of inches between his mouth and the instrument
75 said microphone, a receiver, a telescopic tubular
- 75
2,131,529
thereby allowing view and access to a desk and
at the same time permitting the location of re
ceiver suiiiciently close to his ear to ensure that
the incoming speech sounds are heard exclusively
. by him.
15. A telephone sub-set assembly comprising in
combination a base, a microphone secured to said
base at a ?xed angle and directed away from
said base, a housing surrounding said microphone
and secured to said base, an enlarged mouth
piece ampli?er for said transmitter having a par
titioned passage therethrough the surfacesof
which passage and of the partitions of said pas
sage being all parallel to the axis of the mouth
piece or inclined at 45° thereto for collecting
sounds at its open end and transmitting them
in intensi?ed form with the minimum of distor
tion to the transmitter for permitting generation
of normal intensity speech currents by said
microphone to speech uttered at 10 to 20 inches
distant from its open end and an automatic dial
switch located within the open end of said mouth
piece.
16. A telephone sub-set assembly comprising
in combination a base, a microphone secured di
rectly to said base in close proximity thereto, a
5
"
inclined at 45° to the axis, a receiver and a
telescopic support arm for said receiversecured
at one end to said base by means permittingxade ' ' '
justmentof the vertical angle of said telescopicpx
support and also the movement bodily of said
telescopic arm and said receiver from one side of
the microphone to the other.
17. A telephone sub-set assembly comprising '
in combination a base member, a microphone se
cured to the upper surface of said base member,
an enlarged mouthpiece ampli?erfor extending
the sound response distance of said microphone,
said mouthpiece having its open end directed in
an upwardly inclined direction away from said
base and having a partitioned passage there
through the surfaces of which passage and of the
partitions therein being all parallel to the axis
of the mouthpiece or inclined at 45° thereto with
internally disposed members locatedcentrally in
said passage and having surfaces inclined at 45°
20
to said axis, a receiver and an extendible and col
lapsible supporting means secured at one end to
said base member at a point behind said mouth
piece and substantially in alignment with the
direction of the open end of the mouthpiece so
mouthpiece ampli?er in front of and axially - as to enable the receiver to be located at any
aligned with said microphone and directed at a point along a path adjacent to and parallel .with
?xed angle away from said base, said ampli?er the said mouthpiece direction up to a distance
within the extended response distance ofrsaid
150 having a passage with the surfaces of alternate ‘ microphone.
portions thereof parallel to its axis and inclined
at 45° thereto and internally disposed surfaces
'
DQUGLAS- STUART SPENS ‘STEUART.
.30
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