U.S. patent number 3,781,492 [Application Number 05/290,905] was granted by the patent office on 1973-12-25 for headset.
This patent grant is currently assigned to International Standard Electric Corporation. Invention is credited to Anthony C. Batchelor, Ronald D. Carter, William D. Cragg, Leslie E. B. Dymoke-Bradshaw.
United States Patent |
3,781,492 |
Cragg , et al. |
December 25, 1973 |
HEADSET
Abstract
A headset includes a main housing containing a miniature
demountable earphone, a microphone pre-amp and a snap-on earpiece.
The housing is connected to one end of an adjustable boom having a
pressure gradient microphone at the other end. The microphone has a
piezoelectric disc transducer mounted midway from either end of a
cylindrical housing and perpendicular thereto, the cylinder halves
being separate acoustic resonators of predetermined frequency to
provide an upper limit of operation.
Inventors: |
Cragg; William D. (Harlow,
EN), Dymoke-Bradshaw; Leslie E. B. (Edgeware,
EN), Batchelor; Anthony C. (London, EN),
Carter; Ronald D. (Warwick, EN) |
Assignee: |
International Standard Electric
Corporation (New York, NY)
|
Family
ID: |
10450584 |
Appl.
No.: |
05/290,905 |
Filed: |
September 22, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Oct 21, 1971 [GB] |
|
|
48,953/71 |
|
Current U.S.
Class: |
379/430;
381/173 |
Current CPC
Class: |
H04R
1/105 (20130101); H04R 1/08 (20130101); H04R
17/02 (20130101); H04R 5/0335 (20130101); H04R
1/1016 (20130101) |
Current International
Class: |
H04R
1/10 (20060101); H04m 001/05 (); H04r 001/28 () |
Field of
Search: |
;179/156A,121D,180 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cooper; William C.
Claims
We claim:
1. A pressure gradient microphone for a communications headset,
including a housing of molded plastic formed as a hollow cylinder
with both ends apertured for the ingress of sound but otherwise
substantially closed and a piezoelectric disc transducer element
inside the housing with its major surfaces normal to the
longitudinal axis of the housing, in which the disc is mounted
halfway along the cylinder by an endless ring seal between its edge
and the adjacent inside surface of the housing, and in which the
apertured cylinder halves on each side of the disc are acoustic
resonators at a predetermined frequency to provide an upper limit
of the microphone output at said frequency.
2. A microphone as claimed in claim 1, and in which the ring seal
is of rubber or a rubber-like material such as not to apply rigid
edge clamping to the disc.
3. A microphone as claimed in claim 1, and in which the cylinder
halves on each side of the disc contain open celled plastic foam to
provide acoustic resistance.
4. A microphone as claimed in claim 1, and in which the transducer
element comprises a piezoelectric disc with an electrode on each
major surface thereof, and a second disc of equal acoustic
stiffness attached face to face with the piezoelectric disc.
5. A microphone as claimed in claim 4, and in which the second disc
is a flexible metal disc.
6. A microphone as claimed in claim 1, in which the housing is
divided transversely with respect to the longitudinal axis of the
cylinder into two open ended parts, a casing and a cap, which snap
fit together, in which the ring seal secures the disc to the casing
part at its open end, and in which electrical connection wires from
the disc are led out of the housing through the casing part.
7. A microphone as claimed in claim 6, in which a portion of the
cap part near its open end having its wall thickness reduced from
the outside projects into a portion of the casing part near its
open end having its wall thickness reduced from the inside, and in
which the reduced end portion of the cap part is shorter than the
reduced end portion of the casing part thus providing a groove in
the inside surface of the housing in which the disc is located.
8. A communications headset having a pressure gradient microphone
at the outer end of a boom, in which the boom is a tube carrying
the microphone cable inside it, in which the longitudinal axis of
the boom towards its outer end is coincident with the longitudinal
axis of the microphone housing, and in which the boom and
microphone configuration is such that when the apertured cylinder
end of the microphone furthest from the boom is positioned in front
of one corner of the user's mouth, then the apertured cylinder end
of the microphone adjacent the boom is displaced away from the
user's mouth.
9. A communications headset as claimed in claim 8, in which the
boom and microphone are held together by the outer end of the boom
tube fitting into an integral tubular extension from the closed end
of the casing part of the microphone housing, in which the
electrical connection wires of the microphone are led through a
hole in the casing closed end into the tubular extension and hence
to the microphone cable in the boom tube, and in which the tubular
extension is of smaller section than the casing part of the housing
with sound ingress apertures being provided in the casing closed
end outside the tubular extension.
10. A communications headset having an insert type earphone and a
microphone, and adapted to be worn by pressure against both sides
of the user's head exerted via an under-the-chin band; in which one
end of the under-the-chin band is attached to a main housing which
contains the insert earphone, the housing and under-the-chin band
being adapted, together with an earpiece, to position the insert
earphone acoustic outlet opposite the user's ear canal; in which a
tube associated with the microphone has one end attached to the
main housing and is adapted to extend adjustably around the user's
face towards his mouth; and in which the headset cable for
connection to the earphone and microphone has one end attached to
the main housing.
11. A headset as claimed in claim 10, in which the under-the-chin
band, microphone tube and headset cable are attached to the main
housing by extending into three tubular cavities in a lower portion
of the housing, and in which the earphone is in an upper portion of
the housing at the front of a tubular cavity whose axis is
perpendicular to the microphone tube cavity in the lower
portion.
12. A headset as claimed in claim 11, in which the microphone tube
is a one-piece boom carrying the microphone at its lower end near
the user's mouth, in which the upper portion of the boom is
slidable up and down in its tubular cavity in the main housing, and
in which a cable from the microphone is carried within the boom up
into the main housing where it is led radially into a cylindrical
cavity whose axis perpendicular to the tubular cavity holding the
upper end of the boom and out of said cylindrical cavity on its
axis, the arrangement being such that when the boom is pushed in
the upper end of the microphone cable moves into the cylindrical
cavity and is accommodated around its periphery.
13. A headset as claimed in claim 12, and in which the upper
portion of the boom and the main housing tubular cavity in which it
is accommodated are adapted to allow the boom to be rotated around
its own axis through less than one full turn.
14. A headset as claimed in claim 13, in which the upper portion of
the boom has a radial projection at its top end, and in which the
tubular cavity holding the upper portion of the boom has a portion
extending for part of its length with a sector of diameter greater
than the boom to accommodate said radial extension at the top of
the boom, the length and the sector size of said portion being
adapted together with said radial extension to limit the sliding
and rotative movements respectively of the boom.
15. A headset as claimed in claim 12, in which the main housing is
a two-part molded plastic comprising a cover portion on the back of
a casing portion, in which the tubular cavity holding the upper
portion of the microphone boom is formed by a groove in the back of
the casing and a cooperating groove in the cover, and in which the
cylindrical cavity accommodating the upper end of the microphone
cable is partly formed by a recess in the cover.
16. A headset as claimed in claim 15, and in which the cylindrical
cavity accommodating the upper end of the microphone cable is
coaxial with the tubular cavity at the front of which the insert
earphone is located.
17. A headset as claimed in claim 16, and in which a microphone
preamplifier is housed behind the insert earphone.
18. A headset as claimed in claim 15, and in which the two tubular
cavities in the main housing into which extend the under-the-chin
band and headset cable respectively are side by side in a separate
plane from the tubular cavity holding the upper portion of the
microphone boom.
19. A headset as claimed in claim 10, and in which the
under-the-chin band is detachably attached to the main housing so
that use as a handset is enabled by the removal of the
under-the-chin band.
20. A communications headset comprising a one-piece boom which
mounts a microphone at its lower end, wherein the upper portion of
the boom is slidable up and down in a tubular cavity in a main
housing, and a cable from the microphone is carried within the boom
up into the main housing where it is led radially into a
cylindrical cavity whose axis is perpendicular to the tubular
cavity holding the upper end of the boom and out of said
cylindrical cavity on its axis, whereby when the boom is pushed in,
the upper end of the microphone cable moves into the cylindrical
cavity and is accommodated around its periphery.
Description
This invention relates to headsets for use by telephone operators
or other persons using communications systems in a handsfree
manner.
SUMMARY OF THE INVENTION
The invention provides a pressure gradient microphone for a
communications headset, including a housing of molded plastics
formed as a hollow cylinder with both ends apertured for the
ingress of sound but otherwise substantially closed and a
piezoelectric disc transducer element inside the housing with its
major surfaces normal to the longitudinal axis of the housing, in
which the disc is mounted halfway along the cylinder by an endless
ring seal between its edge and the adjacent inside surface of the
housing, and in which the apertured cylinder halves on each side of
the disc are acoustic resonators at a predetermined frequency to
provide an upper limit of the microphone output at said
frequency.
According to the invention there is also provided a communication's
headset having a microphone at the outer end of a boom, in which
the microphone is as described in the previous paragraph, in which
the boom is a tube carrying the microphone cable inside it, in
which the longitudinal axis of the boom towards its outer end is
coincident with the longitudinal axis of the microphone housing,
and in which the boom and microphone configuration is such that
when the apertured cylinder end of the microphone furthest from the
boom is positioned in front of one corner of the user's mouth then
the apertured cylinder end of the microphone adjacent the boom is
displaced away from the user's mouth.
The invention further provides a communications headset having an
insert type earphone and a microphone, and adapted to be worn by
pressure against both sides of the user's head exerted via an
under-the-chin band; in which one end of the under-the-chin band is
attached to a main housing which contains the insert earphone, the
housing and under-the-chin band being adapted, together with an
earpiece, to position the insert earphone acoustic outlet opposite
the user's ear canal; in which a tube associated with the
microphone has one end attached to the main housing and is adapted
to extend adjustably around the user's face towards his mouth; and
in which the headset cable for connection to the earphone and
microphone has one end attached to the main housing.
According to the invention there is still further provided a
communications headset, in which a one-piece boom carries a
microphone at its lower end, in which the upper portion of the boom
is slidable up and down in a tubular cavity in a main housing, and
in which a cable from the microphone is carried within the boom up
into the main housing where it is led radially into a cylindrical
cavity whose axis is perpendicular to the tubular cavity holding
the upper end of the boom and out of said cylindrical cavity on its
axis, the arrangement being such that when the boom is pushed in
the upper end of the microphone cable moves into the cylindrical
cavity and is accommodated around its periphery.
BRIEF DESCRIPTION OF THE DRAWINGS
A communications headset according to the invention will now be
described with reference to the accompanying drawings, in
which:
FIG. 1 shows a front view of the headset;
FIG. 2 shows a longitudinal section view of the main housing of the
headset, also showing the earphone and the upper portion of the
microphone boom;
FIGS. 3 and 4 show a side view and an underneath view respectively
of the main housing;
FIG. 5 shows a side view, in the direction of the arrow A on FIG.
2, of the cover part of the main housing and indicates the
microphone cable when the microphone boom is in the fully retracted
position, and FIG. 5A shows again the top part of the main housing
cover in order to indicate the position of the microphone cable
when the microphone boom is in the fully extended position;
FIG. 6 shows a side view, in the direction of arrow B on FIG. 2, of
the casing part of the main housing;
FIG. 7 shows a longitudinal section view of the casing and cap
portions of the microphone housing, enlarged with respect to FIG.
1; and
FIG. 8 shows the construction of the piezoelectric disc transducer
element incorporated in the microphone, enlarged with respect to
FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, the headset includes a main housing 10
which locates against one side of the user's head. A detachable
earpiece 11 clips onto the acoustic outlet nipple of an insert
earphone contained in the housing 10. A boom tube 12 extends from
the lower end of the housing 10 and is adjustably adapted to extend
around the user's face towards his mouth. At the outer end of the
boom 12 is a microphone 13. The headset cable 14 for connection to
the earphone and microphone has one end attached to the housing 10
from where it can hang freely to a dress clip when the headset is
in use. One end of an under-the-chin band 15 is attached to the
main housing 10. The headset is adapted to be worn by pressure
exerted against both sides of the user's head via the band 15; the
housing 10 and the band 15 being adapted, together with the
earpiece 11, to position the insert earphone acoustic outlet
opposite the user's ear canal.
Referring now to FIGS. 2 to 6, the main housing is a two-part
plastics molding comprising a cover portion 16 on the back of a
casing portion 17. The cover 16 and casing 17 are held together in
any convenient manner, preferably by undercutting one of the parts
to form a male portion so that it snap fits into the other part
forming a female portion with an adhesive to complete the fixing.
The microphone boom 12, headset cable 14, and under-the-chin band
15 are attached to the main housing by extending into three
parallel tubular cavities 18,19,20 respectively in a lower portion
of the housing, and the earphone 21 is in an upper portion of the
housing at the front of a tubular cavity 22 whose axis is
perpendicular to the three tubular cavities in the lower
portion.
The insert earphone 21 is a magnetic diaphragm electro-acoustic
transducer of the miniature "button" type as used with hearing
aids. As shown in FIGS. 2 and 3 it is located at the front of the
housing cavity 22 by a lip 171 of the casing over the otherwise
exposed front cover 211 of the earphone 21 with the acoustic outlet
nipple 212 at the center protruding in front of the casing lip 171.
As shown in FIG. 2 the earphone 21 is without its usual back cover,
a ring 23 with a disc (not shown) behind it holding it and
providing an air volume behind the earphone diaphragm. The earphone
21, ring 23 and disc are assembled into the casing 17 from the
rear. In one alternative arrangement a complete earphone (i.e. with
its back cover) is used, inserted into the casing 17 from the front
of the cavity 22 and held in place by a turned-over lip which could
be broken to enable the earphone to be replaced complete if
necessary. As already described with reference to FIG. 1, the
detachable earpiece 11 clips directly onto the outlet nipple 212 of
the earphone 21. As shown in FIG. 1, the earpiece 11 has a small
diameter end portion 111 to enable a fit against the user's ear
canal. In an alternative arrangement, the earpiece could have a
larger diameter end portion to fit the outer ear; some people will
find this more pleasant to use and it also provides a good
seal.
As already described, the microphone boom 12 is a one piece
plastics tube whose upper portion is located in the tubular cavity
18 in the main housing. The cavity 18 is formed by a groove 161 in
the cover 16 whose constant diameter is a sliding fit around the
boom tube 12, and a cooperating groove in the back of the casing 17
which consists of a lower portion 172 of the same diameter as the
groove 161 and an upper portion 173 of greater diameter. Inserted
in the top of the tube 12 is a stem having a top portion of the
same diameter as the tube 12 except for a radial projection 121
(see FIG. 2) which is a sliding fit in the increased diameter
groove 173. Thus the boom tube 12 is slidable up and down in the
cavity 18 over a distance equal to the length of the groove portion
173 less the length of the radial projection 121 i.e. about two
centimeters. Also the boom tube is rotatable around its own axis
through an angle determined by the distance around the periphery of
the groove 173 less the thickness of the radial projection 121,
i.e. about 150 degrees. This angle of rotation is sufficient for
the microphone to be put forward of whichever ear the headset main
casing is mounted on, and together with the 2 centimeters range for
extension and retraction enables the microphone to be positioned by
any user just in front of the corner of the lips.
A microphone cable 122 (see FIGS. 5 and 5A) from the microphone 13
is carried within the boom tube 12 into the cavity 18 in the main
housing from where it is led through the groove 162 in the cover 16
radially into a cylindrical cavity 24 (see FIG. 2) which is coaxial
with and the same diameter as the cavity 22 at the front of which
the earphone 21 is located. The cavity 24 is formed between a
recess 163 in the cover 16 and a plate 25 located in the back of
the cavity 22, and the microphone cable 122 is led out of the
cavity 24 on its axis through a hole in the center of the plate 25.
In an alternative construction, where the earphone 21 inserted into
the casing 17 from the front, the plate 25 can be formed integrally
with the back of the casing 17.
In the fully retracted position of the boom 12, as shown in FIG. 5,
the microphone cable 122 goes up and then right around the
periphery of the cavity 24. When the boom 12 is pulled down to its
extended position, the cable 122 is pulled through the guide groove
162 in the cover 16 and comes to the dashed line position shown on
FIG. 5A. When the boom 12 is pushed back again the cable spiral
automatically expands. In this way 2 centimeters of cable is
accommodated in a small space without becoming tangled.
It will now be appreciated that the main reason for the arrangement
which limits the rotative movement of the boom 12 to less than one
full turn (in fact 150.degree. as previously described) is to
prevent continuous turning of the boom 12 which would eventually
break the microphone cable 122. Without this limitation, continuous
turning could occur by the user turning the boom 12 forward to get
it in front of his mouth when putting on the headset, then turning
further forward to remove the headset, then all the way round
(instead of back) when next putting the headset on.
The microphone on the end of the boom 12 will now be described in
detail with respect to FIGS. 1 and 7. The microphone housing is
formed as a hollow cylinder of circular cross-section. The housing
is divided transversely with respect to the longitudinal axis of
the cylinder into two open ended parts, a casing 31 and a cap 32.
The casing 31 has a portion 311 near its open end having its wall
thickness reduced from the inside and a circular rib 312 projecting
inwardly therefrom. The cap 32 has a portion 321 near its open end
having its wall thickness reduced from the outside and a circular
groove 322 in its outer surface. The casing 31 and cap 32 snap fit
together by the cap portion 321 projecting into the casing portion
311 with the groove 322 fitting over the rib 312, and are keyed by
a peg 323 on the cap 32 fitting in a recess 313 in the casing 31.
The reduced end portion 321 of the cap 32 is shorter than the
reduced end portion 311 of the casing 31 thus providing a groove in
the inside surface of the housing in which a piezoelectric disc
transducer element 33 is located with its major surfaces normal to
the longitudinal axis of the housing.
On assembly, before fitting the cap 32 onto the casing 31, the
transducer element 33 is mounted in the casing 31 by an edge
encircling thin filler 34 of soft rubber or rubber like material
which seals the element 33 to the adjacent inside surface of the
cylinder. The seal 34 does not apply rigid edge clamping to the
element 33 so providing good attenuation of mechanical vibrations
between the housing and the element 33. Electrical connection wires
331a, 331b from the element 33 are led through a hole 315 in the
wall 314 which closes the casing part 31 of the microphone housing
into a tubular extension 35 integral with the wall 314 and hence to
the microphone cable in the boom tube 12 which fits into the
tubular extension 35. The wire 331a extends from the center of the
back of the element 33 and the wire 331b extends from the edge of
the element 33 through a notch 36 in the inside surface of the
casing 31 adjacent the element 33.
The tubular extension 35 is of smaller section than the casing 31
and six sound ingress apertures 316 are provided in the sloping
portion of the casing end wall 314 outside the tubular extension.
Six sound ingress apertures 325 are also provided on the periphery
of the wall 324 which closes the cap part 32 of the microphone
housing. The cylinder end walls 314 and 324 are equidistant from
the element 33. The microphone housing cylinder has a length
(between the end walls 314 and 324) of about 32 millimeters and a
diameter of about 9 millimeters, and the element 33 has a diameter
of about 7 millimeters and a thickness of about 1 millimeter. The
apertured cylinder half on each side of the element 33 forms an
acoustic resonator at 4,000 Hz to provide an upper limit of the
microphone output at this frequency.
The transducer element 33 will now be described in more detail with
reference to FIG. 8. A thin disc 332 of piezoelectric ceramic
material (lead-zirconate-titanate) has electrodes 333 and 334
applied as by evaporation (or by painting) to the major surfaces
thereof. The material of the electrodes 333 and 334 is typically
gold, nichrome or silver and in intimate contact with the disc
surface. After application of the electrodes, the disc is polarized
by subjection to a voltage via the electrodes of the order of 25KV
per cm through the thickness of the disc, so that a voltage
difference will appear between the electrodes when the disc is
stretched radially.
The electrodes 333 and 334 cover the whole of the respective major
surface of the disc almost to the periphery thereof, and the disc
is mechanically bonded and electrically connected face to face with
a thin flexible metal disc 335 typically of aluminum, brass or
nickel iron, e.g. Permalloy D, about equal in thickness to the
piezoeletric disc 332 and having an acoustic stiffness equal to the
acoustic stiffness of the disc 332. The latter disc 332 is as thin
as can conveniently be made, about 0.002 inches to 0.0025 inches.
The lead wire 331a is attached to the electrode 333 at the face of
the ceramic disc 332, and the lead wire 311b is attached to the
edge of metal disc 335 and the electrode 334.
The composite disc 332, 335 together with electrodes 333 and 334
and lead wires 331a and 333b, constitute the piezoelectric disc
transducer element 33 of the microphone 13.
Referring back to FIG. 1, the longitudinal axis of the boom 12
towards its outer end is coincident with the longitudinal axis of
the microphone 13, and thus the boom and microphone confirguration
is such that when the cylinder end of the microphone furthest from
the boom (with apertures 325) is positioned in front of one corner
of the user's mouth then the cylinder end of the microphone
adjacent the boom (with apertures 316) is displaced sideways away
from the user's mouth.
The microphone 13 is equally open to speech sounds at the two sets
of apertures 325 and 316, so it is responsive to the pressure
gradient between the two sets of apertures and the transducer
element 33 is driven by the pressure difference between its two
faces. Sound waves arriving at some distance greater than 1 foot
due to ambient noise produce very little pressure difference across
the element 33 at frequencies where the wavelength is large
compared to the distance between back and front surfaces i.e. for
all frequencies up to about 5,000 Hz. However with the apertures
325 very near the lips, the microphone is in the region of
spherical wave propagation from the mouth and the well known bass
boost effect comes into operation whereby the pressure gradient
increases with decreasing frequency below 5,000 Hz. That is to say
that the user's speech sounds are boosted compared to far sounds
and so the microphone is noise cancelling. The element 33 should
have its first resonant mode in the upper range of the speech band,
between 3,500 Hz and 6,000 Hz to give a smooth response over the
whole speech band.
Since the microphone 13 is used very near the mouth, normal air
blasts of speech will tend to produce turbulent flow round the
cylinder housing. The noises of turbulence, "blasting" are greatly
reduced by the provision of open celled plastics foam, e.g. of
polyurethane, (not shown) behind the apertures in the cylinder
halves on each side of the element 33. This added acoustic
resistance has a two fold effect: firstly it reduces the
unidirectional air flow impinging directly on the element, and
secondly it reduces the sharp edges which generate turbulence.
Referring now back to FIG. 2, the microphone cable which is led
through the center of the plate 25 is connected to a pre-amplifier
26 (shown in dotted outline), constructed as a printed circuit
board disc on which components are mounted and located in the
cavity 22 behind the earphone 21. The piezoelectric transducer
microphone 13 is a high impedance device, and the purpose of having
the pre-amplifier 26 in the headset main housing is to raise the
microphone output signals to a level such that they are not subject
to undue interference along the headset cable 14. At the other end
of the headset cable the pre-amplifier output is fed into another
amplifier the output of which will match the microphone to the
characteristics of the communication circuit to which the headset
is connected, e.g. an operator's circuit in a telephone
exchange.
The headset cable 14 enters the main housing through the tubular
cavity 19 in the casing 17 in front of the groove 173 forming part
of the tubular cavity 18 which holds the microphone boom 12. The
top of the cable 14 has a grommet arranged to snap fit into the
casing 17 by a bayonet action. The headset cable contains five
wires; two to supply input signals to the earphone 21, two to take
the microphone output signals from the pre-amplifier 26, and one to
carry the necessary power supply for the pre-amplifier 26.
Connection of these five wires from the earphone 21 and
preamplifier 26 is made in the cavity 27, between the cavities 19
and 22, provided by a recess 174 (see FIG. 6) in the casing 17. A
terminal block for this purpose can be provided by five connector
pins insert molded into the casing 17 and projecting into the
cavity 27.
The under-the-chin band 15 is a plastics tube having one end
inserted into the hole 20 in the casing 17 by the side of the hole
19 holding the top end of the headset cable. The other end of the
tube 15 fits into a plastics molded holder 40 (see FIG. 1) having a
peg 41 on which a face pad 42 is retained. The tube 15 is shaped so
that it opens out when worn and exerts sufficient pressure to hold
the earpiece 11 into the ear on one side of the user's head and the
face pad 42 to the bony part of the face in front of the ear on the
other side of the user's head.
As an alternative to the face pad 42 an earpiece similar to the
earpiece 11 can be retained on the peg 41 of the holder 40. Such an
earpiece will hold the headset more securely to the head than the
face pad 42 and may be preferred by some users; in this case
coaxial holes through the holder 40 and the earpiece will maintain
the ability of the user to listen to his surroundings while using
the headset. Otherwise, the headset can be provided with a double
earphone configuration. In this case the holder 40 will be replaced
by a differently shaped molding adapted to hold the second
earphone, which will also be of the insert type with an earpiece
similar to the earpiece 11 clipped directly onto its outlet nipple,
and the wires to this second earphone will be retained inside the
tube 15.
The first mentioned end of the under-the-chin band 15 is simply
stuck by adhesive into the hole 20 so that it is at the correct
angle with respect to the housing 10 for when it is worn. An
alternative fixing for the under-the-chin band 15, which can be
employed with the single earphone version of the headset, is to
provide a snap fitting arrangement between the band 15 and the hole
20 (with means for keying them at the correct angle) so that the
user can detach the band 15 at will. In the absence of the band 15
convenient use as a handset is enabled simply by holding the
housing 10 to one side of the head with the earpiece 11 in the
ear.
It is to be understood that the foregoing description of specific
examples of this invention is made by way of example only and is
not to be considered as a limitation on its scope.
* * * * *