An electro-acoustic transducer includes a housing enclosing an electro-acoustic transducer device and having an opening by which the diaphragm side of the transducer device is exposed to the outside, and a ring provided to the outer surface of the perimeter of the opening. The outer perimeter of the ring is adapted to be softer and more pliable than the housing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an electro-acoustic transducer advantageously 
applied to a small-sized earphone unit, headphone unit or a small-sized 
microphone unit. 
2. Description of the Prior Art 
As the electro-acoustic transducer of the type in which a housing enclosing 
an electro-acoustic transducer device is inserted into and attached within 
the ear's concha, when the transducer is in use, there is proposed in the 
art a so-called inner ear type headphone unit. 
Such headphone apparatus is shown in FIG. 1 and includes a housing 102 
enclosing a speaker unit which is the electro-acoustic device. This 
housing 102 is formed with a size such that it can be introduced into the 
ear's concha and has an open sound-radiating surface of the speaker unit 
101. A connecting cord 103 supplying acoustic signals to the speaker unit 
101 has its ends 104 connected as by soldering to input terminals 105 of 
the speaker unit 101. The connecting cord 103 is fed out of the housing 
102 to the outside by way of a cord extraction opening 106. 
An ear pad ring 107 is provided on the portion of the housing 102 facing to 
the ear's concha and on the perimeter of the front side of the speaker 
unit 101. This ear pad ring 107 is engaged with a rib 102a provided on the 
perimeter of the open portion of the housing 102, and is attached to this 
portion by auxiliary securing means, such as adhesive. 
The housing 102 is formed of a relative hard material in consideration that 
it has to hold the speaker unit 101 in position and for providing certain 
acoustic effects. On the other hand, the ear pad ring 107 is formed of a 
relatively soft material for providing good contact feel with the inner 
wall of the ear's concha and insertion of the ring into the ear's conchae 
of different sizes. 
In order that the portion of the connection cord 103 extracted through the 
extraction opening 106 may be protected from accidents such as cord 
breakage caused by repeated cord flexure, a cylindrical cord strain-relief 
bushing 108 is provided on the housing 102 extending from the cord 
extraction opening 106. The cord bushing 108 is formed of a relatively 
soft material, similar to the ear pad ring 107, and is provided with 
peripheral slots 109 to allow the bushing 108 to flex easily. The portion 
of the connection cord 103 extracted through the cord extraction opening 
106 may be bent smoothly as it is encased within the cord bushing 108 when 
a stress is applied from outside to prevent breakage of the cord at the 
edge of the cord extraction opening 106. 
In the operation of the above described headphone unit, when the housing 
102 is introduced into the ear's concha, the ear pad ring 107 is deformed 
under a pressure applied from the inner wall of the ear's concha. The ear 
pad ring 107 is adapted to close the ear's concha completely by abutting 
on the inner wall of the ear's concha by its own resiliency. With the 
ear's concha thus closed completely, the sound may be reproduced by the 
speaker unit 101 with optimum electro-acoustic characteristics. 
In will be noted that, since the size of the ear's conchae will differ from 
one person to another, it may occur that the above described headphone 
unit cannot be introduced into the ear's concha, or the ear's concha 
cannot be closed satisfactorily by the ear pad ring 107, with the result 
that optimum acoustic characteristics are not obtained. 
That is, with the outside diameter d.sub.1 of the ear pad ring 107, the ear 
pad ring cannot be deformed to an outside diameter d.sub.0 of the rib 
102a. Therefore, when the ear's concha has an inside diameter less than 
the outside diameter d.sub.0 of the rib 102a, the housing 102 cannot be 
introduced into the ear's concha. On the other hand, when an ear's concha 
has the inside diameter larger than the outside diameter of the ear pad 
ring 107, a void or gap is formed between the ear pad ring 107 and the 
inner wall of the ear's concha, so that the ear's concha is not closed 
completely. 
When the ear's concha is not closed completely in this manner, the output 
is lowered especially in the lower frequency range of the acoustic 
characteristics, as shown at C in FIG. 9, with result that optimum 
electro-acoustic characteristics cannot be realized. 
It is noted that the acoustic characteristics shown at B in FIG. 9 are 
those obtained when the ear's concha is closed as normally in the above 
described conventional headphone unit. 
For maintaining the optimum acoustic characteristics as described above, it 
is necessary that the ear pad ring 107 be formed of a softer material and 
with an increased thickness as that it may be deformed radially more 
easily and with a larger amount of deformation. However, when the housing 
102 is mounted to or detached from the ear's concha, a stress is applied 
to the ear pad ring 107 tending to displace the ear pad ring 107 away from 
the housing 102 in the direction shown by arrow F FIG. 1 under the force 
of friction with the inner wall of the ear's concha. When the ear pad ring 
107 is formed of a soft and pliable material, the ear pad ring is deformed 
easily under such stress. When the ear pad ring 107 is deformed under the 
stress in this manner, both the aforementioned engaging and auxiliary 
securing means tend to be loosened so that the ear pad ring may be readily 
detached from the rib 102a. 
In short, when the material of the ear pad ring is formed of a softer 
material, the size range of the ear's conchae into which a given ear pad 
ring can be introduced is enhanced, while the contact feel of the 
apparatus with the ear's concha is improved. However, when the ear pad 
ring is formed of a softer material, the ear pad ring is more likely to be 
detached from the housing, so that of the earphone unit durability is not 
assured. For this reason, the desired durability may only be assured at 
the sacrifice to some extent of the aforementioned acoustic 
characteristics and the use or contact feel. 
The same inconvenience as felt with the ear pad ring arises with the cord 
bushing 108. That is, when the cord bushing is formed of a softer 
material, the connection cord 103 may be protected more reliably, however, 
the cord is more likely to be detached from the housing 102. 
In our copending Japanese Laid-open Patent Publication No. 23299/1987, 
there is proposed an electro-acoustic transducer in which the housing 
enclosing the speaker unit, ear pad ring and the cord bush are molded 
integrally from the same material for facilitating the assembling 
operation and improving the durability. However, in this electro-acoustic 
transducer, since the portion contacting the ear's concha and the housing 
adapted to hold the speaker unit are formed of the same material, the 
material suitable for both the contacting portion and the housing cannot 
be used, such that the contacting portion and the housing need be formed 
of a material having only moderate hardness. 
OBJECT AND SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an 
electro-acoustic transducer free from the deficiencies of the prior-art 
headphone unit. 
It is another object of the present invention to provide an 
electro-acoustic transducer wherein good use feel, positive protection of 
the connection cords and sufficient durability may be achieved. 
It is a further object of the present invention to provided an 
electro-acoustic transducer, such as a headphone unit, wherein the ear pad 
ring or the cord bush are not detached from the housing after repeated use 
of the transducer. 
The above and other objects of the present invention will become apparent 
from the following description especially when read in conjunction with 
the accompanying drawings. 
In accordance with the present invention, there is provided an 
electro-acoustic transducer comprising a housing enclosing an 
electro-acoustic transducer device, said housing including an opening by 
which the diaphragm side of the electro-acoustic transducer device is 
exposed to the outside, and a ring provided to the outer surface of the 
perimeter of said opening and having its outer periphery softer than said 
housing. 
In the electro-acoustic transducer of the present invention, at least the 
outer surface portion of the housing around the opening by which the sound 
radiating side or sound input side of the electro-acoustic transducer unit 
is exposed to the outside is formed of a material other than the material 
of the remaining portion of the housing, so that these portions are formed 
of separate materials different in color and/or material, these materials 
being strongly bonded to each other.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A first embodiment of the present invention in which it is applied to a 
headphone apparatus attached to and used in the ear's concha similarly to 
the above described conventional system, is explained by referring to the 
drawings. 
The headphone unit according to the first embodiment of the present 
invention as shown in FIG. 2 and includes a housing 2 enclosing a speaker 
unit 1 as the electro-acoustic device. 
This speaker unit 1 is provided with a magnetic circuit including a magnet 
and a yoke, a coil bobbin driven by the magnetic circuit, and a diaphragm 
attached to this coil bobbin. The electric signals supplied to the coil 
bobbin are converted into sounds by the vibration of the diaphragm in 
well-known manner. 
The housing 2 is of a size such that it can be introduced into the ear's 
concha, and is provided with an opening 2a so that the sound radiating 
side of the speaker unit 1 is facing to the outside at the opening 2a. A 
connecting cord 3 adapted to supply the electrical signals to the speaker 
unit 1 has its leads 4 connected as by soldering to an input terminals 5 
of the speaker unit 1. The connecting cord 3 is fed out of the housing 2 
to the outside by way of the cord extraction opening 6. 
The housing 2 is shown in FIGS. 2 and 3 and includes a main body 7 covering 
the rear side of the speaker unit 1, an ear pad 8 formed around the 
opening 2a and a cord bushing 9 extending out of the cord lead-out opening 
6. 
Since it is necessary to hold the shape of the housing 2 in its entirety 
and to provide good acoustic effects, the main body 7 is formed of a 
relatively stiff material having the rubber hardness of the order of 90 
degrees, such as ABS resin. 
The ear pad 8 is formed on that portion of the perimeter of the opening 2a 
of the housing 2 that contacts the inner wall of the ear's concha by what 
is called a double-shot molding. 
By "double-shot molding" is meant a method of double injection molding 
including the steps of forming a portion of a first material using a first 
metal mold, placing the portion of the first material in a predetermined 
position of a second metal mold and injecting and molding a second 
material in the second metal mold to form a molded article composed of the 
first and the second materials rigidly connected and united to each other. 
When a two-color injection molding machine is employed, after the portion 
of the first material is molded, the predetermined movable portion of the 
metal mold may be shifted and the second material injected and molded to 
form a molded article formed of two kinds of materials. 
For providing a soft feel on contact of the ear pad 8 with the inner wall 
of the ear's concha, and for making it possible to introduce the ear pad 8 
into the ear's conchae of different sizes, the ear pad 8 is formed of a 
relatively soft and pliable material having a rubber hardness of about 60 
degrees, such as urethane, or an elastomeric material having a still lower 
rubber hardness. The material of the ear pad 8 is of a different color 
from the material of the main body 7. The inner side of the ear pad 8 is 
formed with a slot 8a for holding the speaker unit 1. The speaker unit 1 
is held in position with its peripheral portion received within the slot 
8a. 
The cord bushing 9 is adapted for protecting the portion of the connecting 
cord 3 that is fed out by way of the cord extraction opening 6 from 
breakage caused by repeated flexure, and is formed with a cylindrical 
shape on the line of extension of the cord extraction opening 6. The cord 
bushing 9 is formed by the double-shot molding from the same material as 
that of the ear pad 8. A plurality of annular slots 10 are formed on the 
outer peripheral surface of the cord bushing 9 to permit the cord bushing 
9 to be flexed readily. The portion of the connecting cord 3 that is 
extracted through the cord extraction opening 6 is supported by the cord 
bushing 9 so that it may be bent smoothly as it is sheathed in the cord 
bushing 9 on application of an external force to prevent incidental 
breakage otherwise caused by flexure of the connecting cord in contact 
with the edge of the cord extraction opening 6. 
A through-hole 11 is formed at the portion of main body 7 facing to the 
rear surface of the speaker unit 1. The through-hole 11 is provided for 
improving acoustic effects. The through-hole 11 is surrounded by a 
through-hole frame 12. By providing the through-hole 11 on the rear side 
of the main body 7, optimum frequency response characteristics may be 
produced up to the low frequency range of the frequency response curve 
even for a small-sized speaker unit. The through-hole 11 and the frame 12 
thus make up an acoustic pipe or reflex port adapted for compensating the 
decrease in response in the low frequency range of the frequency response 
curve. The frame 12 is provided mainly for decoration purposes and is 
formed of the same material as the ear pad 8 and the cord bushing 9 by the 
double-shot molding. 
The ear pad 8, cord bushing 9 and the frame 12 are formed simultaneously 
from the same material and are connected with one another by runners 13. 
These runners or ribs are formed for extending along the inner surface of 
the main body 7. 
According to the above described first embodiment of the present invention, 
the molding of the housing 2 in its entirety and optimum acoustic 
properties are assured by the main body 7, while the soft feel of the 
portion of the unit contacting with the ear's concha is assured by the ear 
pad 8 and the cord bushing 9. The main body 7, ear pad 8 and the cord 
bushing 9 are formed by double-shot molding of two different kinds of 
material that are firmly bonded together by virtue of double-shot molding 
and are unlikely to be peeled off from each other after repeated or 
prolonged usages. 
Although the housing of the electro-acoustic transducer in the first 
embodiment of the present invention is formed of two kinds of materials 
that are different in hardness and color, it may also be formed of two 
kinds of materials different only in color or in hardness by the 
double-shot material molding. 
A second embodiment of the present invention will be explained by referring 
to the drawings. FIG. 4 shows a housing 202 and an electro-acoustic 
transducer or speaker unit 201 enclosed in the housing 202. 
The speaker unit 201 includes a magnetic circuit composed of a magnet and a 
yoke, a coil bobbin driven by the magnetic circuit and a diaphragm 
attached to the coil bobbin. The electrical signals supplied to the coil 
bobbin are converted into sounds or voice by the vibrations of the 
diaphragm, in a well-known manner. 
The housing 202 is of a size such that it can be introduced into the ear's 
concha. The side of the housing 202 corresponding to the sound radiating 
side of the speaker unit 201 is formed with an opening 202a. For holding 
the speaker unit 201 in position, and for providing acoustic effects, the 
housing 202 is formed of a relatively stiff material having a rubber 
hardness of about 90 degrees, such as ABS resin. The speaker unit 201 is 
held in position with its peripheral portion fitted in a mating recess 
202b formed on the inner wall of the opening 202a. A connecting cord 203 
supplying electric signals to the speaker unit 201 has its terminal 
portions 204 connected as by soldering to an input terminals 205 of the 
speaker unit 201. The connecting cord 203 is also fed out of the housing 
202 through a cord extraction opening 206. 
For protecting the portion of the connecting cord 203 extracted through the 
cord extraction opening 206 from accidents such as cord breakage caused by 
repeated cord flexure, a cylindrical cord bushing 207 is provided on a 
line of extension of the cord extraction opening 206, as in the 
aforementioned conventional headphone unit. The cord bushing 207 is formed 
of a relatively soft and pliable material and moreover has a plurality of 
annular slots 208 as shown, so that it may be flexed easily. The portion 
of the connecting cord 203 extracted out of the cord extraction opening 
206 is supported by the cord bushing 207 so that it may be flexed smoothly 
as it is encased in the cord bushing 207 when an external force is applied 
thereto. In this manner, the risk of accidents such as the cord breakage 
otherwise caused by the flexure of the cord in contact with the edge of 
the cord extraction opening 206 may be minimized. 
The housing 202 is fitted, as shown in FIGS. 4 and 5, with a ring member 
209 on the perimeter of the opening 202a. This ring member 209 is formed 
by a base ring 210 and an elastic ring 211 provided on the perimeter of 
the base ring 210, as shown in FIGS. 7 and 8. These rings 210, 211 are 
formed by double-shot molding from respective different materials. 
The base ring 210 is formed of the same material as the housing 202, and 
with a toroidal profile with an outside diameter D.sub.0 as shown in FIGS. 
4 and 7. The toroidal or ring-shaped peripheral wall of the base ring 210 
is formed with plural circumferentially extending recesses 210a, as shown 
in FIG. 5, for engaging with mating projections 202c provided on the outer 
wall of the housing 202 about the opening 202a. The spacing between two 
neighboring recesses 210a is formed as a rib 210b. The base ring 210 is 
fitted to the housing 202 in a position with the projections 202C being 
fitted to the recesses 210a. The elastic ring 211 is formed of a material 
having a rubber hardness of, for example, 60 degrees, or of a softer 
material, such as so-called elastomer, having a rubber hardness of 20 to 
40 degrees, and is molded on the outer perimeter of the base ring 210 by 
the above described double-shot molding. The ring 211 has a prescribed 
outside diameter shown at D.sub.1 in FIG. 4. The portion of the elastic 
ring 211 receiving the base ring 210 is recessed to accommodate the base 
ring 210, while the portions of the ring 211 corresponding to the ribs 
210b are formed with tongue-like supporting portions 211a. The elastic 
ring 211 has its one and other peripheral edge surfaces 211b, 211c and the 
supporting portions 211a operatively associated with the peripheral edge 
surfaces and 210c, 210d and the ribs 210b of the base ring 210, as best 
shown in FIG. 6. 
It the above described headphone unit, the outside diameter of the elastic 
ring 211 shown at D.sub.1 in FIG. 4 is selected to be sufficiently larger 
than the size of the largest possible ear's concha of the users, while the 
outside diameter of the base ring 210 shown at D.sub.0 in FIG. 4 is 
selected to be sufficiently smaller than the size of the smallest possible 
ear's concha of the users. 
When the housing 202 is introduced into the ear's concha, since the elastic 
ring 211 is formed of a material of low hardness and is recessed, it can 
be easily deformed from the outside diameter in the undeformed state of 
the elastic ring 211 to the outside diameter approximately equal to the 
outside diameter of the base ring 210. In this manner, the sealing 
properties of the housing 202 with respect to the ear's concha when the 
housing is inserted into the ear's concha are improved, so that 
satisfactory acoustic properties are obtained in which, as shown at A in 
FIG. 9, the output in the low frequency range is improved as compared to 
that of the above described conventional headphone unit. 
The soft contact feel of the portion of the housing 202 contacting with the 
ear's concha may also be achieved. The base ring 210 and the elastic ring 
211 are formed by the double-shot molding so that the materials of the 
rings 210, 211 are strongly bonded together without the risk of peeling 
after repeated usage or application. 
It is noted that the acoustic characteristics shown at P in FIG. 9 
represent those in the ideal complete sealing state of the housing with 
respect to the ear's concha. 
It is noted that the electro-acoustic transducer of the present invention 
is not limited to the above described headphone unit, but may also be 
applied to other earphone or microphone units. 
For example, when a microphone unit is constructed in accordance with the 
present invention and the rings are provided to the outer side of the 
opening of the housing exposing the sound input side of the 
electro-acoustic transducer unit, the effect of the noises generated by 
contact of the user's hands or fingers etc. with the housing on the 
electro-acoustic transducer unit may be minimized. Also, since the base 
ring and the elastic ring are attached to the manually gripped portion of 
the housing, the housing may be gripped more comfortably. 
According to the first embodiment of the electro-acoustic transducer of the 
present invention, as described hereinabove, the outer surface of the 
opening of the housing by which at least the diaphragm of the 
electro-acoustic transducer is exposed to the outside, is formed of a 
material different from the material of the remaining portion. 
Hence, the portion of the housing that is formed by double-shot molding is 
formed of materials different in color and/or hardness and that are united 
strongly to each other. 
Therefore, when the so-called inner ear type headphone unit is constituted 
in accordance with the present invention, the portion of the housing 
contacting with the inner wall of the ear's concha is formed of a soft and 
pliable material to provide a soft contact feel with the ear's concha, 
while the main body of the housing is formed of a relatively stiff 
material to provide optimum acoustic characteristics and reliable holding 
of the speaker unit. In addition, the two materials of different hardness 
are connected rigidly to each other for assuring durability of the 
headphone unit. 
The number of component parts is also reduced and the assembling operation 
is simplified since the operation can be achieved by simply fitting the 
electro-acoustic transducer unit, such as the speaker unit, into the 
housing formed by double-shot molding. 
In addition, according to the second embodiment of the present invention, a 
base ring is provided on the outer surface of the perimeter of the opening 
of the housing, by which the sound radiating side or the sound input side 
of the electro-acoustic transducer is exposed to the outside, and an 
elastic ring is provided on the outer periphery of the base ring that is 
formed of an elastic material by double-shot molding. The elastic ring is 
subject to considerable deformation and the two materials constituting the 
elastic ring are united together strongly by the double-shot molding. 
Therefore, when the so-called inner ear type headphone unit is designed and 
constructed in accordance with the present invention, satisfactory contact 
feel and optimum acoustic characteristics may be maintained even when the 
unit is attached to the ear's conchae of different size. In addition, the 
two materials of different hardness may be formed together strongly for 
assuring improved durability of the headphone unit.