Note: Descriptions are shown in the official language in which they were submitted.
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2~94~7
BAcRGRouND OF THE INYI~GI~
The present invention relate~ generally to a two-way
communications earset with a filter which i~ worn in or at the ear
of the user for use in two-way voice communication~ and which i~
operated hands-free. The earset can transmit the user's voice and
receive the voice signals of another party simultaneously without
cau~ing feedback.
Modern wireless technolog~es have advanced to the extent that
portable, wirele~ and mobile telephones have become ~mall in size
and are used widely. Such portable telephones typically include a
handset requiring the use of at lea~t one hand for communication.
A di~advantage of the handset type of telephone i~ that they
are inconvenient to use in front of 8 computer or while driving a ; ~ -
car. In ~uch in~tances, the n~er must u~e ~ hand to hold the
handset while typing at the keyboard, which i~ very difficult to
do, or whlle holding the ~teering wheel o~ a car, which is
dangerous. Altern~tively, the user must hold the telephone
handset to their ear wlth their ~houlder, which is very
uncomfortable.
In order to solve this drawback, hands-free telephone~ have
been developed. A conventional two-way communicationq apparatus
used with hands-~ree telephones comprises a headband including a
spe~er po~ltioned ln front of one ear ~nd a boom at~ached tO the
headbsnd with a small microphone at one end of the boom. With the -
boom connected to the headband, the microphone extends in front of
the mouth of the user. However, this type of hands-free telephone
2094667 ~:
is not convenient to use because it is cumbersome and because it
disturbs the hair of the user.
Another conventional two-way communications system used with
hands-free telephones includes a structure which hangs from the
ear of the user. This type of communications system include~ a
speaker positioned in front of the user~s ear and a boom h~ving a
microphone extending in front of the mouth of the user. Aga$n,
such a structure i~ not convenient for the user because it ~-~
typically does not h~ng well at the ear and because it 18 bulky to
carry owing to the boom.
15Yet another conventional two-way communication system
comprises a ~peaker and a microphone both housed in an earset unit
which is worn in the ear of the user. Such an ear~et does not
require use of hands to operate and does not have a boom extending ~ - -
in front of the user's mouth. However, a drawback of this earset
18 that users cannot increase the sound volumes of elther the
speaker or the mlcrophone. Therefore, the use of thls type of
ear~et is limited to quiet environments.
In addition, microphone sensitivity in such conventional
earset~ i8 set to a low level. As a result, the user 18 difficult
to hear. Also, because the sensitivity of the speaker i~ set at a
low level a~ well, the user tend~ to cover the earset with a hand
in order to obtaln improved communications in a noisy environment.
However, thls tends to cause feedback. ~ecause of these
drawbacks, conventional ear~ets include a warning regarding the
tendency for feedback and are not widely used.
35 -2-
209~7
S Accordingly, an object of the present invention is to provide
an earset for use in two-way voice communication~ which i8 worn in ---
or at the ear of the user and which is operated hands-free.
Another ob~ect of the present invention i8 to provide an
earset which transmits the user~ 8 voice and receive~ voice signals
from another party simultaneously without feedback caused by
acoustic or mechanical coupling between the ~peaker and the
microphone.
A further ob~ect of the present invention i~ to provlde an
ear~et which delivers an adequate level of sound to the user
without causing feedback, while also delivering an ndequate level
of sound to a receiver at the other end of the communication ~ -
system.
A still further ob~ect of the present invention is to provide
an earset which includes a mechanical or electrical filter that
eliminate~ audio frequencies tending to cause feedback.
Additional ob~ects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The ob~ects and advantages of the invention may be
realized and obtained by means of the instrumentalitiea and
combinations particularly pointed out in the appended claim~
SUMMARY OF TR~ _INV~NTION
To achieve the ob~ects in accordance with the purposes of the
30 pre~ent invention, as embodied and described herein, the earset of ~; -
the present invention comprises a two-way simultaneous voice
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20946~7
tran~mitting and receiving device comprising a case comprising an
enlarged portion adapted to be placed in an ear auricle of a user
and a hollow portion extending along a direction parallel to a
mouth of the user, whersin the enlarged portion houses a speaker
with an output led to an ear canal of the user and the hollow
portion houses a mlcrophone, and means, sltuated within an audio
signal loop coupling the speaker to the microphone, for filtering
a high end range of audio frequencies that causes feedback.
The present inventlon further comprlses a two-way ~:.
slmultaneous volce transmittlnq and recelvlng device comprising a
lS case including an enlarged portlon adapted to be placed in an
aurlcle of a user's ea~ and a hollow portlon extending parallel to
a mouth of the user, wherein the hollaw portion hou~es a
microphone, and the enlarged portion houses a ~peaker wlth an
output to an ear canal of the user, whereln the speaker passes
frequencles ln a range of 300 to 1000 Hz and has a hlgh end cut
off frequency below 2.5 XHz.
Alternatively, the present lnvention comprises a two-way ~ :
simultaneous voice transmittlng and recelvlng device comprising a
case lncluding an enlarged portlon adapted to be placed in an
aurlcle of a user's ear and a hollow portlon extending parallel to
a mouth o~ the user, whereln the enlarged portlon houses a speaker
wlth an output led lnto an ear can~l of the user, and the hollow
portlon hou~es a mlcrophone, and whereln the mlcrophone passes
frequencies in a range of 300 to 1000 Hz and has a high end cut
off frequency below 2.5 KHz.
",,','.. s-, , ,~ " ~ , " ~ ;"", ~ :.
209~6~7
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and
con~titute a part of the specification, illustrate the presently
preferred apparatus of the present invention ~nd, together with
the general description given above and the detailed de~cription
of the preferred embodiments given below serve to explain the
principles of the invention. In the drawingss `~`
Fig. 1 is a side view of an earset according to a f$rst `
embodiment of the pre~ent invention inserted in the ear of a user; ~ ~
Fig. 2 is sectional view of the first embodiment; ~-
lS Fig. 3 is a side view of an earset according to a second
embodiment of the present invention inserted in the ear of a user; ~ ~ -
Fig. 4 is a sectional view of a mechanical filter used in the
earset according to the present invention;
Fig. 5A i8 a circuit dlagram of low pass electrical filter
20 used in the earset according to the present invention; ;
Fig. 5B is a graphical representation of the frequency
characteristlcs of the low pass electrical filter shown in ~;
Fig. SA;
Fig. 6A is a circuit diagram of a band pass electrical filter
used in the earset according to the present invention;
Fig. 6B is a graphical representation of the frequency
characterlstlcs of the band pass electrical filter shown in ~ -
Fig. 6A;
Fig. 7 is a graphical representation showing the definition ~;
. .
30 of the cut off frequency within the frequency band without ripple. ;
,.~
35 ~5~ ~
..... , . , . ., . , , .. , .. . " , . . . . . . .... . . .. . .
20~ 7
Fig. 8 is a graphical representation showing the definition
of the cut off frequency within the frequency band with ripple.
Fig. 9A is a block diagram of a frequency compensating
filter; and
Fig. 9B ls a graphical representation of the frequency
characterist~cs of the compensatlng electrical filter shown in
Fig. 9A.
:
DETAILED DESCRIPTION OF THE PREF~M ED EMBODIMENTS
A first embodiment of the earset accordlng to the present
invention is described with reference to Figs. 1 and 2. AB shown
in Fig~. 1 and 2, the ear~et 1 has an L-shaped configuratlon and
is preferably made of plastic. The short arm of the ~-shaped
earset 1 includes an enlarged portion la which is inserted in the
ear canal of the user. The enlarged portion 1~ includes an earset
component portion lb and an insertion portion lc.
The enlarged portion la is placed in the ear auricle of the
user and the insertion portion lc is inserted lnto the ear canal.
The insertion portion lc is preferably shaped 80 that the ear
canal of the user will not be completely clogged by the device and
so that the devlce will not be 80 loose that feedback due to
leaked ~ound is caused.
A speaker 3 is housed in the earset component portion lb and
is supported by resllient material 4. The output of the speaker 3
i~ input to the insertion part lc and is fed into the ear canal of
the user. The speaker 3 can preferably be elther a magnetic-type
speaker or dynamic-type speaker. As shown in Figs. 1 ~nd 2, the
2~945~7
,
. -
5 speaker 3 is situated in the earset component portion lb. -~
However, in accordance with the present invention, the speaker 3
can be placed in an alternate location, so long as the output from ;
the speaker 3 is guided into the ear canal of the user.
The long arm of the L-shaped earset 1 preferably includes a
hollow portion ld which has a small hole le at the lower end
thereof and an electret type microphone 5 at an upper portion
thereof. In accordance with the present invention, the microphone
5 can be either a bidirectional-type or a unidirectional-type
microphone. A sound pipe 2 iB also contained within the hollow
portion ld and connects the small hole le and the microphone 5.
In operation, the microphone 5 detects the voice signals of the
user through the small hole le ~nd the sound pipe 2.
In the embodiment shown in Figs. 1 and 2, a filter 6 is
placed within the sound pipe 2 and is situated between the
m$crophone 5 and the small hole le. The fllter 6 passes audio
frequencies withln a preferred range of 300 to 1000 Hz with a cut
off frequency of preferably below 2.5 KHz, as described ln greater
, " :
detail below. Additionally, as also described ln more detail
below, the filter 6 c~n be located at alternate loc~tions in the
earset. A wire 7 extends through the hollow portion ld and
combines the wires from the speaker 3 and the microphone 5.
The e~rset 1 is operated in the following manner. When the
earset 1 is situated ln the ear of the user, electrlcal sign~ls
which are received are fed vla the wire 7 to the speaker 3. The
speaker 3 emits sound to the ear canal of the user via a hole lf
in the insertion portlon lc.
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20946~7
The voice signal of the person using the ear~et 1 pas~es ~ -
through the small hole le and filter 6 and reaches the
microphone 5. The microphone 5 converts the sound to electrical
signals that are sent via the wire 7 to an amplifier, which is not
shown ln Flgs. i or 2.
Fig. 3 shows a second embodiment of an earset accordlng to
the present invention. As shown in Flg. 3, the device has a two- -
piece construction including a two-way wireless communication
device 8 connected to an earset 1. The communication device 8
includes a transmitter/recelver at the front portion of the ear
~, -
lobe. The communication device also includes a battery cell
located st the back portion of the ear lobe. The battery cell and
the transmitter/receiver remain connected to the ear lobe by ~
pinching mechanism located therebetween. The earset 1, shown in
Flg. 3, 18 substantially the s~me a8 that shown in Fig~. 1 and 2.
In order to design the eArset 1 of the present invention 80
that it most efficiently conducts two-way voice communications,
the unique sound field around the auricle of the ear wns studied
by the inventors of the present lnvention. This sound field was
found to extend not only in front of the auricle, but al80 in the
area surrounding the auricle and to result from a comblnation of
the sound near the aurlcle, the ear canal and the head. It was
al80 determ~ned that the sound field generates sound reflection,
diffraction and resonance.
As a result of the inventors~ study of the sound field,
acoustlc and mechanical coupllng between the speaker 3 and the
microphone 5 wa~ determlned to increase selectively at a few
2~94667 :
S specific frequencies between 1 XHz and 3.4 XHz. The~e specific -
frequencies vary depending on the type of earset worn by the user
and the voice characteristics of the user.
It was also observed that when the sound volume of the
speaker 3 i8 increa~ed and when the sensitivity of microphone 5 i8
increased, feedback tends to occur at the identified spec$fic
frequencies. In addition, when the ear~et l is used under heavy
ambient noise, the user tends to cover the ear containing the
earset 1 with his hand in order to block out the ambient noi~e. ~-
However, such hand placement acts as an ear muff and presents the ~ ~;
optimal condition for feedback to occur at these specific
frequencies. Feedback between the speaker 3 and the microphone 5
also occurs when 8 portion of the voice output of speaker 3 is
leaked. This leaked portion is reflected off the auricle
structure of the ear and lnput to the microphone 5 via the small
20 hole le. -
In order to reduce the deleterious a'ffects of acoustic
coupling and feedback described above, 8ignals within the area of
the specific frequencies are reduced. Although it is well known
that reducing signals wlthin a certain frequency range can damage
the quality of voice communications, according to the pre~ent
Lnvention, the speciflc identified frequencies can be reduced
without lowering the quality of voice communications.
Additionally, acoustic coupling and feedback can also be
signlficantly reduced. --~
30Specifically with respecl: to reducing the identified
frequencles, the inventors of the present lnvention found that if
_ g _
--, .. , . , .. , . . . . ~ .. . ~ .. . . . ...... ..
.~:. . ~.; ,........... , . , . . . , j, . .
. :~. : .. :. , :
. ., ~ . , ; ~
2094~67 ~
the high end cut off frequency was made too low, the quality of
voice communicatlons would be unacceptable. Conversely, if the - ;-
high end cut off frequency was set too high, feedback occurred too
readily. The lnventors also considered that when sound passes
from a free sound f$eld to the ear drum, the sound pressure of
10 6ignals between 1 KHz to around 2.5 RHz incresses. ~ ;-
By balancing the effect~ of acoustlc snd mechanical coupling,
the likelihood of feedback, and sound pressure with sn acceptable
level of voice communication, according to the present invention,
the filter 6 preferably is conflgured to pass frequencies in the
range of 300 to 1000 Hz and to preferably have a high end cut off
frequency of below 2.5 RHz.
Additionally, the filter 6 is situated in the ear~et 1 in an
audio signal loop coupling the speaker 3 and the microphone 5.
The audio signal loop is defined as electrical or mechanical
connection between the speaker 3 and the microphone 5. By placing
the filter anywhere within the audio signal loop, feedback between
the speaker 3 and microphone 5 can be substantlally reduced.
Several different placements of the filter 6 are
contemplated. For example, with the fllter 6 coupled to the
speaker 3, the speaker 3 will preferably have output
characterlstics that pass low frequencies in the range of 300 Hz
to 1,000 Hz and have a high end cut-off frequency of below
2.5 KHz. Alternatively, with the filter 6 coupled to the
microphone 5, electrical signals from the microphone 5 will
preferably have signal ch~racteristLcs that pass low frequencies
in the range of 300 Hz to 1,000 Hz and have a hlgh end cut-off
--10--
. :.,
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.:
5 frequency of below 2.5 XHz. And alternatively, two or more -
filters with portions of the desired frequency response can be -;
allocated between the qpeaker 3 and microphone 5 in the audio
signal loop.
....~ ....~
In addition to reducing acoustic coupling and feedback and
.. ~.. ~ - .
producing an acceptable voice signal, it is desirable that the
earset 1 in of the present invention be ~ensltlve to human voice
signalq, but not to ambient noise or nolse that 1~ leaked from the
speaker 3. Because the earset 1 lq ~mall in size and is mounted ~ -
at the entrance of the ear canal of the user, it iq preferable
t~at the earset 1 have a structure which provldes a greater
. ~ ,.
sensitivity to voice signals and a lesser ~ensltivity to sound --~-
,, -, ,
reaching the earset 1 from other dlrections.
To achleve this result, mechanical fllter 61 i~ u~ed to
, .
improve the directional sensitivity of the earset 1. Fig. 4 is a
~lde vlew of a mechanlcal fllter 61 which may be employed ln the
earset 1 shown in Figs. 1-3. A~ shown in Fig. 4, the filter 61 is
preferably made of a fiber sheet coiled 80 that the sheet flts
into the cylindrically ehaped hollow portion ld.
Preferably, the filter 61 comprises a coil of highly fibrous ~ ;
25 paper tightly wound and filling the hollow portion ld, which ~
~: .,
preferably has a diameter of 6 mm. The mechanical filter 61 is
constructed 80 that lt has the frequency characteristic~ described
above. ~he resultant frequency characterlstic can be varied by
changing the density of the coil, ie., reducing the number of
co~l-q.
: '
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,., ,~ ,,,, ~
2094~7
With such a colled ~tructure, sound coming from a direction
parallel to the axis of the mechanical filter 61 passes through to
microphone 5 with less attenuation than sound coming from other
directions. Becau~e voice signals coming from the user primarily
emanate along an axis parallel to the axis of the mechanical
filter 61, the~e signals are less attenuated than those of other
signal~ reaching ~he microphone 5 and the sensitivity to voice
signals is therefore improved.
In the embodiment of the mechanicsl filter 6 shown in Fig. 3,
the ~tructure of the coiled fiber sheet achieves the desired
frequency response and improves the sensitivity of the earset 1 to
voice ~ignal~. Alternatively, the mechanical filter 61 may be
constructed of glass wool, rock wool, felt, materials such as high
density sponge, or fibres made of cotton and pulp. More
specifically, the mechanlcal filter 61 may comprise a cigarette
filter, compri~ing cotton fiber~, because it has been found that
cigarette filters can achieve the desired frequency
characteristics. Additionally, a cigarette filter fits withln the
hollow portlon ld and are readily available.
It should al~o be noted that Figs. 1 and 2 ~how an embodiment
ln which a mechanlcal filter 6 is positioned in front of
microphone 5. However, as discus~ed above, a mechanical filter 6
with a simllar frequency response can alternativsly be placed in
front of the speaker 3. It i8 al~o contemplated that a fir~t
mechanical filter 6 with a portion of the desired filter
characteristics be placed in front of the microphone 5 while
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2094667
another mechanical filte~ 6, having another portion of the desired
frequency response, be positioned in front of the speaker 3.
Alternatively, the filter 6 may preferably comprise ~-
electrlcal component~, as shown in Figs. SA and 6A. Fig. 5A shows
a low pa~ filter 62 comprising an operational amplifier 9 which
can be used 8~ the filter 6 of the earset 1. Fig. 6A show~ a band
pass filter 63 also comprising an operation~l ~mplifier 10 which
can be used as the filter 6 of the earset 1. Fig. 5~ and Fig. 6B ~-
show the frequency responses of the filters shown in Fig. SA and ~;
Fig. 6A, respectively.
Preferably, the operational amplifier may comprise a National
Semiconductor LM324 type operational ampl$fier although
alternative devices are known or can be designed by those of
ordlnary skill in the art. Additionally, as described with the
mechanical filter 61, the low pass filter 62 and the band pass
fllter 63 are preferably placed in the audio loop between the
speaker 3 snd the microphone 5.
As descrlbed above, accordlng to the present lnventlon, the
high end cut off frequency of the filter 6 is preferably below
2.5 RHz. When one of the low pass fllter 62 or the band pass
fllter 63 are used as the fllter 6 of the earset 1, a
determination of the high end cut off frequency is made depending
on the char~cteristics of the filter 6. That i8 ~ the high end cut
off frequencies for a frequency band with or wlthout amplitude
ripple, as shown ln Fig. 7 ~nd Flg. 8, respectlvely, will be
dlfferent.
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20~46~7 - ~
S More specifically, in accordance with the present invention,
the high end cut off frequency of the low pass or band pass
filter~ 62 and 63 i~hown, respectively, in Fig~. SA and 6A is
defined such that if the filter 6 does not ha~e a ripple
characteristic within the frequency range allowed to pass
therethrough, as ~hown in Fig. 7, the cut-off freguency of the
filter 6 is defined as that after which an output from the filter
6 becomes 3 dB below the maximum amplitude within the sllowsble
frequency range. Alternat$vely, if the filter 6 does have a
ripple characterlstic with$n the frequency range allowed to pass
lS therethrough, as shown in Fig. 8, tha cut-off frequency is defined
as that frequency after which an output from the filter 6 becomes
3 dB below the average amplitude within the allowed frequency
range.
However, constructed as shown in Flgs. 5A and 6A, the
filters 62 and 63, may cut off certain high frequency components
of the speech signals and may therefore deteriorate voice
communications. In order to make up for this, an alternative
filter 64 which includes a compen~ating circuit can be used.
Fig. 9A i8 a circuit dlagram of such a compensation filter
64. The compensnting filter 64 shown in Fig. 9A, improYes the
1089 of high frequencies which may be filtered out by filter~ 62
and 63, shown in Figs. SA and 6A. Fig. 9B is ~ graphical
representation of the frequency response of the circuit shown in
Fig. 9A.
More specifically, in operation, the microphone S of the
earset 1, shown in Figs. 1-3, produces an electrical slgnal output
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-:.
6a. Output 6a i~ fed into audio band limiting filter 6b which as
~hown in Fig. 9~ produces a band pass filter response similar to
that ~hown in Fig. 6B. It i~ also contemplated that the output 6a
can emanate from the ~peaker 3.
The output 6a is also input to high end audio select filter
10 6cl of the high end audio amplitude limiter 6c. The high end - -
audio select filter 6cl passes selected high end audio ~;~
frequencie~. The frequency response of the high end audio select
filter 6cl $8 shown in Flg. gB. The output of the hlgh end audio
select filter 6cl is fed into amplitude limiter 6c2 which limit~
the output of the high end audio select filter to a predetermined
level. The output of the amplitude limiter 6c2 is fed into
attenuator 6d. The outputs of audio band limiting filter 6b and
attenuator 6d are added by the adder 6e. ~ ;
A graphical representation of the frequency response of the
filter 64, ~hown in Fig. 9A, is shown in F~g. 9~. The frequency
response includes the both the 6b characteristlcs, the output from
the audio band limiting filter, Mnd the 6cl characteristic~, the
output from the attenuator 6d. Accordlngly, with the filter 64 of
the present invention, the amplitude~ of high frequencies are
controlled below a certain level b~ amplitude limiter 6c2 ~o that
feedback wlll not occur. In addition, because some high
frequencie~ are left ln the resultant output signal, ~8 a result
of the addition of high end signal~ to those of the audio band
limiting filter 6b, the resultant voice signal will not be
deteriorated.
, ~ :
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2~9~67
Other embodiments of the invention will be apparent to those
skilled in the art from consideration of the specification and
practice of the invention disclosed herein. It is intended that
the specification and examples be considered as exemplary only,
with the true scope and spirit of the invention being indicated by
the following claims.
