Electrical audio signal processing systems and devices – Hearing aids – electrical – Specified casing or housing
Reexamination Certificate
1999-01-08
2004-06-15
Harvey, Minsun Oh (Department: 2747)
Electrical audio signal processing systems and devices
Hearing aids, electrical
Specified casing or housing
C381S322000
Reexamination Certificate
active
06751328
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an earphone without impulse noise for protection against conductive hearing loss, which can prevent the sound waves direction of loudspeaker thereof is not directly transmitted to the tympanic membrane located in the most inner side of external auditory canal. The middle ear can be protected against conductive hearing loss caused by the direct impact of the sound pressure.
BACKGROUND OF THE INVENTION
It is conventionally know that the sound is defined as a physical energy and is transmitted in the form of energy. The farther the sound travels the greater energy it contains (like thunder or sound from gunshots). Therefore, energy in the sound is measured by the logarithm system while decibel(s) is often used as the unit to measure the sound intensity. However, the “decibel” is not an absolute value, but a relative value, such that the decibel means a comparison of the intensity between two sounds. Hence, if we say how many decibels a sound has, it means that how many times its pressure greater than a certain reference one. When an audiometer is used to measure the hearing and the decibels increase from 0 to 60, it is indicated that the energy in the sound increases by 10
6
. However, even a sound pressure with 60 decibels isn't a loud sound, and it's nearly equal to a great sound a few feet away from us in our daily life.
A human ear, as shown in
FIGS. 1
to
3
, consists of three main parts—the external ear
10
, the middle ear
20
, and the inner ear
30
. The external ear
10
includes the helix
11
, the antihelix
12
, the auricle
13
, the concha
14
, the antitragus
15
, the tragus
16
, and the external auditory canal
17
whose length of an adult is about 24 mm. The tympanic membrane
171
is located in the most inner side of the external auditory canal
17
. The external auditory canal
17
and the middle ear
20
are separated by the tympanic membrane
171
while the middle ear
20
is the ear drum formed between the external ear
10
and the inner ear
30
and having the malleus
21
, the incus
22
and the stapes
23
, wherein the end of the malleus
21
lies hidden in the tympanic membrane
171
while the body of the malleus
21
and the head of the incus
22
are joined together to be a joint. Besides, the incus
22
has a short leg
221
and a long leg
222
, wherein the short leg
221
leans on the wall of the ear drum while the end of the long leg
222
is linked to the head of the stapes
23
. The end of the stapes
23
is formed as a foot shape, as shown in FIG.
2
.
Moreover, the inner ear
30
includes the cochlea
31
and the labyrinth
32
, wherein the cochlea
31
controls the human hearing system while the labyrinth
32
maintains balance in the body. These two fine parts are enclosed by a capsule; in addition, some perilymphs in the most outer layer thereof cover the cochlea
31
and the labyrinth
32
. These perilymphs are functioned as an air cushion to provide an excellent protection when the head gets an intense vibration. In fact, the cochlea
31
and the labyrinth
32
are floating in the fluid of the lymphs. The inside of the cochlea
31
consists of three parts—the scala vestibuli, the scala tympani, and the cochlear duct containing perilymph. The nerve cells in the cochlea
31
contain about 30,000 hairlike nerve endings. Besides, the oval window
33
and the round window
34
are located near the wall surface of eardrum of the middle ear
20
while the base of the stapes rests against the opening of oval window
33
and the inner side thereof is attached to the scala vestibuli
311
of the cochlea
31
so that the cochlea
31
can receive the sound pressure transmitted from the auditory ossicies while the round window
34
is attached to the scala tympani
312
of the cochlea
31
in order to directly receive the sound transmitted from the eardrum of the middle ear
20
.
Furthermore, after the sound pressure is transmitted from the tragus
17
to the tympanic membrane
171
, a portion of the sound pressure is partially reflected back to the tragus
76
while another portion of the sound pressure passes through the tympanic membrane
171
into the middle ear
20
. The portion of the sound pressure that has been transmitted into the middle ear
20
has a certain part pass through the malleus
21
and the incus
22
into the foot-shaped end of the stapes
23
(those who consist of the malleus
21
, the incus
22
, and the stapes
23
is hereafter called auditory ossicles), and then through the oval window
33
into the cochlea
31
of the inner ear
30
. The rest of the sound pressure is transmitted by the air medium in the eardrum into the cochlea
31
of the inner ear
30
.
Consequently, the sound pressure transmitted into the human ear is divided into two parts to enter the inner ear
30
; however, the sound transmitted by the way of auditory ossicles into the oval window
33
is more effective and important than that transmitted by the air medium through eardrum into the round window
34
. The reason is that 99.9% of the energy of the sound pressure transmitted into the eardrum of the middle ear
20
and passing by way of the air medium through the round window
34
into the perilymph of the cochlea
31
is consumed or reflected back by the fluid surface. Only 0.1% of the energy is able to pass through the perilymph into the cochlea
31
.
Accordingly, the most effective way of the sound transmission is carried out from the tympanic membrane
171
through the auditory ossicles into the oval window
33
. However, when the sound pressure is transmitted to the end of the stapes
23
and strikes the oval window
33
, it directly passes through the incompressible perilymph into the cochlea
31
while the sound pressure is not consumed or reflected by the fluid surface. Presently, the perilymph containing the sound pressure stimulates the hairlike nerve endings in the cochlea
31
to generate a displacement or a bending, and this motion can turn the mechanical force in the sound pressure into electrochemical impulses that are carried up the acoustic nerve to auditory cortex of the brain. At last, it is the sound we can understand.
In view of the above, we realize that sense of hearing of the human ear is generated by the movement of the hairlike nerve endings, that even a slight displacement of the hairlike nerve endings causes the sense of hearing. Therefore, the sense of the human ear is very sharp and the perceptible pitch is also very wide. Generally, the perceptible frequency range of human beings is about 20~20000 Hz while the intensity range 10
12~
10
2
W/m
2
and the sound pressure less than 180 dB. However, not all perceptible sounds are suitable for the human ear to receive. The pitch in the improper range (sound pressure over 90 dB is so-called noise) easily causes the damage of the auditory part in the ear. The factory workers under a long-time exposure to the industrial noise without wearing any hearing protectors (like earplug or earphone) have the hearing damage possibility up to 25% after a few years.
The reason lies in that the sound pressure of the industrial noise stimulates the hairlike nerve endings in the ear to generate a displacement or a bending. They return to the original state when leaving this noise circumstance for a period. The restoring effect of the hairlike nerve endings worsens more and more with the time and causes the hearing damage in the inner ear. This kind of hearing loss mostly belongs to the perceptive hearing threshold while the other kind is mostly caused by a direct strike on the head or an instant impulse noise, resulting in a damage of the ear membrane or the auditory ossicles so that the sound pressure transmitted in the middle ear
20
simultaneously enters the oval window
33
and the round window
34
in the vestibuli
33
and it is counteracted by each other. Accordingly, a hearing loss is caused. This kind of conductive function loss in the middle ear is called conductive hearing loss.
Obviously, the hearing loss resulting fr
Chan Raymond Y.
David and Raymond Patent Group
Harvey Minsun Oh
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