Electricity-to-sound transducer

Details Electricity-to-sound transducer Electricity-to-sound transducer

2001-09-28

2003-11-25

Kuntz, Curtis (Department: 2643)

Electrical audio signal processing systems and devices

Electro-acoustic audio transducer

Electromagnetic

C381S407000, C381S423000, C381S424000, C381S431000, C381S412000

Reexamination Certificate

active

06654475

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an electricity-to-sound transducer such as a slender speaker having high sound quality.
With increased popularization of high-vision and wide-vision etc., TV sets with wide screens have widely been used. There is, however, increased demands in Japan for thin and not-so-wide TV sets and also audio component systems due to relatively poor Japanese housing conditions.
Speaker units for TV sets are for example one of the causes for TV sets that inevitably become wide. Because speaker units are mostly set on both sides of a cathode ray tube. Thus, most known speaker units have been not so wide such as rectangular and oval types. However, as cathode ray tubes become wide, there is a strong demand for slender speaker units as narrow as possible and for high sound quality that matches high picture quality in high-vision and wide-vision.
Known slender-type speakers, however, cannot meet such a demand due to distributed vibration that easily occurs in the long axis direction because of one-point driving at the center section of a slender diaphragm. This results in a peak dip in reproduced acoustic-pressure frequency characteristics in middle and high tone ranges, thus decreasing sound quality.
The applicant for this patent application has proposed, in Japanese Patent Application No. 10-192048, an electricity-to-sound transducer with flat frequency characteristics for high sound quality with less distributed vibration even though it is made as a slender structure.
This electricity-to-sound transducer is described with reference to
FIGS. 5
to
8
.
A reinforcing member
40
is inserted from above into each slot
38
formed at an almost center section of a diaphragm
31
in the longitudinal direction and almost perpendicular to this longitudinal direction. The diaphragm
31
is supported by the reinforcing member
40
. Several materials can be used as the member
40
for supporting the diaphragm
31
, such as metal, resin and wood. The member
40
is formed in a long rod with cuts
41
provided on the bottom surface at a constant interval. A voice coil
33
is passed through each cut
41
and wound around each of main vibrating portions
31
a
at the base section.
A magnetic field is generated around the voice coil
33
by magnets
35
to cause a drive current flowing the coil
33
for generating an electromagnetic force. The main vibrating portions
31
a
are vibrated by the electromagnetic force, and thus the diaphragm
31
is vibrated. During this vibration, however, distributed vibration is prevented from occurrence at the center section of the diaphragm
31
in the longitudinal direction because the slots
38
on the center section are supported by the reinforcing member
40
.
Formed on the upper surface of each main vibrating portion
31
a
are convex semi-circular cylinder portions
39
a
and concave semi-circular cylinder portions
39
b
provided alternately in the longitudinal direction. This structure has a high mechanical strength (rigidity) against force to be applied in a direction perpendicular to the longitudinal direction. Without this structure, it could happen that a main vibrating portion
31
a
starts to vibrate larger or smaller than the neighboring one with no vibration in synchronism with each other at the border between the two vibrating portions. Such large and small vibration components are, however, complimentarily prevented from occurrence by employing the structure explained above.
FIG. 9
illustrates vibration occurring on the diaphragm
31
of the electricity-to-sound transducer described above in a free-vibration mode. Observed around the slots
38
is distributed vibration restricted in the free-vibration mode. Also restricted is distributed vibration occurring around the center section of the diaphragm
31
in the longitudinal direction.
FIG. 10
illustrates a result of numerical analysis on the frequency response characteristics of vibration amplitude around the center section of the diaphragm
31
. The solid line “A” indicates the result on the electricity-to-sound transducer disclosed in Japanese Patent Application No. 10-192048. The dot line “B” indicates the result on another known electricity-to-sound transducer. Observed in this figure is that the known transducer suffers from amplitude depression at frequencies of about 13.5 KHz or more whereas, for the transducer in the Patent Application above, the frequency characteristics is improved such that peaks are depressed at a high frequency range around 10 KHz while depression at frequencies of about 13. 5 KHz or more is not so badly and this continues to 15 KHz.
These electricity-to-sound transducers, however, have drawbacks as discussed below with reference to
FIGS. 11 and 12
.
The diaphragm
31
is protected from distributed vibration at its center section in the longitudinal direction by means of the reinforcing member
40
inserted in the slots
38
from above, as indicated by arrows in
FIG. 11
, in the direction perpendicular to the longitudinal direction.
Considerably deep slots must be formed as the slots
38
for depth H shown in
FIG. 11
for stably sustaining the reinforcing member
40
. Such a deep slot, however, causes a problem in that an upper edge
34
a
of a voice coil bobbin
34
touches a lower edge
38
a
of each slot
38
when the bobbin wound a voice coil
33
is inserted from the bottom of the diaphragm
31
, so that the bobbin cannot be fit in the prescribed position.
On the other hand, a slot
38
formed as not so deep for resolving such a problem on the voice coil bobbin
34
cannot resolve the problem in that the diaphragm is fallen inwardly at the center section as discussed above.
SUMMARY OF THE INVENTION
A purpose of the present invention is to provide an electricity-to-sound transducer that has a new structure for a diaphragm and a voice coil bobbin attached to the diaphragm with less abnormal vibration which may otherwise occur in the longitudinal direction due to natural frequency of the diaphragm, for normal sound irradiation in response to a large input.
The present invention provides an electricity-to-sound transducer comprising: a diaphragm having an asymmetric shape which is flat when viewed from a direction of vibration, with major and minor axes, having continuous curvatures of concavity and convexity in a direction of sound irradiation, provided with a slot formed almost at a center of the diaphragm in a direction perpendicular to a longitudinal direction of the diaphragm; an edge portion formed as surrounding an outer periphery of the diaphragm, an inner section of the edge portion being connected to the outer periphery, the edge portion sustaining the diaphragm for vibration; a voice coil bobbin having a winding portion around which a voice coil is wound split into two portions in the longitudinal direction of the diaphragm, the bobbin being attached to a rear surface of the diaphragm while the two portions are joined to each other, the joined portions forming a reinforcing beam that reaches a rear surface of a bottom of the slot of the diaphragm; a magnetic circuit for applying flux to the voice coil for vibration; and a frame for sustaining the outer periphery of the edge portion.
Moreover, the present invention provides an electricity-to-sound transducer comprising: a diaphragm having an asymmetric shape which is flat when viewed from a direction of vibration, with major and minor axes, having continuous curvatures of concavity and convexity in a direction of sound irradiation, provided with a slot formed almost at a center of the diaphragm in a direction perpendicular to a longitudinal direction of the diaphragm, the slot having walls on a bottom of slot, on both ends of the slot in a direction of the major axis and on both ends of the slot in a direction of the minor axis, the slot protruding in a direction of a rear surface of the diaphragm to form a protrusion; an edge portion formed as surrounding an outer periphery of the diaphragm, an inner section of the edge portion being connected to

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