U.S. patent number 3,922,504 [Application Number 05/538,176] was granted by the patent office on 1975-11-25 for electroacoustic transducer.
This patent grant is currently assigned to Foster Electric Co., Ltd.. Invention is credited to Yougi Honda, Kenichiro Kishikawa.
United States Patent |
3,922,504 |
Kishikawa , et al. |
November 25, 1975 |
Electroacoustic transducer
Abstract
An electroacoustic transducer wherein a diaphragm of a
nonmagnetic and insulative material having thereon a series of
conductors is disposed between a pair of magnetic circuits opposing
one another through a slight clearance so that the conductors will
lie in magnetic flux flowing between opposite polarity ends of at
least a pair of permanent magnets in each magnetic circuit and will
move in directions transverse the flux when the diaphragm is
vibrated. The magnets in one of the magnetic circuits on sound
passing side of the diaphragm are made smaller than those of the
other circuit in their size in opposing direction of the respective
circuits.
Inventors: |
Kishikawa; Kenichiro
(Musashino, JA), Honda; Yougi (Fussa, JA) |
Assignee: |
Foster Electric Co., Ltd.
(Tokyo, JA)
|
Family
ID: |
24145832 |
Appl.
No.: |
05/538,176 |
Filed: |
January 2, 1975 |
Current U.S.
Class: |
381/408 |
Current CPC
Class: |
H04R
9/047 (20130101) |
Current International
Class: |
H04R
9/00 (20060101); H04R 9/04 (20060101); H04R
009/02 () |
Field of
Search: |
;179/115.5PV,111R,117,119R |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
3013905 |
December 1961 |
Gamzon et al. |
|
Foreign Patent Documents
Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: Stellar; George G.
Attorney, Agent or Firm: Wolfe, Hubbard, Leydig, Voit &
Osann, Ltd.
Claims
What is claimed is:
1. An electroacoustic transducer comprising
a pair of magnetic circuits respectively including at least a pair
of permanent magnets and a soft iron plate bridged between opposite
polarity ends of said magnets and opposing one another through a
clearance so that magnetic flux flowing between the other ends of
the magnets will be superposed on another as oriented in the same
direction and along said clearance, said soft iron plate in one of
said magnetic circuits having perforations for allowing sounds to
pass therethrough, and
a diaphragm made of a non-magnetic and insulative material and
extended within said clearance between the pair of magnetic
circuits, said diaphragm having at least on one surface a series of
conductors substantially extending in a direction transverse said
magnetic flux direction,
said permanent magnets in said magnetic circuit of the side having
said perforations being smaller than those in the other magnetic
circuit in the dimension in opposing direction of the magnetic
circuits.
2. The transducer according to claim 1 wherein said permanent
magnets having the smaller dimension are of a material which is
high in the coercive force and energy product.
3. The transducer according to claim 2 wherein said material for
the permanent magnet is rare earth cobalt magnet.
4. The transducer according to claim 1 wherein said series of
conductors is in zigzag shape.
5. The transducer according to claim 1 wherein said series of
conductors is disposed intermediate between the respective
permanent magnets of the respective magnetic circuits which are
adjacent in the magnetic flux direction.
Description
This invention relates to electroacoustic transducers and, more
particularly, to an electroacoustic transducer comprising a
flexible diaphragm made of a nonmagnetic and insulative material
having a series of conductors and a plurality of permanent magnet
arranged as opposed to each other with magnetic pole surfaces and
through a slight clearance on both surfaces of said diaphragm.
A known electroacoustic transducer of this kind has such structure
as is shown, for example, in FIGS. 1 and 2, in which 1 is a
diaphragm made of membrane of a nonmagnetic material, 2, 2', 2" . .
. and 3, 3', 3" . . . are a plurality pair of elongated permanent
magnets, each of the respective pairs 2 and 3, 2' and 3', 2" and 3"
. . . of which is arranged as opposed to each other with magnetic
pole surfaces through a slight clearance on both sides of the
diaphragm 1 and in parallel relation to adjacent pairs so that,
while the magnetic poles of the respective pairs adjacent one
another in expanding direction of the membrane 1 will be
alternately of different polarities, the poles of each pair
opposing will be of the same polarity. 4, 4' . . . are parallel
strip conductors formed on the diaphragm 1 by such a means as a
printing or the like so as to be respectively positioned
intermediate between the adjacent magnets 2 and 2', 2' and 2" . . .
or 3 or 3', 3' and 3" . . . , which conductors are connected at the
respective ends with one another so as to be at least one zigzag
shaped continuous conductor, as shown in FIG. 2. 5 and 6 are soft
iron plates bonded respectively on outside surfaces of the
respective groups of the magnets 2, 2', 2" . . . and 3, 3', 3" . .
. on each side of the diaphragm 1 and one of them, for example, the
iron plate 5, is provided with perforations 7 for allowing sounds
to pass therethrough, between the adjacent magnets 2 and 2', 2' and
2" and so on. Dotted lines shown in FIG. 1 in spaces between the
opposing and adjacent magnetic pole surfaces represent magnetic
flux distribution.
The operation of the electroacoustic transducer shown in FIGS. 1
and 2 shall be explained next.
Referring to FIG. 1, the opposing surfaces of, for example, the
pair of magnets 2' and 3' are of S-pole and those of adjacent pairs
of the magnets 2 and 3, 2" and 3" are N-pole, so that the magnetic
flux will be caused to flow from the respective opposing N-poles to
the respective adjacent S-poles so as to be substantially in
parallel with the plane of the diaphram 1. The parallel sections 4,
4' . . . of the continuous conductor are disposed thus in such
magnetic flux at right angles with respect to the flowing direction
of the flux.
In case an electric current is passed through the continuous
conductor in the above arrangement, the diaphragm 1 on which the
conductor is provided is subjected to an electromagnetic force
effective in a direction perpendicular to the plane of the
diaphragm. While the direction of the electric current flowing each
of the parallel sections 4, 4' . . . of the conductor is opposite
to one another, the direction of the magnetic flux traversing each
of such sections 4, 4' . . . is also opposite to one another.
Consequently, the diaphragm 1 is subjected to a driving force
effective in a fixed direction, so that the electroacoustic
transducer will be utilized as a speaker operated in response to
the direction and magnitude of the current passed through the strip
conductor.
It is obvious that in case the diaphragm 1 is caused to be vibrated
by a sound contrarily to the above, there is produced an
electromotive force in the conductor on the diaphragm 1 vibrated,
so that the electroacoustic transducer will be able to be utilized
as a microphone.
In the above described known electroacoustic transducer, it is
necessary to balance the magnetic forces of the permanent magnets
opposed to each other and, therefore, bar-shaped ferrite magnets of
the same dimensions or volume have been used but, in order to
elevate the acoustic reproduction effeciency, it is desirable that
the volume of the permanent magnets is made as large as
possible.
On the other hand, it is also necessary to provide the perforations
7 between the adjacent magnets and, therefore, in order to make the
volume of the opposing permanent magnets large enough, their
dimension in the direction in which they are opposing, that is the
height must be necessarily made larger. In such case, however, the
adjacent ones of the permanent magnets 2, 2' . . . and the
perforations 7 therebetween will act on each other to produce a
resonance phenomenon within cavities 8 inside the respective
perforations 7. Therefore, as shown by a curve A of dotted line in
FIG. 5, certain peak and dip will appear in the reproduction
frequency characteristic in the high acoustic range and any good
quality acoustic reproduction or transducing cannot be
expected.
The present invention is suggested to remove the above mentioned
problems in the electroacoustic transducers referred to,
successfully improving the frequency characteristic by making the
height of each one of the opposing pairs of the permanent magnets
on the side disposed adjacent the perforations to be smaller than
that of the other so that the volume of cavities in which the
before described resonance phenomenon occurs will be made smaller
as much as possible.
The present invention shall be explained in detail in the following
with reference to certain preferred embodiments shown in
accompanying drawings, in which:
FIG. 1 is a fragmentary sectioned view of a known electroacoustic
transducer showing essential parts thereof;
FIG. 2 is a plan view of a diaphragm used in the transducer of FIG.
1;
FIG. 3 is a similar view to FIG. 1 showing an embodiment of the
present invention;
FIG. 4 is also a similar view to FIG. 1 showing another embodiment
of the present invention; and
FIG. 5 shows output sound pressure-to-frequency characteristics of
the electroacoustic transducer of the structure shown in FIG.
3.
Referring to FIG. 3 showing an embodiment of the electroacoustic
transducer of the present invention, a plurality pair of elongated
permanent magnets 2 and 3 are arranged as opposed respectively
through a slight clearance on both sides of a diaphragm 1 which is
made of such nonmagnetic and insulative material as a plastic film
and provided on a surface with such conductors 4 as are shown in
FIG. 2. The magnetic pole surfaces of the respective pairs of the
permanent magnets parallelly adjacent in expanding direction of
said diaphragm will have alternately different polarities and the
magnetic pole surfaces opposed to each other through said diaphragm
will have polarities identical with each other. The conductor 4
provided by such means as, for example, printing on the diaphragm
is formed to be of a zigzag shape having parallel conductor parts
arranged so as to be intermediate between the adjacent ones of the
permanent magnet. Further, soft iron plates 5 and 6 are bonded
respectively on the outside surfaces of the magnet on the opposite
sides of the diaphragm 1. Only the soft iron plate 5 on one side of
them is provided with perforations 7 for radiating or passing
sounds therethrough between the magnets 2. In this formation, the
present invention has a feature that the height of the permanent
magnets 2 arranged on the sound radiating side of the diaphragm is
formed to be smaller than the height of the magnets 3 arranged on
the nonsound radiating side.
As a result of experimentally making an electroacoustic transducer
of this structure, it has been confirmed that the before described
cavity resonance phenomenon shifts out of the audible frequency
band and that, as shown by a curve B of solid line in FIG. 5, the
acoustic reproduction frequency characteristic reaches a flat and
sufficiently high frequency. Further, in such case, the opposite
magnetic forces will be unbalanced. However, if such permanent
magnet having a high holding force and energy product as a rare
earth cobalt magnet is used for the permanent magnet 2, on the
sound radiating side, even if the height, that is, the volume of
the permanent magnet 2 is reduced, it will be possible to balance
the opposed magnetic force.
Referring next to FIG. 4 showing another embodiment according to
the present invention, the energy product is increased by enlarging
the width of the permanent magnets 3 arranged on the non-sound
radiating side of the diaphragm 1 until, for example, they mutually
engage, while the volumes of the permanent magnets 2 arranged on
the sound radiating side of the diaphragm are reduced to make the
hollows 8 inside the perforations 7 small without changing the
density of the magnetic flux intersecting the conductor 4.
As described above, according to the electroacoustic transducer of
the present invention, the acoustic reproduction frequency
characteristic can be effectively improved by shifting the cavity
resonance phenomenon out of the audible frequency band by making
the height of the permanent magnets positioned on the sound
radiating or passing side of the diaphragm in the respective pairs
of the permanent magnets 2 and 3 opposing are made smaller than
that of the other magnets on the non-sound radiating or passing
side.
The present invention can be utilized extensively for speakers,
headphones, microphones and the like electroacoustic
transducers.
* * * * *