A planar type electroacoustic transducer comprising a diaphragm; at least one magnet plate on which are formed a plurality of mutually different and spaced magnetic poles in a matrix shape of columns and rows so as to face the diaphragm at a distance enough to involve the facing surface of the diaphragm within magnetic fields associated with the magnetic poles; and an electric conductor formed on the diaphragm to run in alternate directions of a column and a row along a path corresponding to the spaces defined between the respective magnetic poles without straightforwardly passing by any two magnetic poles of a same column or row. This diaphragm may be provided with ribs to further minimize the development of partial vibrations of the diaphragm. Those portions of the conductor running in regions of weak magnetic fields may have an enlarged size or smaller length to reduce the impedance of the conductor.

BACKGROUND OF THE INVENTION 
(a) Field of the Invention 
The present invention pertains to planar type electroacoustic transducers 
which are employed in headphones, loadspeakers, microphones or like 
devices. 
(b) Description of the Prior Art 
As electroacoustic transducers for converting electric signals to acoustic 
signals or for converting acoustic signals to electric signals, there have 
been developed various types of transducers including electrostatic type 
and electrodynamic type transducers. As electroacoustic transducers for 
use in, for example, headphones, there have been developed transducers of 
electrodynamic and planar types. As such example, FIG. 1 shows a 
diagrammatic partial plan view of a known planar type electroacoustic 
transducer arrangement. FIG. 2 is a sectional view taken along II--II in 
FIG. 1. In FIG. 1, there is provided, on a planar type diaphragm 1, a 
flexible electric conductor 2 in a wave-like pattern. A magnet plate 3 is 
arranged beneath the diaphragm 1 as shown in FIG. 2. This conductor 2 has 
straightly extending portions and curved portions which connect adjacent 
straightly extending portions to each other. The magnet plate 3 is 
provided with parallel rows of magnetic poles which are arranged to change 
in alternate fashion from one row to another. The straightly extending 
portions of the electric conductor 2 are arranged to be positioned between 
the respective rows of the magnetic poles so that each row having the same 
single pole extends along the straightly extending portions of the 
electric conductor 2. The magnetic fields which are produced at the 
straightly extending portions of the electric conductor 2 by these 
magnetic poles are indicated at symbols A, A, . . . in FIG. 2. Broken 
lines in FIG. 2 represent a part of the lines of magnetic flux. 
The operation of the electroacoustic transducer shown in FIGS. 1 and 2 is 
as follows. If an electric current is caused to flow through the electric 
conductor 2 in the direction indicated by the arrow B shown in FIG. 1, a 
force acts on every portion of the conductor 2, excluding the curved 
portions thereof, in the direction indicated by the arrow E shown in FIG. 
2 in accordance with Fleming's left-hand rule, so that the diaphragm 1 is 
lifted upwardly in FIG. 2. Conversely, if an electric current is caused to 
flow through the electric conductor 2 in a direction opposite to that 
shown by the arrow B in FIG. 1, the diaphram 1 is caused to descend 
downwardly in FIG. 2 toward the magnet plate 3. Thus, if a current 
carrying audio signal is caused to flow through the conductor 2, the 
diaphragm 1 will vibrate upwardly and downwardly in FIG. 2 in accordance 
with the current of the audio signals, so that the electric signals can be 
converted to acoustic signals. 
However, in such known electroacoustic transducer as mentioned above, 
especially in conventional planar types of such devices, the electric 
conductor provided on a diaphragm is oriented to run merely in upgoing and 
downgoing directions on the diaphragm, and thus, there is the disadvantage 
that partial vibrations of the diaphragm tend to appear at sites between 
the adjacent runs of the conductor. Moreover, in such a conventional 
electroacoustic transducer, the diaphragm is simply flat in shape, and 
accordingly the diaphragm is poor in rigidity, and this also causes nodes 
of vibration mode to develop at portions of the diaphragm located between 
adjacent runs of the conductor, leading to development of partial 
vibrations. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a planar 
type electroacoustic transducer which is free of those disadvantages of 
prior art devices and which minimizes the development of partial 
vibrations in a diaphragm. 
Another object of the present invention is to provide such improved planar 
type electroacoustic transducer as described above, which is capable of 
accomplishing an effective use of magnetic fields of the magnet pieces 
which constitute the transducer. 
A further object of the present invention is to provide a planar type 
electroacoustic transducer as described above, which is capable of 
providing quality sounds due to the abovementioned features. 
Yet another object of the present invention is to provide a planar type 
electroacoustic transducer as described above, which is capable of 
improving the conversion efficiency between electric signals and acoustic 
signals. 
Still further object of the present invention is to provide a planar type 
electroacoustic transducer as described above, which permits the 
employment of magnets of desired various configurations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As stated above, it is the primary object of the present invention to 
provide an improved planar type electroacoustic transducer which minimizes 
the development of partial vibrations in the diaphragm which tend to 
appear in conventional planar type transducers. 
In accordance with an aspect of the present invention, magnet pieces are 
arranged in a matrix form of columns and rows, leaving intervals or spaces 
between any adjacent magnet pieces in the columns and rows, in such manner 
that the magnetic poles at their surfaces differ from adjacent ones in the 
respective columns and rows, and an electric conductor is arranged to run 
on a diaphragm along the spaces difined between the magnet pieces of the 
matrix of columns and rows in such manner that the electromagnetic forces 
which are generated on this conductor when an electric current is caused 
to flow through this conductor are oriented in a certain single direction. 
An embodiment of the present invention will hereunder be described by 
referring to the drawings. 
FIG. 3 is an explanatory diagrammatic side elevation of an embodiment of 
the planar type electroacoustic transducer of the present invention, 
showing the basic principle of this invention. FIG 4 is a diagrammatic 
exploded view of the embodiment shown in FIG. 3. 
The planar type electroacoustic transducer shown in this basic embodiment 
is of the arrangement comprising an electric-conductor-carrying diaphragm 
5, an upper magnet plate generally indicated at 6 having a plurality of 
spaced magnet pieces, and a lower magnet plate generally indicated at 7 
having positionally corresponding plurality of spaced magnet pieces, said 
upper and lower magnet plates 6 and 7 being provided to sandwich the 
diaphragm 5, leaving equal distances between the respective free surfaces 
of the magnet pieces and their corresponding surfaces of the diaphragm 5, 
so that the free surfaces of these magnet pieces on the respective 
opposingly arranged upper and lower magnet plates 6 and 7 face each other. 
In FIG. 3, the broken lines containing arrows represent part of the 
magnetic flux of the respective magnet pieces. As shown in FIG. 4, the 
lower magnet plate 7 is comprised of 16 magnet pieces 8, in this 
embodiment, which are arranged in a matrix form of columns and rows 
provided at right angles relative to each other on a yoke plate 9 which is 
made with a ferromagnetic material in such manner that these magnet pieces 
are disposed at equal intervals relative to each other leaving spaces 
therebetween. These magnet pieces 8, 8, . . . are magnetized in a 
direction perpendicular to the surface of the yoke plate 9, and they are 
arranged so that the magnetic poles at the respective surfaces of these 
magnet pieces are different from adjacent ones in all the columns and 
rows. Also, the yoke plate 9 is provided with a plurality of acoustic 
signal passage apertures 13, 13, . . . for discharging, to the outside of 
the magnet plate 7, acoustic signals produced by vibrations of the 
diaphragm 5, in a same manner and in positional coincidence with those 
acoustic signal passage apertures 13, 13, . . . of the upper magnet plate 
6 which will be described later. That is, the upper magnet plate 6 is 
formed in exactly the same manner as that of the lower magnet board 7, and 
has 16 magnet pieces 11, 11, . . . which are carried on a yoke plate 12 
provided with acoustic signal passage apertures 13, 13, . . . 
corresponding in number and arrangement as those of the lower magnet plate 
7. 
The magnet pieces 8, 8, . . . of the lower magnet plate 7 and those magnet 
pieces 11, 11, . . . of the upper magnet plate 6 are made of magnets of 
either the ferrite group or RCo.sub.5 group. The symbol R in said 
RCo.sub.5 group magnets represents a rare earth element such as Sm 
(Samarium) and Ce (Cerium). More particularly, RCo.sub.5 group magnets 
include, for example, Samarium Cobalt SmCo.sub.5, Cerium Cobalt 
CeCo.sub.5, Copper-Substitution Samarium Cobalt Sm(Co, Cu, Fe).sub.5, and 
Copper-Substitution Cerium Cobalt Ce(Co, Cu, Fe).sub.5. 
The diaphragm 5 which is employed in the present invention is made with a 
film of a high molecular material such as polyethylene terephthalate 
(P.E.T.), polyimide and polyethylene, and carries on one surface thereof 
an electric conductor 10 which is made with an electroconductive metal 
such as aluminum and copper. This electric conductor 10 is arranged on the 
diaphragm 5 so as to run in alternate directions of rows and columns of 
the matrix along the paths positionally corresponding to the spaces 
defined between the respective magnet pieces 8, 8, . . . of columns and 
rows of the lower magnet plate 7, in such manner that the electromagnetic 
forces which are developed by the magnetic fields which, in turn, are 
formed by the magnet pieces 8, 8, . . . , if an electric current is caused 
to flow through the conductor 10, are oriented in a certain single 
direction at all portions of the conductor 10 which is subjected to these 
electromagnetic forces. It should be noted that the respective magnet 
pieces 11, 11, . . . of the upper magnet plate 6 are arranged so that the 
magnetic poles at the respective surfaces of these magnet pieces 11, 11, . 
. . are identical with the magnetic poles at their opposing respective 
surfaces of those magnet pieces 8, 8, . . . of the lower magnet plate 7, 
as shown in FIG. 3. 
Next, the operation of the above-stated example having the foregoing 
arrangement will be described. 
FIG. 5 is an explanatory diagrammatic plan view showing the positional 
relationship between the magnet pieces 8, 8, . . . of the lower magnet 
plate 7, as an aid to explain the operation. It should be noted that the 
broken lines with arrows in FIG. 5 represent magnetic fields or magnetic 
flux, which are formed by the magnet pieces 8, 8, . . . 
Let us now assume that an electric current is caused to flow through the 
electric conductor 10 in a direction indicated by the arrow C. The 
electric current flows through the conductor 10 which is located within 
the magnetic fields formed by the magnet pieces 8, 8, . . . Accordingly, 
in accordance with Fleming's left-hand rule, the respective portions of 
the conductor 10 are subjected to electromagnetic forces of a same phase 
running in the direction leading from the rear side of the sheet of 
drawing toward the front side of this drawing. Conversely, if an electric 
current is caused to flow through the conductor 10 in a direction 
indicated by the arrow D in FIG. 5, the respective portions of the 
conductor 10 will be subjected to electromagnetic forces of an equal phase 
running from the front side of the sheet of drawing toward the rear side 
of this drawing, in accordance with Fleming's right hand rule. Therefore, 
when an AC current of low frequency, such as an audio signal current, 
flows through the conductor 10, conductor 10 will vibrate in accordance 
with the AC current. As a result, the diaphragm 5 which carries the 
conductor 10 will be caused to vibrate in accordance with this AC current, 
and thus the AC current is converted to an acoustic signal. These types of 
operations are utilized in, for example, headphones and loudspeakers in 
which such arrangement is provided. 
On the other hand, if an acoustic signal is applied to the diaphragm 5, 
this diaphragm will vibrate in accordance with the acoustic signal applied 
thereto. This will be accompanied by vibration of the conductor 10 which 
is carried on the diaphragm 5. As a result, the respective portions of 
this conductor 10 will naturally traverse the magnetic flux formed by the 
magnet pieces 8, 8, . . . , and thus and electromotive force is induced in 
the conductor 10 in accordance with Fleming's right-hand rule. Thus, the 
acoustic signal is converted to an electric signal by the operation 
described above. 
FIG. 6 shows another embodiment of the present invention. This embodiment 
is concerned with an instance wherein the magnet pieces provided on each 
of the upper and lower magnet plates 6 and 7 are nine (9) in number. FIG. 
6 shows the positional relationship between the magnet pieces 8, 8, . . . 
of the lower magnet plate 7 and the electric conductor 10. It should be 
noted, however, that those portions of the conductor 10 which are enclosed 
in circles X of one-dot-chain-lines and those portions indicated at Y 
which are larger in size than the remainder of the conductor represent the 
regions where the magnetic fields are weak as will be understood from the 
nature of magnets, and where, thus, efficiency of the electroacoustic 
conversion is small. Accordingly, it will become possible to lower the 
overall impedance or the power loss of the conductor 10 as a whole by 
reducing the lengths of these portions X and by enlarging the size of the 
portions Y, thus decreasing the impedance of these portions. FIG. 6, 
however, shows the instance of arrangement that those portions of the 
conductor 10 located at the periphery of the magnet pieces are enlarged in 
size. FIG. 7 shows an instance wherein those portions of the conductor 10 
which are marked by X in FIG. 6 are arranged to run in a diagonal pattern, 
to thereby reduce the overall length of the conductor 10, whereby the 
abovesaid loss can be reduced. 
Description of the present invention has been made above with respect to a 
basic embodiment shown in FIGS. 3 and 4, wherein there are provided an 
upper magnet plate 6 and a lower magnet plate 7. It should be noted, 
however, that the provision of two upper and lower magnet plates 6 and 7 
is not mandatory. The present invention may be equally effectively 
constructed with only a combination of one magnet plate and a diaphragm 5 
carrying thereon an electric conductor 10. 
It should be understood also that the number of magnet pieces for the 
magnet plate is not limited to 16 as shown in FIG. 4 or to 9 as in FIG. 6, 
but that any desired number of magnet pieces can be employed. 
It should be noted further that the conductor 10 shown in FIG. 4 is 
provided as a single conductor, but that the conductor 10 may be provided 
to run in double, or triple, . . . fashion. Such example is shown in FIG. 
8. In such case also, it is effective to reduce the impedance of those 
portions X and Y in a manner as described above. 
Description has been made above with respect to an instance of the 
so-called anistropic structure, i.e. where, as shown in FIG. 4, the upper 
magnet plate 6 and the lower magnet plate 7 are constructed by securing 
magnet pieces 11, 11, . . . and 8, 8, . . . to a yoke plates 12 and 9, 
respectively, so that the N-S poles of these magnet pieces are oriented in 
a direction perpendicular to the diaphragm 5. It should be understood, 
however, that an isotropic structure may be employed as shown in FIG. 9. 
In this embodiment shown in FIG. 9, the magnet pieces of the upper and 
lower magnet plates 6 and 7 are magnetized so that the magnetic poles are 
arranged to lie parallel with the diaphragm 5. 
As another aid to minimize the development of partial vibrations of the 
diaphragm, there are provided, in accordance with another aspect of the 
present invention, ribs on the diaphragm. These ribs are provided at such 
sites of the diaphragm where nodes of vibration modes of the diaphragm 
tend to develop easily, so that the conductor is arranged to run at sites 
other than those regions where the ribs are provided, to thereby 
practically reduce partial vibrations of the diaphragm and to provide 
quality sounds. Moreover, in accordance with this aspect of the present 
invention, the size of those magnet pieces which face each other via the 
diaphragm is varied, to thereby obtain effective use of the magnetic flux 
formed by magnet pieces. 
FIG. 10 shows an explanatory diagrammatic plan view of an embodiment 
wherein the total number of the magnet pieces is eight (8). In practice, 
however, the total number of magnet pieces will be greater than just eight 
(8). It should be understood that a transducer having such a greater 
number of magnet pieces may be easily materialized as will be seen from 
the description made hereunder. 
In FIG. 10, and FIGS. 11 and 12 which are sections of the structure shown 
in FIG. 10, the upper magnet plate 6a is constructed with a yoke plate 12a 
which, in turn, is made with a ferromagnetic material, and four (4) magnet 
pieces 11a, 11b, and 11c and 11d. These magnet pieces 11a through 11d are 
arranged on the yoke plate 12a in columns and rows via spaces intervening 
therebetween. There are provided, in those portions of the yoke plate 12a 
located at positions corresponding to the spaces between the respective 
magnet pieces, a plurality of sound-passage apertures 13a, 13a, . . . for 
discharging to the outside of the plate those acoustic signals produced by 
the diaphragm 5a. The magnet pieces are arranged so that those which are 
located diagonally relative to each other, i.e. those 11a and 11c, and 
those 11b and 11d, have equal heights, respectively, as noted in FIGS. 11 
and 12. Also, those magnet pieces 11a and 11c have a height smaller than 
the height of those magnet pieces 11b and 11d. Also, these magnet pieces 
11a through 11d of the upper yoke plate 12a are magnetized in an 
orientation perpendicular to the yoke plate 12a. Also, the magnetic poles 
of these magnet pieces 11 a through 11d located on that side facing the 
diaphragm 5a are arranged so that the magnet piece 11a has an N pole, and 
the magnet piece 11b has an S pole, the magnet piece 11c has an N pole and 
the magnet piece 11d has an S pole, so that the magnetic poles are 
different from each other in the adjacent column and row of the matrix. 
These magnet pieces 11a through 11d may be made with those materials 
described previously with respect to the embodiments shown in FIGS. 3 and 
4. 
The diaphragm 5a is provided at such position as facing the magnet pieces 
11a through 11d, and it may be made with a material same as that described 
in the embodiment shown in FIGS. 3 and 4. This diaphragm 5a alone is shown 
in perspective view in FIG. 13. As will be noted in FIG. 13, this 
diaphragm 5a is provided with a protruding rib 14a at a position 
corresponding to the location of the magnet piece 11a, a recessed rib 14b 
at a position corresponding to the location of the magnet piece 11b, a 
protruding rib 14c at a position corresponding to the location of the 
magnet piece 11c, and a recessed rib 14d at a position corresponding to 
the location of the magnet piece 11d, by an appropriate manufacturing 
means such as heat-press molding technique. An electric conductor 10a 
which is made with an electroconductive material such as aluminum and 
copper is provided to run at sites other than the locations of these ribs 
14a through 14d, i.e. at such positions corresponding to the spaces 
defined between the respective magnet pieces 11a through 11d. Furthermore, 
at the marginal portions of the diaphragm 5a, there is provided a spacer 
15. In a manner as described with respect to the embodiment shown in FIGS. 
3 and 4, the electric conductor 10a is arranged to run in the pattern of 
columns and rows within the magnetic fields which are formed by the magnet 
pieces 11a through 11d, in such manner that, when an electric current is 
caused to flow through this conductor 10a, the respective portions of this 
conductor 10a are subjected to electromagnetic forces delivered by the 
magnetic fields and that these electromagnetic forces are oriented in a 
certain single direction. The diaphragm 5a may be formed with U-shaped or 
V-shaped edges on the inner side of the spacer 15, though not illustrated 
here. The protruding ribs and recessed ribs 14a through 14d may be formed 
after the conductor 10a and/or the spacer 15 have been provided on the 
diaphragm 5a. 
At positions facing the other side of the diaphragm 5a, i.e. on that side 
of the diaphragm 5a opposite to the side facing the upper magnet plate 6a, 
there are provided magnet pieces 8a, 8b, 8c and 8d which are secured to a 
lower yoke plate 9a, to jointly constitute a lower magnet plate 7a. These 
magnet pieces 8a through 8d are positioned to face, via the diaphragm 5a, 
those magnet pieces 11a through 11d of the upper magnet plate 6a, 
respectively. The direction in which the magnet pieces 8a through 8d are 
magnetized is perpendicular to their yoke plate 9a. Also, the magnetic 
poles of these magnet pieces 8a through 8d on that side facing the 
diaphragm 5a are equal to those magnetic poles at those surfaces of the 
magnet pieces 11a through 11d, respectively, of the upper magnet plate 6a 
which are faced by the magnet pieces 8a through 8d of the lower magnet 
plate 7a. Also, in much the same way as for those magnet pieces of the 
upper magnet plate 6a, the magnet pieces 8a and 8c have a same height, 
whereas those magnet pieces 8b and 8d have another same height. 
Furthermore, the height of the magnet pieces 8a and 8c are greater than 
the height of the magnet pieces 8b and 8d. That is, as will be understood 
from FIGS. 11 and 12, the heights of the magnet pieces 11a through 11d of 
the upper magnet plate 6a and the heights of the magnet pieces 8a through 
8d of the lower magnet plate 7a are set in correspondence with the 
recessed or protruding configurations of these ribs 14a through 14d which 
are formed on the diaphragm 5a. Thus, the respective magnet pieces which 
face each other via the intervening diaphragm 5a differ in their height 
relative to each other. By this arrangement, the magnetic gap between the 
upper magnet plate 6a and the lower magnet plate 7a is reduced, so that 
the magnetic fields which are formed by the respective magnet pieces will 
act effectively on the electric conductor 10a. It should be understood 
that, other than the arrangement per se of the lower magnet plate 7a 
described above, this lower magnet plate 7a is same with the upper magnet 
plate 6a with respect to the material and so forth. 
Description will next be made of the operation of the planar type 
electroacoustic transducer having the aforesaid arrangement. FIG. 14 shows 
the positional relationship between the magnet pieces 8a through 8d of 
the lower magnet plate 7a and the electric conductor 10a to explain the 
operation. It should be noted that the broken lines with arrows in FIG. 14 
represent the directions of the magnetic fields which act upon the 
conductor 10a. 
Description of operation will first be made of the instance wherein this 
instant embodiment is applied to headphones or like devices. In FIG. 14, 
let us assume that an electric current is caused to flow through the 
conductor 10a in the direction indicated by the arrow A. This means that 
the electric current flows through the conductor 10a which lies within the 
magnetic fields which are formed by the magnet pieces 8a through 8d. 
Accordingly, the respective portions of the conductor 10a are subjected to 
electromagnetic forces of a same phase and running in the direction of B 
shown in FIG. 14, in accordance with Fleming's right-hand rule. 
Conversely, in case an electric current is caused to flow in the direction 
of arrow C, the respective portions of the conductor 10a will be subjected 
to electromagnetic forces of a same phase and running in the direction D. 
Therefore, in case an AC current of low frequency such as an audio signal 
is caused to flow through the conductor 10a, the conductor 10a will 
vibrate in accordance with this AC current of low frequency. As a result, 
the diaphragm 5a on which the conductor 10a is secured will vibrate, and 
the vibration of this diaphragm 5a will be derived as an acoustic signal. 
Next, description will be made of the operation in case an acoustic signal 
is applied to the diaphragm 5a. This means the operation in the instance 
that the present invention is applied to a microphone. In case an acoustic 
signal is applied to the diaphragm 5a, the diaphragm will vibrate in 
accordance with the acoustic signal applied thereto. In accordance 
therewith, the conductor 10a will vibrate. As a result, the respective 
portions of the conductor 10a will traverse the magnetic flux which is 
formed by the magnet pieces 8a through 8d. In accordance with Fleming's 
right-hand rule, there is induced an electromotive force within the 
conductor 10a. In other words, the acoustic signal applied to the 
diaphragm 5a is converted to an electric signal. 
Next, description will be made briefly of the process of manufacture of 
those magnet pieces which are employed in the respective embodiments of 
the present invention, by referring to FIGS. 15A and 15B, and the FIGS. 
16A through 16D. 
FIGS. 15A and 15B show the steps of making a magnet plate from an isotropic 
magnet powder such as isotropic barium ferrite. As a first step, the 
isotropic magnet powder is subjected to compression-molding to provide a 
compact 17 shown in FIG. 15A. Then, this compact 17 is subjected to 
sintering at a required temperature, and thereafter the resulting product 
is magnetized as shown in FIG. 15B. 
FIGS. 16A through 16D show the steps of making a magnet plate from an 
anisotropic magnet powder such as anisotropic strontium ferrite. As a 
first step, the anisotropic magnet powder is subjected to 
compression-molding into a compact 17a as shown in FIG. 16A. After this 
compact 17a is sintered at a predetermined temperature, a molding resin 18 
is filled in the recessed portion of the compact 17a, as shown in FIG. 
16B. Then, the bottom portion of the resulting compact 17a is removed by 
either machining or grinding as shown in FIG. 16C. Finally, a yoke plate 
19 is caused to adhere to the bottom surface of the compact 17a in a 
manner as shown in FIG. 16D. Thereafter, the resulting product is 
magnetized. 
As in the embodiment shown in FIGS. 3 and 4, it should be understood that, 
in the later embodiments also, the provision of both the upper magnet 
plate 6a and the lower magnet plate 7a is not always necessary. Also, the 
conductor 10a may be provided to run in double or triple or any desired 
number of turns. The pattern of run of the conductor and the size thereof 
at such portions where the magnetic field is weak may be as described in 
connection with the embodiment of FIGS. 6 and 7. 
The magnet pieces employed in the present invention may have their plan 
shapes which are not limited to the square shape shown in FIG. 4 or FIG. 
6. They may be made to have round or rectangular shapes as shown in FIG. 
17. 
In the embodiment shown in FIGS. 10 through 16, the diaphragm is provided 
with recessed and/or protruding ribs. Therefore, the rigidity of the 
diaphragm is increased also. Thus, it is possible to expand the range of 
piston-like movements of the diaphragm as a whole. Also, the conductor is 
arranged to run, in the modified embodiment, avoiding those regions where 
there tend to develop nodes of vibration modes of the diaphragm due to the 
provision of the ribs, and this also contributes to an expansion of the 
range of piston-like movements of the diaphragm. As a result, it is 
possible to provide planar type electroacoustic transducers having 
minimized partial vibrations of the diaphragm and accordingly deliver 
quality sounds. Furthermore, the different heights of the opposing magnet 
pieces contributes to an improvement of effective action of magnetic 
fields upon the conductor. 
As referred to above, the present invention can be suitably applied to 
headphones and like devices. However, it may be effectively applied to 
microphones and like devices.