Speaker

An elastic material such as rubber is employed as the material of a diaphragm and the diaphragm is constructed in such a state that tension is made to exist intrinsically therein, whereby the vibration of the diaphragm when the vibration is applied to it has a large amplitude at the center thereof, gets smaller when approaching the perimeter thereof and finally reaches zero at the edge portion. Accordingly, almost no phenomenon occurs in which air in front and air in the rear of the diaphragm interfere with each other, a speaker box is not required and a tone of good quality may be reproduced.

BACKGROUND OF THE INVENTION 
The present invention relates to a speaker that has a unique diaphragm. 
There are several types of speakers that have been heretofore used 
including a moving coil type speaker, but a diaphragm is provided as one 
element thereof in any case. 
The diaphragm which has been used so far is composed of what is called a 
rigid body formed with nonelastic material such as paper into a cone 
shape. 
In a diaphragm made of a rigid body as described above, a shearing 
phenomenon is presented between the air contacting the diaphragm directly 
and the air existing in the peripheral end area of the diaphragm when the 
diaphragm vibrates. As a result, the air in front and the air in the rear 
of the diaphragm interfere (negates) with each other, and this phenomenon 
becomes remarkable particularly in the bass region. Accordingly, the 
speaker is generally housed in a housing in order to suppress such a 
phenomenon to a certain extent, but it is still impossible to suppress 
such a phenomenon completely, thus deteriorating the tone quality. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a speaker which 
dissolves drawbacks of the conventional technique described above and has 
no mutual interference of the air in front and in the rear of the 
diaphragm. 
The abovementioned object of the present invention may be attained by 
adopting the following means. That is, there is provided a speaker 
characterized in that a diaphragm composed of an elastic material such as 
rubber is held in a configuration such that tension exists in the 
diaphragm, and a central member composed of a rigid material is attached 
at the center of the diaphragm, whereby it is easy both to apply tension 
to the diaphragm and to connect the diaphragm with a converter such as a 
voice coil.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In a speaker according to the present invention, a diaphragm 1 composed of 
an elastic material such as rubber is stretched on an outer frame 2 having 
an annulus ring shape or a square annulus shape and the central portion 
thereof is connected with a converter 3 such as a voice coil through a 
coupling portion 4. 
Furthermore, the diaphragm 1 is installed under such a condition that 
tension exists intrinsically therein when it is stretched on the outer 
frame 2. Otherwise, after the diaphragm is stretched on the outer frame 2, 
a tension vesting piece 5 such as a spring or a rubber band, etc., is 
disposed as shown in FIG. 2 so as to result in producing tension in the 
diaphragm 1. 
When the diaphragm 1 made of an elastic material which is stretched under 
such a condition that tension exists intrinsically therein is vibrated by 
the converter 3, the vibrating state at that time is such that the central 
portion of the diaphragm 1 has the maximum amplitude, the amplitude 
becomes smaller as one approaches the peripheral edge portion of the 
diaphragm 1, and the amplitude becomes zero at the fixed portion with the 
outer frame 2. Accordingly, no shearing phenomenon is generated between 
the air contacting the diaphragm 1 directly and the air around the 
diaphragm 1, resulting in no mutual interference between the air in front 
and in the rear of the diaphragm 1. 
Furthermore, among vibrations applied to the diaphragm 1, the vibration for 
bass that has a low frequency tends to be transmitted close to the 
peripheral end area of the diaphragm 1 against the tension existing 
intrinsically in the diaphragm 1, but the vibration for a high-pitched 
tone that has a high frequency tends not to be transmitted so far to the 
peripheral end area because the transmittance thereof is suppressed by the 
tension existing in the diaphragm 1. Accordingly, when vibrations of 
various compasses are transmitted to the diaphragm 1, such a state is 
created that the vibration in the high compass is laid on top of the 
vibration in the low compass, and natural tone quality in which various 
compasses are fixed may be reproduced. 
According to the present invention, a central member composed of a rigid 
material such as hard paper, plastic, wood or metal is attached in some 
cases in such a configuration as to integrate it with the diaphragm at the 
central portion of the diaphragm composed of elastic material as described 
above. By doing so, it becomes easy to maintain an internal tension which 
is appropriate for the diaphragm under a uniform condition. 
The present invention will be described in detail hereinafter with 
reference to specific embodiments. 
EXAMPLE 1 
In Example 1, a diaphragm 1 made of rubber is stretched on an outer frame 2 
in such a configuration as to include tension intrinsically therein as 
shown in FIG. 3. As shown in FIG. 4 which shows the internal structure 
thereof, the diaphragm 1 is provided with a hole 6 for fitting a voice 
coil 3' at the center thereof, and a coupling portion 4 of the voice coil 
3' is inserted through hole 6 so as to couple the diaphragm 1 with the 
voice coil 3'. Besides, in FIG. 4, numeral 7 denotes a permanent magnet, 
and 8 denotes a frame body. 
When various tones were reproduced with the speaker of Example 1 having the 
above-described structure, a tone of a very good quality was reproduced 
over a wide compass without employing a housing. 
EXAMPLE 2 
As to Example 2, as shown in FIG. 5 which is a perspective view of a 
speaker according to Example 2 and FIG. 6 which is an explanatory view of 
the internal structure thereof, a rigid central member 9 composed of 
plastic is fitted at the center of the diaphragm 1 made of rubber of 
Example 2 so as to be integrated with the diaphragm 1. Tension of the 
diaphragm 1 is applied to some extent when it is stretched on the outer 
frame 2, but the inner structure thereof is formed in such a manner that a 
spring 5' is disposed in the rear of central member 9 and the fixed 
portion between the diaphragm 1 and the coupling portion 4 is pulled to 
the rear of the diaphragm so that an appropriate tension is applied to the 
diaphragm 1 as shown in FIG. 6. In the speaker according to Example 2, it 
is possible to obtain an appropriate tension of the diaphragm 1 by 
adjusting the tensile force of the spring 5'. 
With the speaker of Example 2 having the above-mentioned structure, a tone 
of very good quality can also be reproduced over a wide compass without 
using a housing similarly to Example 1. 
EXAMPLE 3 
As shown in FIG. 7 which shows the internal structure, Example 3 has such a 
structure that a spring 5" which pushes the diaphragm 1 forward is 
disposed in the rear of the diaphragm 1 and the central portion of the 
diaphragm 1 is maintained in such a configuration that the central portion 
of the diaphragm 1 is made to project slightly forward thereby to apply 
tension to the diaphragm 1. With the speaker according to Example 3, it is 
also possible to obtain an appropriate tension of the diaphragm 1 by 
adjusting the pressing force of the spring 5" similarly to Example 2. 
With the speaker according to Example 3 having the above-described 
structure, a tone of very good quality can be reproduced over a wide 
compass without using a housing, and furthermore, it is possible to expand 
the tone toward a wider direction. 
As described above, according to the present invention, the diaphragm 
itself is composed of an elastic material and a condition of maintaining 
tension inside is obtained. Accordingly, there occurs almost no shearing 
phenomenon between the vibrating air and the fixed air which has always 
occurred in a conventional speaker which employed a diaphragm made of a 
rigid material. Thus, a tone of good quality may be reproduced without 
using a housing, and a tone of wide compass may be reproduced with a 
single diaphragm only, whereby a thin, light-weight and compact unit may 
be obtained. Furthermore, the diaphragm and the converter are coupled with 
each other at the central portion only and easily detached from each 
other. Therefore, a desired tone quality is obtainable simply by replacing 
the diaphragm with one having a different thickness of the elastic body 
forming the diaphragm and tension existing therein.