Patent Publication Number: US-6215887-B1

Title: Thin type speaker having a secondary diaphragm

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a thin type speaker, and more specifically to a speaker having a diaphragm of which the surface is covered with a secondary diaphragm. The secondary diaphragm can enhance the power capacity of the speaker and gives the speaker a larger flat effective bandwidth, with less noise. The speaker can be produced at low cost. 
     2. Description of the Prior Art 
     A conventional thin type speaker, as shown in FIGS. 1 and 2, is used in earphones, notebook computers, or miniature type radios and cassette recorders. The prior art speaker is generally composed of an enclosure  10 , a mylar cone diaphragm  20 , a yoke  30 , a sound coil  40 , a magnet  50 , a washer  60  and a tab  70 . The yoke  30  and the enclosure  10  can be integrated into a single piece. The diaphragm  20  is made of plastic material. Such a structure and materials were not changed in the past. After a wide application in the field, it becomes evident that the power capacity of the thin type speaker is rather small (around 0.3 watt). The vibration of the diaphragm  20  often produced noises and the fo value is high while the low frequency effect is poor. Also, the effective bandwidth is small (approximately between 1200 Hz and 10000 Hz). The dB value is around 83.4 dB at 1.26 volts (refer to FIG. 3 for details). Thus the actual sounding effect is not satisfied. 
     SUMMARY OF THE INVENTION 
     The primary object of the invention is to provide a thin type speaker having a secondary diaphragm which speaker consists of an enclosure, a mylar cone vibration diaphragm, a yoke, a sound coil, a magnet, and a washer. The vibration diaphragm is further provided with a secondary diaphragm on the surface thereof. The secondary diaphragm is made of sponge, cloth, paper, cardboard, or isolating fabric. With such a structure, the speaker can have larger tensioning at a higher power output and thus enhance the power capacity. It has been proven by tests that the power capacity of such a speaker can reach 1.5 volts. Also, the inventive speaker has larger flat effective bandwidth, which is approximately between 400 Hz and 20000 Hz, with less noise, and low costs in manufacturing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of a conventional thin type speaker. 
     FIG. 2 is a cross sectional view of the conventional speaker shown in FIG.  1 . 
     FIG. 3 is a test data diagram of the conventional thin type speaker. 
     FIG. 4 is an exploded view of a thin type speaker according to the invention. 
     FIG. 5 is a cross sectional view of the speaker shown in FIG.  4 . 
     FIG. 6 is a perspective view of the speaker assembly according to the invention. 
     FIG. 7 is a test data diagram of the speaker according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIGS. 4 to  6 , the invention is a thin type speaker having a secondary diaphragm. The speaker comprises an enclosure  1 , a mylar cone diaphragm  2 , a yoke  3 , a sound coil  4 , a magnet  5 , and a washer  6 . The enclosure  1  is provided with a tab  7  at a chosed position. More specifically, the invention is an improvement made on the configuration of the diaphgram  2 . Other parts such as the enclosure  1 , the yoke  3 , the sound coil  4 , the magnet  5 , the washer  6 , and the tab  7  are similar to those included in the conventional structure and thus will not be detailed here. Also, the enclosure  1  and the yoke  3  can be integrated into a single piece, which has been known to the public. 
     The improvements made on the configuration of the diaphgram according to the invention primarily include a secondary diaphragm  21  attached to the surface of the mylar cone diaphragm  2 . The secondary diaphragm  21  is configured to have a shape and size corresponding to the vibration surface of the diaphragm  2  so that it can be completely adhered to the diaphragm  2 . The secondary diaphragm  21  is made of materials such as sponge, cloth, paper, carboard, or isolating fabric. With such an arrangement, the diaphragm  2  has a secondary diaphragm  21 , which can cooperate with other conventional parts to form a thin type speaker. 
     The way to assemble the above components is as follows. A tab  7  is attached to a position corresponding to the notch  11  of the enclosure  1 . Next, the yoke  3  having a cap configuration is placed in the central hole of the enclosure  1 , with the rim  31  thereof coupled with the outer wall of the central hole to form a firm engagement. Alternatively, the yoke  3  and the enclosure  1  can be integrated into a single piece. Further, the magnet  5  and the washer  6  are placed into the yoke  3 . A sound coil  4  is disposed under the diaphgram  2  in advance. After that, the sound coil  4  together with the diaphragm are placed into the enclosure  1  in such a way that the sound coil  4  embraces the magnet  5  and the washer  6 , with two conductor wires  41  and  42  connected to the tab  7  on the enclosure  1  by soldering. These two conductor wires  41  and  42  of the sound coil  4  further connect to a wire connector  9  via external conductor wires  81  and  82 . 
     The enclosure  1  described above has an inner wall surface, attached to which is a grille  12  that can prevent dusts and tiny particles from invading, which may affect the frequency response of the diaphragm  2 . 
     A diaphragm having a secondary diaphragm according to the invention and combined with other conventional parts has been completed and tested by the inventor. FIGS. 7 and 3 respectively show the test data of the inventive speaker and a conventional one. As shown in the diagrams, for a conventional speaker, the power capacity of a conventional speaker is only 0.3 watt and the fo value is high. Furthermore, the conventional speaker lacks a low frequency effect and the effective frequency bandwidth is between 1200 Hz and 10000 Hz. The dB value at the 1.26 volt is around 83.4 dB. Thus evidently the sound effect is not good. However, the test data of a speaker according to the invention indicates that the power capacity reaches 1.5 watts and the speaker has a larger and flat frequency bandwidth from 400 Hz to 20000 Hz. The improvement in the speaker performance is considerable and is innovative and useful in the industry. On the other hand, the inventive speaker is easy-to-make. The manufacturing cost of the inventive speaker is low but the effect is great. 
     From the above description, the improvements according to the invention is indeed a significant innovation for conventional thin type speakers. The performance of the inventive speaker is evidently superior to conventional ones. 
     The present invention is by no means restricted to the above-described preferred embodiments, but covers all variations that might be implemented by using equivalent functional elements or devices that would be apparent to a person skilled in the art, or modifications that fall within the spirit and scope of the appended claims.