Acoustics – Diaphragm – Critically defined material or coating
Patent
1983-03-29
1984-07-17
Cannon, James C.
Acoustics
Diaphragm
Critically defined material or coating
179181R, 181170, 428224, 428251, 428252, 428283, 428284, 428285, 428287, 428337, 428339, 428408, 428902, G10K 1300, H04R 704, H04R 710
Patent
active
044600607
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD TO WHICH THE INVENTION BELONGS
The present invention relates to a vibratory diaphragm for a loudspeaker. More particularly, it relates to a vibratory diaphragm for use in a loudspeaker of the sound appliances such as home stereophonic phonographs, autostereos, television receivers, radios or tape recorders.
BACKGROUND ART OF THE INVENTION
A vibratory diaphragm for a loudspeaker (hereinafter referred to as the "diaphragm"), so far, has mostly been made of paper. The principal reasons why paper diaphragm has widely been used are; that the raw material is easily obtainable, that relatively flat regenerating frequency characteristics can be obtained because of its high internal loss, and that an efficiency is high because it has low density and hence is light in weight. However, on the other hand, a paper diaphragm has disadvantages that a sound distortion generates and an upper regenerating frequency limit is low, because it has low specific modulus and begins a separation vibration at a relatively low frequency. Moreover, because paper easily absorbs moisture, the paper diaphragm has a disadvantage that sound quality is influenced by environments.
On the other hand, a metal diaphragm made of metal such as beryllium, boron or titanium has a feature that the upper regenerating frequency limit is high, because of the very high specific modulus compared with the paper diaphragm. However, because the metal diaphragm has very low internal loss, sharp peaks and dips appear in the regenerating frequency characteristics. Moreover, because such metals are inferior in malleability and ductility, they have disadvantages that it is difficult to form thin and to form in a cone- or dome-like.
Recently, in contrast with such paper and metal diaphragms, a diaphragm made of filament or fiber reinforced plastics (hereinafter referred to as the "FRP diaphragm") is beginning to be used in some loudspeakers. For example, in the specification of Japanese patent unexamined publication Nos. 59416/78 or 106026/78, an FRP diaphragm made of thermosetting resin such as phenolic or epoxy resin reinforced by carbon filament fabric is described.
This FRP diaphragm has a feature that the specific modulus and the upper regenerating frequency limit are high, because it employs carbon filaments having high specific modulus, especially in the form of fabric of continuous filaments. However, the internal loss is fairly small compared with the paper diaphragm, though it is larger than that of the metal diaphragm, so that sharp peaks and dips also appear in the regenerating frequency characteristics. Moreover, especially in loudspeaker of as high input power as more than several tens of watt, heat generation at the voice coil is so great that the temperature at a connection between the voice coil and the diaphragm will be as high as more than 200.degree. C. In such a case, because the aforementioned conventional FRP diaphragm employs the resin of low heat-durability such as phenolic or epoxy resin, the specific modulus of the diaphragm drops and the upper regenerating frequency limit and a sound pressure level especially at high frequency area of the regenerating frequency characteristics, become lower. The same phenomena is more remarkable when used for a long time under the burning sun, as an autostereo or an autoradio.
On the other hand, in the specification of Japanese patent unexamined publication No. 158800/80, a diaphragm made of composite material composed of polyimide resin and graphite flakes is described. This diaphragm has the internal loss almost equal to that of the paper diaphragm and the specific modulus is also fairly high. Moreover, a drop of the regenerating frequency characteristics by heat is little matter unlike in the aforementioned FRP diaphragm, because the employed polyimide resin has a high heat resistance. However, the diaphragm has a rather fatal disadvantage for a diaphragm that the mechanical strength is low.
Namely, in order to obtain high specific modulus and large internal loss, this convention
REFERENCES:
patent: 3930130 (1975-12-01), Boszor
patent: 3935924 (1976-02-01), Nagao et al.
patent: 4076098 (1978-02-01), Ward
patent: 4281223 (1981-07-01), Vgaji et al.
patent: 4291781 (1981-09-01), Niguchi
patent: 4315557 (1982-02-01), Nakoya et al.
patent: 4342803 (1982-08-01), Stengle
patent: 4359132 (1982-11-01), Parker et al.
patent: 4410768 (1983-10-01), Nakamura et al.
Hasumi Shigeru
Nishidoi Takashi
Tanaka Kazuo
Cannon James C.
Toray Industries Inc.
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