Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Patent
1981-07-16
1983-01-25
Ives, P.
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
428156, 428495, 4284239, 428421, 3461351, 264153, 264201, 264294, 264322, 428447, 428516, 428517, 428520, 428521, 428522, 428523, B32B 302, G11B 362
Patent
active
043703712
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a rubber sheet for the turntable of a record player.
BACKGROUND ART
The rubber sheet for turntable is used to isolate a disc record from acoustic outputs from a loudspeaker, vibrations of a record player itself, etc., thereby preventing the occurrence of howling and the deterioration of SN ratio due to vibrations of the disc record itself during its reproduction. The howling is a sort of oscillation phenomena due to the feedback of acoustic outputs from a loudspeaker to a pickup and occurs due to the transmission of vibrations from the speaker to the record player via the floor or rack where the record player is mounted, or due to the direct vibrations of the record player cabinet caused by a sound pressure from the loudspeaker. It is needless to say that any normal playback of the disc record cannot be effected when the howling occurs. Even where no howling takes place, the frequency response of the pickup output would be altered and local resonance and the like would be caused by such external vibrations, and the tone quality of reproduced sounds would be affected adversely by the increase of inter-modulation distortion, the deterioration of transient phenomena, etc. The howling takes place mostly due to external vibrations from the floor or rack where the record player is mounted. The majority of such external vibrations is of the order not more than 100 Hz and particularly includes a superlow frequency component of approximately 5 to 10 Hz. To provide for an effective inhibition of howling, a rubber sheet for turntable which exhibits excellent vibration-absorbing properties in such superlow frequency region is desirable.
However, conventional rubber sheets for turntable which are made of natural rubber, isoprene rubber, chloroprene rubber, butyl rubber, styrene-butadiene rubber, butadiene rubber, silicone rubber or urethane rubber, or mixtures thereof are inferior in vibration-absorbing properties, especially in the superlow frequency range, and are unable to protect effectively the tone quality of reproduced sounds from deteriorating due to howling or external vibrations.
DISCLOSURE OF INVENTION
The inventor has made extensive and thorouth researches on the development of a rubber sheet for turntable which effectively inhibits the tone quality of reproduced sounds from deteriorating due to howling or external vibrations and permits reproduced sounds as faithful as source sounds themselves (for example, human voices themselves). As a result, it has been found that the above described object can be achieved by a rubber sheet which is a sheet-like cured molding of a rubber composition and has a hardness within the range from 30.degree. as measured with an A-type rubber hardness tester to 15.degree. as measured with an F-type rubber hardness tester and an impact resilience of not less than 40%.
In the foregoing, the A-type rubber hardness tester is a rubber hardness tester provided in JIS K 6301-1969. Further, the F-type rubber hardness tester means Asker F-type rubber hardness tester made by Kobunshi Keiki Mfg. Co., Ltd., which is mainly used for measurements of hardness of foam rubber, urethane foam or the like. Although being solid rubber, some of the cured rubber in accordance with the present invention is too low in hardness to measure by means of the A-type rubber hardness tester which is used in measuring hardness of conventional solid rubbers. To this end, the lower limit of hardness of the cured rubber in accordance with the present invention is defined by the hardness value as measured with the F-type rubber hardness tester.
An intermediate hardness between the measuring range of the A-type rubber hardness tester and that of the F-type rubber hardness tester may be measured with a C-type rubber hardness tester. The C-type rubber hardness tester as used herein means one provided in the Society of Rubber Industry Japan Standard SRIS-0101 and is used to measure such intermediate hardnesses between the measuring ranges of the A-type and F-type rubber
REFERENCES:
patent: 2351293 (1944-06-01), Saunders
patent: 3130110 (1964-04-01), Schmidt
patent: 3285561 (1966-11-01), George
patent: 3455531 (1969-07-01), Baker
patent: 3900999 (1975-08-01), Callan
Hohyu Rubber Co., Ltd.
Ives P.
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