Note: Descriptions are shown in the official language in which they were submitted.
Title: "Sound Reproducing Apparatus"
This invention concerns sound reproducing apparatus
and more particularly, but not exclusively, phonograph
record playing apparatus.
The theoretically ideal operation of phonograph record
playing apparatus is such that the stylus engages the groove
of a record and moves only in response to the spiral form of
the groove and the modulations therein. However, in practice,
additional movements can and frequently do occur in response
to many other causes. These causes are primarily vibrations
in other components of the apparatus be they mechanical such
as bearings, electrical ~uch as chokes and transformers, and
electromechanical such as loudspeakers. Additional undesir-
able movements can result from distortions in the record
itself, records not always being flat in overall form but
often being warped.
Many and varied proposals have been made in relation to
the reduction of undesirable movements from different causes,
out few if any of these proposals are entirely successful in
the respective aims.
An object of the present invention is to effect further
reductions of undesirable movements. The invention in fact
embraces a number of different forms associated with different
causes of undesirable movements but which forms each involve
the use of visco-elastomeric material to damp undesirable
movements. In this connection it is to be understood that the
undesirable movements are commonly of low frequency, and often
large amplitude, compared to those of the stylus in tracking
the groove modulations. A visco-elastomeric material in this
context is one having liquid or liquid-like properties whiGh
can afford damping of the former movements, but having elas-
tomeric pxoperties which cause little or no distortion to the
latter movements. Such material can be liquid or solid.
Examples of solid material suited to this purpose are des-
cribed in United Kingdom Patent Specification No. 1,564,195
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which are characterized by being basically elastomeric but
have a delayed recovery after compression. This delayed
recovery is due to liquid-like properties resulting from a
polymeric structure involving short and long chains and which
will tend to selectively damp movements of low frequency and
large amplitude. Liquids having similar properties can be
produced by extension of the processes described in said
specification.
In accordance with the present invention there is
provided a recording or reproducing turntable comprising a
layer of visco-elastomeric material consisting essentially
of a flexible polyurethane of essentially linear structure
containing unsatisfied hydroxyl groups and having a compression
set of less than 15%, an elongation break of at least 500~,
and a recovery which is delayed after compression by at
least 0.7 seconds.
These and other objects and advantages of the present
invention will become more apparent as the following description
proceeds.
To the accomplishment of the foregoing and related
ends, the invention, then, comprises the features herein-
after fully described in the specification and particularly
pointed out in the claims, the following description and the
annexed drawings setting forth in detail certain illustrative
embodiments of the invention, these being indicative, however,
of but a few of the various ways in which the principles of
the invention may be employed.
In said annexed drawings:
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Figure 1 is a diametrical section of a turntable in
accordance with the invention;
Figure 2 is another form of turntable;
Figure 3 is a schematic illustration of a stylus arm
in accordance with the present invention;
Figure 4 is a schematic illustration of the invention
as a suspension component; and
Figure 5 is a section through a speaker illustrating
various applications of the invention.
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Considering then specific forms of the invention:
a f~rst form as seen in Figure 1 comprises a mat 10 of visco-
elastomeric material for location on the turntable 11 for
~upporting the record. Such a mat is suit~bly made of solid
material according to the above specification as a circular
disc of 300mm diameter and 3mm thickness except for a
central area of llOmm diameter which is recessed by lmm to
receive the record label, and of course a central aperture
for passage of the turntable record-receiving spindle 12
therethrough.
In a modification of this mat as seen in Figure 2, an
additional, upper layer 14 preferably of glass, although
possibly of other rigid material, is also incorporated. The
two layers 14 and 16 of this mat are suitably permanently
bonded together as a laminated structure.
A second form of the invention, as seen in Figure 3,
involves a paddle 18 depending from the further end portion
of the stylus-carrying arm 20, the paddle being immersed in
a visco-elastomeric liquid 22 held in a bath 23. Paddle
arrangements are already known but employ silicone liquid
which exhibits normal Newtonian physical properties whereas
the presently proposed liquid is effectively non-Newtonian.
Aaso~ the present liquid will have properties less variable
~ith temperature and have low viscosity, if applied to the
both before reaction such as in said specification, compared
to ~ilicone liquid.
Another form of the invention, seen in Fi~ure 4, involves
u~e of visco-elastomeric material in suspension components 24.
Thi~ material cn be employed as solid pads seen at 25 to
replace or operate in conjunction with conventional springs.
Such pads may incorporate liquid or gas-filled cavities,
typ~cally air, the cavities ma~ be vented to atmosphere or may
be e~losed.
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A further form ofthe invention involves the use of
pads such as just described, gaskets, or other support or
encapsulation to isolate electromagnetic and other components
which may introduce undesired vibrations. Such components
include loudspeakers shown generally at 30 which, more
specifically, can employ such visco-elastomeric material
over the cabinet 31 as seen at 32, between the drive unit 33
and baffle 34 as seen at 35, between the baffle 34 and cabinet
walls as seen at 36, and to support and control the cone 37
in relation to its drive unit as seen at 38.
Yet another form of the invention involves supporting the
stylus-cantilever assembly by a structure of visco-elastomeric
material.
While the invention has been described with more parti-
cular reference to phonograph record reproducing apparatus,
it will be appreciated that it is applicable in some specific
forms to other sound reproducing apparatus involving
common components.
