Note: Descriptions are shown in the official language in which they were submitted.
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Tlle invcntioll relates to loudsl)eakcrs.
The inventio~-l providcs a loudspeaker comprising a
frame, magnet means carried by the frame? a diaphragm
assembly, and suspension means movably mounting the diaphragm
assembly in the frame and comprising a suspension extending
between the frame and the periphery of the diaphragm
assembly, the diaphragm assembly having an inner sleeve
portion carrying a first coil within the magnetic field of
the magnet means, a tapering centrally apertured portion
surrrounding and extending outwardly from the inner sleeve
portion at a position thereon adjacent to the first coil,
an outer portion closing the end of the inner sleeve portion
remote from the first coil and extending radially outwardly
from the inner sleeve portion, the outer edge of the outer
portion being connected to the tapering centrally apertured
portion at a position outwardly of the`inner sleeve portion, and
an outer sleeve portion surrounding the inner sleeve portion
and carrying a second coil within the magnetic field of
the magnet means, the outer sleeve portion extending co-
axially towards the magnet means at or adjacent thesuspension.
The diaphragm assembly is thereby rigidified without
a large increase in weight whereby it is ensured that the
diaphragm moves with the same velocity over its entire
area. Conveniently, the enclosed space within the diaphragm
assembly is filled with a-foamed plastics material, to help
eliminate resonances withi:n the diaphragm assembly.
The loudspeaker as described can include means pro-
viding an output signal responsive to movement of the
diaphragm assembly and regulator means responsive to the
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output signal to provide a control signal for influencing
the movement of the diaphragm assembly.
It thus becomes possible to ensure that the
diaphragm assembly moves only within an optimum range
of positions. Thus if the assembly were to be driven by an
excessive force, the sleeve or former on which the speech
coil is wound could engage the magnet means, so limiting
the diaphragm excursion in one direction with an adverse
effect on the quality of sound reproduction and the
possibility of damage to the loudspeaker.
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The control signal can be applied to control an amplifier
driving the speech coil or coils to limit the drive output
and/or for the application to the diaphragm assembly of a
bias to counter such an excessive amplifier drive output
thereby ensuring smooth operation.
The control signal can additionally or instead
be applied to change the waveform of the drive signal. For
example, the waveform can be shifted relative to the base
reference line to correct, or to introduce a desired asymmetry
in the waveform, that is, to obtain equality or a desired
inequality of amplitude between the positive and negative
portions. Such an alteration in the waveform can if
appropriate be combined with an overall reduction in amplitude.
These control effects on the signal supplied to drive the
loudspeaker are of course equivalent as regards the resulting
diaphragm movement to the bias applied directly the diaphragm.
The invention will be readily understood from the
following illustrative description and accompanying drawing,
in which:
Figs. 1 and 2 are sectional side views respectively
of first and second loudspeakers embodying the invention, both
represented in a very schematic manner, with respective biassing
means shown in simplified block dlagram form.
As appears from Fig. 1, the first loudspeaker 10
embodying the invention has a diaphragm assembly, which may be
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constructed of conventional materials, comprising a circular
or elliptical substantially planar diaphragm 12. The
expression "s~lbstantially planar" covers not only strictly
planar constructions but also those have a slight overall
curvature and/or annular or radial corrugations. The diaphragm
12 is mounted by a flexible corrugated suspension 14 in a
surrounding rigid frame 16 incorporating permanent magnet
means 17 which may be apertured as at 15. The magnet means
comprises one or two magnets providing a strong magnetic
field across a concentric pair of annular recesses 18 and 19
in which are received coils 20 and 22 wound on respective
concentric inner and outer sleeves or formers 24 and 26. The
inner sleeve 24 extends coaxially from the diaphragm 12 and
provides this with structural support. The outer sleeve 26
extends from the diaphragm 12 at the periphery, adjacent the
suspension 14. The diaphragm assernbly is provided with further
structural reinforcement by a flared or tapering portion 28
extending from at or near the periphery of the diaphragm 12-
to the inner sleeve 24. The portion 28 is frusto-conical but
; 20 may instead be curved for example exponentially. An auxiliary
suspension (not shown) for the diaphragm assembly may be
located adjacent the position at which the or each sleeve former
extends into its annular recess.
The annular space 29 between the diaphragm 12, the
sleeve 24 and the reinforcing portion 28 may be sealed but
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the portion 28 may be apertured or perEorated. Ilowever,
resonances are preferably avoided by fil1ing -the space with a
light filler material for example a foamed plastics material.
In use, a drive signal from an amplifier 30, to
which a signal to be reproduced is supplied at input 31, can
be applied to both coils 20 and 22 to obtain louclspeaker sound
reproduction of high quality. Preferably however the coil 20
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comprises two independent coils the output of one, which is
representative of the diaphragm assembly movement, heing fed
to a regulator unit 32 including a variahle gain amplifier
34. The output of the unit 32 is applied to the second
independent coil to bias the diaphragm assembly in a manner
and for the purpose as previously described. Additionally,
as shown, or instead, the output or an output of the unit 32
is applied to control of the functioning of the drive amplifier
30, again in the manner and for the purpose described.
In Fig. 2, which illustrates the second loudspeaker
110 embodying the invention, parts which are so similar to
corresponding parts of the loudspeaker as not to require
comment, are given the same reference numerals as in Fig~ 1.
Significantly modified parts are indicated by the reference
of Pig. 1 raised by 100..
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It will be seen that the diaphragm assembly of the
loudspeaker 110 has a composite diaphragm formed by a circular
or elliptical portion 112 and an outer annular portion 127
of the reinforcing portion 128 defined between the connection
thereof to the portion 112 and the suspension 14. The outer
sleeve 26 is connected at or adjacent the suspension to this
outer annular portion 127. The loudspeaker 110 is also
associated with a different arrangement of biassing mean from
those described with reference to Fig. 1. The amplifier drive
signal is again applied only to the outer coil 22 and the
inner coil 20 is used to provide a signal representative of
diaphragm assembly movement which is applied through a simple
regulator unit 40 comprising a variable attenuator 41 and a
rectifier 42 directly to the coil 22.
It will be evident that a signal representative of
diaphragm movement can be obtained otherwise than from an
auxiliary coil, for example, capacitatively, and that this
signal after any appropriate treatment, for example,
amplification or attenuation, can be applied to influence
diaphragm assembly movement in any one or more of the ways
described, in particular by being fed to a second auxiliary
coil or to the speech coil, or to one or both speech coils
if two are provided, or by being used to control a main
amplifier providing a drive signal to the speech coil or
coils. The or each auxili-ry coil can be located at any
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convenient position on the diaphragm ass~mbly, and can for
example be wound coaxially within or around the speech coil.
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