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DESCRIPTION
One of the bottlenecks of contemporary compact devices like PDAs, mobile phones,
etc. is speakers.
Limitations on size make manufacturers put into such compact devices speakers with
poor quality of sound and low output. This work addresses this
problem. Look at Figure 1 to get main ideas being put into the
Linear Speaker.
Figure 1
The Linear Speaker comprises stressed Membrane (it tends to increase
its curvature) made from elastic material which is fixed to Housing on
one end. Another end of the Membrane is attached to the Activating Plate
of the Activator. The Activating Plate is a thin plate of light alloy approximately
as wide as the Membrane and long enough to provide sufficient travel. Another
end of the Activating Plate is connected to the Spring which is attached
to the Housing. In idle state elastic force of the Membrane is in equilibrium
with elastic force of the Spring. The Activating Plate is placed between
two 3-Phase Windings which are similar to windings of common 3-phase linear
motor. Figure 2 presents a probable view of the Linear Speaker. Variant without the Spring
is also possible, in this case the Membrane isn’t stressed in the idle
state (but certainly curved anyway).
Figure 2
WAY OF OPERATION
The Activating Plate moves in accordance with input Audio Signal. Reciprocating
movement of the Activating Plate causes appropriate lateral movement of
the Membrane due to change of its curvature, what is the source of sound.
In order to make the metallic Activating Plate move in accordance with
input Audio Signal principle of 3-phase linear motor is used. To provide
minimal distortion the frequency of alternating current should be several
times higher than the highest frequency of the Speaker, e.g. it may be
about 100 KHz. Shift of the Activating Plate is proportional (assuming
that elastic force of the Membrane is appr. the same in working range of
its shift) to the Amplitude of alternating current, direction of this shift
depends on Phase Difference between currents supplied to different windings.
Conditionally we call these Phase Differences positive and negative. Positive
Phase Difference leads to moving of the Activating Plate out of the Activator
(curvature of the Membrane increases). Negative Phase Difference leads
to moving of the Activating Plate into the Activator (curvature of the
Membrane decreases). Figure 3 contains plots which explain this.
Figure 3
Since all the moving parts of the Speaker can be made extremely light,
the quality of sound can be superb in wide frequency and output ranges.
The Linear Speaker can be made very thin (several millimeters), so it can
be easily placed on the sides of portable’s LCD (ideal position for speakers
in a portable) as well as inside compact housing of a mobile phone or a PDA. As for output of the Linear Speaker it can be very high
depending on size, parameters of Membrane, etc..
DOUBLE LINEAR SPEAKER
Another embodiment of the Linear Speaker is the Double Linear Speaker.
Look at Figure 4 to get ideas being put into the Double Linear Speaker.
Figure 4
The Double Linear Speaker comprises two stressed Membranes
(each of
them tends to increase its curvature) as shown on Figure 4, made of elastic
material which is fixed to Housing on one end. The other end of each Membrane
is attached to the Activating Plate of the Activator. In idle state elastic
force of each Membrane is in equilibrium with elastic force of the other one. The two Membranes may be identical
(same size, curvature, elastic properties, etc.). They also may differ, so that, for
instance, Membrane
1 may be better suited for reproducing low and middle frequencies, and
Membrane 2 may be better suited for high frequency. In this case we have
Two-Band Speaker.. Figure 5 presents a probable view of the Double Linear
Speaker.
Figure 5
The Linear Speaker remains unbeatable where light weight,
high output, and compact size are especially
important, e.g. in mobile phones with "hands free" feature.
© 2003 by Vitaly Gnatenko
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