Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02826710 2013-09-10
LOUDSPEAKER ENCLOSURE
FIELD OF THE INVENTION
The present invention relates to a loudspeaker enclosure, and more
particularly to a loudspeaker
enclosure having a noise interference reducing structure.
BACKGROUND OF THE INVENTION
The primary role of the loudspeaker enclosure is to prevent sound waves
generated by the
rearward-facing surface of the diaphragm of an open driver from interacting
with sound waves
generated by the forward-facing surface of the diaphragm. Since the forward-
and rearward-
generated sound waves are out of phase with each other, any interaction
between the two in the
listening space creates a distortion of the original sound signal generated by
the forward-facing
surface of the diaphragm. Additionally, since the forward- and rearward-
generated sound waves
travel different paths, the sound waves arrive at the listener's location at
slightly different times,
introducing complex echo and reverberation effects that will very likely
interfere with the
original signal
Unfortunately, loudspeaker enclosures can generate significant noise
interference disturbing the
original sound signal. The rearward-generated sound waves interact with the
enclosure
generating acoustic and mechanical resonances in the enclosure and acoustic
reflections/diffractions from the inside walls of the enclosure which impede
the driver's
movement - distorting the generation of the original sound signal - and,
furthermore, are
transmitted through the diaphragm ¨ resulting in a superposition with the
original sound signal.
Numerous attempts have been made to reduce the noise interference inside the
loudspeaker
enclosure as well as within the structure/body of the loudspeaker enclosure
such as, for example,
selection of various materials used for the enclosure to increase mass and/or
stiffness, as well as
disposing various materials inside the enclosure to provide internal
absorption. Unfortunately,
these attempts generally provided only a limited reduction of the noise
interference and/or are
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very expensive to implement.
Furthermore, to ensure proper performance of the driver it is often desired to
have a
predetermined airload acting on the rearward-facing surface of the diaphragm.
It is desirable to provide a loudspeaker enclosure that has substantially
reduced noise
interference.
It is also desirable to provide a loudspeaker enclosure that has substantially
reduced noise
interference while providing an airload acting on the rearward-facing surface
of the diaphragm.
It is also desirable to provide a loudspeaker enclosure that has substantially
reduced noise
interference and is manufactured at substantially reduced cost.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a loudspeaker
enclosure that has
substantially reduced noise interference.
Another object of the present invention is to provide a loudspeaker enclosure
that has
substantially reduced noise interference while providing an airload acting on
the rearward-facing
surface of the diaphragm.
Another object of the present invention is to provide a loudspeaker enclosure
that has
substantially reduced noise interference and is manufactured at substantially
reduced cost.
According to one aspect of the present invention, there is provided a
loudspeaker enclosure. The
loudspeaker enclosure comprises a wall structure having an opening for
enabling transmission of
a sound signal therethrough with the sound signal being generated by a
diaphragm of a
loudspeaker driver disposed inside the loudspeaker enclosure. The wall
structure further has an
aperture disposed therein. A membrane covers an inside end of the aperture in
a substantially
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sealed fashion.
The advantage of the present invention is that it provides a loudspeaker
enclosure that has
substantially reduced noise interference.
A further advantage of the present invention is that it provides a loudspeaker
enclosure that has
substantially reduced noise interference while providing an airload acting on
the rearward-facing
surface of the diaphragm.
A further advantage of the present invention is to provide a loudspeaker
enclosure that has
substantially reduced noise interference and is manufactured at substantially
reduced cost.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the present invention is described below with
reference to the
accompanying drawings, in which:
Figures la and lb are simplified block diagrams illustrating a perspective
view and a
cross sectional view, respectively, of a loudspeaker enclosure according to a
preferred
embodiment of the invention;
Figures lc and 1 d are simplified block diagrams illustrating a perspective
outside and
perspective inside view, respectively, of a corner of the loudspeaker
enclosure according
to a preferred embodiment of the invention; and,
Figures 2a to 2d are simplified block diagrams illustrating a cross sectional
view of an
aperture of the loudspeaker enclosure according to a preferred embodiment of
the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
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,
Unless defined otherwise, all technical and scientific terms used herein have
the same meaning as
commonly understood by one of ordinary skill in the art to which the invention
belongs.
Although any methods and materials similar or equivalent to those described
herein can be used
in the practice or testing of the present invention, the preferred methods and
materials are now
described.
While the description of the preferred embodiments hereinbelow is with
reference to a
loudspeaker enclosure having rectangular walls, it will become evident to
those skilled in the art
that the embodiments of the invention are not limited thereto, but are also
applicable for
differently shaped loudspeaker enclosures.
Furthermore, while the description of the preferred embodiments hereinbelow is
with reference
to a sealed loudspeaker enclosure, it will become evident to those skilled in
the art that the
embodiments of the invention are not limited thereto, but are also applicable
for other types of
loudspeaker enclosures that produce an acoustic pressure point within the
enclosure when
interacting with the rearward generated sound waves produced by the driver
diaphragm resulting
in a noticeable reduction of the noise interference.
Furthermore, while the description of the preferred embodiments hereinbelow is
with reference
to tuning to the resonance frequency of the loudspeaker enclosure, it will
become evident to those
skilled in the art that the embodiments of the invention are not limited
thereto, but are also
applicable for tuning to other frequencies that produce an acoustic pressure
point within the
loudspeaker enclosure when interacting with the rearward generated sound waves
produced by
the driver diaphragm resulting in a noticeable reduction of the noise
interference.
Referring to Figures la to ld, a loudspeaker enclosure 100 according to a
preferred embodiment
of the invention is provided. The loudspeaker enclosure 100 comprises at least
one aperture 102
disposed in the wall structure 100A, 100B, 100C thereof. The aperture 102
extends from the
inside of the loudspeaker enclosure 100 to the outside. An inside end of the
aperture 102 is
covered by membrane 106 in a substantially sealed fashion, as illustrated in
Figure ld and as will
be described in more detail hereinbelow.
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In operation, a sound signal is generated by movement of diaphragm 12 of
loudspeaker driver 10
disposed inside the loudspeaker enclosure 100 and transmitted through opening
101 disposed in
the wall structure 100A of the loudspeaker enclosure 100. The primary role of
the loudspeaker
enclosure 100 is to prevent sound waves generated by the rearward-facing
surface of the
diaphragm 12 ¨ facing the inside of the of the loudspeaker enclosure 100 ¨
from interacting with
sound waves generated by the forward-facing surface of the diaphragm 12 ¨
facing the outside.
As is well known in the art, loudspeaker enclosures can generate significant
noise interference
disturbing the original sound signal. The rearward-generated sound waves
interact with the
loudspeaker enclosure generating acoustic resonances in the structure of the
enclosure and
acoustic reflections/diffractions from the inside surface of the loudspeaker
enclosure which
impede the driver's movement - distorting the generation of the original sound
signal - and,
furthermore, are transmitted through the diaphragm ¨ resulting in a
superposition with the
original sound signal. Therefore, the main objective of present day
loudspeaker enclosure design
is to substantially reduce the noise interference while still providing
airload acting on the
rearward-facing surface of the diaphragm 12.
This objective is achieved in the loudspeaker enclosure 100 by transmitting
acoustic energy
generated by the rearward-facing surface of the diaphragm 12 through the
aperture 102 to the
outside, with the transmission being substantially limited to one direction ¨
i.e. from the inside of
the loudspeaker enclosure 100 to the outside ¨ and , preferably, to acoustic
energy at a frequency
being approximately the fundamental frequency of the entire loudspeaker
enclosure 100, i.e. the
lowest frequency at which the entire loudspeaker enclosure 100 resonates. The
size of the
aperture 102 is determined such that the acoustic impedance of the airmass
inside the aperture
102 has sufficient stiffness for preventing transmission of acoustic energy
therethrough and a
resonance frequency being approximately the fundamental frequency of the
loudspeaker
enclosure 100. The membrane 106 is determined to have a resonance frequency
corresponding to
the resonance frequency of the airmass inside the aperture 102 to enable
transmission of acoustic
energy through the aperture 102 at the resonance frequency. Placing of the
membrane 106 to
cover the inside end of the aperture 102 ensures that the transmission of the
acoustic energy is
substantially limited to the direction from the inside of the loudspeaker
enclosure 100 to the
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outside. One skilled in the art can readily determine the size of the aperture
102 in dependence
upon the loudspeaker driver employed and the volume and the stiffness of the
loudspeaker
enclosure 100, as well as the size, material, and tension of the membrane 106.
It is noted that,
while it is preferred to transmit the acoustic at the fundamental frequency of
the entire
loudspeaker enclosure 100, it is possible to achieve a reduction of noise
interference by
transmitting the acoustic energy at other frequencies that produce an acoustic
pressure point
inside the enclosure when interacting with the rearward generated soundwave of
the driver.
Preferably, the aperture 102 is disposed in a corner ¨ detail A - of the
loudspeaker enclosure 100,
as illustrated in Figures 1 c and ld, and further preferably, is oriented
along a line connecting the
inside corner with the outside corner, as illustrated in the cross sectional
view in plane 104 of
Figures 2a to 2d. Placing the aperture 102 in the corner is preferred, since
the loudspeaker
enclosure 100 is stiffest in the corner and the pressure ¨ mechanical and
acoustic ¨ is the highest
in the corner. Alternatively, the aperture 102 is disposed at a different
location, for example, in
proximity to the corner, or has a different orientation, for example, oriented
from the inside
corner to a location in proximity to the outside corner.
While, it is further preferred to dispose eight apertures 102 in the
loudspeaker enclosure 100 with
one aperture 102 in each corner thereof, the invention is not limited thereto,
but different
numbers of apertures are employable, for example, four apertures 102 disposed
in the back
corners of the loudspeaker enclosure 100. Even a single aperture 102 provides
a noticeable
reduction of the noise interference.
As illustrated in Figures 2a, a pyramidal shaped corner member 108
substantially conforming to
the inside corner of the loudspeaker enclosure 100 is disposed therein and
mounted to the inside
surface thereof using, for example, an adhesive. A bore forming the aperture
102 is then drilled
through the corner member 108 and the loudspeaker enclosure 100 from the
inside corner to the
outside corner. The corner member 108 provides contact surface 110 for
mounting the membrane
106 thereto to cover the inside end of the aperture 102 in a substantially
sealed fashion using a
suitable adhesive.
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=
Optionally, as illustrated in Figure 2b, the cross section of the aperture 102
is increased towards
the outside end forming a horn like structure for improving the acoustic
impedance match
between the air in the aperture 102 and the outside air. The horn like
structure is provided, for
example, by beveling 112 the outside end portion of the aperture 102. Of
course, various other
shapes are implementable such as, for example, increasing the cross section
from the inside end
to the outside end of the aperture 102 in a linear or curved fashion.
Alternatively, as illustrated in Figure 2c, the bore forming the aperture 102
is countersunk 114 to
provide the contact surface 110 for the membrane 106.
Further alternatively, as illustrated in Figure 2d, a tube 116 comprising the
aperture 102 is
disposed in the loudspeaker enclosure 100. The membrane 106 is then mounted to
an end portion
of the tube 116 using, for example, a suitable adhesive. Preferably, the tube
is made of a
substantially stiff material such as, for example, a metal.
As is evident, the invention is also implementable by providing an aperture
102 having a cross
section other than circular such as, for example, oval or rectangular.
In an exemplary implementation, a loudspeaker enclosure made of Medium Density
Fiberboard
(MDF) and having a wall thickness of approximately 7mm was used. The invention
was
implemented using off-the-shelf materials and standard manufacturing methods.
The aperture
102 ¨ having a circular cross section ¨ was provided by drilling a bore with a
diameter of
0.71mm (# 70 drill bit) from the inside corner to the outside corner. The
contact surface 110 was
provided using a corner member 108 made of MDF. The membrane 106 was
implemented using
a Teflon tape ¨ 3M Type 63 or 60 PTFE. It is noted that the membrane 106 is
implementable
using various types of sheet materials that have sufficient flexibility and
resonate at the resonance
frequency of the airmass in the aperture 102.
The present invention has been described herein with regard to preferred
embodiments. However,
it will be obvious to persons skilled in the art that a number of variations
and modifications can
be made without departing from the scope of the invention as described herein.
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