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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to
loudspeaker systems, and more particularly to systems having very low resonant frequencies.
BACKGROUND OF THE INVENTION Loudspeaker systems are provided with loudspeaker
components that are adapted to operate in different frequency regions, including in particular
the bass, mid and treble regions. The bass range components include certain subwoofer speaker
systems that can operate alone in the lowest frequency range between about 30 and 100 Hertz.
Usually, such very low subwoofer systems require large loudspeakers and large containers for
the efficiency of coupling with the ambient air and for the reproduction of sound in the desired
30 to 100 hertz range. Large dimensions are required, at least in part, because of the need to
control the resonant frequency of the system. For example, one end closed air column operating
as a quarter wave system resonating at 30 Hz has a length of 9 feet or more, and even 4 feet or
more when folded. A 12 inch woofer's normal aperture reflective (bass reflex) container with a Q
of 0.53 has an optimum capacity of 6.75 cubic feet.
Having a resonant frequency not higher than the lowest frequency reproduced by the system is
important in the speaker system design. The resonant frequency depends on the increased mass
and the reduced stiffness to obtain a lower resonant frequency. However, speakers for most
applications need to be attached to the container at low frequencies to avoid interference
between the acoustics generated on the front and back of the vibratory drive, for example the
speaker cone. The container adds stiffness to the system but the mass is small. The smaller the
container, the higher the stiffness and the higher the resonant frequency of the system. The
system mass is mainly supplied by the moving part of the loudspeaker itself, as larger mass
loudspeakers are preferred for low frequency sound reproduction. Furthermore, large speakers,
which require large containers, are desirable to match the acoustic impedance of the air.
While bass reflex containers increase efficiency, they require large containers for low frequency
sound reproduction. Furthermore, efficiency is less important due to the increased power of
more widely available and economically available amplifiers. The oversize of such systems is an
important drawback. It has been attempted to use small diameter speakers and small containers
for use at very low frequencies. Small systems are less effective because small diameter speakers
have relatively poor impedance to match the acoustic impedance of the surrounding air. Thus, it
is not common to use loudspeaker transducers smaller than about 8 inches in diameter that
produce very low frequencies due to poor coupling to ambient air, and small used often with
small speakers The container produces high stiffness. Therefore, a large speaker is used, which
essentially requires a large container. Efficient very low frequency speakers of suitable small
dimensions have not been used before. Thus, the object of the present invention is to perform
low frequency sound reproduction with increased efficiency and small parts.
SUMMARY OF THE INVENTION In practicing the principles of the present invention in
accordance with a preferred embodiment, a loudspeaker system having a low resonant frequency
is coupled to a vibratory drive (speaker cone) and a vibratory drive having a driver. Speakers
with a mass that is Means synchronized with and co-operating with the drive are provided for
vibrating a mass synchronized with the drive. In a particular embodiment, the oscillatory mass to
be coupled comprises the mass of air confined between the oscillatory drive and the second
oscillatory drive, the two drivers being an integral between the two drivers It is driven by the
same mechanical phase so as to vibrate the air entrapped body. The arrangement adds a large
mass to the speaker system without essentially affecting the stiffness of the system. One
vibratory driver is coupled to the vibratory air mass and is coupled to both the other driver
vibratory air mass and the ambient air.
rectangular container 10 of substantially conventional speaker container construction and shape
is provided with a rigid continuous septum 12 which extends completely across the container,
The container is divided into two substantially equal closed halves 14, 16 defining respectively a
closed air chamber 18, 20. The enclosed chambers 18, 20 are of approximately equal volume
and shape. The first speaker 24 is attached to the bulkhead 12. The partition 12 is provided with
a hole having the same size as the opening of the cone 22 of the speaker in the partition. The
cones used in common loudspeakers are attached to the bulkhead with loudspeaker frame (not
shown) and flexible mounting and are electromagnetically driven. The vibrating cone 22 which is
driven is called a "vibration driver" and produces vibrations of the air in contact with the cone.
Thus, one side 21 of the cone 24 of the speaker 24 referred to as the "front" is in contact with
the air in the chamber 20, and the other side 23 referred to as the "rear" is in contact with the air
enclosed in the chamber 18.
The portion 16 of the container having the front or output wall 26 is suitably perforated to
mount a second conventional speaker 30, which is identical to the speaker 24 and is flexibly
mounted to the speaker frame in the usual manner It has a vibratory drive in the form of a cone
The two speakers are driven mechanically in phase so that they are in phase and transfer the
same directional force to the air mass of the chamber 20 confined between them.
From one point of view, the two speakers are considered to operate "push-pull". One speaker
cone moves in the direction pushing the confined air mass and the other cone moves
simultaneously in the direction pulling the confined air mass. In the configuration of FIG. 1, the
two speakers are synchronized with each other and mechanically and electrically in phase with
each other. The two speakers are electrically connected in parallel to be driven by the same
electrical signal from one amplifier (not shown). The in-phase operation, as seen in FIG. 1, also
moves the cone 32 of the speaker 30 to the right when the cone 22 of the speaker 24 moves to
the right and vice versa. It is similar. Thus, the operation of the two speakers due to the air mass
of the chamber 20 being configured and sandwiched between the two speakers results in the
oscillation of air of one integral mass with all parts of the air mass moving and vibrating
simultaneously. The integral mass of the oscillating air mass is synchronized with the vibration of
the speaker cone. The air mass of the chamber 20 does not alternately receive compression and
expansion. On the other hand, the air mass of the chamber 18 is driven only by the speakers 24
and is confined within the rigid container wall of the chamber 18. This air acts like a spring and
is compressed as the speaker cone 22 moves to the left as seen in FIG. 1 and expands as the
speaker cone moves to the right. The air in the chamber 18 primarily adds stiffness to the system
and the air in the chamber 20 primarily adds mass. Preferably, the ratio of the mass (inertance)
of the air of the chamber 20 to the stiffness of the air of the chamber 18 is between about 1 and
The described construction of the double speaker, double chamber container of FIG. 1 provides a
practical and equivalent system for the spring and the mass vibration system, in which the spring
is air confined within the chamber 20 of the container. Given by mass. The mass is given by the
mass of air contained in the chamber 20.
The parts of the system containing the air confined in the speakers 24 and the room 18 operate
in the same manner as a conventional speaker system. The air mass in the chamber 18 acts
primarily like a spring to supply most of the system stiffness. The mass is mainly given to the
chamber 18 by the relatively low mass parts of the moving part of the loudspeaker 24. On the
other hand, the part of the speaker system that includes both the speakers and the air mass
contained in the chamber 20 is not a spring but a mass that is coupled to the speaker 24 to
effectively couple the speaker 24 mainly to the ambient air Act as. This is a bond, which
comprises the mass of the air of the chamber 20 and the mass of the moving parts of the two
speakers. For a container room 20 of about 1 cubic foot container and a conventional 8 inch
speaker, the mass of air confined in the room 20 is considerably larger than the mass of the
moving part of the speaker. The mass of air in the chamber 20 is driven without compression or
expansion, but is as effective as a one-piece oscillating mass by means of the in-phase
loudspeakers on either side of the mass of air. As a result, the air mass is added to the mass of
the total oscillatory system. However, as mentioned above, the mass of air in the chamber 20 is
considerably larger than the mass of moving parts such as cones, compliant moving elements
and moving coils of the speaker, which considerably reduces the resonant frequency of the
system. From one point of view, the confined air mass of the chamber 20 together with the mass
of the moving part of the speaker provides an additional mass coupled to the loudspeaker system
comprising the loudspeaker 24 and the chamber 18. As is well known by the increased mass of
the vibrating system, the resonant frequency is reduced.
In one example system where the speakers are 8 inches in diameter, each chamber 18 and 20
has a capacity of about 1 cubic foot, and the mass enclosed and added within the chamber 20 is
at least 1 ounce, typically Much larger than about half an ounce of the mass of the moving parts
of the 8 inch speaker. The increase in mass of air in the chamber 20 in the embodiment thus
described lowers the normal resonant frequency of the system. Furthermore, the addition of
chamber 20 and speakers 30 lowers the Q of the system and thus broadens the resonance peak.
FIG. 2 shows a variant of the system of FIG. 1 comprising substantially equal halves of a rigid
container 110 of similar shape with a rigid continuous partition 112 to which the first
loudspeaker 124 is attached. There is. The speaker 124 acts on the air contained in the chamber
118 of the container, whose operation mainly acts as a spring supplying the stiffness of the
resonant system. A second speaker 130 is attached to the outer wall 126 and is contained within
the second chamber 120 of the container. The two speakers are driven in the same mechanical
phase as each other with respect to the air contained in the chamber 120, but in this
arrangement they are electrically driven 180 ° out of phase with each other. In FIG. 2, the two
speakers are electrically powered so that the two cones provide the same directional mechanical
force to the air in the chamber 120 as the rear of the cones of both speakers contact the air
being confined in the chamber 20. Must be driven out of phase with each other. In other words,
the two speakers are driven so that their cone motions are synchronized to each other and to a
single motion of air trapped between the two speaker cones in the chamber 120. The cones move
in the mutually promoting direction. Thus, the cone 132 of the speaker 130 is inside the air of
the chamber 120, ie in the direction of the arrow 125, while the cone 122 of the speaker 124 is
moving in the direction of the arrow 123, ie outside the air confined in the chamber 120. It is
moving. Thus, the two speakers provide the same mechanical phase force to vibrate the air
trapped in the chamber 120 as an integral between the two speakers. Similar to the arrangement
of FIG. 1, in this embodiment, the air in the chamber 120 does not compress, expand, but moves
as one.
The structure of FIG. 2 is more suitable for a tower speaker, the long dimension of the container
is vertical, and the structure of FIG. 1 is more suitable for a speaker system where the long
dimension is located laterally.
If deemed necessary or desirable, any of the configurations described herein may be drilled as
shown by the duct 140 shown in phantom in FIG.
The duct 140 extends inside the chamber 118 and is a conventional pipe for passing air around
the open port 142. This part of the system (but with the exception of the additional mass of the
chamber 120 and the second speaker 130) is similar to the configuration and regulations for the
container of a conventional bass reflex speaker. It is recognized that the system with ducts of FIG.
2 is more efficient than a system without ducts. However, a sealed system without ducts is
believed to provide an even more pleasing sound. Furthermore, sealed ductless systems have
relatively low total harmonic distortion. Ductless systems using 8-inch speakers have been found
to have a total harmonic distortion of less than 2% at 40 Hz, while systems with ducts have been
found to be 6%, but in the vicinity of the resonant frequency It has high efficiency.
In addition to the increased mass of the system and thereby the substantially lower resonant
frequency, the air mass in the chamber 20 stabilizes both speakers and minimizes distortion by
the vibration of a single body of the total air mass in the chamber, of the speaker cone Give
support for.
Although the speaker system is described with respect to a relatively small (8 inch aperture)
speaker, the principles of the invention apply to larger speakers as well.
Even if such a speaker is formed with a large mass, the increase in the oscillating air mass gives
an even lower resonant frequency. In order to minimize system space requirements, it is
desirable to mount large speakers in small containers. However, the smaller the container, the
greater the stiffness of the enclosed air and the higher the resonant frequency of the enclosed
speaker. The system described can be attached to small containers, even large speakers. The
increased stiffness of the small vessel combines the increased mass of air confined within the
second chamber 20, 120 of FIGS. 1 and 2 and acts thus as a mass rather than a spring. It is at
least partially compensated by the occurrence.
FIG. 3a shows a variant in which the rigid container 210 has a fixed, continuous dividing wall
212 to which is attached a first speaker 224 which cooperates with the air mass in the chamber
218 operating mainly as a spring of the resonant system There is. The second speaker 230 is
attached to the outer wall 226 of the second chamber 220. The two speakers are driven in phase
(electrically and mechanically in this arrangement) and are confined in the air of chamber 220,
which causes the body of air to move effectively as a vibrating device that does not compress and
expand between the speakers The purpose is to supply the same direction ("push-pull") force to
the body being pinched.
The enclosed body of air in the chamber 220 driven as an integral vibrating mass and coupled to
the speaker 224 adds a significant amount of mass to the vibrating speaker by substantially
lowering the resonant frequency.
FIG. 3 b is identical to FIG. 3 a except that a duct 240 is provided, which is connected to the
opening 242 of the container wall, where the chamber 226 (which supplies the stiffness of the
system) mounts the two speakers 224 and 230. Indicates a system identical to the one shown.
The body of air confined within the chamber 220 acts as a vibrating mass which greatly reduces
the natural frequency of the system, and the air within the speaker 224 and the chamber 226
acts as a normal speaker with a ducted (Bath reflex) container Do. The arrangements of FIGS. 3a
and 3b operate in the same manner as the arrangements of FIGS. 1 and 2, and the description
relating to the previous embodiment applies equally to the embodiments of FIGS. 3a and 3b.
In all of the embodiments described herein, the speakers are placed at different locations along
one or more axes of the speaker, thereby providing a "push-pull" operation to the air-trapped
body. The speaker cones facing the air in each chamber may be front or back, as long as the
speakers exert a "push-pull" force on the vibrating air mass with which the speakers vibrate as
Loudspeaker systems are provided which have a considerably lower resonant frequency even
with the use of small containers by the provision of an oscillatory mass which is oscillated in
synchronism with the electrical signals which cause the loudspeaker oscillations. The
arrangement is because the confined air mass acts as a spring mainly supplying the stiffness of
the resonant system, and the second confined air mass moves more effectively as a vibrating
device than compression and expansion 2 It is driven by the force supplied by the loudspeakers
on two different sides. Such mass is added to the system in a simple and effective way where
small containers can be used at very low frequencies.
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jph05236586, description
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