Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Mounting or support feature of housed loudspeaker
Reexamination Certificate
1999-08-09
2002-07-09
Mei, Xu (Department: 2644)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Mounting or support feature of housed loudspeaker
C381S150000, C381S386000, C181S148000, C181S199000, C029S594000
Reexamination Certificate
active
06418231
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of high fidelity audio reproduction; and, more particularly, concerns subwoofer loudspeaker systems that produce high quality, low distortion and low-frequency sound.
2. Prior Art
In the field of high fidelity sound reproduction, a high quality audio system is normally comprised of: a) a signal source, which is generally music or soundtracks from: i) films; ii) compact disk players; iii) laser disk players, and the like; b) a “preamplifier” which receives signals from the signal source and provides an audio signal to a power amplifier which amplifies the signal; and c), loudspeakers that can reproduce the sound from the signal source. Generally, loudspeakers are single enclosures designed to produce most of the audible frequency range, which is from 20 Hertz (“Hz”) to 20,000 Hz.
Modern recording technologies have allowed music and film Producers to make recordings having wider dynamic ranges—i.e., higher signal-to-noise ratios—and more extended frequency response. Furthermore, many music and film recordings contain more low frequency information than those of only a few years ago. This is especially true in film soundtracks, where recordings of special effects such as explosions are commonplace.
In response to the increased low frequency sound in recordings, a growing number of audio systems are adding an additional type of loudspeaker to their existing array of loudspeakers. This type of loudspeaker is known as a “subwoofer”. Subwoofers are specialized loudspeakers which reproduce only the lowest frequencies of the audible frequency range—viz., those frequencies ranging from approximately 20 Hz, or lower, to about 80 to 120 Hz. These low frequencies are difficult for many full range loudspeakers to reproduce because the bass drivers for full range loudspeakers must handle a wider frequency range—i.e., their frequency response must extend much higher in the audible frequency range, often to about 2,500 Hz or even higher depending upon the design of the loudspeaker. Adding a subwoofer to an audio system relieves the full range loudspeaker from reproducing the lowest frequencies, thereby improving its performance. In addition, certain standards are being set for the reproduction of film soundtracks at home which require the use of one or more subwoofers. Such standards include THX® (a registered trademark of Lucas Film, Ltd.) certification from Lucas Film and Dolby AC-3 Surround Sound® (a registered trademark of J.C. Penney Company, Inc.) from Dolby Laboratories. Dolby AC-3 Surround Sound® even has an audio channel dedicated to only low frequency information.
Conventional design of a subwoofer involves the placement of one or more large bass drivers into a large cabinet—e.g., typically a cabinet enclosing a volume of space ranging from about 8 cubic feet to about 27 cubic feet. Bass drivers, known as “woofers”, generally include a circular “diaphragm” or “cone” which can be constructed of many different materials including paper, plastic, kevlar, etc. Woofer cones have a certain diameter—viz., the bore of the cone is equal to pi×radius
2
(&pgr;r
2
). Prior art subwoofer cones capable of high acoustic output generally have a diameter of at least ten inches, and often greater.
The circumference of the cone is affixed to a “surround” or “suspension”, which is then affixed to the driver's frame. The suspension enables the cone to move in and out of the driver frame at a particular frequency and returns it to a null position when no sound is produced. The peak-to-peak distance traveled by the cone is known as the “stroke” of the driver—sometimes referred to as the “excursion” of the driver. Generally, the drivers installed in prior art subwoofers have a peak-to-peak stroke or excursion of between 0.4″ and 0.6″. Prior art suspensions are constructed of flexible, compliant materials such as relatively thin rubber, impregnated cloth, expanded synthetic cellular foam such, for example, as expanded cellular polyethylene (“PE”) surround foam, or similar materials which are compressed to a thickness of about 0.02″ and which are not self-supporting, which have historically produced very little resistance to peak-to-peak cone movement, and which are capable of standing off box pressures of only on the order of nominally about 0.1 lbs/in
2
and, at best, only about 0.15 lbs/in
2
.
Movement of the cone about the suspension causes air to be moved, which is what produces the sound heard and, in the case of bass, felt by the listener. The amount of air that can be moved by a driver is directly related to the bore and stroke of the subwoofer cone. Thus, to increase the amount of air that a subwoofer can move, the bore, the stroke, and/or both the bore and stroke, can be increased. However, and as will be discussed below, simply increasing the bore and/or the stroke has disadvantages.
At the center of the cone, the driver is affixed to the “motor” of the cone which is comprised generally of a single electrical conductor placed within a magnetic field. In the prior art, the electrical conductor is a single electrical wire wrapped around a cylinder. This arrangement is know as the “voice coil” of the driver. The voice coil is wrapped around a voice coil former which is, in turn, affixed to the cone of the driver and placed in proximity to a magnet. When current is run through the voice coil, magnetic fields are created around the voice coil. These voice coil magnetic fields interact with the magnetic fields of the magnet, which causes the voice coil former to move. The voice coil former's movement causes the movement of the cone. Cone movement, as discussed above, causes movement of air which produces sound. Producing sound at higher volumes requires greater cone movements. Greater cone movements are produced when the voice coil and the driver's magnet have greater magnetic field interactions; and, this increased magnetic field interaction is produced when the voice coil has more current running through it.
To reproduce low frequencies at high volume levels, a subwoofer must be capable of moving large quantities of air. Typical prior art subwoofers for use in the home can move approximately one-hundred thirty cubic inches of air. For louder audio volumes, it is desirable that the subwoofer be capable of moving even more air—for example, one-hundred eighty cubic inches of air. A typical fifteen inch diameter woofer, which has a cone diameter of approximately thirteen inches and a stroke of approximately 0.6 inches, can move approximately eighty cubic inches of air. Therefore, generally a prior art subwoofer will utilize two of these drivers; and two drivers are able to move approximately one-hundred sixty cubic inches of air.
One disadvantage of having a driver with a fifteen inch cone is that it is difficult to design a cone of that size which is rigid enough to resist distortion when the cone has such a large surface area.
Another example of a prior art subwoofer utilizes four twelve inch drivers. Each of these drivers has a cone diameter of approximately ten inches and a stroke of approximately 0.6 inches. Such a subwoofer can move approximately one-hundred ninety cubic inches of air. However, such a subwoofer suffers from the disadvantage that four drivers are required; and, this greatly increases the size of the cabinet required, cost and weight.
Of course, it is possible to increase the stroke of the driver, and thus increase the amount of air that is moved by the driver. However, when the stroke of the driver is increased, the efficiency of the driver is substantially reduced, as less of the voice coil will remain in the magnetic gap.
Prior art subwoofer systems invariably require a large cabinet. One reason, as seen from the above, is that many prior art subwoofer systems utilize several large drivers so that they can move enough air for adequate performance. However, large cabinets are necessary for prior art subwoofers for reasons having nothing t
Hughes Law Firm PLLC
Hughes, Esq. Robert
Mei Xu
LandOfFree
High back EMF, high pressure subwoofer having small volume... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High back EMF, high pressure subwoofer having small volume..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High back EMF, high pressure subwoofer having small volume... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2826227