Acoustics – Sound-modifying means – Housing or enclosure
Reexamination Certificate
2001-08-31
2003-06-03
Dang, Khanh (Department: 2837)
Acoustics
Sound-modifying means
Housing or enclosure
C181S146000, C181S151000
Reexamination Certificate
active
06571909
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the art of loudspeakers employed in the amplification of sound, particularly those used with high fidelity sound reproduction, and in the minimization of distortion and refraction of sound through the enclosure in which the loudspeakers are housed.
2. Description of the Prior Art
The reproduction of audio sound requires the use of electroacoustic transducers. The transducers transform the input signal into audible sound energy. The transducers are conventionally mounted within an enclosure. Conventional loudspeaker enclosures introduce interference into the atmosphere in which the speakers are housed. Among the types of interference introduced are reflection of sound within the speaker enclosure, enclosure vibration, and diffraction of sound at edges and anomalies of the speaker enclosure.
Some prior art loudspeakers have been designed with features that attempt to defeat some of these problems by different means. Some speaker manufacturers have devised internal baffle systems that prevent the direct “bounce-back” of the rear sound wave produced by the transducer. This problem has also been addressed by installing elongated cones within a speaker to diffuse and dissipate these sound waves. Other manufacturers have created intricate rigid structures within speaker enclosures to defeat cabinet vibration. Others have designed foam covered front baffles that dampen “bounce-back” sound waves.
These designs have failed to mitigate all the interference introduced by the loudspeaker enclosure and have required the introduction of irregular parts or expensive construction techniques.
SUMMARY OF THE INVENTION
Conventional loudspeakers that incorporate electroacoustic transducers fail to produce pure sound. This is so, at least in part, because the enclosures in which the loudspeakers are housed produce interference with the sound that the loudspeakers generate. Examples of this interference are internal reflections, enclosure vibrations, and diffraction.
Reflection of sound occurs when a sound wave bounces off a surface. In traditional loudspeakers, which have a horizontal cross-section shaped like a parallelogram, reflection commonly occurs from the sound produced by the acoustic transducer reflecting off the back wall of the enclosure toward the front baffle in which the transducers are mounted. This reflection produces uneven and conflicting sounds for the listener. Sound may also be reflected off the walls, floor, or ceiling of a room in which a loudspeaker is placed. This type of sound is commonly referred to as a “secondary wave”.
Enclosure vibration, like all vibration, creates an interfering sound wave. Generally, an enclosure vibrates due to both the sound wave that is projected from the rear of the transducer and the vibration of the transducer at the point at which it is connected to the front baffle. The enclosure vibration creates an interfering sound wave that travels in essentially all directions, unlike the directed sound produced by the transducers.
Diffraction occurs when a sound wave encounters a discontinuity in the medium through which it is traveling. A sound wave produced by a transducer mounted on a flat surface will travel along the face of that surface until the surface ends. At this point, the sound wave bends to fill the space available to it. This bending alters the sound wave and corrupts the original sound wave. Diffraction also occurs when a sound wave travels through one medium and into a different medium. This type of interference is also commonly caused by traditional loudspeaker enclosures. Sound enters the medium from which the enclosures are built, typically from the interior of the enclosure, and travels through that medium to a point where it enters the surrounding atmosphere. Sound waves typically leave the medium of the enclosure at a point that presents a discontinuity, such as an edge or a corner of the enclosure. The sound produced by diffraction normally differs greatly from that produced by the loudspeaker in timing, pitch, and timbre.
Prior art speakers have employed several methods to defeat these forms of interference. One common method of damping this interference is the mounting of damping material, such as acoustic foam, on the interior of the enclosure walls. Although this technique has some effectiveness in defeating reflection within the enclosure, the foam in prior art speakers fails defeat interference caused by enclosure vibration or secondary waves. Furthermore, traditional loudspeaker enclosures have a back wall that is parallel or substantially parallel to the front baffle. The sound reflected off the back wall of the enclosure is dispersed not only through the front baffle, but also through the transducers themselves. Finally, traditional loudspeaker enclosures fail to defeat interference created by diffraction of sound at the edges of the enclosure.
It is an object of the present invention to provide a loudspeaker enclosure that significantly reduces internal acoustic reflections, enclosure vibrations, and diffraction of sound off the edges of the loudspeaker enclosure.
It is a further object of the present invention to minimize internal acoustic reflections and diffraction in a loudspeaker enclosure to provide an improved sound field and improved sound reproduction.
It is an additional object of this invention to provide a loudspeaker enclosure that is comprised of materials that are widely available and inexpensive to obtain.
Additional objects of the invention will be set forth in the description that follows, and will become apparent to those skilled in the art upon examination of the following.
The present invention provides a loudspeaker enclosure arrangement that reduces, by a large degree, internal acoustic reflections, enclosure vibrations, and diffraction off the surfaces and edges of the loudspeaker enclosure. The loudspeaker exterior surfaces and edges are covered with acoustic damping foam. The enclosure is shaped to dissipate sound waves within the enclosure, rather than allowing the sound waves to reflect off its walls. To achieve the objects set forth above, the present invention comprises a loudspeaker in which the exterior of the side walls are prevented from communicating interfering sound by the placement of exterior sound-damping foam blocks. The present invention also comprises a loudspeaker enclosure that has a triangular horizontal cross section. Internal sound waves diminish toward the distal point of the enclosure and are not reflected forwardly.
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patent: 5682436 (1997-10-01), Sakamoto
patent: 5731555 (1998-03-01), Anagnos
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Dang Khanh
Napier James A.
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