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  Speaker system with improved frequency responseUSPTO Application #: 20070256888Title: Speaker system with improved frequency response Abstract: A speaker enclosure includes a first set of walls defining a first box, a second set of walls defining a second box disposed within the first box to define an enclosed compartment between the first set of walls and the second set of walls, an aperture located at least one of the second set of walls defining an opening between the internal volume of the second box and the enclosed compartment, and an alternative density transmission medium affixed to one or more surfaces of the first set of walls and/or the second set of walls in the enclosed compartment. (end of abstract) Agent: Kevin J. Mcneely, Esq. - Washington, DC, US Inventor: Jan Plummer USPTO Applicaton #: 20070256888 - Class: 181199000 (USPTO) Related Patent Categories: Acoustics, Sound-modifying Means, Housing Or Enclosure (e.g., Sound Confining And Absorbing), Speaker Type The Patent Description & Claims data below is from USPTO Patent Application 20070256888. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This utility patent application is a continuation of U.S. patent application Ser. No. 10/709,538 filed on May 12, 2004. BACKGROUND OF THE INVENTION [0002] A typical loudspeaker is an electro-dynamic transducer attached to a diaphragm of some depth, diameter and shape. Electro-dynamic describes a transducer that moves back and forth in response to an alternating voltage source to stimulate adjacent air molecules. Some of these types of loudspeakers may be considered a commodity and are inexpensive. They are typically mounted on a baffle as part of an existing product or structure; in some form of housing for practical containment or in some cases a specialized enclosure is utilized to enhance the bass performance. [0003] One problem with these types of loudspeakers is that the driver may have a favorable acoustic impedance only over a narrow range of frequencies depending on its size. The smaller driver generally has unfavorable acoustical impedance for lower frequencies and vise versa for larger ones. The enclosure also favors a narrow range of frequencies and for other frequencies it may react violently creating a plethora of incoherent internal standing waves that modulate the diaphragm with nonsymmetrical vibration patterns. These random internal modulations disturb the natural dispersion pattern of the driver and cause electrical feedback (reactance) to the amplifying source. Brute force power and heavy gauge wiring are current attempts to minimize this problem for the amplifier and the effects on sound quality. [0004] Another problem is the general acoustic impedance differential that exists on either side of the driver diaphragm. The diaphragm must work simultaneously in two different acoustic environments as the enclosure creates standing waves that constantly modify the drivers' acoustic impedance in most of its frequency range. Reflected waves from the room cause additional modifications of the drivers' acoustic impedance more as the frequencies go lower towards that of the rooms' dimensions. Smaller enclosures can be worse because of the even higher frequencies that are reflected internally and the lack of low frequency capabilities. [0005] Two identical drivers will sound different due to their operating enclosure. One solution with mid-range speakers is to produce units with a solid basket behind the diaphragm. This may prevent random standing waves from interfering with the other drivers but it may create extreme backpressure for the range of frequencies produced by the midrange driver. This causes the driver to see a distinct acoustic impedance differential throughout its operating range thereby preventing it from producing a natural sound. [0006] Loudspeaker driver dimensions favor a certain range of frequencies thus making a single size for all frequencies difficult if wide axis listening is desired. It is a design goal to produce loudspeakers of the smallest dimensions necessary at minimum cost while maintaining the proper loudness level while retaining the sonic presentation of full frequency range, low distortion and wide-constant dispersion. A solution is the use of multiple drivers operating for a common acoustic purpose. This is reflected current loudspeaker designs in an effort to produce subjectively accepted loudspeakers. [0007] When a single driver is used, it is typically designed to favor lower or higher end frequencies while attempting to maintain quality in the middle ranges. The human ear tends to more sensitive to the higher frequencies but the human ear-brain combination prefers to hear all of the frequencies in the spectrum without phase or frequency aberrations to interrupt the flow of energy of the event otherwise it will appear to be artificial. The reproduction of sound is typically for either of two purposes and that is communication and entertainment. The latter requires unencumbered sonic balance and dispersion to balance the energy in the listening environment. [0008] The continued efforts to perfect sound reproduction with predictable field results depend greatly on a solution to solve the dilemma of the enclosure. Engineers recognize the drivers' enclosure as a design challenge. The use of the apparatus as explained in the pending application can improve sound quality. SUMMARY [0009] Application of the device improves the reproduction of the full range of audio frequencies using a specific technique that allows for the delay of sound waves in a very short distance within a defined space to create beneficial standing waves over a wide frequency range. [0010] The device utilizes a closed loop embedded acoustic transmission line (EATL) and does not provide an exit path for the wave into the ambient environment for the wave. Dynamically the internal enclosure volume varies due to the EATL construction acting with a constant pressure relative to frequency. [0011] Normally a transmission line is used to carry energy in one direction from an originating point to a consumption or load point. An audio transmission line provides a path wave of energy to deliver the wave to a physically distant point. Any panels spaced too far apart will cease to be a wave-guide. The optimal panel spacing depends on the volume of air involved with the wave energy. [0012] The typical acoustic transmission line conveys acoustic energy away from the rear of the driver to the terminus in an attempt to prevent the back wave energy from reflecting back on the driver thereby interfering with the radiated output of the driver. The terminus describes the wave energy exit and can be at the front, rear or bottom of the TL enclosure. Large dimensions are required for existing TL designs to have any effect on other than midrange frequencies. [0013] The proposed invention relates to loudspeakers and in particular methods of improving the quality of reproduction for very low, low, middle and higher frequencies, reducing the relative enclosure dimensions, reducing the costs and dependency on the rooms' acoustics for consistent results. The improvements reflect on a manner of enclosing the driver that frees it from dependence on its general ambient acoustic environment and allows small drivers of essentially the same diameter to function as full range units or subwoofer units that operate with full range units primarily to extend the response into the lowest registers of the frequency spectrum. [0014] In one general aspect, a speaker enclosure includes a first set of walls defining a first box, a second set of walls defining a second box disposed within the first box to define an enclosed compartment between the first set of walls and the second set of walls, an aperture located at least one of the second set of walls defining an opening between the internal volume of the second box and the enclosed compartment, and an alternative density transmission medium affixed to one or more surfaces of the first set of walls and/or the second set of walls in the enclosed compartment. [0015] Embodiments may include one or more of the following features. For example, the surfaces of the first and second set of walls that define boundaries of the enclosed compartment may be first and second wave-guides. As another example, a termination member may be positioned at ends of the pair of wave-guides, the termination member having a surface defining a third wave-guide. In this embodiment, the first, second and third wave-guides are configured as an embedded acoustic transmission line. [0016] The alternative density transmission medium may have a first alternative density transmission medium attached to outer surfaces of the first set of walls and/or a second alternative density transmission medium attached to inner surfaces of the second set of walls to define a channel in the enclosed compartment. As another feature, the alternative density transmission medium includes open cell urethane foam. [0017] The enclosed compartment may be a sealed compartment with a single opening provided by the aperture. As another feature, a port may be installed in one of the first set of walls. [0018] A front wall common to the first and second set of walls may include an opening to receive a loudspeaker. As another feature, at least three of the second set of walls may be attached to a front wall of the first box. [0019] In still another general aspect, a speaker system includes a first cabinet, a second cabinet disposed within the first cabinet to define an enclosed compartment between inner surfaces of the first cabinet and outer surfaces of the second cabinet, an aperture in the first cabinet to define an opening that connects the internal volume of the first cabinet with the volume of the enclosed compartment, an alternative density transmission medium affixed to one or more of the inner surfaces of the first cabinet and/or outer surfaces of the second cabinet and a loudspeaker mounted on a wall of the first cabinet. [0020] Embodiments may include one or more of the above or following features. For example, the loudspeaker may be center mounted along a radial axis of the aperture. [0021] As another feature, the alternative density transmission medium may include open cell foam attached to inner surfaces of the first cabinet and/or outer surfaces of the second cabinet. In addition, inner surfaces of the first cabinet and the outer surfaces of the second cabinet that define boundaries of the enclosed compartment may be first and second wave-guides configured as an embedded acoustic transmission line. Continue reading... Full patent description for Speaker system with improved frequency response Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Speaker system with improved frequency response patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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