Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Having acoustic wave modifying structure
Reexamination Certificate
2000-03-14
2002-01-29
Le, Huyen (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Having acoustic wave modifying structure
C381S340000, C381S182000, C381S186000
Reexamination Certificate
active
06343134
ABSTRACT:
BACKGROUND OF THE INVENTION
The field of the invention relates to a loudspeaker including a compression chamber, a first electroacoustic transducer disposed inside the compression chamber, a horn and a second electroacoustic transducer disposed outside the compression chamber.
U.S. Pat. No. 4,138,594 teaches a small dimension low frequency loudspeaker which includes a folded exponential horn which provides a unitary curved sound path from an electro-acoustic transducer at the throat of the horn to a volume into which sound is radiated at the mouth of the horn. The length of the horn is such that, at an exponential rate of expansion between the throat and the mouth, the mouth, when it is bounded by at least one planar surface, such as a floor, a ceiling, and/or walls of a room, has adequate area to enable reproduction of low audible frequencies. The low frequency loudspeaker has an effective low end cut-off frequency of 55 Hz. U.S. Pat. No. 4,210,223 teaches a low frequency loudspeaker apparatus includes a folded exponential horn which is divided to provide a bifurcated curved sound path from at least one electroacoustic transducer that is positioned at the throat of the horn to a volume into which sound waves are radiated that is located at the bifurcated mouth of the horn. The mean length of the folded exponential horn is such that, at an exponential rate of expansion between the throat and the bifurcated mouth, the area of the mouth is adequate for reproduction of low frequencies in the audible range. The low frequency loudspeaker apparatus has an effective low end cut-off frequency of 38 Hz. and affords 99 dB SPL output at three meters with one watt input which corresponds to about 20% efficiency measured in free space. Presence of a single boundary surface, such as a stage floor adjacent the mouth of the folded exponential horn, improves amplitude response by 3 to 6 dB. A small dimension low frequency folded exponential horn loudspeaker has a unitary sound path for direction of acoustical waves from an electroacoustic transducer to a volume into which the acoustical waves are radiated.
High fidelity sound reproduction requires reproduction of low audible frequencies. W. B. Snow, “Audible Frequency Ranges of Music, Speech, and Noise,” Jour. Acous. Soc. Am., Vol. 3, July, 1931, p. 155, for example, indicates that high fidelity sound reproduction of orchestral music requires that the frequency band should extend to as low as 40 Hz. It is well established that loudspeakers, in order to reproduce a given frequency range, must have dimensions based on the wavelength which corresponds to the lowest frequency in the range. In the case of one type of loudspeaker, the exponential horn loudspeaker, for example, the area of the exponential horn mouth is determined on the basis of the wavelength of the lowest frequency to be reproduced. At an early date, to obtain high fidelity sound reproduction with exponential horn loudspeakers, and, in particular, the inclusion of low audible frequencies, large exponential horn loudspeakers were constructed. For example, theater loudspeakers as large or larger than eight feet in length and four feet by four feet in transverse dimensions were built in order to obtain reproduction of low audible frequencies. Later, the outside dimensions of the exponential horns were reduced by folding, but even then the dimensions of the mouths were large for reproduction of low audible frequencies. More recently, folded exponential horn loudspeakers with reduced mouth dimensions have been used in proximity to boundary surfaces, such as a floor, a ceiling, and/or walls of a room, to increase the effective mouth area so that low audible frequencies are reproduced while at the same time the dimensions of the low frequency loudspeakers are minimized. See, for example, Sandeman, U.S. Pat. Nos. 1,984,550, 2,310,243 and 2,373,692, and Klipsch, “La Scala, ” Audio Engineering Society Preprint No. 372, Apr. 1965. The low frequency folded exponential horn loudspeakers, such as those which are disclosed in the above-cited references, have small dimensions and, when their mouths are located proximate planar surfaces, enable reproduction of low audible frequencies. However, each of these low frequency folded exponential horn loudspeakers is structurally complex due to the structure of the folded exponential horn which defines the sound path from the electroacoustic transducer to the volume into which sound is radiated. Perhaps the simplest construction appears in the above-cited Audio Engineering Society publication. In that construction, the folded exponential horn is bifurcated to define a double sound path. Due to the complex structure, the production of high fidelity, small dimension, low frequency folded exponential horn loudspeakers has required considerable craftsmanship. High quality control in manufacture has been necessary to assure that the construction meets specifications.
Consequently, the cost of low frequency folded exponential horn loudspeakers has been high.
U.S. Pat. No. 5,212,732 teaches a loudspeaker system of the dipole type, particularly for use in surround sound, reverberation and similar applications. A speaker system includes a pair of woofers having dual voice coil drivers mounted on oppositely facing baffles (e.g., front and rear facing). Preferably, each baffle also includes a high frequency speaker mounted thereon. On a first baffle (e.g., front), both voice coils of the dual voice coil driver and the voice coil of the high frequency speaker are driven in-phase, and on the other baffle (e.g., rear), the second voice coil of the dual voice coil driver and the voice coil of the high frequency speaker are driven out-of-phase from those from the first baffle but in-phase with one another. The coils of the speakers are driven from suitable filter circuits.
U.S. Pat. No. 5,212,732 teaches a loudspeaker system of the dipole type, particularly for use in surround sound, reverberation and similar applications. The speaker system includes a pair of woofers having dual voice coil drivers mounted on oppositely facing baffles (e.g., front and rear facing). Each baffle also includes a high frequency speaker mounted thereon. On a first baffle (e.g., front), both voice coils of the dual voice coil driver and the voice coil of the high frequency speaker are driven in-phase, and on the other baffle (e.g., rear), the second voice coil of the dual voice coil driver and the voice coil of the high frequency speaker are driven out-of-phase from those from the first baffle but in-phase with one another. The coils of the speakers are driven from suitable filter circuits. Various forms of loudspeaker systems have been developed, and the types of speakers as well as the technologies involved pertaining to woofers, tweeters, mid-range and other forms of speaker systems are well known. Stereo sound systems using front speakers with or without some form of woofer or subwoofer, along with rear and/or side speakers, have become prevalent particularly for sound systems used to reproduce sound in “home theater” video systems for playing back video motion pictures and similar program material. The typical installation comprises a pair of front speakers positioned to either side of the TV screen, preferably with a center speaker and/or a subwoofer, and along with a pair of right and left side speaker and/or a pair of left and right rear speakers.
An Audio Engineering Society (AES) paper entitled “New Factors in Sound for Cinema and Television” by Tomlinson Holman, presented at the 89th Convention of the Audio Engineering Society, Los Angeles, Calif., Sep. 21-25, 1990, and reprinted in the Journal of the AES, Volume 39, No. 7/8, (preprint #2945) notes that the best directivity pattern for the “surround” loudspeakers is not the conventional forward radiating direct radiator, but rather dipolar radiation with the principal lobes of the dipole pointed, not at the listening area, but at the room surfaces with the null in the radiation pattern pointed at listeners, and that the best su
Johansen W. Edward
Le Huyen
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