Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – By modifying fluid flow
Patent
1995-08-18
1998-10-20
Le, Huyen
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
By modifying fluid flow
381153, 318119, H04R 2500
Patent
active
058259015
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a rotary low frequency sound reproducing apparatus and method and more particularly to a computer-aided rotary electromechanical transducer and method for reproduction of sound in the first two octaves of the audible frequency spectrum.
BACKGROUND OF THE INVENTION
The reproduction of the first two octaves of audible low-frequency sound, from 20 to 80 Hz, is a long-standing problem in that large volumes of air must be moved. For a given loudness of a reproduced low-frequency sound, the air volume moved must be doubled for each halving of reproduced sound frequency.
Many solutions have been attempted. Low-frequency voice-coil-and-cone loudspeakers with highly compliant suspensions have been used. However, the long cone travels needed are difficult to achieve with linearity. Nonlinearities introduce intermodulation distortion, the modulation of higher reproduced frequencies by lower reproduced frequencies. More serious attempts to produce the lowest frequencies in sound isolate the lower two octaves from higher frequencies for reproduction through "subwoofer" loudspeakers.
Direct radiator voice-coil-and-cone loudspeakers, which have at best an efficiency of a few percent, have been used as subwoofers in 12 to 30 inch frame sizes in large cabinets of several cubic feet in volume. Required driving powers are also large, typically several hundred watts. Subwoofer low-frequency response is limited by resonance of the voice-coil-and-cone masses in combination with compliance of the voice-coil support "spider", the cone flexible surround, and the air compliance of a closed cabinet, if used. Together these set an effective lower limit to the frequencies of output sound since it is difficult to drive a loudspeaker below its low-frequency resonance. Closed-loop (negative feedback) servomechanisms controlling voice-coil movements have been used to reduce these effects but they may leave the cone and flexible surround free to flex in unwanted modes at high amplitude, limiting usable power output by the onset of distortion.
In auditoria and stadia, horn-type radiators driven by fairly conventional voice-coil-and-cone transducers have also been used as subwoofers with efficiencies in the 30 to 50 percent range. Their limitation in the domestic environment is that for reasonable performance the perimeter of the horn mouth must be of the order of the wavelength of the lowest reproduced sound, e.g., over 50 20 feet at 20 Hz. Recently, horns of the type disclosed in U.S. Pat. No. 4,564,727 have been driven from externally cooled servomotors through pulley, belt, and cone arrangements, achieving remarkable sustained acoustic outputs.
Most recently, in U.S. Pat. No. 4,763,358, the use of a positive-displacement rotary-vane pump is disclosed. If of suitable size it should be able to produce usable output to and below the 20 Hz limit of audibility. The rotary vane pump may be used to drive a horn, though the required horn mouth size (above) practically excludes it from the domestic user environment. If used as a direct radiator, rotary vane pump efficiency is similar to that of voice-coil-and-cone direct radiators. At high output, most of the input power must be dissipated as heat, usually from within a closed cabinet. Though their volumetric efficiency is high relative to that of voice-coil-and-cone loudspeakers, since much of rotary vane device volume may be swept by the vanes, the devices and their cabinetry can be large. Cabinetry structure for devices having only full-length ports in pump-enclosure sidewalls is awkward. Motor wear and noise, bearing noise, and seal-leakage noise can be problematic in a quiet, e.g., home or auto, user environment. Port-turbulence noise must be managed--a nominal 15 inch diameter, 9 inch long rotary acoustic radiator moves about 6 times the air volume in a single stroke as does a conventional 15 inch loudspeaker.
Position sensing has heretofore been disclosed for rotary acoustic radiators to provide negative feedback information active in the same frequency band as
REFERENCES:
patent: 4136971 (1979-01-01), Varlamov et al.
patent: 4525657 (1985-06-01), Nakase et al.
patent: 4564727 (1986-01-01), Danley et al.
patent: 4625657 (1986-12-01), Little et al.
patent: 4703236 (1987-10-01), Janssen
patent: 4763358 (1988-08-01), Danley
patent: 4874975 (1989-10-01), Hertrich
patent: 5140641 (1992-08-01), Danley et al.
patent: 5191618 (1993-03-01), Hiesey
Le Huyen
MacPherson Alan H.
LandOfFree
Rotary low-frequency sound reproducing apparatus and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Rotary low-frequency sound reproducing apparatus and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rotary low-frequency sound reproducing apparatus and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-254191