Abstract:
The invention presents a design of optimum edges for antennas of loudspeakers, microphones, hydro-speakers, hydro-phones, brass and wind instruments, and ultrasonic transducers. These edges have a serrated-roll shape, and enhance the acoustical field strength uniformity. Loudspeakers, hydro-speakers, and ultrasonic transducers will become more effective in radiating acoustical power. The quality of these apparatuses are enriched. The musical tone emitted by loudspeakers, brass and wind instruments becomes more smooth, mellow, rich, clean, and elegant.

Description:
This is a Continuation-In-Part of the pending application: Appn. Number: 07/612,997 Filing Date: Nov. 15, 1990 now abandoned. 
     TECHNICAL FIELD OF THE INVENTION 
     This invention is on improving acoustical antennas for enhancing the performance of loudspeakers, microphones, hydro-speakers, hydro-phones, brass and wind instruments, and ultrasonic transducers. The invention will reduce spatial irregularity of sound created by edge diffraction and enrich the quality of these apparatuses. 
     BACKGROUND OF THE INVENTION 
     Loudspeakers, microphones, hydro-speakers, hydro-phones, brass and wind instruments, and ultrasonic transducers are apparatuses all of which we will refer to as acousducers. They may have different designs, shapes, and drivers, but they all have an opening which interacts directly with surrounding medium, that can either be air, liquid, or solid. Openings are usually the mouths or end surfaces of tubes, horns, cones, and wedges which are a part of any acousducer. Loudspeakers, microphones, hydro-speakers, and hydro-phones all have these mouths; likewise the brass and wind instruments, as well as certain string instruments, for example, the Chinese two string instruments. Some ultrasonic transducers have a radiating end surface as well. 
     Mechanical parts associated with the mouth or end surface of an acousducer are mainly responsible of radiating or receiving sounds. The whole structure of mechanical parts is special and directly affects the spatial distribution of the sounds radiated to or selection of the sounds received from the environment, thus it plays the role of an antenna for the acousducer. We will refer to the whole mechanical parts as the acoustical antenna. Conventionally, the acousducers are treated as vibrating objects. The emphasis of a conventional treatment is on the quality of frequency responses for these acousducers. The spatial radiation pattern of sounds generated or received by these acousducers is often not considered. This restricted view has prevented us from gaining deeper understanding of the acousducers. 
     The finite size of a mouth or end surface creates appreciable side lobes and spatial irregularities in sound generation or reception. The irregularities are all resulted from the edge diffraction of the acoustical antenna opening and lead to performance degradation of acousducers, because edge diffraction spreads sounds toward or receiving sounds from undesirable directions. 
     In light of the above, there is a need in the art to minimize edge diffractions of acoustical antennas. The loudspeakers, hydro-speakers, and ultrasonic transducers will then become more effective in radiating acoustical power. The microphones, hydro-phones, and ultrasonic transducers will be more effective in selecting sounds for reception. The quality of brass and wind instruments and loudspeakers will be enriched. The tone emitted by them becomes more smooth, mellow, rich, clean, and elegant. 
     THEORY 
     An acoustical antenna projects sound waves through its mouth or end surface onto an aperture at the surrounding mediums. The wave field at each point of the aperture as defined by the projection becomes a new source of a secondary spherical wave and is known as Huygens&#39; wavelet. The envelope of all Huygens&#39; wavelets emanating from the antenna aperture at any instant of time is then used to describe the transmitting wave from the antenna at a later time. The above mechanism is known as the famed Huygens-Fresnel Principle. Mathematically, this principle can be represented by the Rayleigh-Sommerfeld diffraction formula which is a Fourier type integration. 
     The aperture of any antenna must be finite in size. This restriction imposes a abrupt “rectangular” window on the Rayleigh-Sommerfeld diffraction formula for an untreated antenna. It is well known in Fourier analysis that a rectangular window leads to high side lobes. These side lobes can be properly reduced by employing smooth tapered windows before evaluating the Fourier transformation. The edge treatment of an antenna to reduce its edge diffractions corresponds to an imposition of a smooth tapered window onto the Rayleigh-Sommerfeld diffraction formula. The serrated and rolled edge treatments differ in methods of tapering. The former is restricted to the magnitude tapering of the wave field at the aperture of an antenna, and the latter is mainly confined to phase tapering with little controls on the magnitude. The wave field has two independent components -- magnitude and phase. Any abrupt change in either component will lead to high side lobes and edge diffractions. Both serrated and rolled edge treatments are only restricted to one respective component, while neglecting the other. The abrupt change cannot be optimally removed with either of these two methods. The present invention treats both components simultaneously; therefore leading to much better side lobe reduction and a smaller size for the added skirt. 
    
    
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention advantageously satisfy the above identified need in the art, and provide acoustical antennas which are low in edge diffractions and side lobes. In particular, an embodiment of an inventive acoustical antenna comprises a body, which further comprises a skirt, and a serrated-roll edge. 
     In a preferred embodiment of the present invention, the antenna body is tightly jointed with the body or the supporting structure of its hosting acousducer. Irregularities of the antenna body and the joint to its host will create internal reflections, which disturbs the sound generated by the acousducer. In a further preferred embodiment, the antenna body and the joint all are smooth and continuous. Any unavoidable irregularities should be kept as minimum as possible. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A complete understanding of the present invention may be gained by considering the following detailed description in conjunction with the accompanying drawing, in which: 
     FIG. 1 shows a diagram of a skirt with a serrated-roll edge for use in fabricating embodiments of the present invention. 
     FIG. 1 a  the skirt in FIG. 1 as viewed from the top. 
     FIG. 1 b  shows an embodiment of a transducer with a serrated-roll edge skirt which is fabricated in accordance with the present invention. 
     FIG. 2 shows an embodiment of a loudspeaker with a serrated-roll edge skirt which is fabricated in accordance with the present invention. 
     FIG. 2 a  the embodiment of the loudspeaker in FIG.  2 . 
     FIG. 3 shows an embodiment of another loudspeaker with a serrated-roll edge skirt which is fabricated in accordance with the present invention. 
     FIG. 3 a  shows a preferred embodiment of the loudspeaker with a serrated-roll edge skirt. 
     FIG. 4 shows an embodiment of a looped brass instrument with a serrated-roll skirt fabricated in accordance with the present invention. 
     FIG. 5 shows a diagram of a solid skirt with a serrated-roll edge for use in fabricating embodiments of the present invention. 
     FIG. 6 shows an embodiment of an ultrasonic transducer with a solid serratedroll skirt fabricated in accordance with the present invention. 
     FIG. 7 shows an embodiment of a transducer with a serrated-roll skirt fabricated in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows embodiment  100  of a skirt  100  with a serrated-roll edge, which is fabricated according to the present invention. The skirt is rigid-walled and cylindrically symmetric. It receives acoustical powers from the lower input throat  110  and radiates sounds from the upper output opening  120 , or vice versa. The interior rim  111  of the lower throat  110  and the circumference  130  of the upper opening cross section are all circular. The interior wall of the skirt  100  is smoothly finished and continuously formed. The interior wall is smoothly and continuously rolled back, as the skirt opens gradually from its receiving throat  110  to its radiating opening  120 . Any radian curve  140  along the interior well is smooth and continuous. 
     The perimeter curve  150  is smooth and continuous. It means that the radius of curvature and a certain number of its derivatives at every point on the perimeter curve  150  are continuous. Each serration of the edge tapers down slowly and may revert to a scalloped shape, as the serration  160  progresses gradually from the valley points  171  and  172  to the tip  173 . The exterior wall  180  of the skirt  100  may be finished according to the designers artistic taste. 
     As those of ordinary skill in the art should readily appreciate that the number of serration, the roll back rate, the tapering curvature, the depth of serration and the size of the skirt are determined by the requirements on the desired width and shape of the main lobe; the acceptable level of side lobes; the allowance of the spatial sound irregularity; and the imposed restrictions on the physical dimensions of the entire skirt. The process from a set of requirements to the objective skirt is an optimum process, which requires a theoretical calculation. The calculation is based on Rayleigh-Sommerfield diffraction formula and variational principles which are well known to those of ordinary skill in the art. The resulted calculations leads to the number of serration, the roll back rate, the tapering curvature, the depth of serration and the size of the skirt. In the engineering implementation of the serrated-roll skirt, the smoothness, the continuity, the rollback rate, the tapering curvature, and the depth of serration have to be strictly maintained and the deviation level has to be kept as low as possible. As those of ordinary skill in the art will readily appreciate, the interior wall of the skirt must be rigid and stiff to assure the perfection of the implementation. Sometimes, imposed physical restrictions may prevent a perfect implementation of the present invention, then precautions have to be taken to minimize the undesirable variations as much as possible. 
     FIG. 1 a  the top view of embodiment  100  in FIG.  1 . The circular interior rim  111  of the lower throat  110  and the circular circumference of the upper opening cross section  130  assure the smoothness and continuity of the skirt. 
     FIG. 1 b  shows embodiment  190  of a transducer with a serrated-roll edge skirt  100  which is fabricated in accordance with the present invention. The transducer may be a loudspeaker, microphone, hydro-speaker, hydro-phone, or an ultrasonic transducer. The driver  191 , which is well known to those of ordinary skill in the art, can be crystal, electric, magnetic, ribbon, or others. The cover  192  is just for the protection of the driver  191 . 
     FIG. 2 shows embodiment  200  of a loudspeaker with a serrated-roll edge skirt  210  which is fabricated in accordance with the present invention. The original loudspeaker is comprised of the driver  220 , enclosure  230 , and horn  240  which are well known to those of ordinary skill in the art. The original skirt  250  is removed by a crosscut  260  which is perpendicular to the skirt axis  270 . The serrated-roll edge skirt  210  joints to the original skirt at the cut  260  smoothly and continuously. It means that the radii of curvature and a certain number of their derivatives at both sides of the cut  260  are equal to assure any radian curve  280  crosscutting the joint and along the interior wall remain smooth and continuous. 
     FIG. 2 a  the embodiment  200  of an invented loudspeaker in FIG. 2 with the original skirt  250  removed. The steps described above are mainly for the illustration purpose. Any one with ordinary skills would appreciate that, for small loudspeakers with serrated-roll edges, it is easier and cost less in manufacturing each of these loudspeakers as a whole unit rather than through steps outlined above. The theoretical analysis of conventional speaker skirts are based on a quasi-one-dimensional model of sound propagation in a duct of variable cross-sectional area, which is cylindrically symmetric and angle independent. Conventional skirts, which were constructed under the guidance of these analysis, have circular cross sections, hence the original skirt  250  is often circular. The sound propagation in a duct is governed by Webster&#39;s wave equation with the assumption that the wave is uniform over the cross section area. Webster&#39;s wave equation is no longer applicable for the serrated skirt, hence the wave is no longer uniform over the cross section area of the skirt with serration. 
     FIG. 3 shows embodiment  300  of a loudspeaker with a serrated-roll edge skirt which is fabricated in accordance with the present invention. The enclosure  310 , the driver  320 , the speaker cone  330  and the soft suspension ring  340  are well known to those of ordinary skill in the art. In accordance with the present invention, the length of the rigid-walled skirt  350  should be relatively shorter than that of a conventional horn with a same size opening. The skirt  350  is firmly mounted on the enclosure  310 . The throat of the skirt  350  should be nearly equal to the opening of the speaker cone  330 , but less than the inner circle of the inner rim of soft suspension ring  340 . The clearance between the skirt  350  and the speaker cone should be sufficient for the possible speaker cone  330  excursion. The tangents of the radian curves at the interior throat rim of the skirt  350  should be all parallel to the axis of the skirt  350 . 
     In a preferred embodiment of the present invention, the serrated-roll skirt  350  of a loudspeaker  300  is mounted on the enclosure  310  through a specially designed structure  360  as in FIG. 3 a . The skirt  350  is firmly fastened to the structure  360  at the skirt&#39;s waist  370 . The hallowed space  380  as surrounded by the enclosure  310 , the suspension ring  340 , the skirt  350  and the structure  360  is filled with acoustically absorptive material to remove the diffracted sound from the suspension ring  340 , from the edge of the enclosure&#39;s opening, and from the outer rim of the skirt&#39;s throat. 
     FIG. 4 shows embodiment  400  of a looped brass instrument with a serrated-roll skirt  410  fabricated in accordance with the present invention. The instrument body  420  is well know to those of ordinary skill in the art. The original skirt is removed by a crosscut  430 . The serrated-roll edge skirt  410  joints to the original instrument body at the cut  430  smoothly and continuously. It means that the radii of curvature and a certain number of their derivatives at both sides of the cut  430  are equal to assure any radian curve cross cutting the joint and along the interior wall remain smooth and continuous. Accordance with the present invention, the exterior wall of the skirt  410  may be finished according to the designer&#39;s artistic taste. The invented skirt will not only reduce edge diffraction and enrich the tone quality of the brass instrument, but will also make it more visually attractive by the artistically designed edge serration. 
     FIG. 5 shows a diagram of a solid skirt  500  with a serrated-roll edge for use in fabricating embodiments of the present invention. Any one with ordinary skills would appreciate the needs of a solid skirt to couple an ultrasonic source with a solid object in the non-destructive testing of materials and in the medical diagnostics. The solid skirt delivers acoustical power to or from an ultrasonic driver through the lower end surface  510 , and radiates or receives sounds through the upper end surface  520  to or from environment. Furthermore, any one with ordinary skills should readily appreciate that the solid skirts may take different shapes to satisfy various test and diagnostic objectives. These shapes may be truncated cones and cropped wedges. The exterior wall  530  is serrated and rolled back at the end of the radiating surface  520  to form a serrated-roll edge  540 . 
     FIG. 6 shows embodiment  600  of an ultrasonic transducer comprising solid skirt  610  with a serrated-roll edge. Ultrasonic drive  620  is mounted at the receiving end of solid skirt  610 . The ultrasonic drive is an apparatus which is well know to those of ordinary skill in the art. The driver might be a piezoelectric plate and its accessories. If it is important to minimize external interference which either comes from the external sources, or from the surrounding environment, then the ultrasonic driver is covered by enclosure  630 , which is filled by damping material  640  to reduce internal reflections within the enclosure. The manners, in which the enclosure is installed and the damping material is placed, are well known to those of ordinary skill in the art. 
     FIG. 7 shows embodiment  700  of a transducer with a serrated-roll skirt fabricated in accordance with the present invention. The transducer can be a loudspeaker, microphone, hydro-speaker, hydro-phone, or an ultrasonic transducer. As those of ordinary skill in the art will readily appreciate, a transducerr with embodiment  700  is highly directional. The transducerr comprises reflector  710 , which further comprises skirt  720  with serrated-roll edge  730 . The driver  740  of the transducer is mounted above reflector  710  through supports  750 . Reflector  710 , driver  740 , and supports are well known to those of ordinary skill in the art. 
     OBJECTIVES AND ADVANTAGES 
     Embodiments of the present invention is a new design to enhance the performance of loudspeakers, microphones, hydro-speakers, hydro-phones, brass and wind instruments, and ultrasonic transducers. The performance enhancement arises from the edge treatment of their openings or end surfaces for reducing side lobe level and sound distribution disturbance. The side lobe and disturbance reductions arising from the present invention 1) enrich the quality of loudspeakers, microphones, and brass and wind instruments; 2) enhance the volume of brass and wind instruments; 3) increase the efficiency and broaden the frequency response of loudspeakers, microphones, hydro-speakers, and hydro-phones; 4) reduce the unwanted interference among speakers, hydro-speakers; 5) enhance the low frequency response of woofers; 6) effectively beam acoustical radiations from hydro-speakers and ultrasonic transducers; 7) reduce the vulnerability revealed by hydro-speakers, and increase the selection ability of hydro-phones. 
     The invented edge will provide better acousducer performance than either of the serrated edge or rolled edge. The invented edge and its host as a whole can be massively manufactured through molding, stamping, and other methods to satisfy the high volume commercial needs on high performance, small in size, and low in cost of loudspeakers, microphones, hydro-speakers, hydro-phones, brass and wind instruments, and ultrasonic transducers. 
     SUMMARY, RAMIFICATIONS, AND SCOPE 
     The discussions and drawings given above contain many specifications, they should not be construed as limiting the scope of the invention but merely providing illustrations. Those skilled in the art recognized that further embodiments of the present invention may be made without departing from its teachings. For example, serrated edges with rolls can take many designs and shapes. The serration shape and roll back rate may vary even within a loudspeaker, microphone, hydro-speaker, hydro-phone, brass or wind instrument, or an ultrasonic transducers. Furthermore some portions of the edge for an acousducer may not have a serrated-roll shape. Speakers and phones may be mounted under a surface, the present invention can be implemented through mounting mechanisms as well as on their radome designs. 
     Thus the scope of the invention should be determined by appended claims and their legal equivalent, rather than by the examples given.