Acoustic apparatus

Abstract: An acoustic apparatus adapted to be heard only by a specific person or persons in one space without being worn by the user as in the case of an earphone. Sound signals emanating from the apparatus do not leak to the outside and are not affected by the surrounding moise. Basically, the apparatus is arranged such that a sound source (13) is disposed in one focus of a reflector (11, 35) having an ellipsoidal surface of revolution, and sound signals are heard at the other focus. To increase the number of specific hearers, if the central portion of the reflector (35) is made into a non-ellipsoidal surface of revolution, or a cross section having an ellipsoidal surface of revolution (45) is extended orthogonally to the cross section by a predetermined length, the range of the other focus expands. In addition, by arranging a plurality of reflectors (51A, 51B), it is possible to hear different sound signals within the effective areas of the respective reflectors (51A, 51B) without mutual interference of the sounds.

Description: The present invention relates to an acoustic system suitable for use in providing isolated acoustic zones in larger rooms such as exhibition halls or train stations. Particularly, the invention relates to means for directing sound to a specific person or persons located at a specific space within a larger room, without disturbing surrounding people. In conference or lecture halls, selective listening is commonly done by the use of earphones in a headset. Earphones have the disadvantage of discomfort and considerable inconvenience when used over longer periods of time. Conventional loudspeakers do not provide sufficient directionality to be able to direct and restrict sound to a specific space. On the other hand, the principle of an acoustic lens is known for use in directing sound waves from a specific sound source to converge the sound waves. The United States Patent US-A-4,421,200 discloses an elliptically shaped transducer enclosure for sound transmission. An acoustically reflective shell is shaped in the form of an ellipsoid of revolution having two focal points along the elliptical axis. Transducers for sound transmission are placed at one of the distinct foci such that sound produced is reflected on the elliptical shell and directed substantially to the other foci. Two or more such reflective shells with respective transducers can be provided, whereby the sound generated by the transducers is focused and concentrated at a common focus. The United States Patent US-A-2,643,727 also discloses a sound transmitting device based on the use of an ellipsoidal reflector acting as an acoustic lens. The disclosed sound transmitting device comprises a loudspeaker diaphragm and a concave sound reflector in the form of an ellipsoid, the diaphragm being located at one focal point of the ellipsoid. The ellipsoidal surface is dimensioned such that the second focus lies outside of the reflector. When several such transmitter devices are employed, they are disposed in such a manner that the points of concentration thereof, coincide with one another. The basic principle of an ellipsoidal reflector acting as an acoustic lens is shown in Fig. 1. Examples of the use of acoustic reflectors are illustrated in Figs. 2 to 6. Fig. 1 indicates a hollow ellipsoid of revolution 1 having two foci 2, 3. Sound waves emanating from one of the focal points 2 are reflected by the inner surface of the ellipsoid 1 and directed to the other focus 3. The same principle would apply to light reflection. Figs. 2 and 3 illustrate the type of transmitting devices discussed in the above-mentioned US-A-2,643,272. In the drawings, reference numeral 10 denotes the surface of an ellipsoid of revolution, while the numeral 11 denotes a reflector the surface of which follows part of the ellipsoid. In Fig. 2, the reflector 11 is affixed to a wall 12, while in Fig. 3, the reflector 11 is affixed to a desk top 16. A sound producing means 13, such as a loud speaker, is disposed at one focus A of the ellipsoid of revolution 10. The reflector 11 is arranged such that the other focus B is located at a position where a person will be sitting, for example in a chair 14. As shown in Figs. 2 and 3, a user 15 seated in the chair 14 will receive the sound from the loudspeaker 13, which has been reflected and directed substantially to his head portion. Such arrangements can be made to converge sound to a specific region and can function as a hearing aid for persons having difficulty in hearing. They can also be used for listening to music, whereby sound is concentrated to the listener at focus B, but is less audible to persons located outside of the reflector 11. Figs. 4, 5 and 6 illustrate further arrangements of reflector systems for concentrating and/or directing sound waves. In Fig. 4, the acoustic (sound) signal is conducted along a pipe 26 from a loudspeaker 22. An opening 27 is provided at the end of the sound conducting pipe 26, the end being located at the foci S 1 . In Fig. 5, the reflector surface 35 has a central portion formed as a paraboloid of revolution 35A, while the peripheral portion is formed as an ellipsoid of revolution 35B. A sound source is located at the focus S 1 . Fig. 6 illustrates an arrangement of a reflector 45, the figure showing a cross section in a plane lying orthogonal to a ellipsoidal axis containing the two foci. If the reflector were shaped as an ellipsoid of revolution about the axis, this cross section would be circular. In the arrangement of Fig. 6, the cross section is of elliptical shape, whereby the second focus is not at one point, but is broadened to become several foci in an area about what would have been the single second focus. The arrangement provides less concentration but an increased number of users is accommodated in the more broadly focused area. The above arrangements of sound transmission or projection devices make use of the principle of focusing sound waves making use of variously curved reflector surfaces. Where multiple reflector surfaces and multiple sound sources are employed, for example in US-A-4,421,200 and US-A-2,643,727 as discussed above, the purpose has been to concentrate sound at one particular point or area. There are however instances, such as exhibitions, lecture halls, train stations or other public facilities where the need arises to simultaneously provide various listeners with different information content or information in different languages. It is the object of the present invention to provide an acoustic system in which independent acoustic zones can be formed much closer to one another than would be possible with conventional speaker systems and without requiring the listeners to wear earphones. This object is achieved according to the present invention by an acoustic system as defined in the attached Claim 1. Embodiments of the system are defined in the Claims 2 to 4. According to a preferred embodiment, reflectors formed of an ellipsoidal surface are integrated into a ceiling panel for use in building construction. A plurality of such reflectors can be arranged in the ceiling of an exhibition hall, whereby isolated acoustic zones are created therebelow. A user can move into or out of the isolated acoustic zones to receive various but different acoustic information. For example, information can be given in different languages. Also, different music or different presentations can be provided in the independent acoustic spaces or zones created below the respective reflectors. Further objects and advantages of the present invention will become apparent from the following description of embodiments in conjunction with the accompanying drawings. Figure 1 is a diagram schematically illustrating the basic principle of an acoustic lens; Figures 2 and 3 are schematic diagrams illustrating applications of an acoustic reflector; Figure 4 is a cross sectional view of an apparatus employing a sound conducting pipe; Figure 5 is a cross sectional view of an apparatus with another reflector surface; Figure 6 is a cross sectional view of a reflector surface taken perpendicular to the main ellipsoidal axis; Figure 7 is a schematic illustration of an acoustic system in accordance with an embodiment of the present invention; Figure 8 is a perspective view illustrating a preferred embodiment of the present invention. Before discussing explicit embodiments of the present invention, some applications of the single reflector systems are indicated. These modifications do not fall under the terms of the appended claims, but indicate further alternative uses of ellipsoidal sound reflecting structures in sound transmitting devices, some of which are known. As discussed above, the arrangements of Figs. 2 and 3 direct sound emanating from a source 13 at a focus A to be received by a user at a focus B. In addition to a sound source, these devices can also be provided with a light reflecting surface. The concentrated light can serve to facilitate reading by the user. In addition, by concentrating light, the user could visually confirm the position of the second focus B into which sound is to be converged, thereby facilitating the use of the device. In the arrangement of Fig. 4, the loudspeaker 22 is disposed outside of the reflector, thereby greatly reducing the interference of the reflected sound waves if the loudspeaker itself were located at the first focus S 1 . This becomes a problem for larger loudspeakers with a higher output. In the arrangement of Fig. 4, it is possible to increase the output of the loudspeaker without disturbing the sound field inside the reflector 25. It is therefore possible to increase the level of the focused sound to a higher level at the second focus S 2 . In the arrangement of Fig. 5, the reflector comprises an inner surface formed by a paraboloid of revolution 35A and a peripheral surface being an ellipsoid of revolution 35B. Sound emitted from the focus S 1 is reflected in parallel from the paraboloid surface 35A at the central portion of the reflector as shown in Fig. 5. The ellipsoidal surface provides a concentration of the reflected sound to the second focus S 2 . In the arrangement of Fig. 5, the area into which sound is directed is expanded about the second focus S 2 . By proper adjustment of the paraboloid surface with respect to the ellipsoid surface, the sound level in the localized area can be made substantially uniform. It is also possible to provide localized sound for a larger number of people. Embodiment of the Present Invention Fig. 7 illustrates an embodiment of the present acoustic system by which two reflectors 51A, 51B are disposed at a predetermined distance from one another. Each of the reflectors 51A, 51B has an ellipsoidal surface of revolution having two foci along the ellipsoidal axis. A loudspeaker 52 is disposed in each reflector separately at the first focus position. Different sound signals are supplied to the two loudspeakers 52. The sound signals emanating from each loudspeaker 52 are reflected by the ellipsoidal surfaces and the sound waves 53 converge with directivity towards the other focus. Fig. 7 also shows sound level distributions which arise under the respective reflectors 51A, 51B. In this manner, independent acoustic zones or spaces are formed for the users 54. The solid line A is the sound pressure distribution (sound level) in dB of reflector 51A, while curve B is the distribution 51B. In the example, the distance between the two reflectors (distance between their adjacent peripheral edges) is 60 cm and the diameter of each reflector is 90 cm. The sound signals issuing from the loudspeakers are reflected and converged having sharp directivity as described above. In the present example, the level of the surrounding background noise is 60 dB. As can be seen in Fig. 7, the sound emanating from the reflector attenuates to the outside to a value falling below the background noise level. In this manner, the sound under the reflector 51A is masked by the background noise and cannot be heard when standing under the other reflector 51B. The reverse is of course also true. In this manner, independent acoustic zones are formed by the reflectors 51A, 51B respectively. Again observing the example shown in Fig. 7, when the background noise is 60 dB, almost the entire area covered by the respective reflectors receive a signal level from the loudspeaker 52 which is above 60 dB. If the sound pressure of the background noise is 60 dB + 10 dB = 70 dB or above, noise transmitted from the outside will be partially heard within the peripheral regions under the respective reflectors. In the example shown in Fig. 7 however, the sound levels of the curves A and B are 70 dB and more and it will be appreciated that these signals are sufficient to provide the isolated acoustic zones . The level of the surrounding noise in such places as quiet exhibitions is about 50 dB, while noisy places have about 75 dB. In either case, it is not possible to hear the outside background noise within the reflector zones as long as the concentrated sound pressure is 10 dB or more above the surrounding noise. The acoustic system of the present invention has numerous advantages in application. In an exhibition hall, the acoustic system can be employed to present information of different content or in different languages. In a train station or other public facility, the present acoustic system can be used for the purpose of public address or announcements at only specific locations within the train station for those having slight or moderate hearing deficiencies. In concert halls or lecture halls, the present system can be optimally provided in special places for those who are hard of hearing. In restaurants equipped for music reproduction, the acoustic system can be used for directing music to be heard only by a specific group of people. In addition, it could be used in a restaurant for making announcements to specific people. A practical application would also be the transmission of speech at international conferences or at training facilities. Fig. 8 illustrates a further embodiment of the invention in which the reflectors 51A, 51B are constructed integrally with a ceiling panel 55. The reflectors are incorporated as a part of the ceiling element. With this construction, the acoustic system can be readily utilized in various building structures such as restaurants and conference halls. As is apparent from the foregoing description, the present invention allows the transmission of a plurality of different sound signals to specific independent zones within a larger space.

Claims: An acoustic system comprising: a plurality of reflectors (51A, 51B) each formed with an ellipsoidal surface having two foci on an axis, each reflector (51A, 51B) having an upper closed portion enveloping the upper one of said two foci and a downward open portion, said plurality of reflectors being disposed at a predetermined distance from each other; and a plurality of sound sources (52) respectively disposed at positions of the upper foci of said reflectors (51A, 51B) and directed upwardly, characterized in that the axes of the respective reflectors extend in substantially vertical direction and lie parallel to one another, whereby independent acoustic zones are formed below the respective reflectors (51A, 51B). The acoustic system of claim 1, wherein a sound pressure level on the axis of at least one of said reflectors (51A, 51B) is set to be higher by a predetermined value than a background noise level outside said one of said reflectors. The acoustic system of claim 2, wherein said predetermined distance is determined by spacing the vertical axes of the reflectors (51A, 51B) such that the sound level on the axis of any one reflector from its sound source attenuates radially to be lower than the background noise level at the position of the axes of any other of said reflectors (51A, 51B). The acoustic system of claim 1, 2 or 3, wherein the reflectors (51A, 51B) of the acoustic system are integrated into a ceiling panel (55) for use in building construction.

Inventors: ONO HIROSHI, ONO, HIROSHI
Applicants: GEN ENGINEERING CO, GEN ENGINEERING CO., LTD.
Application year: 1990
Main classification: G10K11
IPC codes: G10K11