Acoustics – Sound-modifying means – Intensifying horn
Patent
1988-06-23
1989-11-07
Fuller, B. R.
Acoustics
Sound-modifying means
Intensifying horn
181144, 181190, 181191, 181192, 381156, 381160, G10K 1110
Patent
active
048785610
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an omnidirectional sound emitter with separate sources of sound, each comprising a funnel-shaped horn. More particularly, the invention relates to a sound emitter which is adapted to emit acoustic energy through 360.degree. in a predetermined plane, for example the horizontal plane, without producing any appreciable acoustic effect in directions perpendicular to said first plane, for example straight up and straight down, said horns having their respective sound-emitting end openings directed toward the central portion of the sound emitter and mounted in spaced-apart relationship.
Sound emitters of the above-mentioned type may be used for generating for example acoustic alarm signals, such as an air-raid alarm and the like, where it is desired to produce a sound field which is symmetrical through 360.degree. about the emitter in the horizontal plane within the desired frequency range, and at the same time to restrict as much as possible the emitted acoustic loss upwards and downwards.
To make the emitter satisfy these desiderata, i.e. to emit acoustic energy within a lobe restricted in the vertical plane, certain demands are made on the emitter, and so far these demands could not be adequately met.
Theoretically, an infinitesimal point source of sound gives a spherically symmetrical sound representation, and a linear sound source of infinitesimal or negligible thickness gives a sound representation which is symmetrical with respect to the longitudinal axis of the sound source. Increasing dimensions of the sound source give a more or less directed radiation, a directional effect which is mainly dependent on the wavelength of the sound in relation to the sound-emitting opening of the sound source. More particularly, the sound-emitting opening must be small in relation to the wavelength concerned, if the undesired directional effect is to be avoided.
This entails special problems in connection with sound sources equipped with horns. In order to achieve adequate acoustic adaptation of the sound emitting part of the sound source to the surrounding medium, a horn is required which has a comparatively large opening area in relation to the wavelength and a length suitable for the frequencies concerned. For the frequencies used in the generation of alarm signals, such horns in particular will obtain relatively large outer dimensions, something that is, according to the theory, a cause of considerable difficulties with respect to the directional effect of the sound at certain frequencies.
It is already known within the art to arrange the sources of light in a sound emitter of the type mentioned by way of introduction in such a manner that the open ends of the horns are directed away from one another to emit sound in a direction away from the centre of the sound emitter. Such arrangements are disclosed in, for example, Swedish patent specification 79013 and the Swedish registered designs 34,314 and 34,315. These arrangements which, as a consequence of their relatively large dimensions at the sound-emitting openings of the horns, suffer from the above-mentioned directional problem, also exhibit the phenomenon that the sound from one side of the emitter may obliterate the sound from the other side of the emitter by interference.
Omnidirectional sound emitters are, furthermore, previously known from the Swedish registered designs 32,215, 32,216 and 32,217. These emitters comprise saucer-shaped horns coaxially mounted with their concave surfaces facing one another and with their peripheral edges in spaced-apart relationship, such that an annular sound gap is formed between the horns. Theoretically, the sound representation from such a sound emitter may be resembled to the sound representation from a filamentary circular sound source of non-negligible diameter. Because of this non-negligible diameter, the sound representation of the emitter will obtain theoretically, and also in actual practice, zero or nodal points in a plane coinciding with the circle at certain frequencies which lie in
REFERENCES:
patent: 2297972 (1942-10-01), Wills
patent: 2550359 (1951-04-01), Levy
patent: 2832843 (1958-04-01), Wiessner
patent: 2969848 (1961-01-01), Farwell
patent: 3477540 (1969-11-01), Rizo-Patton
patent: 3842203 (1974-10-01), Weisberg
Lindblom Boris
Lunden Peter
Nilsson Jerry
Tengstrand Goran
Fuller B. R.
Satt Communications AB
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