Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Mounting or support feature of housed loudspeaker
Patent
1997-05-07
2000-10-03
Loomis, Paul
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Mounting or support feature of housed loudspeaker
381182, H04R 2500
Patent
active
061283959
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a loudspeaker system comprising various loudspeakers which are arranged in accordance with a predetermined pattern and have associated filters, which filters all receive an audio signal and are equipped to transmit output signals to the respective loudspeakers such that they, during operation, generate a sound pattern of a predetermined form.
A loudspeaker system of this type is disclosed in U.S. Pat. No. 5,233,664. The system described in said patent comprises m loudspeakers and N microphones, which are arranged predetermined distances away from the loudspeakers. Each loudspeaker receives an input signal from a separate series circuit of a digital filter and an amplifier. Each of said series circuits receives the same electrical input signal, which has to be converted into an acoustic signal. The digital filters have filter coefficients which are adjusted by a control unit, which receives, inter alia, output signals from the microphones. The loudspeakers are arranged in a predetermined manner. The objective is to be able to generate a predetermined acoustic pattern. During operation the control unit receives the output signals from the microphones and, on the basis of these, adjusts the filter coefficients of the digital filters until the predetermined acoustic pattern has been obtained. Loudspeakers in a linear array, in a matrix form and in a honeycomb structure are described in the embodiments.
The directional sensitivity of the known loudspeaker system can be controlled up to about 1400 Hz for the embodiments with a linear array and a matrix arrangement. An upper limit of about 1800 Hz is cited for the honeycomb structure. This upper limit is inadequate for many audio applications and it would be desirable to provide a loudspeaker system which can control the directional sensitivity up to frequencies of about 10 kHz.
In J. van der Werff, "Design and Implementation of a Sound Column with Exceptional Properties", 96th Convention of the AES (Audio Engineering Society), Feb. 26-Mar. 1, 1994, Amsterdam, an analogue loudspeaker system is described in which the individual loudspeakers are arranged at non-equidistant spacings along a straight line. The gaps between the individual loudspeakers are calculated on the basis of the criterion of maintaining the side lobes of the acoustic pattern transmitted during operation so as to be at a suitably low level. The density of the number of loudspeakers per unit length is greater in the vicinity of the acoustic centre than at a distance away from this.
The primary objective of the present invention is to provide a loudspeaker system which has a controlled directional sensitivity over as wide a frequency range as possible.
A further objective of the invention is to provide a loudspeaker system wherein the maximum deviation of the directional sensitivity is as far as possible constant over the envisaged frequency range.
To this end, the invention provides a loudspeaker system according to the type described above, characterised in that the loudspeakers have a mutual spacing, which, insofar as physically possible, substantially corresponds to a logarithmic distribution, wherein the minimum spacing is determined by the physical dimensions of the loudspeakers used. By not making the mutual spacing of the loudspeakers equidistant but adapting it to the frequency requirements, it is possible to control the directional sensitivity up to, certainly, 8 kHz. The side lobe level is reduced at the same time. By choosing a logarithmic distribution, the maximum deviation of the directional sensitivity over the envisaged frequency range is kept as constant as possible and spatial aliasing at higher frequencies is counteracted. Primarily it is not so much the form of the sound pattern as the transmission angle which is controlled.
There are various possibilities for the arrangements. For instance, the loudspeakers can be arranged along a straight line, in which case the said distribution extends from a central loudspeaker in one direction along said line.
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Duran B.V.
Harvey Dionne N.
Loomis Paul
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