FR2691867A1 - Spatial set=up process for monophonic sound source - involves cutting up initial acoustic band into sub-bands, with each band having separate electro-acoustic reproducer horizontally spaced - Google Patents

Abstract

The process involves separating an acoustic band into sub-bands and sending each sub-band separately to an electro-acoustic reproducer. These reproducers are separated in space to surround the listener. In one particular application, the notes or groups of notes of the musical scale are reproduced by sound sources spaced along the horizontal for each octave and then vertically for each successive octave. The configuration can be curved, cylindrical or hemispherical. The highest octave (2) is made up of 12 semi-tones and each circle represents an electro-acoustic reproducer. To reduce the complexity of the installation, the total number of feeder circuits through a unique modulation line, each circuit for selective sound amplification, has an attributed sub-band. The low current is of the order of 30 mA per amplifier for about thirty circuits so that the general base current is of the order of one amp. USE - Sound reproduction for music, speech or sounds in monophonic and stereophonic systems.

Description

 The present invention relates to a method of spatial distribution of sound sources intended to give the listener the impression of being immersed in a sound environment, whether musical, spoken or noisy.

 The purpose of stereophonic listening is to allow the listener to reconstruct the location of the sound sources at the time of recording. The notion of localization of sources is in this case very important.

 The method according to the invention uses either a monophonic recording or a direct sound recording (microphone or output from an electronic instrument) and disperses them in the space surrounding the listener, which thus loses all notion of localization of the sound message, or according to a particular application, replaces the concept of localization of the transmitting source, by that of localization in space of a frequency or a determined frequency band.

 This dispersion is ensured by a frequency division of the acoustic band (20 HZ - 20 KHZ) into sub-bands each assigned to a point in space where they are broadcast by electro-acoustic reproducers. The number of sub-bands depends on the degree of sophistication desired and on the central frequency of the sub-band, on the principle that the higher this frequency, the more marked will be its directivity, the narrower will be the sub-band, the more numerous will be the sound sources.

 The diffusion of each sub-band is ensured by a selective active enclosure, that is to say by a loudspeaker and an enclosure specially adapted to the central frequency.

This enclosure is powered by a built-in selective amplifier whose bandwidth corresponds to the sub-banding of the overall acoustic band.

 FIG. 1 gives an example of such a division into sub-bands.

 The first sub-band, for example from 20 to 200 HZ (1), will be broadcast by an enclosure of the "boomer" type. Given the absence or very weak directivity of these frequencies its location in the listening room will be of no importance.

Figure 2 gives a non-limiting example of sub-band cutting inspired by the division of the musical scale into octaves. Each horizontal line represents an octave and each circle represents a sound source. For example, octave 8 (2) has been split into 12 sub-bands, i.e. a semitone per sound source (which represents an extreme case) and octave 3 (3) into two sub-bands, by example do to fa (4) and soil to si (5). Octaves -1, 0, 1 and 2 are supported by a "boomer" (not shown). (6) would be octave 4, (7) octave 5, (8)
Octave 6, (9) octave 7.

 Starting from this same figure, we can consider various spatial configurations.

Line BB 'represents the floor of the listening level and line AA' the highest part.

 - The most unfavorable case is that where AA'B'B is a plane, for example a wall. The directivity will be obtained by directing the sound sources towards the listening point considered to be the most favorable.

 - If the AA'B'B plane is curved (left surface), its concave part towards the listening point, the situation will be improved.

 - If the lines AB and A'B 'are combined, a cylinder will be obtained.

 - If moreover the points A and A 'are confused we will have a half-sphere.

 In these last two cases, the arrangement in horizontal lines could be replaced by a disposition in a single spiral by putting the various horizontal lines end to end; for example, in the upward direction, placing the source (10) after the source (11).

 We see that in such a case, the notion of localization of the source is replaced by that of localization of a note, each note having its precise replacement in the space surrounding the listener.

 In the case of a spoken message and for the process which has just been described, the fundamental and its harmonics will have a preferred direction, direction which will vary from one speaker to another. If, on the other hand, the distribution of the sub-bands is "any", any global notion of location will be lost. Such a division into sub-bands would perhaps improve the listening conditions for premises with marked resonances and significant reverberations.

From a practical point of view, it can be noted that:
- The speakers are each specially assigned to a frequency band, their design is facilitated and their performance optimized.

 - To reduce the complexity of the installation, all the speakers are supplied by a single modulation line, each speaker by its built-in selective amplifier taking the sub-band which has been allocated to it. Figure 3 shows schematically this device. It shows: the active speaker (12) comprising a selective amplifier (13) and its loudspeaker (19).

 - The average power to be supplied by each amplifier is very small, which greatly eases the problem of cooling the output semiconductors.

 - The continuous power supply of the amplifiers can also be supplied by a single power supply (single or bipolar). If we use a quiescent current of the order of 30 mA per amplifier, for around thirty speakers, the quiescent current which the general power supply must supply will be of the order of an ampere.

 - The set of three wires (14) can be current electrical installation cable with 3 (unipolar supply) or 4 conductors. Possibly an additional conductor if one wishes to separate the supply and modulation masses (15). Being continuous, the supply wires (16) will not induce hum voltage on the modulation wire (17). The latter, to avoid reception of any unwanted radiation, must be supplied at a relatively high voltage (a few volts or tens of volts) and at low impedance. All the wires of the cable (14) being at low voltage, the safety conditions of the installation are improved.

 It is obvious that in order not to distort the audible message, the acoustic level must be as uniform as possible over the entire acoustic range. This assumes that each selective amplifier is provided with a level adjustment (18) to compensate for the differences in performance of the various speakers and possibly the acoustic characteristics of the listening location.

 For an existing sound installation, the selective amplifiers cannot be housed in the speakers but must be grouped in a cabinet, each output supplying the speaker that has been assigned to it.

Claims (3)

 1) Method for producing a sound space effect from a monophonic source characterized by the division of the frequency band to be reproduced into sub-bands (1) each assigned to a point in the space where they will be broadcast by an electro-acoustic reproducer.  2) Method according to claim 1 characterized (Fig. 2) in that one has the electroacoustic reproducers to reproduce in space and ascendingly, horizontally, the succession of notes from the musical range, isolated (2) or grouped (4) and (5), and vertically, the succession of octaves (3), (6), (7), (8), (9), (2) according to a plane concave with respect to the listener, or better cylindrical or hemispherical.  3) Device for the spatial distribution of a monophonic sound source, for implementing the method according to claim 1 or 2, characterized in that it consists of a cable (14) carrying only low voltages both for the power supply (16) as for the modulation (17) of the active speakers (12) each comprising a power amplifier (13) supplying a loudspeaker (19) and provided with a level adjustment (18).