A multi-channel one-piece active acoustic enclosure, for a use in a first operating mode where this enclosure is intended to be used in isolation in front of a listener with a first direction directed towards this listener, this enclosure comprising: - a central channel, with a central loudspeaker whose main axis of the characteristic directivity pattern is oriented according to said first direction; - lateral channels, respectively left and right, each with a lateral loudspeaker (18L, 18R), whose main axis of the characteristic directivity diagram is oriented according to a second direction (D2L, D2R) perpendicular to the first direction, in opposite directions for the left loudspeaker and for the right loudspeaker; - separator means, adapted to receive as an input a composite stereo signal to be reproduced including a left signal and a right signal and to deliver as an output combinations of these left and right signals; and - combiner means (24, 26, 28), adapted to distribute between the central channel and the lateral channels, according to a predetermined distribution, combinations of the signals delivered by the separator means, characterized in that: - the separator means are means adapted to extract from the composite stereo signal, based on an analysis in the frequency domain with comparison of the levels of respective spectral energy of the left and right signals (L, R) of the composite stereo signal: a mono component, common to the left and right signals, and pure left lateral component (L'), and a pure right lateral component (R'); - the combiner means (24, 26, 28) comprise filtering means adapted to modify the directivity diagram (B, B') rendered in each lateral channel so as to create therein a cancelling direction (Δ), these filtering means being double pressure gradient filtering means receiving as an input both of the pure left (L') and right (R') lateral components and delivering as an output both a left filtered signal (L") and a right filtered signal (R"), each of the left and right filtered signals (L", R") being derived from the two pure left (L') and right (R') lateral components received as an input; and - the combiner means (24, 26, 28) are adapted to distribute: • to the central channel, a signal derived from the mono component; • to the left lateral channel, the left filtered signal (L"); and • to the right lateral channel, the right filtered signal (R"). - a central channel, with a central loudspeaker whose main axis of the characteristic directivity pattern is oriented according to said first direction; - lateral channels, respectively left and right, each with a lateral loudspeaker (18L, 18R), whose main axis of the characteristic directivity diagram is oriented according to a second direction (D2L, D2R) perpendicular to the first direction, in opposite directions for the left loudspeaker and for the right loudspeaker; - separator means, adapted to receive as an input a composite stereo signal to be reproduced including a left signal and a right signal and to deliver as an output combinations of these left and right signals; and - combiner means (24, 26, 28), adapted to distribute between the central channel and the lateral channels, according to a predetermined distribution, combinations of the signals delivered by the separator means, - the separator means are means adapted to extract from the composite stereo signal, based on an analysis in the frequency domain with comparison of the levels of respective spectral energy of the left and right signals (L, R) of the composite stereo signal: a mono component, common to the left and right signals, and pure left lateral component (L'), and a pure right lateral component (R'); - the combiner means (24, 26, 28) comprise filtering means adapted to modify the directivity diagram (B, B') rendered in each lateral channel so as to create therein a cancelling direction (Δ), these filtering means being double pressure gradient filtering means receiving as an input both of the pure left (L') and right (R') lateral components and delivering as an output both a left filtered signal (L") and a right filtered signal (R"), each of the left and right filtered signals (L", R") being derived from the two pure left (L') and right (R') lateral components received as an input; and - the combiner means (24, 26, 28) are adapted to distribute: • to the central channel, a signal derived from the mono component; • to the left lateral channel, the left filtered signal (L"); and • to the right lateral channel, the right filtered signal (R"). • to the central channel, a signal derived from the mono component; • to the left lateral channel, the left filtered signal (L"); and • to the right lateral channel, the right filtered signal (R").