Apparatus for reproduction of sound
Apparatus for reproducing sound including at least three loudspeakers ( 5, 6, 7 ) mounted in a substantially sealed enclosure. The three loudspeakers may be mounted to a wall of the enclosure so that they are all directed away from, and evenly spaced around, a common point. Two speakers may be driven with the respective out of phase signals comprising the difference between two stereo channels and another speaker with the sum of those channels.
1. Apparatus for reproducing sound comprising at least three loudspeakers mounted in a substantially sealed enclosure, the loudspeakers being directed away from the enclosure in respective substantially evenly spaced directions, the apparatus further comprising a drive arranged to enable the loudspeakers to be driven with a two channel stereo audio signal, wherein the drive is arranged to drive all loudspeakers with a signal comprising in phase low frequency components of the sum of the two channels and to drive two of the loudspeakers with respective out of phase signals comprising the difference of the two channels, wherein the directions in which all the speakers are directed are substantially in the same plane.
2. Apparatus as claimed in claim 1 wherein each speaker is mounted substantially the same distance from a common point in the enclosure.
3. Apparatus as claimed in claim 2 wherein each speaker is directed away from the common point in a direction which is angularly spaced from that of adjacent speakers by an angle of substantially 360°/n where n is the number of speakers.
4. Apparatus as claimed in claim 1 wherein each speaker is directed in a direction extending radially from a common point.
5. Apparatus as claimed in claim 1 wherein the enclosure includes a substantially cylindrical wall or substantially spherical wall and the speakers are mounted to the wall.
6. Apparatus as claimed in claim 5 wherein the enclosure is substantially cylindrical with closed ends.
7. Apparatus as claimed in claim 1 wherein the enclosure comprises a wall substantially in the shape of a regular polygon.
8. Apparatus as claimed in claim 1 wherein the loudspeakers are arranged substantially symmetrically.
9. Apparatus as claimed in claim 1 wherein the drive includes a low pass filter operative to attenuate frequencies higher than a specific frequency in the range 120 Hz to 200 Hz, from the drive signal used to drive each loudspeaker.
10. Apparatus as claimed in claim 1 wherein the two speakers are driven with respective out of phase signals comprising high frequency components of the difference of the two channels.
11. Apparatus as claimed in claim 10 wherein the drive includes a high pass filter operative to attenuate frequencies below a specific frequency in the range 200 Hz to 120 Hz from the out of phase drive signals.
12. Apparatus as claimed in claim 11 wherein the drive is arranged to drive another loudspeaker with a signal comprising the sum of the two channels.
13. Apparatus as claimed in claim 1 wherein the drive includes an amplifier arranged to produce an electrical output signal for driving one or more loudspeakers, wherein the current of the output signal is substantially proportional to the voltage of an input electrical signal to the amplifier.
14. Apparatus as claimed in claim 13 wherein the amplifier is comprised in a negative feedback loop.
15. Apparatus as claimed in claim 1 , wherein one of the loudspeakers is driven by a signal that is unfiltered.
16. Apparatus as claimed in claim 1 , wherein the enclosure is a single undivided enclosure.