Method and apparatus to direct sound
The invention relates to sonic steerable antennae and their use to achieve a variety of effects. The invention comprises a method and apparatus for taking an input signal, replicating it a number of times and modifying each of the replicas before routing them to respective output transducers such that a desired sound field is created. This sound field may comprise a directed beam, focus beam or a simulated origin. Further, “anti-sound” may be directed so as to create nulls (quiet spots) in an already existing sound field. The input signal replicas may also be modified in way which changes their amplitude or they may be filtered to provide the desired delaying. Reflective or resonant surfaces may be used to achieve a surround sound effect, a microphone may be located in front of an array of loudspeakers, beams of light may be used to identify the present focal position, a limiting device may be used to ensure that clipping or distortion is reduced when more than one input signal is output by the same device and the concept of beam directivity may be used to achieve input nulls or beams in a microphone made up of an array of input transducers. Further, sound field shaping information may be associated with an audio signal to be broadcast.
1. A method of causing plural input signals representing respective channels to appear to emanate from respective different positions in space, said method comprising:
providing a sound reflective or resonant surface at each of said positions in space;
providing, in one enclosure, an array of at least 6 output transducers distal from said positions in space; and
directing, using said array of output transducers, sound waves of each channel towards the respective position in space to cause said sound waves to be re-transmitted by said reflective or resonant surface;
said step of directing comprising:
obtaining, in respect of each transducer, a delayed replica of each input signal delayed by a respective delay selected in accordance with the position in the array of the respective output transducer and said respective position in space such that replicas for transducers closer to the respective position in space are delayed more than replicas for transducers further from the position in space such that the sound waves of the channel are directed towards the position in space in respect of that channel;
summing, in respect of each transducer, the respective delayed replicas of each input signal to produce an output signal; and
routing the output signals to the respective transducers.
2. A method according to claim 1 , wherein said step of obtaining, in respect of each output transducer, a delayed replica of the input signal comprises:
replicating said input signal to obtain a replica signal in respect of each output transducer;
delaying each replica of said input signal by said respective delay selected in accordance with the position in the array of the respective output transducer and said respective position in space.
3. A method according to claim 1 further comprising:
calculating, before said delaying step, the respective delays in respect of each input signal replica by:
determining the distance between each output transducer and the position in space in respect of that input signal;
deriving respective delay values such that the sound waves from each transducer for a single channel arrive at said position in space simultaneously.
4. A method according to claim 1 further comprising:
inverting one of said plural input signals;
obtaining, in respect of each output transducer, a delayed replica of said inverted input signal delayed by a respective delay selected in accordance with the position in the array of the respective transducer, so that sound waves derived from said inverted input signal are directed at a position in space so as to cancel out at least partially sound waves derived from that input signal at that position in space.
5. A method according to claim 4 , wherein said step of obtaining, in respect of each output transducer, a delayed replica of said inverted input signal comprises:
replicating said inverted input signal to obtain a replica signal in respect of each output transducer;
delaying each replica of said inverted input signal by a respective predetermined delay selected in accordance with the position in the array of the respective output transducer.
6. A method according to claim 4 , wherein said inverted input signal is scaled so that the sound waves derived from said inverted input signal cancel sound waves derived from that input signal at said position in space.
7. A method according to claim 6 , wherein said scaling is selected by determining, in respect of the input signal which has been inverted, the magnitude of sound waves at said position in space and selecting said scaling so that sound waves derived from said inverted input signal have the same magnitude at that position.
8. A method according to claim 1 , wherein at least one of said surfaces is provided by a wall of a room or other permanent structure.
9. An apparatus for causing plural input signals representing respective channels to appear to emanate from respective different positions in space, said apparatus comprising:
a sound reflective or resonant surface at each of said positions in space;
an array of at least 6 output transducers in a single enclosure distal from said positions in space; and
a controller for directing, using said array of output transducers, sound waves of each channel towards that channel's respective position in space such that said sound waves are re-transmitted by said reflective or resonant surface;
said controller comprising:
replication and delay means arranged to obtain, in respect of each transducer, a delayed replica of the input signal delayed by a respective delay selected in accordance with the position in the array of the respective output transducer and said respective position in space such that replicas for transducers closer to the respective position in space are delayed more than replicas for transducers further from the position in space such that the sound waves of the channel are directed towards the position in space in respect of that input signal;
adder means arranged to sum, in respect of each transducer, the respective delayed replicas of each input signal to produce an output signal; and
means to route the output signals to the respective transducers such that the channel sound waves are directed towards the position in space in respect of that input signal.
10. An apparatus according to claim 9 , wherein said controller further comprises:
calculation means for calculating the respective delays in respect of each input signal replica by:
determining the distance between each output transducer and the position in space in respect of that input signal;
deriving respective delay values such that the sound waves from each transducer for a single channel arrive at said position in space simultaneously.
11. An apparatus according claim 10 , wherein at least one of said surfaces is a wall of a room or other permanent structure.
12. An apparatus according to claim 9 , wherein said controller further comprises:
an inverter for inverting one of said plural input signals;
second replication and delay means arranged to obtain, in respect of each output transducer, a delayed replica of said inverted input signal delayed by a respective delay selected in accordance with the position in the array of the respective transducer and a second position in space so that sound waves derived from said inverted input signal are directed at said second position in space so as to cancel out at least partially sound waves derived from that input signal at said second position in space.
13. An apparatus according to claim 12 , wherein said controller further comprises a scaler for scaling said inverted input signal so that the sound waves derived from said inverted input signal cancel sound waves derived from that input signal at said second position in space.
14. An apparatus according to claim 9 , wherein said surfaces are reflective and have a roughness on the scale of a wavelength of sound frequency it is desired to diffusely reflect.
15. An apparatus according to claim 9 , wherein said surfaces are optically-transparent.
16. An apparatus for causing plural input signals representing respective channels to appear to emanate from respective different positions in space, for use with reflective or resonant surfaces at each of said positions in space, said apparatus comprising:
an array of at least 6 output transducers in a single enclosure distal from said positions in space; and
a controller for directing, using said array of output transducers, sound waves of each channel towards that channel's respective position in space such that said sound waves are retransmitted by said reflective or resonant surface;
said controller comprising:
replication and delay means arranged to obtain, in respect of each transducer, a delayed replica of the input signal delayed by a respective delay selected in accordance with the position in the array of the respective output transducer and said respective position in space such that replicas for transducers closer to the respective position in space are delayed more than replicas for transducers further from the position in space such that the sound waves of the channel are directed towards the position in space in respect of that input signal;
adder means arranged to sum, in respect of each transducer, the respective delayed replicas of each input signal to produce an output signal; and
means to route the output signals to the respective transducers such that the channel sound waves are directed towards the position in space in respect of that input signal.
17. An apparatus according to claim 16 , wherein said controller further comprises:
calculation means for calculating the respective delays in respect of each input signal replica by:
determining the distance between each output transducer and the position in space in respect of that input signal;
deriving respective delay values such that the sound waves from each transducer for a single channel arrive at said position in space simultaneously.
18. An apparatus according to claim 16 , wherein said controller further comprises:
an inverter for inverting one of said plural input signals;
second replication and delay means arranged to obtain, in respect of each output transducer, a delayed replica of said inverted input signal delayed by a respective delay selected in accordance with the position in the array of the respective transducer and a second position in space so that sound waves derived from said inverted input signal are directed at said second position in space so as to cancel out at least partially sound waves derived from that input signal at said second position in space.
19. An apparatus according to claim 18 , wherein said controller further comprises:
an inverter for inverting one of said plural input signals;
second replication and delay means arranged to obtain, in respect of each output transducer, a delayed replica of said inverted input signal delayed by a respective delay selected in accordance with the position in the array of the respective transducer and a second position in space so that sound waves derived from said inverted input signal are directed at said second position in space so as to cancel out at least partially sound waves derived from that input signal at said second position in space.