Interresting.
Do you have references on these measures of phase variations, and perturbation of environment. As a former PhD in mathias Fink's Lab, I'm interested in those results, because of the possibility offered by time reversal to compensate 'in average' for the medium, and maybe not to be disturbed by local variations.
The main advantage of time reversal techniques is their robustness : they are quite insensitive to modification in the propagation medium or at its boundaries.
The reason of this robustness is that time reversal provide basically a compensation for each propagation path, and thus final quslity does not depend on a specific path.
Furthermore, when the medium is reflective, and propagation chaotic, more paths exist between two points, and time reversal becomes more robust to small variations ( such as fish, waves, etc...)
Experiments made ny SCRIPPS in Italy were conducted for periods of several days, showing this robustness over time
Good idea, but I don't think it could be useful for such an application :
To achieve active noise canceling in a volume, you need to create a wave with the same wave vector (i.e. that comes from the same direction) with opposite phase. The proposed system does not provide a flexible way to modify this wave vector. Sound generation happens in the axis of the transducer, so the direction of wave can't be modified.
Traditional loudspeakers (and A LOT of signal processing ) provide better flexibility : an array of loudspeakers allows you to create the wavefront you need.
Re:Low frequency performance, impossible?
on
Focusing Audio
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· Score: 1
This system won't be subject to the law you suggest for traditional loudspeakers. Since it uses nonlinearity in the air, you can't make a direct relation between them, but...
Sound generation frequency range is directly linked to the size of the 'virtual antenna' you create using ultrasounds, and this size is limited by two phenomena : diffraction and attenuation.
So to lower the cutoff frequency, you have two solutions : limit the diffraction of the ultrasonic beam (i.e. increase the size of the transducer) or increase emission level to counteract attenuation (i.e. you reduce sensitivity), so the problems are the same, but for very different reasons!
Slashdot Mirror
Interresting.
Do you have references on these measures of phase variations, and perturbation of environment. As a former PhD in mathias Fink's Lab, I'm interested in those results, because of the possibility offered by time reversal to compensate 'in average' for the medium, and maybe not to be disturbed by local variations.
Sylvain Yon
The main advantage of time reversal techniques is their robustness : they are quite insensitive to modification in the propagation medium or at its boundaries.
The reason of this robustness is that time reversal provide basically a compensation for each propagation path, and thus final quslity does not depend on a specific path.
Furthermore, when the medium is reflective, and propagation chaotic, more paths exist between two points, and time reversal becomes more robust to small variations ( such as fish, waves, etc...)
Experiments made ny SCRIPPS in Italy were conducted for periods of several days, showing this robustness over time
Good idea, but I don't think it could be useful for such an application : To achieve active noise canceling in a volume, you need to create a wave with the same wave vector (i.e. that comes from the same direction) with opposite phase. The proposed system does not provide a flexible way to modify this wave vector. Sound generation happens in the axis of the transducer, so the direction of wave can't be modified. Traditional loudspeakers (and A LOT of signal processing ) provide better flexibility : an array of loudspeakers allows you to create the wavefront you need.
This system won't be subject to the law you suggest for traditional loudspeakers. Since it uses nonlinearity in the air, you can't make a direct relation between them, but... Sound generation frequency range is directly linked to the size of the 'virtual antenna' you create using ultrasounds, and this size is limited by two phenomena : diffraction and attenuation. So to lower the cutoff frequency, you have two solutions : limit the diffraction of the ultrasonic beam (i.e. increase the size of the transducer) or increase emission level to counteract attenuation (i.e. you reduce sensitivity), so the problems are the same, but for very different reasons!