Acoustic apparatus

1. An acoustic apparatus comprising:

an amplitude modulation unit configured to generate a first signal by modulating an amplitude of a carrier wave signal having a frequency of an ultrasonic band, based on an acoustic signal;

a phase control unit configured to generate a second signal and a third signal by controlling a phase of the first signal, respective phases of the second signal and the third signal being approximately opposite;

an amplification unit configured to amplify the second signal and the third signal;

a first parametric loudspeaker configured to radiate a first sound wave toward a first control point located on a directional axis of the first parametric loudspeaker, based on the amplified second signal, the directional axis being a normal line passing through a center of a radiation surface of the first parametric loudspeaker;

a first reflection unit having a first concave to receive a sound wave and reflect the sound wave toward the first control point, a focal point of the sound wave reflected by the first concave being the first control point; and

a second parametric loudspeaker configured to radiate a second sound wave toward the first concave, based on the amplified third signal,

wherein the amplification unit amplifies the second signal and the third signal so that a sound pressure of the first sound wave is approximately equal to a sound pressure of the second sound wave at the first control point.

2. The acoustic apparatus according to claim 1 , wherein

the first concave is an ellipsoid of revolution having a first focus and a second focus,

the second focus is positioned at the first control point, and

the second parametric loudspeaker is located at a position of the first focus.

3. The acoustic apparatus according to claim 1 , wherein

the first concave is a paraboloid of revolution having a first focus, and

the first reflection unit is located so that a sound pressure-distribution of the second sound wave reflected by the first concave is maximum at the first control point.

4. The acoustic apparatus according to claim 3 , wherein

the second parametric loudspeaker has an axis along a direction to radiate the second sound wave, and

the axis is matched with a symmetric axis of the paraboloid of revolution,

further comprising:

a movable unit configured to move the second parametric loudspeaker along the axis.

5. The acoustic apparatus according to claim 1 , wherein

the phase control unit generates a fourth signal by controlling the phase of the first signal,

a phase of the fourth signal is approximately opposite to a phase of the second signal, and

the first parametric loudspeaker radiates the first sound wave toward a second control point,

further comprising:

a second reflection unit having a second concave to receive a sound wave and reflect the sound wave toward the second control point, a focal point of the sound wave reflected by the second concave being the second control point; and

a third parametric loudspeaker configured to radiate a third sound wave toward the second concave, based on the fourth signal.

6. The acoustic apparatus according to claim 5 , wherein

the amplification unit amplifies the fourth signal.

7. The acoustic apparatus according to claim 1 , wherein

the frequency of the ultrasonic band is larger than or equal to 20 kHz.

8. The acoustic apparatus according to claim 1 , wherein

the phase of the first signal is equal to any of a phase of the second signal or a phase of the third signal.