Ultra-directional speaker

• US 6,678,381 B1
• Filed: 11/23/1998
• Issued: 01/13/2004
• Est. Priority Date: 11/25/1997
• Status: Expired due to Term

• Current Assignee: NEC Personal Computers, Ltd.
• Original Assignee: NEC Corporation
• Inventors: Manabe, Koji
• Primary Examiner(s): Harvey, Minsun Oh
• Assistant Examiner(s): Grier, Laura A.
• Application Number:
  US09/197,675
• Time in Patent Office: 1,877 Days
• Field of Search: 381/77-79, 381/82, 381/160, 381/182, 381/98-99
• US Class Current: 381/77
• CPC Class Codes: H04R 2217/03 Parametric transducers where sound is generated or captured by the acoustic demodulation of amplitude modulated ultrasonic waves
• CPC Class Codes: H04R 3/12 for distributing signals to two or more loudspeakers specially adapted for hearing aids H04R25/407

Abstract

The ultra-directional speaker of the present invention comprises: an audio generator for generating an audio signal; an ultrasonic generator for generating an ultrasonic signal; a frequency modulator for frequency modulating the ultrasonic signal with the audio signal to produce a frequency modulated ultrasonic signal; and an electro-acoustic transducer for transducing the frequency modulated ultrasonic signal into acoustic waves.

Claims

1. An ultra directional speaker comprising:

an audio generator which generates an audio signal;

ultrasonic generators which generate ultrasonic signals of different frequencies;

frequency modulators which frequency modulate said ultrasonic signals with said audio signal to produce frequency modulated ultrasonic signals; and

a plurality of electro-acoustic transducers, which receives different frequency modulated ultrasonic signals respectively and transduce said frequency modulated ultrasonic signals to emit ultrasonic waves in a predetermined frequency band included in said frequency modulated ultrasonic signals,

wherein said electro-acoustic transducers are driven by said frequency modulators connected to said ultrasonic generators respectively.

2. An ultra-directional speaker according to claim 1, further comprising amplifiers for amplifying said frequency signals, said amplifiers being connected between said frequency modulators and said electro-acoustic transducers.

3. An ultra-directional speaker according to claim 1, wherein said ultrasonic generators generate said ultrasonic signals in a frequency range of 20 kHz to 1000 kHz.

4. An ultra-directional speaker according to claim 1, further comprising a reflection plate that generates a virtual sound source effect by reflecting the ultrasonic waves and audible sound waves included in acoustic waves from said elector-acoustic transducers, and converging said ultrasonic waves and said audible sound waves at a specific point.

5. An ultra-directional speaker according to claim 4, wherein said reflection plate has a curved reflection surface.

6. An ultra-directional speaker according to claim 1, further comprising a filter for selectively absorbing said ultrasonic waves.

7. An ultra-directional speaker according to claim 1, wherein said ultrasonic generators generate said ultrasonic signals in a predetermined frequency band.

8. An ultra-directional speaker according to claim 7, wherein the predetermined frequency band is in the ultrasonic wave band of approximately 40 kHz.

9. An ultra-directional speaker according to claim 7, wherein the predetermined frequency band is in the ultrasonic wave band from 100 kHz to 300 kHz.

10. An ultra-directional speaker according to claim 7, wherein said ultrasonic generators generate aid ultrasonic signals exclusively in said predetermined frequency band.

11. An ultra-directional speaker according to claim 7, wherein said predetermined frequency band is between 20 kHz and 1000 kHz.

12. An ultra-directional speaker according to claim 7, wherein said predetermined frequency band is between 90 kHz and 110 kHz.

13. An ultra-directional speaker according to claim 1, wherein each of said electro-acoustic transducer include:

a selective filter which passes only a portion of each of said frequency modulated ultrasonic signal which lies within a predetermined frequency band; and

an ultrasonic vibrator for converting said filtered frequency modulated ultrasonic signal into acoustic waves.

14. An ultra-directional speaker according to claim 13, wherein said predetermined frequency band corresponds to frequencies at or above 20 kHz.

15. A method for driving a speaker which includes a plurality of electro-acoustic transducers for outputting ultra-directional acoustic waves of different frequencies from an audlo signal using ultrasonic carrier waves, comprising the steps of:

frequency modulating said ultrasonic carrier waves of different frequencies with said audio signal to produce frequency modulated ultrasonic signals;

driving said electro-acoustic transducers with said frequency modulated signals having different frequencies, and

emitting acoustic waves of a specified frequency band included in said frequency modulated signals,

wherein said electro-acoustic transducers are driven by a plurality of different frequencies modulators connected to a plurality of ultrasonic generators, respectively.

16. A method according to claim 15, wherein said ultrasonic carrier waves have a frequency range of 20 kHz to 100 kHz.

17. A method of claim 15, wherein said specified frequency band is in the ultrasonic wave band at approximately 40 kHz.

18. A method of claim 15, wherein said specified frequency band is in the ultrasonic wave band from 100 kHz to 300 kHz.

19. A method of claim 15, wherein said specified frequency band is between 20 kHz and 1000 kHz.

20. A method of claim 15, wherein said specified frequency band is between 90 kHz and 110 kHz.

21. A method for driving a speaker which includes a plurality of electro-acoustic transducers, for outputting ultra-directional acoustic waves from an audio-signal using ultrasonic carrier waves of different frequencies, comprising the steps of:

frequency modulating said ultrasonic carrier waves of different frequencies with said audio signal to produce frequency modulated signals having different frequencies;

driving said plurality of electro-acoustic transducers with said frequency modulated signals; and

emitting acoustic waves in specified frequency bands included in said frequency modulated signal in order to enhance a sound pressure to a listener.