An Alternative design for loudspeakers using the non-linear interaction of sound waves

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An Alternative design for loudspeakers using the
non-linear interaction of sound waves

• 18-796 Seminar
• Ratish J. Punnoose

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Basic Idea

• Ex An ultrasonic signal at 200kHz and another
  one at 201kHz will generate a 1kHz tone and a
  401kHz signal which is inaudible to the human
  ear.

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Basic Idea (Contd)

• If an AM signal with a non-zero carrier amplitude
  is passed through Air, it is self-demodulated

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Difficulties

• Need powerful ultrasonic sources
• modulating these without distortion is difficult
• Need an array of transducers that have to be
  precisely controlled.
• Conventional ultrasonic transducer elements
  introduce too much distortion.

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Features

• Physically small speakers
• No need for crossovers, tweeters, woofers, voice
  coils
• Power efficient
• Directionality
• Resultant audio retains directionality of
  ultrasound source
• Acoustic Spotlight

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Features (Contd)

• By altering the direction of projection, audio
  can be made to originate from different locations

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History

• First attempts created a single tone (1975)
• Audio tone made directive using a transducer
  array by Ricoh, Japan (1983)
• Systems developed for audio frequencies at MITs
  Media Labs and at American Technology Corporation
  (1998).
• At present, sound quality is a little worse than
  conventional speakers.

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References

• Yoneyama, M. The audio spotlight An
  application of nonlinear interaction of sound
  waves to a new type of loudspeaker design.
  Journal of the Acoustical Society of America,
  vol. 73 no.5, p. 1532-6
• http//school.discover.com/awards/arc97/9707-7G.ht
  ml
• http//www8.zdnet.com/pcmag/news/trends/t961113a.h
  tm
• http//sound.media.mit.edu/pompei/
• http//www.audioworld.com/news/9609/26b.html
• http//www.acoustics.org/133rd/2pea.1.html
• http//www.atcsd.com/HTML/whitepaper.html

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Question1 Volume range of the ultrasound speaker?

• The volume range of the ultrasound speaker is
  comparable to traditional speakers but the
  physical size is smaller. The exact amplitude
  depends upon the amount of power fed in. The
  speakers can easily take in 50Watts of power.
  But since their acoustical impedance is better
  matched to the acoustical impedance of air, they
  are more efficient and can produce sound several
  dBs lounder than a traditional speaker with the
  same power capability.

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2. How to use two ultrasounds to create 3D sound
from any point?

• Currently, the only technology developed is to
  use the self-demodulation of a single ultrasound
  signal to create a sound. This wave can be
  projected onto a surface of the room and then a
  listener will perceive the wave as originating
  from that point. The technology as described
  cannot be used to created 3D sound from any point
  in space. It can only be used to make sound
  originate from any surface in a room.