This document discusses audio spotlighting technology which uses ultrasonic energy to create narrow beams of sound similar to light beams. It exploits the non-linearity of air to generate audible sound from inaudible ultrasound, producing a highly directional sound beam. The technology was pioneered in the 1960s for sonar but more recent developments have improved directivity and reduced distortion. It works by modulating audio signals onto ultrasonic carriers, which generate audible sound through nonlinear interactions in air as they propagate. This allows sound to be focused onto a specific area without others nearby hearing it.

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CHAPTER 1
INTRODUCTION
Hi-fi speakers range from piezoelectric tweeters to various kinds of mid-range speakers and
woofers which generally rely on circuits ant large enclosures to produce quality sound,
whether it dynamic, electrostatic or some other transducer – based design. Engineers have
struggled for nearly a century to produce a speaker design with the ideal 20Hz – 20,000Hz
capability of human hearing and also produce a narrow beam of audible sound.
Audio spot lighting is a very recent technology that creates focused beams of sound
similar to light beams coming out of a flash light. Specific listeners can be targeted with sound
without others nearby hearing it, i.e. to focus the sound into a coherent and highly directional
beam. It makes use of non-linearity property of air.
The Audio spotlight developed by American Technology Corporation uses ultrasonic
energy to create extremely narrow beams of sound that behaves like beam of light. Audio
spotlight exploits the property of non-linearity of air. A device known as parametric array
employs the non-linearity of the air to create audible by products from inaudible ultrasound,
resulting in extremely directive and beam like sound. This source can projected about an
area much like a spotlight and creates an actual specialized sound distant from a transducer.
The ultrasound column acts as a airborne speaker, and as the beam moves through the air
gradual distortion takes place in a predictable way. This gives rise to audible components
that can be accurately predicted and precisely controlled.

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CHAPTER 2:
THEORY
The regular loudspeakers produce audible sound by directly moving the air molecules. The
audible portions of sound tend to spread out in all directions from the point of origin.
They do not travel as narrow beams. In fact the beam angle of audible sound is very wide, just
about 360 degrees. This effectively means that the sound you hear will be propagated through
the air equally in all directions. Conventional loudspeakers suffer from amplitude
distortions, harmonic distortion, inter - modulation distortion, phase distortion, crossover
distortion, cone resonance etc. Some aspects of their mechanical aspects are mass, magnetic
structure, enclosure design and cone construction.
In order to focus sound into a narrow beam, you need to maintain a low beam angle that
is dictated by wavelength. The smaller the wavelength, less the beam angle and hence, the
more focused the sound. The beam angle also depends on the aperture size of the speaker. A
large loudspeaker will focus the sound over a smaller area. If the source loudspeaker can
be made several times bigger than the wavelength of the sound transmitted, then a finely
focused beam can be created. The problem here is that this is not a very practical solution, thus
the low beam angle can be achieved only by making the wavelength smaller and this can be
achieved by making use of ultrasonic sound.
FIG 1 : F.JOSEPH POMPEI AT THE MIT LAB. PROPAGATION OF SOUND BEAM
FROM AUDIO SPOTLIGHTING DEVICE

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CHAPTER 3:
TECHNOLOGY OVERVIEW
The technique of using a nonlinear interaction of high – frequency waves to generate low –
frequency waves was originally pioneered by researchers developing underwater sonar
techniques in 1960’s. In 1975, an article cited the nonlinear effects occurring in air. Over the
next two decades, several large companies including Panasonic and Ricoh attempted to develop
a loudspeaker using this principle. They were successful in producing some sort of sound
but with higher level of distortion (>50%). In 1990s, Woody Norris a Radar Technician
solved the parametric problems of this technology.
Audio spotlighting works by emitting harmless high frequency ultrasonic tones that human
hear cannot hear. It uses ultrasonic energy to create extremely narrow beams of sound that
behave like beams of light. Ultrasonic sound is that sound which have very small wavelength
– in the millimeter range. These tones make use of non-linearity property of air to produce
new tones that are within the range of human hearing which results in audible sound. The
sound is created indirectly in air by down converting the ultrasonic energy into the frequency
spectrum we can hear.
In an audio spotlighting sound system there are no voice coils, cones or enclosures. The result
is ‘sound with a potential purity and fidelity which we attained never before’. Sound
quality is no longer tied to speaker size. This sound system holds the promise of replacing
conventional speakers in homes, movie theaters and automobile – everywhere.

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FIG 2: CONVENTIONAL SPEAKERS
FIG 3: AUDIO SPOTLIGHTING

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CHAPTER 4:
RANGE OF HEARING
The human ear is sensitive to frequencies ranging from 20 Hz to 20,000 Hz. If the range of
human hearing is expressed as a percentage of shift from the lowest audible frequency to the
highest it spans a range of 100,000 percent. No single loudspeaker element can operate
efficiently over such a wide range of frequencies.
Using this technology it is possible to design a perfect transducer which can work over a wide
range of frequency which is audible to human hear.
FIG 4: RANGE OF HEARING

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CHAPTER 5:
WORKING
The original low frequency sound wave such as human speech or a music is applied into an
audio spotlight emitter device. This low frequency signal is frequency modulated with ultrasonic
frequencies ranging from 21 kHz to 28 kHz. The output of the modulator will be the modulated
form of original sound wave. Since ultrasonic frequency is used the wavelength of the
combined signal will be in the order of few millimeters. Since the wavelength is smaller
the beam angle will be around 3 degree, as a result the sound beam will be a narrow one with a
small dispersion.
FIG 5: AUDIO SPOTLIGHTING EMITTER

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While the frequency modulated signal travels through the air, the nonlinearity property of air
comes into action which slightly changes the sound wave. If there is a change in a sound wave,
new sounds are formed within the wave. Therefore if we know how the air affects the sound
waves, we can predict exactly what new frequencies (sounds) will be added into the sound
wave by the air itself. The new sound signal generated within the ultrasonic sound wave will
be corresponding to the original information signal with a frequency in the range of 20 Hz
to 20 kHz will be produced within the ultrasonic sound wave. Since we cannot hear the
ultrasonic sound wave we only hear the new sounds that are formed by non – linear action of the
air. Thus in an audio spotlighting there are no actual speakers that produces the sound but the
ultrasonic envelope acts as the airborne speaker.
FIG 6: DIRECTIVITY

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The new sound produced virtually has no distortions associated with it and faithful
reproduction of sound is freed from bulky enclosures. There are no woofers or
crossovers. This technology is similar in that you can direct the ultrasonic emitter towards
a hard surface, a wall for instance and the listener perceives the sound as coming from the spot
on the wall. The listener does not perceive the sound as emanating from the face of the
transducer, but only form the reflection of the wall. For the maximum volume (sound
level) that trade show use demands, it is recommended that the Audio Spotlight speaker,
more accur ately called a tr ansducer, is mounted no more than 3 meters from the average
listeners ears, or 5 meters in the air. The mounting hardware is constructed with a ball joint so
that the Audio Spotlights are easily aimed wherever the sound is desired.
FIG 7: COMPUTER SIMULATION OF SOUND BEAM

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CHAPTER 6:
BEAM DISPERSION
FIG 8: DISPERSION OF SOUND BEAM
Figure shows the dispersion of sound beam from an audio spotlighting emitter. Even
after traveling a distance of 10m the beam covers only an area of 3.2 meter square.

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CHAPTER 7:
BLOCK DIAGRAM
COMPONENTS
1. Power Supply.
2. Frequency oscillator.
3. Modulator.
4. Audio signal processor.
5. Microcontroller.
6. Ultrasonic amplifier.
7. Transducer.
FIG9: BLOCK DIAGRAM OF AN AUDIO SPOLIGHTING SYSTEM

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1. Power Supply: Like all electronic systems, the audio spotlighting system works off DC
voltage. Ultrasonic amplifier requires 48V DC supply for its working and low voltage for
microcontroller unit and other process management.
2. Frequency oscillator: The frequency oscillator generates ultrasonic frequency signals
in the range of (21,000 Hz to 28,000 Hz) which is required for the modulation of
information signals.
3. Modulator: In order to convert the source signal material into ultrasonic signal a
modulation scheme is required which is achieved through a modulator. In addition, error
correction is needed to reduce distortion without loss of efficiency. By using a DSB modulator
the modulation index can be reduced to decrease distortion.
4. Audio signal processor: The audio signal is sent to electronic signal processor circuit
where equalization and distortion control are performed in order to produce a good quality sound
signal.
5. Microcontroller: A dedicated microcontroller circuit takes care of the functional
management of the system. In the future version, it is expected that the whole process
like functional management, signal processing, double side band modulation and even
switch mode power supply would be effectively taken care of by a single embedded IC.
6. Ultrasonic Amplifier: High – efficiency ultrasonic power amplifiers amplifies the
frequency modulated wave in order to match the impedance of the integrated transducers.
So that the output of the emitter will be more powerful and can cover more distance.

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7. Transducer: It is 1.27 cm thick and 17” in diameter. It is capable of producing
audibility up to 200 meters with better clarity of sound. It has the ability of real time sound
reproduction with zero lag. It can be wall, overhead or flush mounted. These transducers ar e
arranged in form of an array called parametric arr ay in order to propagate the ultrasonic
signals from the emitter and thereby to exploit the nonlinearity property of air.
FIG10: PARAMETRIC LOUDSPEAKER

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CHAPTER 8:
MODES OF LISTENING:
There are two modes of listening:
1. Direct Mode.
2. Projected Mode.
FIG11: DIRECTED AUDIO AND PROJECTED AUDIO
Direct Mode: Direct mode requires a clear line of approach from the sound system unit
to the point where the listener can hear the audio. To restrict the audio in a specific area
this method is appropriate.
Projected or Virtual mode: This mode requires an unbroken line of approach from the
emitter of audio spotlighting system, so the emitter is pointed at the spot where the is to
be heard. For this mode of operation the sound beam from an emitter is made to reflect
from a reflecting surface such as a wall surface or a diffuser surface. A virtual sound
source creates an illusion of sound source that emanates from a surface or direction
where no physical loudspeaker is present.

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CHAPTER 9:
ADVANTAGES
1. Can focus sound only at the place you want.
2. Ultrasonic emitter devices are thin and flat and do not require a mounting cabinet.
3. The focused or directed sound travels much faster in a straight line than conventional
loudspeakers.
4. Dispersion can be controlled – very narrow or wider to cover more listening area.
5. Can reduce or eliminate the feedback from microphones.
6. Highly cost effective as the maintenance required is less as compared to conventional
loud speakers and have longer life span.
7. Requires only same power as required for regular speakers.
8. There is no lag in reproducing the sound
DISADVANTAGES
1. Lack of mass production. i.e, each unit must be hand made.
2. The most common form of distortion is clipping

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CHAPTER 10:
APPLICATIONS
1. Automobiles: Beam alert signals can be directly propagated from an announcement
device in the dashboard to the driver. Presently Mercedes – Benz buses are fitted
with audio spotlighting speakers so that individual travelers can enjoy the music of
there on interest.
2. Retail sales: Provide targeted advertising directly at the point of purchase.
3. Safety officials: Portable audio spotlighting devices for communicating with a
specific person in a crowd of people.
4. Public announcement: Highly focused announcement in noisy environments such as
subways, airports, amusement parks, traffic intersections etc.

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5. Emergency rescue: Rescuers can communicate with endangered people far from reach.
6. Entertainment system : In home theatre system rear speakers can be eliminated by the
implementation of audio spotlighting and the properties of sound can be improved.
7. Museums: In museums audio spotlight can be used to describe about a particular object to a
person standing in front it, so that the other person standing in front of another object will not be
able to hear the description.
8. Military applications: Ship – to – ship communications and shipboard announcements.
9. Audio/Video conferencing: Project the audio from a conference in four different languages,
forma single central device without the need for headphones.
10. Sound bullets: Jack the sound level 50 times the human threshold of pain, and an offshoot of
audio spotlighting sound technology becomes a non-lethal weapon.

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CHAPTER 11:
FUTURE OF AUDIO SPOTLIGHTING:
Even the best loudspeakers are subject to distortion and their omni directional sound is
annoying to the people in the vicinity who do no wish to listen. Audio spotlighting system
holds the promise of replacing conventional speakers. It allows the user to control the
direction of propagation of sound. The audio spotlight will force people to rethink their
relationship with sound. Audio spotlighting really “put sound where you want it”.

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CHAPTER 12:
CONCLUSION :
Audio spotlighting is really going to make a revolution in sound transmission and the
user can decide the path in which audio signal should propagate. Due to the unidirectional
propagation it finds application in large number of fields. Audio spotlighting system is going to
shape the future of sound and will serve our ears with magical experience.

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REFERENCE
1. F. JosephPompei. The use of airborne ultrasonics for generating audible sound
beams.
Journal of the Audio Engineering Society, P. J. Westervelt. Parametric acoustic
array.
Journal of the Acoustical Society of America.
2. Thomas D. Kite, John T. Post, and Mark F. Hamilton. Parametric array in air:
Distortion
reduction by preprocessing. Journal of the Acoustical Society of America.
3. Jacqueline Naze Tjotta and Sigve Tjotta. Nonlinear interaction of two
collinear,
spherically spreading sound beams.
4. www.silentsound.co.za – Silent sound
5. www.techalone.com – Audio spotlighting
6. www.howstuffworks.com
7. www.holosonics.com
8. Electronics ForYou – Vol. 40 January 2008