audio spotlighting full report

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Audio Spotlighting
Liji Ramesan Santhi & Sreeja V
Electrical and Electronics Department
Mohandas College of Engineering and Technology

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Abstract
In the present world, distortion sound which was annoying to the people in the vicinity, an audio
spotlighting system was designed as a solution to one of life’s many challenges. Audio spot
lighting is a very recent technology that creates focused beams of sound similar to light beams
coming out of a flashlight. By ‘shining’ sound to one location, specific listeners can be targeted
with sound without others nearby hearing it. This acoustic device comprises a speaker that fires
inaudible ultrasound pulses with very small wavelength which act in a manner very similar to
that of a narrow column. The ultra sound beam acts as an airborne speaker and as the beam
moves through the air gradual distortion takes place in a predictable way due to the property of
non-linearity of air. This gives rise to audible components that can be accurately predicted and
precisely controlled. The targeted or directed audio technology is going to a huge commercial
market in entertainment and consumer electronics and technology developers are scrambling to
tap in to the market. Being the most recent and dramatic change in the way we perceive sound
since the invention of coil loud speaker, audio spot light technology can do many miracles in
various fields. In areas where headsets have previously been needed, why not use multiple audio
spotlights, so that customers can hear naturally

Introduction
Engineers have nearly struggled for half a
century to produce a speaker design with 20Hz –
20000Hz capability of human hearing and also
produce a narrow beam of audible sound...
The directivity of any wave producing source
depends on the size of the source, compared to
the wavelength it generates. Inherent properties
of the air cause the ultrasound to distort in a
predictable way. The distortion gives rise to
frequency components in the audio bandwidth,
which can be predicted and precisely controlled.
By generating the correct ultrasonic signal, we
can create, within the air itself, essentially any
sound desired. The ultrasound column acts as an
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

Loud Speakers Vs Audio Spotlighting
All loudspeakers today have one thing in
common: they are direct radiating-- that is, they
are fundamentally a piston-like device designed
to directly pump air molecules into motion to
create the audible sound waves we hear. The
audible portions of sound tend to spread out in
all directions from the point of origin. They do
not travel as narrow beams—which is why you
don’t need to be right in front of a radio to hear
music. In fact, the beam angle of audible sound
is very wide, just about 360 degrees. This
effectively means the sound that you hear will be
propagated through air equally in all directions.

Conventional loudspeakers suffer from
amplitude distortions, harmonic distortion, phase
distortion, cross over distortion etc.
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, the less the beam angle, and hence,
the more focused the sound. To create a narrow
sound beam, the aperture size of the source also
matters—a large loudspeaker will focus 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.
To ensure that the shortest audible wavelengths
are focused into a beam, a loudspeaker about 10
meters across is required, and to guarantee that
all the audible wavelengths are focused, even
bigger loudspeakers are needed, thus the low
angle beam can be achieved only by making the
wavelength smaller and this can be achieved by
making use of ultrasonic sound. Audio spotlight
looks like a disc-shaped loudspeaker, trailing a
wire, with a small laser guide-beam mounted in
the middle. When one points the flat side of the
disc in your direction, you hear whatever sound
he's chosen to play for you. But when he turns
the disc away, the sound fades almost to nothing.

Working
It's markedly different from a conventional
speaker, whose orientation makes much less
difference. PRO SOUND SYSTEM > Audio Spotlight >
AUDIO SPOTLIGHT TECHNOLOGY
The original low frequency sound wave such as
human speech or music is applied into an audio
spotlight emitter device. This low frequency
signal is frequency modulated with ultrasonic
frequencies ranging from 21 KHz – 28 KHz. The

Point-'N'-Shoot Sound Makes Waves
Researchers have developed technology that can
project a beam of sound so narrow that only one
person can hear it. "Directed" audio sounds like
it's coming from right in front of you even when
transmitted from a few hundred meters away.
Inventors of the new "ventriloquist" technology
say it could provide an added dimension to
entertainment. The military, however, is
investigating using it to confuse opponents or
even inflict pain.
The Audio Spotlight is one of two competing
audio transmission systems that emit a one-foot
square column of sound that can only be heard
by people in its direct path. Joseph Pompeii, a
PhD student at the MIT Media Lab, decided to
develop it while working at audio company
Bose, which he joined at 16 as its youngest-ever
engineer.
output of modulator will be 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 narrow one with a small dispersion.
While the frequency modulated signal travels
through air, the non linear property of air, comes
into action which slightly changes the sound
wave. If there is a Change in the sound waves
new sound waves are formed within the wave.
Therefore new sound signal generated within the
ultrasonic sound wave will be corresponding to
the original information signal 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 air. Thus in an audio spotlighting
there are no actual speakers that produces the
sound but the ultrasonic envelope acts as
airborne speaker.

Components
Power Supply:
The audio spotlighting system works off dc
voltage. Ultrasonic amplifier requires 48V dc
supply for its working and low voltage for
microcontroller and other process management.
Frequency Oscillator:
It generates ultrasonic frequency signals in the
range of 21 KHz to 28 KHz which is required for
modulator of information signals.
Modulator
In order to convert the source signal material into
ultrasonic signal a modulation scheme is
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 such a way that you can direct
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 from the
reflection of wall. For the maximum volume that
trade show use demands it is recommended that
the audio spotlight speaker more accurately
called transducer is mounted no more than three
meter from the average listener ears or five
meters in the air. The mounting hardware is
constructed with a ball joint so that the audio
spotlights can easily aimed wherever the sound
is desired.
required which is achieved through a modulator.
In addition error correction is needed to reduce
distortion without loss of efficiency
Audio signal processor:
Signal is sent to electronic signal processor
circuit where equalization and distortion control
are performed in order to produce a good
equalization signal.
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 mode of power supply would be effectively
taken care of by a single embedded IC.
Ultrasonic amplifier:
High efficiency ultrasonic power amplifier
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 distortion.
Transducer:
It is 1.27cm thick and 17” in diameter. It is
capable of producing audibility up to 200mwith
better clarity of the sound. It has the ability of
real time sound reproducibility with zero lag.
These transducers are arranged in the form of an
array called parametric array in order to
propagate the ultrasonic signals from the emitter
and thereby to exploit the non linearity property
of air.

Conclusion
Although the project didn’t succeed, there are
several issues to be gained. It is really going to
make a revolution in sound transmission and the
user can decide the path in which audio signal
should propagate. It is going to shape the future
of sound and will serve our ears with magical
experience.
Reference
1. F Joseph Pompei:The use of airborne
ultrasonic for generating audible sound
beams- Journal of the Audio Engineering
Society
2. P J Westervelt, Parametric
Acoustic array-Journal of the
Acoustical society of America.
3. The past, present and Future of Audio Signal
Processing, IEEE signal Processing
Magazine(pages 30-57,sept 1999)
4. silentsound.co.za-silent sound.
5. techalone.com-Audio Spotlighting
6. holosonics.com
7. Electronics for you- volume 40 (January
2008)
8. fileguruapps/audio_spotlighting_
ieee paper(2009)