ABSTRACT - Latest Seminar Topics for Engineering … · Web viewWhen inaudible ultrasonic sound...
Transcript of ABSTRACT - Latest Seminar Topics for Engineering … · Web viewWhen inaudible ultrasonic sound...
INTRODUCTION
Imagine you could point the same way you can point light with, say, a flash light.
Suppose speakers existed that could send focused beams of sound where ever thy pointed. You
could speak in to a megaphone and send the sound to a single person. Or you could have five
types of music playing on the same dance floor. You wouldn’t have to worry about turning the
music down at night to keep the neighbors happy, so long as you didn’t point it in their
direction. Thanks to recent advancement in audio engineering, the kinds of products may soon
be a reality. Researchers have discovered a way to project acoustic waves as thin beam of sound:
step into the beam and projected sound fills your ears.
Directional audio is a technology that creates-focused beams of sound, similar to
the light beam coming out of a flashlight. The technology that powers this is known as audio
spotlighting. It uses a combination of non-linear acoustics and some complex mathematics in
order to focus sound into a coherent and highly directional beam. It is under development in
Holosonics Research Labs and the American Technology Corporation.
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DIRECTING THE SOUND
Properties of audible sound:
• The human hearing ranges from a frequency of 20Hz to 20 KHz.
• Wavelength varies between 2cm to 17m.
• Beam angle - 360 degrees.
The audible portion of sound tends to spread out in all directions from the point of
origin. The beam angle of audible sound is very wide, just about 360 degrees. This means the
sound that you hear will be propagated through air equally, in all directions, which is why you
don’t need to be right in front of a radio to hear the music.
In order to focus sound into a narrow beam the requirement is:
1. A low beam angle
-The smaller the wavelength, the lesser the beam angle and hence more focused the
sound. The human hearing ranges from a frequency of 20Hz to 20 KHz. Therefore the audible
sound is mixture of signals with varying wavelength between 2cm to 17m. Except for very low
wavelength, just about the entire audible spectrum tends to spread out at 360 degrees.
2. Large aperture size
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. But this is not a very practical solution.
This is where the ultrasound came to the rescue.
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PROPERTIES OF ULTRASOUND
The frequency ranges above 20 KHz
The wavelength is less than 2crn
Small beam angle hence highly coherent and directional.
SPECIAL FEATURES OF AUDIO SPOTLIGHTA COMPARISON WITH CONVENTIONAL LOUD SPEAKER:-
Creates highly FOCUSED BEAM of sound
Sharper directivity than conventional loud speakers using Self demodulation of finite
amplitude ultrasound with very small wavelength as the carrier
Uses inherent non-linearity of air for demodulation
Components- A thin circular transducer array, a signal processor & an amplifier.
Two ways to use- Direct & projected audio
Wide range of applications
Highly cost effective
THEORY
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IN TO THE DEPTHS OF AUDIO SPOTLIGHTING
TECHNOLOGY
What ordinary audible sound & Conventional Loud Speakers lack?
What we need?
About a half-dozen commonly used speaker types are in general use today. They range
from piezoelectric tweeters that recreate the high end of the audio spectrum, to various kinds of
mid-range speakers and woofers that produce the lower frequencies. Even the most
sophisticated hi-fi speakers have a difficult time in reproducing clean bass, and generally rely on
a large woofer/enclosure combination to assist in the task. Whether they be dynamic,
electrostatic, or some other transducer-based design, 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.
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. Unfortunately, most of the human-audible sound
is a mixture of signals with varying wavelengths—between 2 cms to 17 metres (the human
hearing ranges from a frequency of 20 Hz to 20,000 Hz). Hence, except for very low
wavelengths, just about the entire audible spectrum tends to spread out at 360 degrees. 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 metres across is required, and to
guarantee that all the audible wavelengths are focused, even bigger loudspeakers are needed.
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Here comes the acoustical device “AUDIO SPOTLIGHT” invented by Holosonics Labs
founder Dr. F. Joseph Pompei (while a graduate student at MIT), who is the master brain behind
the development of this technology.
FIG.1:-AUDIO SPOTLIGHT CREATES FOCUSED BEAM OF SOUND UNLIKE
CONVENTIONAL LOUD SPEAKERS
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 — perhaps jazz from a CD. But when he
turns the disc away, the sound fades almost to nothing. It's markedly different from a
conventional speaker, whose orientation makes much less difference.
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HOW IT EVOLVEDThe 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 the 1960s. In 1975, an article cited the nonlinear effects
occurring in air.
Over the next two decades, several large companies including
Panasonic, NC Denon and Rioch attempted to develop a loud speaker based on this principle.
They successful in producing some sort of sound, with extremely high levels of distortion
(>50% THD). This drawback caused the total abandonment of the technology by the end of
1980s.
In the 1990s, Woody Norris, a 65 year old west Coast maverick solved the
parametric problems of this technology with his breakthrough approach.
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HYPERSONIC SOUND EMITTER
ULTRASOUND IN AIR
Researchers discovered that if short pulses of ultrasound were fired into water, the
pulses were spontaneously converted into low frequency sound. Dr. Orhan Berktay established
that water distorts ultrasound signals in a nonlinear, but predictable mathematical way. It was
later found that similar phenomenon happens in air also. When inaudible ultrasonic sound pulses
are fired into the air, the air spontaneously converted the inaudible ultrasound into audible sound
tones, hence proving that as with water, sound propagation in air is just as non-linear, but can be
calculated mathematically. As the beam moves through the air gradual distortion takes place
giving rise to audible component that can be accurately predicted and precisely controlled.
The problem with firing off ultrasound pulses, and having them interfere to
produce audible tones is that the audible component created are nowhere similar to the complex
signals in speech and music which contains multiple varying frequency signals, which interfere
to produce sound and distortion.
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FIG.7:-CONVENTIONAL LOUDSPEAKER & ULTRASONIC EMITTER
BERKTAY’S EQUATION
In 1965, Dr. H.O. Berktay published the first accurate and more complete theory of
distortion of ultrasound signal in air. He uses the concept of modulation envelope. The air
demodulates the modulated signal and the demodulated signal depends on the envelope
function. Berktay assumes the primary wave has the form
P1 (t) = P1 E (t) sin (Wct)
Where we is the carrier frequency and E (t) is the envelope function which in this
case is the speech or music signal
The secondary wave or demodulated wave is given by
P2 (t) d/dt2E (t)
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This is called berktay’s far field solution. The berktay’s solution states that the
demodulated signal is proportional to the second time derivative of the envelope squared. This is
the fundamental expression for the output resulting from the distortion due to air.
HYPERSONIC SOUND TECHNOLOGY
Hypersonic sound technology works by emitting harmless high frequency ultrasonic tones that
we cannot hear. These tones use the property of air to create the new tones that are within the
range of human hearing. The result is an audible sound wave is created directly in the air
molecules by down converting ultrasonic energy into the frequency spectrum we can hear.
In a hypersonic sound system, there are no voice coils, cones cross-over networks 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. The hyper sonic sound system holds the
promise of replacing conventional speakers in homes, movie theaters, automobiles- everywhere.
The ultrasound signal is used as a carrier wave and the audible speech and music
signal are superimposed on it to create a hybrid wave similar to the amplitude modulation. The
resultant hybrid wave is then broadcast. As this wave moves through the air, it creates complex
distortions that give rise to two new frequency sets,
(i) One slightly higher than the hybrid wave. This sideband is identical the original sound
wave
(ii) Slightly lower, than the hybrid wave. This sideband component is a badly distorted
component.
These two sidebands interfere with the hybrid wave and produce the two signal
components - the normal and the distorted components. But the problem that arises is that the
volume of the original sound wave is proportional to that of the ultrasound, while the volume
of the signal’s distorted component is exponential. So, a slight increase in the volume drowns
out the original sound wave as the distorted signal becomes predominant.
An MIT Media labs researcher, Joseph Pompei, managed to crack the problem
by studying current technique and he realized that the focused should have been on the signal’s
distorted component. The technique to create the audio beam is simple,
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SourceSignal
ProcessorUltrasoundamplifier Emitter
Modulate the amplitude to get the hybrid wave
Calculate what the berktay’s equation does to this signal
And do the exact opposite
In other words distort it before the distortion by air takes place. When this wave
is passed through air and what you get is the original sound wave component. But this time
(a) The volume of the original sound wave component is exponentially related to the
volume of the ultrasound beam
(b) The distorted component volume now varies directly as the ultrasound
THE HSS SYSTEM
Source: the audio program source is the source of signal such as a CD player or microphone.
Signal processor: the music or voice from audio source is converted to a highly complex
ultrasonic signal by the signal processor. That is audio source signal modulates ultrasonic signal.
Ultrasonic amplifier: the processed signal is the amplified by the ultrasonic amplifier.
Ultrasonic emitter or transducer: the ultrasonic signal is then emitted into air by
the transducer.
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Since the sound that is contained in ultrasonic energy is highly directional, it forms
a virtual column of sound directly in front of the emitter, much like the light from a flashlight.
All along that column of ultrasonic sound, the air is creating new sounds i.e. the sound that we
already converted to an ultrasonic wave. Since the sound that we hear is created right in the
column of ultrasonic energy, it does not spread in all directions like the sound from a
conventional loudspeaker; instead it stays locked lightly inside the column of ultrasonic energy.
Since you can control and focus the ultrasound beam just like a flashlight, you can
direct it such that you would hear the sound only if you were in the path of the beam. This is
called directed sound
You could also bounce the beam off a reflecting surface, so that people in the path
of the audio reflection can hear the sound. This is known as projected audio. In short, unlike
ordinary speakers, you will hear the sound only if you disrupt the sound beam, whether you
stand in “its path or in the path of a reflection from an acoustic mirroring surface. If you step
away from the path of the sound, you will hear nothing. The sound’s source is not the physical
device you see, but the invisible ultrasound beam that generates it.
Alternative technology:
There is another alternative approach to creating targeted audio, other than the
ultrasound modulation technique. One is the parabolic dish approach that essentially uses
antennae .to focus and direct sound. Here a relatively omni-directional loudspeaker is placed at
the focal point of a parabolic dish pointing towards it. When the loudspeaker generates the
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sound signal, it acts as a point source, emitting waves that reflect off the parabolic dish that is
pointed towards a particular direction. This is very much in use, but the size of the parabolic
dish required to accommodate the longer wavelengths of lower frequencies is too large.
SIGNAL PROCESSING
In order to convert the source program material to ultrasonic signals, a modulation
scheme is required. In addition error correction is needed if distortion is to be reduced without
loss of efficiency. The goal is to produce the audio in the most efficient manner while
maintaining acceptably low distortion levels. The type of modulation adopted also has
importance the requirement is for a method for modulation and distortion reduction mat
Is able to minimize distortion by creating output that matched the ideal modulation
envelope while simultaneously
Does not increase bandwidth requirements i.e. reduction of bandwidth
Allows high modulation index for good efficiency
Allows the lowest possible ultrasound operating frequency for greater output
Preprocessing:
There should be necessary preprocessing for reducing the distortion due to air.
Referring back the Berktay’s equation it can be seen that the demodulation due to the medium
gives an output that is the two-time derivative of the envelope square. Therefore the necessary
preprocessing required are
1. Double integration and
2. Square rooting
The two time derivative operations Berktay’s solution translates to a 12db/octave
high pass slope in the output which can be corrected independent of the modulation scheme,
with an equalization factor.
The Berktay’s solution says that the audio signal will be proportional to the
envelope. Not the spectrum. Therefore there is considerable freedom in choosing the modulation
scheme. The two modulation schemes used are
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1. Double sideband amplitude modulation (DSB) with square root
preprocessing - which results in many sidebands
2. Single sideband amplitude modulation (SSB) - so that the interaction
between the sidebands are eliminated.
DSB SYSTEM
Advantages:
Modulation index can be reduced to decrease distortion, but
Square rooting gives the proper envelope.
Disadvantages:
Reduced efficiency
It requires large bandwidth
The other scheme for modulation is single sideband SSB modulation
SSB SYSTEM
SSB modulation either chooses upper sideband (USB) or lower sideband (LSB)
modulation has a number of advantages
a. USB
Disadvantage:
The frequency response is somewhat erratic
Above resonance or carrier frequency the ultrasonic attenuation and saturation
levels both increase with frequency.
b. LSB
Band limited LSB system should provide the best of both worlds with a potential
for greater output and much more effective distortion reduction.
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Advantages:
Lower side bands are better because there may be efficiency available in emitter design
without sacrificing linearity.
High efficiency resonant devices remain well behaved below resonance.
The low audio frequencies are at higher ultrasonic ranges and therefore have greater
directivity associated with them and vice versa for high audio frequencies further
helping to maintain high directivity at low audio frequencies.
Narrower the bandwidth the greater the system efficiency
Besides being effective from distortion reduction standpoint
Attenuation levels are minimal with decreasing ultrasonic” frequencies.’
Narrow bandwidth provides much greater output by interacting more effectively with
the associated transducer.
Utilizing the above mentioned information, it can be seen that the system that
provides significant advancement is a Single Sideband Processor utilizing a square rooted
envelope reference to calibrate a recursive, zero bandwidth distortion canceller operating as a
lower side band modulator. This is the basis for the proprietary processor currently being
implemented for audio spotlighting.
Square rooting the audio before the modulation gives the proper envelope for a DSB system.
Comparing the envelopes of DSB with square rooting:
The envelope of DSB with square rooting-
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The envelope of SSB-
It can be seen that both the schemes result in a waveform that has the same envelope.
The following is the waveform both put together for comparison.
The blue is the DSB line. The red gives the SSB waveform. It can be seen that though they are
of different values they result in the same envelope.
Hence SSB gives a distortion free signal with no preprocessing or additional signal
conditioning so in case of no preprocessing; SSB is vastly superior to DSB.
SSB also gives a controlled measure of self equalization to the demodulated
audio thus eliminating the effect of the 12db/octave roll off.
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TRANSDUCER TECHNOLOGY
1. To cover a certain frequency range.
2. To have a certain dispersion pattern which In order to make this technology work,
ultrasonic energy must be emitted into the air. Electrical signals are converted into
these acoustic signals by means of an ultrasonic transducer. Acoustic transducers or
emitters can be designed Is sharp.
3. A bandwidth from around 20 KHz to infinity.
4. A sharp dispersion pattern that gives a collimated beam of ultrasound
5. Unlimited output capabilities.
What is practically possible is a usable bandwidth of 20 KHz for use with SSB
modulation giving 20 KHz of audio bandwidth, a resonant peak where the carrier will be placed,
and a falling output level with frequency to provide a measure of self-equalization in the system.
The frequency response of a transducer designed for 500Hz to 20 KHz flat audio response is
much more realistic, because the overall performance will be much better. These will be output
below 500Hz just not at the same level as the rest of the bandwidth.
Collimated beam is a must. In a point source the wave fronts are expanding
spherically around the source, so the intensity falls as the surface area of the sphere grows. With
a plane wave source where the radiating surface area of the diameter is much greater than the
wavelength being emitted, the wave front do not spread appreciably and a collimated beam
results. The only losses in intensity occur due to molecular friction. The attenuation is gradual
over distance. The attenuation grows with increasing frequency so lower operating frequencies
are desirable for minimizing losses.
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SOME OF THE EMITTERS USED ARE
1. Monolithic dim ultrasonic transducers
2. Electrostatic
3. Piezoelectric film
4. Planar magnetic emitters
5. Pressure based PVDF
In the thin film transducers the piezo film generates the greatest ultrasonic output
per unit area while providing easily scalable singular structures of any diameter desired for a
given application. Piezoelectric Film Transducer
The most active piezo film is Polyvinyl dine diflouride or PVDF for short. In order
to be useful for ultrasonic transduction, the film must be polarized or activated. The film needs
to have a conductive electrode material applied to both sides in order to achieve a uniform
electric field through it.
The piezoelectric films operate as transducers through the expansion and
contraction of the x or y axes of the film surface. For use as an emitter, the film will not create
effective motion in the z direction unless it is curved or distended so that the expansion and
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contractions can be converted into z axes movement and create displacement generating
acoustic output.
In one of the simplest implementations of the concept, a sheet of PVDF is taken
and it is laid over a metal late witn an array of holes in it. Pressure or vacuum can be applied to
one side of that plate to create an array of PVDF diaphragms, each with the diameter of the hole
under it. A schematic cross-section of such a device is shown below
The size of the hole is related to the resonant frequency of the carrier signal.
Therefore there is flexibility in calibrating the resonant frequency. Through the use of a new
type of proprietary PVDF film, which is the first purpose built transducer, the current emitter is
stable, repeatable and very practical device to manufacture. It has the following advantages:
Very high efficiency
Attenuated, self equalization slopes at the sideband frequency
Adjustable resonant frequency
Correct bandwidth needed to reproduce the widest band audio.
Repeatable, simplified construction.
Greater than 140db ultrasonic output capability.
Inherently low distortion
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COMPONENTS AND SPECIFICATIONS
Audio Spotlight consists of three major components: a thin, circular transducer array, a
signal processor and an amplifier. The lightweight, nonmagnetic transducer is about .5 inches
(1.27 centimeters) thick, and it typically has an active area 1 foot (30.48 cm) in diameter. It can
project a three-degree wide beam of sound that is audible even at distances over 100 meters (328
feet). The signal processor and amplifier are integrated into a system about the size of a
traditional audio amplifier, and they use about the same amount of power.
SOUND BEAM PROCESSOR/AMPLIFIER Worldwide power input standard
Standard chassis 6.76”/171mm (w) x 2.26”/57mm (h)x 11”/280mm (d), optional rack
mount kit
Audio input: balanced XLR, 1/4” and RCA (with BTW adapter) Custom
configurations available eg. Multichannel
AUDIO SPOTLIGHT TRANSDUCER
17.5”/445mm diameter, 1/2”/12.7mm thick, 4lbs/1.82kg
Wall, overhead or flush mounting
Black cloth cover standard, other colours available
Audio output: 100dB max
~1% THD typical @ 1kHz
Usable range: 20m
Audibility to 200m
Optional integrated laser aimer 13”/ 330.2mm and 24”/ 609.6mm diameter also
available
Fully CE compliant
Fully realtime sound reproduction - no processing lag
Compatible with standard loudspeaker mounting accessories Due to continued
development, specifications are subject to change.
HYPERSONIC SOUND SYSTEM: FACTS AND LIMITS
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The output is proportional to the area of the ultrasonic column.
Ultrasonic design is based directly on emitter diameter,
Directivity directly depended on the length of the ultrasonic column.
Lower modulation index decreases distortion.
Greater modulation index increases gain
Single sideband envelope is equal to square rooted envelope for a single tone.
APPLICATIONS
The audio spotlight is made of a sound processor, an amplifier and the transducer.
Aim the transducer anywhere, and direct and project a three degree wide sound beam that is
audible even at 100 metre.
The following are a brief list of applications made possible by
directed audio
1. Personalized messaging:
Using targeted sound, you could message people in high activity areas, without using
headphones.
2. Discreet announcements:
In museums and exhibitions, using audio spotlighting technique to discreetly inform people,
without raising ambient sound levels, describing each exhibit only to the person standing in
front of it. It can be used in theme parks.
3. Automobiles:Daimler Chrysler MAXXcab prototype truck has four individual audio spotlights in the
truck to let all the passengers enjoy their own choice of music.
4. Audio/video conferencing:
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Project the audio from a conference in four different languages, from a single central device,
without the need for headphones.
5. Targeted advertising:
With targeted announcements at crowd shows, audio spotlighting technology may
possibly be the best way to exhibitors to draw people to their stalls and demonstrate their
products to potential customers. It can be used in supermarket and retail stores. It can be built
into vending machine.
6. Home theatre:
You could be wired up for spotlighting with your home theatre audio system, and
could experience sound as it was originally heard, possessing direction and movement and this
will be tuned to your favorite position for viewing. If you have to watch a show everybody else
detests. Then personalized spotlight can turn of the audio for everyone else.
7.Realistic movies:
With targeted sound, movies could become more realistic, with the sound moving,
along with its source on the screen. Movies could be truer to life and enormously
entertaining.
8. Paging system:
Direct the announcement to the specific area of interest.
9. Ventriloquist systems:
By using tiny sound-focusing devices to beam out voices and having them scatter
against rocks and natural obstacles to the path, they can give the impression of the presence of
people in uninhabited places. This of sort of tricks is known as Psy-ops short form
Psychological operations that are used to fight war of wits against troops.
10. Military applications:
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Ship to ship communication
Shipboard announcement
It’s a substitute to the radio operator’s headphones. To keep track of what is going on
around them, as well as the radio chatter, uses generally keep one ear off the radio
handset. The information can be piped into the operator’s ears, without them having to
wear bulky handsets.
Non lethal acoustic rifles that fire sound pulses. Pump up the normal sound being
transmitted to about 150dB or greater, and you could fire out pulses that could
disorient human targets even causing them severe physical pain. The weapon could be
fine tuned to bring on further discomfort.
Jeep mounted units that can be used or deployed as a mob deterrent.
There are even more interesting application in the pipeline - car based safety audio
systems, discrete speaker phones and many more such interesting application
CONCLUSION
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Directional audio or the hypersonic sound Technology is simply the most revolutionary
sound reproduction system of this century. The opp rtunities for applying this characteristic to
the reproduction of sound-are limitless. We will be able to reproduce sound just the way we
experience it in the real world. Over the next few years, the way we experience sound is going
to change dramatically. It is a true technological paradigm shift. These are just a few of the
virtually limitless number of potential applications. Within the next 3to 5 years sound beam
technology should begin to find its way many deferent areas of our everyday lives. We should
also begin those new many applications in number of deferent areas. So we can conclude- Audio
Spotlighting really “put sound where you want it” and will be “A REAL BOON TO THE
FUTURE.”
REFERENCE
www.ieee.org
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www.google.com
www.answers.com
www.efymag.com
www.digitmag.com
www.illumin.usu.edu
www.thinkdigit.com
www.holosonics.com
www.spie.org
www.howstuffworks.com
www.abcNEWS.com
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