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Audio Spotlighting Seminar Report 2013 INTRODUCTION Hi-fi speakers range from piezoelectric tweeters to various kinds of mid-range speakers and woofers which generally rely on circuits and 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. When you listen to sound over loudspeakers, you don't have any control over where the sound goes. Sometimes you don't want it to go everywhere. Scientists have devised a way to solve that problem. They have figured out how to "steer" sounds by aiming them only where he wants them to go with a device they call Audio Spotlight. Audio spot lighting is a technology that creates focused beams of sound similar to light beams coming out of a flash light. By ‘shining’ sound to one location, 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. Imagine projecting sound in a narrow beam, much like the light from a spotlight! In the past we were limited by sound invading all of the space surrounding the loudspeaker or sound source. Not anymore! With the Audio spotlighting Sound systems, BSc.Electronics Page 1 College of Applied Science,Mallappally

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Audio Spotlighting Seminar Report 2013

INTRODUCTION

Hi-fi speakers range from piezoelectric tweeters to various kinds of mid-range speakers

and woofers which generally rely on circuits and 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. When you listen to sound over loudspeakers, you don't

have any control over where the sound goes. Sometimes you don't want it to go everywhere.

Scientists have devised a way to solve that problem. They have figured out how to "steer" sounds

by aiming them only where he wants them to go with a device they call Audio Spotlight.

Audio spot lighting is a technology that creates focused beams of sound similar to

light beams coming out of a flash light. By ‘shining’ sound to one location, 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.

Imagine projecting sound in a narrow beam, much like the light from a spotlight! In the

past we were limited by sound invading all of the space surrounding the loudspeaker or sound

source. Not anymore! With the Audio spotlighting Sound systems, you can put sound wherever

you want. With a spotlight, when you step into the beam of light, you are clearly illuminated by

the light. When you step out of the beam, you are lit only by the background light. Similarly you

can’t see the beam of sound, but when you step into it, you can hear the sound or narration

inside! Step back out of the beam and the sound is gone! Stepping into the directional sound

beam is like putting on a set of virtual headphones. You can now have several different

soundtracks or musical styles co-exist in one small space, heard only by those who should.

The Audio spotlight developed by American Technology Corporation uses ultrasonic

energy to create extremely narrow beams of sound that behaves like beam of

light.Audiospotlight exploits the property of non-linearity of air. When in audible ultrasonic

pulses are fired into the air, it spontaneously converts the inaudible ultrasound into an audible

sound. 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

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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.

Sound from ultrasound is the name given here to situations when modulated ultrasound

can make its carried signal audible, without needing a receiver set. This happens when the

modulated ultrasound passes through anything which behaves nonlinearly and thus acts

intentionally or unintentionally as a demodulator.

For now, customers are testing out the technology for a variety of uses. But adoption may

be slow due to the cost of the system and the fact that each unit needs to be handmade.Also,

problems with creating low bass tones will keep Audio spotlighting systems out of audiophiles

for the present. On the other hand, this is not preventing Sony from incorporating the technology

in plasma screens for specialty applications. Widespread application of Audio spotlighting could

still be years away, but with companies like Sony interested, it can only speed mainstream

adoption of the technology.

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HISTORY

History is replete with rival inventors battling one another to bring breakthrough

creations to market. Howe and Singer over the sewing machine, Bell and Gray over the

telephone, Edison and Swan over the light bulb.

Now, in that same tradition, two inventors Elwood Woody Norris of Poway, CA-based

American Technology Corporation (ATC), and F. Joseph Pompei, of Watertown, MA’s

Holosonic Research Labs, have harnessed the same scientific principle to create competing

directional-sound systems.

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 dating back to the 1960s. They called this device a parametric array. In 1975, an

article cited the nonlinear effects occurring in air.

Over the next two decades, several large companies, including Matsushita, NC Denon,

and Ricoh attempted to develop a loudspeaker based on this principle. They were successful in

producing some sort of sound, with extremely high levels of distortion (>50%). This drawback

caused the total abandonment of the technology by the end of the 1980's.

Later during the spring of 1996, Elwood Woody Norris one of the founders of American

Technology Corporation was working blind to his competitor in the East within his garage in

Poway CA. He felt that ultrasound could be used to create a sound beam. In July the same year,

he felt that he had a breakthrough and he rushed off to the patent office, and patented the same.

In 1998, Joseph Pompei presented the paper “The Use of Airborne Ultrasonic for

generating Audible Sound Beams” to the Audio Engineering Society, at their 105 th Convention

in san Francisco CA. In 1999 he founded holosonic Research Labs or Holosonics to

commercialize this technology. He named it “Audio spotlighting”.

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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 is a paradigm shift in sound production based on solid principles of

physics. Audio spotlighting technology projects a column of modulated ultrasonic frequencies

into the air. These ultrasonic frequencies are inaudible by themselves. However, the interaction

of the air and modulated ultrasonic frequencies creates audible sounds that can be heard along a

column. This audible acoustical sound wave is caused when the air down-converts the ultrasonic

frequencies to the lower frequency spectrum that humans can hear.

Audio spotlighting technology works by emitting harmless high frequency ultrasonic

tones that we cannot here. These tones use the non-linearity (fig 3.1) property of air to create

new tones that are within the range of human hearing. The result is an audible sound. The

acoustical sound wave is created directly in the air.

In a Audio spotlighting system, there are no voice coils, cones, crossover 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 Audio spotlighting system holds

the promise of replacing conventional speakers in homes, movie theatres, and automobiles

everywhere.

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Fig3.1: Non linear medium

Fig 3.2: Pressure v/s distance curve

At normal atmospheric pressure and a temperature of 20°C, a small audio signal travels

through air at approximately 300m/sec. As the amplitude of the sound signal increases to more

than approximately 100 dB, the speed of sound changes over the course of a single cycle. The

upper part of the waveform sufficiently compresses air molecules to increase the local

temperature and pressure and, therefore, slightly boost the speed of sound. Likewise, the

negative portion of the waveform slows sound propagation. These speed variations result in a

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distorted waveform that resembles a triangular wave (fig3.2). Because triangular waves are rich

in harmonics, the speed variations demodulate the ultrasound signal. The blue line in fig-3.2 is a

pure sine wave, and the red represents the same form after it has propagated through the

nonlinear air for a time.

3.1 CONVENTIONAL SOUND:

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 nature, sound travels in waves spreading in every direction, bouncing off some

surfaces and being absorbed by others. It is certainly not linear. It helps to visualize the

traditional loudspeaker as a light bulb. As with the light bulb, a traditional loudspeaker radiates

sound fairly uniformly in all directions. A listener can stand anywhere in an acoustical

environment and point to the speaker as the source of the sound. Audio spotlighting technology

is much more analogous to the beam of light from a flashlight. Figures 3.3 shows the

conventional speakers distribution of sound and figure 3.4 shows the beam of sound targeted to

particular place. If you stand to the side or behind the light, you can only "see" the light when it

strikes a surface. Audio spotlighting technology is similar in that you can direct the ultrasonic

emitter toward 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 off the wall. Every form of distortion contributed by

a conventional loudspeaker is traceable to some aspect of its mechanical nature: mass, magnetic

structure, enclosure design, cone construction, etc. All form an important part of the final

product's capability to perform its function in as perfect a manner as possible.

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FIG 3.3: CONVENTIONAL SPEAKERS

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FIG 3.4 AUDIO SPOTLIGHTING

Speaker cone motion is subject to the laws of physics. This all-important element, more

than any other in a speaker system, affects the overall purity of sound and can be a source of

various forms of distortion. Ideally, when reproducing sound, the speaker cone should follow

precisely the delicate nuances of any electrical waveform presented to it. The cone or radiating

surface of a perfect loudspeaker would have virtually no mass or resonances over the entire

range of hearing, and would offer perfect linearity while at the same time being able to couple

enough energy into the air to produce any sound level desired.

Audio spotlighting technology does precisely that. It provides linear frequency response

with virtually none of the forms of distortion associated with conventional speakers. Physical

size no longer defines fidelity. The faithful reproduction of sound is freed from bulky

enclosures. There are no woofers, tweeters, crossovers, or bulky enclosures. Also, it is now

possible to dramatically minimize room effects in a listening environment.

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3.2 RANGE OF HUMAN HEARING:

The human ear is sensitive to frequencies ranging from 20Hz to 20,000Hz. If the range of

the human hearing is expressed as a percentage 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. In order to deal with this, speaker

manufacturers carve the audio spectrum into smaller sections (fig3.5), and make use of multiple

transducers and crossovers as necessary. 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. Using a technique of multiplying audible frequencies upwards and

superimposing them on a "carrier" of say, 200,000 cycles the required frequency shift for a

transducer would be only 10%.

Whether they are dynamic, electrostatic, or some other transducer-based design, all

loudspeakers today have one thing in common: they are direct radiating i.e., they are

fundamentally a piston-like device designed to directly pump air molecules into motion to create

the audible sound waves we hear. Audio spotlighting technology produces sound in the air

indirectly as a by-product of some other process. Using Audio spotlighting technology, it is

possible to design nearly a perfect transducer (fig 3.6).

Fig 3.5: AUDIO SPECTRUM

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Fig 3.6: Plot of bass cut, bass boost and normal sound

Depending on the user requirements the bandwidth of Audio spotlighting unit can be

adjusted. The red plot shows the normal usage. The blue plot is the Bass cut plot, where the

lower frequencies are cut. This is very useful for speeches. The black plot is the Bass boost plot,

where the lower frequencies are given importance. This is very useful for musical concerts.

3.3 WORKING OF AUDIO SPOTLIGHTING SYSTEM:

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 range. 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. The

model of spotlighting emitter is shown in firure-3.7.

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FIG 3.7: AUDIO SPOTLIGHTING EMITTER

While the frequency modulated signal travels through the air, the nonlinearity property of

air comes into action. A normal sound wave is a small pressure wave that travels through the air.

As the pressure goes up and down, the nonlinear nature of the air itself slightly changes the

sound wave. If there is 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. If the audio spectrum

could be superimposed on this high frequency carrier, and emitted into the air as an ultrasonic

acoustical wave front, the only thing remaining would be to ‘down convert’ the ultrasonic energy

to sonic energy we could hear. This ultrasonic sound wave (beyond the range of human hearing)

can be sent in to the air with sufficient volume to cause the air to create the required new

frequencies. Since we cannot here the ultrasonic sound, we only hear the new sounds that are

formed by the non linear action of the air.

Example:

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In order to generate a frequency (sound) of 1000Hz, we use ultrasonic waves of

50,000Hz and 51,000Hz frequency. These frequencies, due to nonlinearity and also distortion

produce 101,000Hz (inaudible) and 1000Hz (audible) which is the required frequency.

51,000+50,000=101,000Hz

51,000-50,000=1000Hz

Thus in an audio spotlighting there are no actual speakers that produces the sound but the

ultrasonic envelope acts as the airborne speaker. The directivity of the beam i.e, output of the

system is shown in the figure-3.8.

FIG 3.8: Beam Directivity

The new sound produced virtually has no distortions associated with it and faithful

reproduction of sound is feed 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 from

the reflection of the wall. For the maximum volume (sound level) that trade show use demands,

it is recommended that the audio spotlight speakers, more accurately called a transducer, 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.

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FIG 3.9: COMPUTER SIMULATION OF SOUND BEAM

By creating a complex ultrasound waveform(using a parametric array of ultrasound

sources)figure-3.9 shows computer simulation of sound propagation with complex sets, many

different sources of sound can be created. If their phases are carefully controlled, then these

interfere destructively laterally and constructively in the forward direction, resulting in a

collimated sound beam or audio beam or audio spotlight. Today, the transducers required to

produce these beams are just half an inch thick and lightweight, and the system required to drive

it has similar power requirements to conventional amplifiers technology.

3.4 BEAM DISPERSION:

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Fig 3.10: Dispersion of sound beam

In general, the dispersion is less than 3° in either direction or a total of 6° overall (fig

3.10). Dispersion of the audio wave front can be tightly controlled by contouring the face of the

audio spotlighting ultrasonic emitter. For example, a very narrow wave front might be developed

for use on the two sides of a computer screen while a home theater system might require a

broader wave front to envelop multiple listeners.

In addition, audio spotlight does not follow the traditional loudspeaker inverse-square

law, which dictates that you have a 6dB decrease in level for every doubling of the distance from

the source. This fact means that Audio spotlight can travel much greater distances while

maintaining intelligibility than the sound from conventional speakers.

3.5 WHY ULTRASONIC?

Directivity of the wave depends on its wavelength compared to the transmitting surface.

The larger the source is compared to the wavelength of the sound waves, the more directional

beam results. Assuming that HSS uses 48 kHz, following calculations could be made. The speed

of sound is about 300 m/sec, or 30,000 cm/sec.

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Speed = (wavelength)*(frequency)

=> Wavelength=speed/frequency

i.e. 30,000/48,000 = 0.63 cm.

Normally, the emitter's frontal area is 28 cm x 28 cm, or approx 44 wavelengths square.

This fact is the basic source of the device's tight directionality. When an emitter's size

approximates the wavelength of the emitted signal, a spherical wave front is produced (fig

3.12a), which expands with a surface area proportional to the square of the distance from the

emitter; thus producing inverse-square dispersal of energy across the expanding surface.

Fig 3.11: Types of ultrasonic emitters

A frequency of 1000Hz, for instance, yields a wavelength of 30 cm or about one foot.

Thus a signal in this frequency range, produced by a normal speaker whose diameter might be

approximately one foot, will produce a spherical wave front. However when the wavelength is a

small fraction of the size of the emitter, an essentially flat wave front is produced (fig 3.12b). If it

were truly flat and constrained to a channel, such a signal would lose strength only due to

interactions with the channel, and could travel very long distances. Since our Audio spotlight

beam is not in a channel, it will lose some energy to adjacent air. The ultrasound, whose

wavelengths are only a few millimeters long, are much smaller than the source, and consequently

tend to travel in a straight line. Of course, this ultrasound, which contains frequencies far outside

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our range of hearing, is completely inaudible. But as the ultrasonic beam travels through the air,

the inherent properties of the air cause the ultrasound to distort (change shape) in a predictable

way. This distortion gives rise to frequency components in the audible bandwidth. By generating

the correct ultrasonic signal, we can create, within the air itself, essentially any sound desired.

Both audible sound waves from traditional speakers and ultrasound waves from a

directional-sound system distort when they travel through the air. But, in a traditional sound

system, the distortion slightly degrades the sound a listener ultimately hears. But in a directional-

sound system, the distortion is actually the mechanism that generates the audible sound, breaking

the ultrasound waves into lower-frequency, audible sound waves along a straight, narrow path.

When the waves encounter a solid object or person, they slow, distort and crash together. The

result is the ultrasonic waves re-create the original sound in the air around the object, so humans

can hear it. Variations in the speed of sound cause this phenomenon. Thus, sound from a distant

Audio spotlight speaker seems like its right at your ears because it is actually being created right

at your ears. If you step out of the beam, the waves have nothing to distort and mix them, so the

inaudible ultrasonic waves slide silently past.

The equations that govern nonlinear acoustics is given below

Where,

Audible secondary pressure wave.

K = physical parameter.

Pressure of ultrasonic carrier.

Envelope function (DSB)

Previous equation says that the audible demodulated ultrasonic pressure wave (output signal) is

proportional to the twice differentiated, squared version of the envelope function (input signal).

3.6. COMPONENTS OF AUDIO SPOTLIGHTING SYSTEM:

1. Power Supply.

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2. Frequency oscillator.

3. Modulator.

4. Audio signal processor

5. Microcontroller.

6. Ultrasonic amplifier.

7. Transducer.

FIG 3.12: Block Diagram Of An Audio Spotlighting System

1. Power Supply: Like all electronic systems, the audio spotlighting system works off DC

Voltage, ultrasonic amplifier requires 48v for its working and low voltage. For

microcontroller and other processing unit 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.

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3. Modulator: In order to convert the source program material into ultrasonic signals, a

modulation scheme is required. In addition, error correction is needed to reduce distortion

without loss of efficiency. The goal, of course, is to produce audio in the most efficient

manner while maintaining acceptably low distortion levels.

A DSB scheme is straightforward way to generate the required ultrasonic frequencies

for a given base band signal. From the basic principles of the Fourier analysis,

multiplication in the time domain is analogous to convolution in the frequency domain.

Convolution between a baseband signal and a carrier frequency effectively images the

baseband signal around both sides of the carrier frequency spectral component, as shown in

Fig 3.8. We know that for a DSB system, the modulation index can be reduced to

decrease distortion, because total harmonic distortion increases proportionally with the

square of m. This is because as the side bands gain more power, there is more cross

interference between the side bands rather than between the side bands and the carrier

frequency component.

4. 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.

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Fig 3.13: DSB Signal Representation

5. Audio signal processor: The audio signal is sent to an electronic signal processor circuit

where equalization, dynamic range control, distortion control and precise modulation are

performed to produce a composite ultrasonic waveform. This amplified ultrasonic signal is sent

to the emitter, which produces a column of ultrasonic sound that is subsequently converted into

highly directional audible sound within the air column.

Since ultrasound is highly directional, the audio sound placement is precise. At the heart

of the system is a high precision oscillator in the ultrasonic region with a variable frequency

ranging from 40 to 50 kHz.

6. Ultrasonic Amplifier : High – efficiency ultrasonic power amplifiers amplifies the

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.

7. Transducer: The most active piezo film is polyvinalidene difluoride. This film is

commonly used in many industrial and chemical applications.

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In order to be useful for ultrasonic transduction, the raw film must be polarized or

activated. This is done by one of the two methods. One method yields a ‘uniaxial’ film that

changes length along one axis when an electric field is applied through it. The other method

yields a ‘biaxial’ film that shrinks/expands along two axes. Finally, the film needs to have a

conductive electrode material applied to both sides in order to achieve a uniform electric

field through it.

Piezoelectric films operate as transducers through the expansion and contraction of

‘X’ and/or ‘Y’ axes of the film surface. For use as a hypersonic sound emitter, the film is

to be curved or distended. The curving results in expansion and contraction in the ‘Z’ axis,

generating acoustic output.

The music or voice from the audio source is converted into a highly complex

ultrasonic signal by the signal processor before being amplified and emitted into the air by

the transducer. Since the ultrasonic energy is highly directional, it forms a virtual column

of sound directly in front of the emitter, much like the light from a flash light.

Fig 3.14 shows the structure of piezo sound emitter. When a voltage is applied across

the pins, the red element gets longer while the blue one shortens, causing a bend in the

piezo. When the polarity changes, the opposite bend occurs. The maximum displacement

change is in the center of the element where the cone is attached.

The latest ATC parametric sound generator is a monolithic, thin-film structure

that maintains coherent amplitude and phase across the entire device in a package measuring less

than a half-inch thick (fig 3.15). Because the emitter is larger than the wavelength of the

frequencies involved, it emits the ultrasound wave as a pure plane wave with virtually no

expansion in the beam diameter with distance.

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Fig 3.14: Piezo sound emitter

Fig 3.15: :-Parametric Loudspeaker- Amazing Audio Spotlight

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

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be wall, overhead or flush mounted. These transducers are arranged in form of an array called

parametric array in order to propagate the ultrasonic signals from the emitter and thereby to

exploit the nonlinearity properly of air.

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MODES OF LISTENING

There are two modes of listening:

1. Direct Mode.

2. Projected Mode.

FIG

4.1:

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. This method is appropriate when we want to restrict the audio in a

specific area. Fig 4.1 shows the concept of direct mode.

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

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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. This method is appropriate when we want to send the information to a

large number of people. Fig 4.1 shows the concept of virtual mode.

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ADVANTAGES

1. Small size: Audio spotlighting not only has the conventional speaker's crossover network

and enclosure been eliminated, but the ultra-small radiating ultrasonic emitter is so small and

light-weight that the inertial considerations ordinarily associated with traditional direct-radiation

speakers are virtually non-existent. The voice coil and support structure normally associated with

the conventional speaker used to attach the moving cone in place are eliminated.

2. Single source : Audio spotlighting has the ability to produce nearly the entire audible

spectrum of frequencies from a single source. Hence the improvement in phase response, time

alignment, and frequency response becomes obvious.

3. Ultimate control in audio placement/Highly directional: Audio spotlight can focus sound

only at the place where we want it. This is achieved by controlling the dispersion of the wave.

These focused sound travels much farther in a straight line than conventional counterpart.

4. Minimizes noise pollution: Audio spotlight reduces the unnecessary noise from public

functions or gatherings.

5. Ease of installation: Audio spotlighting has a built-in amplifier, modulator and audio

signal processor. So the headache of installing external components and setting them up for

proper working is avoided.

6. Lowest maintenance cost: Since Audio spotlight system has no mechanical, and very few

electrical components, the maintaining cost very less.

7. Reduced feedback: As Audio spotlight systems allow us to direct the produced audio

away from any live mic, the tendency of feedback is significantly reduced.

8. There is no need to worry about pets, either. Dogs and cats can hear sounds up to perhaps

40,000 Hz, and Audio spotlight system operates well above this range.

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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. By maintaining a beam of

sound, across the traffic, traffic police can use Audio spotlighting to help the blind people

cross the road at the signals.

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5. 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.

6. 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.

7. Military applications: Ship – to – ship communications and shipboard

announcements. And also it is used to misguide the enemy by creating the false

shouting area away from the military camps.

8. Political: With the help of HSS international gatherings, such as the United Nations,

SAARC summit could have translated speech beamed directly to individuals: Spanish at one

seat, Hindi at the other and Arabic at the next. All this without interference or individual

earphones.

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DISADVANTAGES

1. Lack of mass production.i.e, each unit must be handmade.

2. The most common form of distortion is clipping. An LED on top of the Audio spotlight

system reports clipping, which is also perceptible to the listener as a kind of a 'chirping'

effect. If any signal produces distortion, the input level of the source is reduced until

perceptible distortion is eliminated.

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CONCLUSION AND ENHANCEMENTS

“Being the most radical technological development in acoustics since the coil

loudspeaker was invented in 1925... The audio spotlight will force people to rethink their

relationship with sound…”

Audio spotlighting is 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 its finds applications in large number of fields. The main intention of Audio

spotlighting system is to reduce the unnecessary sound and to promote peace and quiet

environment. With the companies like Sony and Bose interested, it is going to shape the

future of sound and will serve our ears with magical experience.

The audio spotlighting holds the promise of replacing conventional speakers. Ultrasonic

emitters have super high impedance, which allows low current in power amplifiers

making them lighter.

The future developments of this technology include a full functioning embedded system,

including modulation, audio processing and distortion control.

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REFERENCES

1. www.techalone.com – Audio spotlighting

2. www.wikipedia.org - Sound from Ultrasound

3. www.holosonics.com

4. www.silentsound.co.za – Silent sound

5. Electronics For You – Vol. 40 January 2008

6. http://www.en.wikipedia.org/wiki/sound_from_ultrasound

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