CHAPTER 01

INTRODUCTION

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

speakers and woofers which generally rely on circuits at large enclosures to produce

quality sound, whether it is dynamic, electrostatic or some other transducers- 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 narrow beam of

audible sound.

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 property of non-linearity of air. A device known as

parametric array employs the non-linearity of air to create audible by products from

inaudible ultrasound, resulting an 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 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.

This audio spotlight technology creates focused beams of sound similar to light

beams coming out of a flashlight. Specific listeners can be targeted with sound without

other hereby hearing it, i.e. to focus the sound into coherent and highly directional beam.

It makes use of non- linearity property of air.

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CHAPTER 02

2.1 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 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 meters (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 meters across is required, and to guarantee that all the audible wavelengths are

focused, even bigger loudspeakers are needed.

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.

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Fig 2.1: 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.

Fig 2.2: F.Joseph Pompei At The Media Lab Of The Massachusetts Institute Of Technology Demonstrates How Invisible Ultrasonic Waves, As Illustrated Here, Could Help "STEER" Sound.

(ABCNEWS.COM)

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2.2 NON-LINEARITY OF AIR

Audio spotlighting exploits the property of non-linearity of air. When inaudible

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

into audible sound tones, hence proved that as with water, sound propagation in air is just

as non-linear, and can be calculated mathematically.

A device known as a parametric array employs the non-linearity of the air to

create audible by-products from inaudible ultrasound, resulting in an extremely directive,

beamlike wide-band acoustical source. This source can be projected about an area much

like a spotlight, and creates an actual sound distant from the transducer. 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. However, the problem with firing off

ultrasound pulses, and having them interfere to produce audible tones is that the audible

components created are nowhere similar to the complex signals in speech and music.

Human speech, as well as music, contains multiple varying frequency signals,

which interfere to produce sound and distortion. To generate such sound out of pure

ultrasound tones is not easy.

Fig 2.3: Ultrasound waves

This is when teams of researchers from Ricoh and other Japanese companies got

together to come up with the idea of using pure ultrasound signals as a carrier wave, and

superimposing audible speech and music signals on it to create a hybrid wave. If the

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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%. No single loudspeaker element

can operate efficiently or uniformly over this range of frequencies. In order to deal with

this speaker manufacturers carve the audio spectrum into smaller sections. This requires

multiple transducers and crossovers to create a 'higher fidelity' system with current

technology.

Fig 2.4:Parametric Loudspeaker- Amazing Audio Spotlight

(Airborne ultrasounds of 28 kHz are envelope-modulated with audio signals.

Inherent non-linearity of the air works as a de-modulator. Thus de-modulated sounds

impinge on our eardrums. We can hear those sounds! )

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%. Building a transducer that only needs to produce waves uniformly

over only a 10% frequency range. In this technology we can ‘put sound where we want’

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Using sound with vision improves retention rates by up to 60%, but how do you

get round the issue of noise pollution to the surrounding area? By using Audio spotlight -

which concentrates the sound just as a spotlight does so only those in the "beam" can hear

your message. Use it outside your shop window, or under your billboard. People can

hear, but can't always know where the sound is coming from. Creative opportunities

AUDIO SPOTLIGHT TRANSDUCER

17.5”/445mm diameter, 1/2”/12.7mm thick

Wall, overhead or flush mounting

Black cloth cover standard, other colours available

Audio output: 100dB max

Usable range: 20m

Audibility to 200m

Optional integrated laser aimer 13”/ 330.2mm and 24”/ 609.6mm diameter also

available

Fully CE compliant

Fully real-time sound reproduction - no processing lag

Compatible with standard loudspeaker mounting accessories Due to continued

development, specifications are subject to change.

CHAPTER 03

3.1 TECHNOLOGY OVERVIEW

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The technique of using non-linear interaction of high-frequency waves to generate

low-frequency waves was originally pioneered by researches developing underwater

sonic techniques in1960’s. In 1975, an article cited the non-linear effects occurring in air.

Over the next two-decades, several companies develop a loudspeaker using this principle.

They were successful in producing some sort of sound but with higher level of distortion

(>50%). In 1990’s Woody Norris a Radar technician solved the parametric problems of

this technology.

Audio Spotlighting works by emitting harmless high frequency ultrasonic tones

that human ear 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 has very

small wavelength-in 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 frequency spectrum we can hear.

In an Audio Spotlighting sound system there are no voice coils. The result is

‘sound with a potential purity and fidelity which we never attained before.’ Sound quality

is no longer tied to speaker size. The sound system holds the promise of replacing

conventional speakers in home, movie theaters and automobile-everywhere.

Fig 3.1: Conventional

speakers

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Fig 3.2: Audio spotlighting

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

3.2 RANGE OF HEARING

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The human ear is sensitive to frequency ranging from 20Hz to 20,000Hz. If 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%. 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 ear

Fig 3.3: Range of Hearing

The idea of amplitude modulation (AM), a technique used to broadcast

commercial radio stations signals over a wide area. The speech and music signals are

mixed with the pure ultrasound carrier wave, and 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, one slightly higher and one slightly lower than the hybrid

wave. Berktay’s equation holds strong here, and these two sidebands interfere with the

hybrid wave and produce two signal components, as the equation says. One is identical to

the original sound wave, and the other is a badly distorted component. This is where the

problem lies the volume of the original sound wave is proportional to that of the

ultrasounds, 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. It was at this point that all research on ultrasound as a carrier wave

for an audio spotlight got bogged down in the 1980s.

CHAPTER 04

9

WORKING PRINCIPLE

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 21KHZ to 28KHZ. The output modulator will

be the modulated form of original sound wave. Since the ultrasonic frequency is used the

wavelength of the combined signal will be in the order of few millimeters. Since the

wavelength is smaller than the beam angle will be around 3 degree, as a result the sound

beam will be a narrow beam with small dispersion.

Fig 4.1: Audio spotlighting Emitter

While the frequency modulated signal travels through the air, the non-linearity

property of air comes into action which slightly changes the sound wave. If there is a

change in 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

(sound) 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 original information

signal with a frequency in the range of 20HZ to 20KHZ will be produced within

ultrasonic sound wave. Since we cannot hear the ultrasonic sound wave we can hear the

new sounds that are formed by non-linear action of air. Thus in an audio spotlighting

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there are no actual speakers that produce the sound but the ultrasonic envelope acts as the

airborne speaker.

A conventional speaker radiates sound in a very wide pattern, often with side

lobes ( also depicted in Fig 4.2) Side lobes do not exist in Audio Spotlight systems; the

beam is much like that from a flashlight. The Audio Spotlight uses the interaction of

ultrasonic sound waves with the air to reproduce audible sounds in a highly directional

pattern. By contrast, a conventional speaker radiates sound in a wide pattern, often with

side lobes that the Audio Spotlight avoids.

Fig 4.2 : Directivity pattern

Focusing on the signal’s distorted component, since the signal component’s

behavior is mathematically predictable, the technique to create the audio beam is simple;

modulate the amplitude to get the hybrid wave, then calculate what the Becktay’s

Equation does to this signal, and do the exact opposite. In other words, distort it, before

Mother Nature does it.

Finally, pass this wave through air, and what you get is the original sound wave

component whose volume, this time, is exponentially related to the volume of the

ultrasound beam, and a distorted component, whose volume now varies directly as the

ultrasound wave.

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

ultrasound sources), 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 spotlight. Today, the

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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

amplifier technology.

Fig 4.3 :Computer Simulation Of Sound Propagation: Complex Set Of High-Intensity Ultrasound Signals Intermodulates Air. Among The Products Is A Collimated Audio "Spotlight".

CHAPTER 05

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ARCHITECTURE

COMPONENTS OF AUDIO SPOTLIGHTING

1. Power supply

2. Voltage Regulator

3. Frequency Oscillator

4. Modulator

5. Audio Signal Processing

6. Microcontroller

7. Ultrasonic Amplifier

8. Transducer

Fig 5.1: Block Diagram of Audio Spotlighting System

1. Power Supply:

Like all electronics system, the audio spotlighting system works off DC

Voltage. Ultrasonic amplifier requires 48 V DC supply for its working and low

voltage for microcontroller and other process management.

2. Voltage regulator:

As the name itself implies, it regulates the input applied to it. A voltage

regulator is an electrical regulator designed to automatically maintain a constant

voltage level. In this diagram, power supply of 5V is required to the

microcontroller. In order to obtain this voltage level, 7805 voltage regulator are to

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be used. The first number 78 represents positive supply and the numbers 05

represent the required output voltage levels.

Fig 5.2: Pin diagram of 7805 Fig 5.3 : Block diagram of 7805

3. Frequency Oscillator:

The Frequency Oscillator generates ultrasonic frequency signals in the

range (21,000Hz to 28,000Hz) which is required for the modulation of

information signals.

Fig 5.4: Frequency Oscillator

4. 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.

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By using a DSB modulator, the modulation index can be reduced to decrease

distortion.

Fig 5.5: DSB modulator waveforms

5. Audio Signal Processing:

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.

Fig 5.6: Audio Signal Processor

6. Micro controller:

A dedicated microcontroller circuit takes care of the functional

management of the system. Microcontroller controls overall operation of the

system. In this A/D convertor is in built in microcontroller. In the future version, it

is expected that the whole process like functional management, signal processing,

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double side band modulation and even switch mode power supply would be

effectively taken care of by a single embedded IC.

7. Ultrasonic amplifier:

High efficiency ultrasonic power amplifier amplifies the frequency

modulated wave in order to match its impedance of integrated transducers. So that

the output of emitter will be more powerful and can cover more distance.

Fig 5.7: Ultrasonic Amplifier

8. Transducer:

It is 1.27cm thick and 17” diameter. It is capable of producing audibility

upto 200meters with a better clarity of sound. It has ability of real time sound

reproduction with zero lag. These transducers are arranged in the form of array

called parametric array in order to propagate the ultrasonic signals from the

emitter and thereby to exploit the non-linearity property.

Fig 5.8:Parametric Transducer

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CHAPTER 06

MODES OF LISTENING

DIRECT AUDIO AND PROJECTED AUDIO:

There are two ways to use Audio Spotlight. First, it can direct sound at a specific

target, creating a contained area of listening space which is called “Direct Audio”.

Second, it can bounce off of a second object, creating an audio image. This audio image

gives the illusion of a loudspeaker, which the listener perceives as the source of sound,

which is called “projected Audio”. This is similar to the way light bounces off of objects.

In either case, the sound’s source is not the physical device you see, but the invisible

ultrasound beam that generates it.

Fig 6.1: Direct Audio And Projected Audio

Hyper Sonic Sound technology provides linear 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. Thus it helps to visualize the

traditional loudspeaker as a light bulb, and HSS technology as a spotlight, that is 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, only from the reflection off the

wall.

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Contouring the face of the HSS ultrasonic emitter can tightly control Dispersion

of the audio wave front. 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.

Fig 6.2: Conventional Loudspeaker & Ultrasonic Emitter

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CHAPTER 07

7.1 APPLICATIONS

Since 2000, Audio Spotlight technology has been installed in a wide range of

applications around the world. From museums, exhibits, galleries, kiosks, to retail stores

and special projects, hundreds of companies have chosen the unique, patented Audio

Spotlight technology to provide high-quality, precisely controlled sound.

Billboard/Advertising

Until now, adding sound to billboards was not an option because of

obvious noise problems; nearby neighbors and businesses would not

tolerate continuous noise from roof-mounted loudspeakers. With the

Audio Spotlight technology, sound can be targeted to a specific area, and

provide audio just to this small region – all the way from a rooftop.

Museums

A popular multimedia exhibit at The Chicago Cultural Center featured

eight traditional loudspeakers in one small room, each corresponding to an

individual speaking voice projected onto the wall. The traditional speakers

caused big problems, disturbing other galleries and making the exhibit

itself difficult to hear and unpleasant. The museum replaced the

loudspeakers with eight Audio Spotlight discs. The result was eight local,

discrete zones of sound, each corresponding to a nearby projected video.

Those standing under a disc hear the sound, while elsewhere in the very

same room, background noise is but a whisper.

Exhibitions/Events

Exhibitions are always full of noise, but very little is intelligible. Even if

you blast out your message on normal loudspeakers, few will thank you

for it. If however you used Audio Spotlight to isolate areas of sound that

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gave visitors to your stand the information they needed, how valuable

would that be. You could give relevant help to individual product ranges

right next to each other, without turning your stand into a cacophony of

noise.

Office and showrooms

Where you have either different product on display or separate screens

showing diverse content, Audio Spotlight can add a touch of magic to

your room. By focusing the sound on just one part of the room, visitors

can receive the information they need without disturbing the other visitors.

7.2 ADVANTAGES

1. Can focus sound only at place you want

2. Ultrasonic emitter devices are thin and flat and don’t require a mounting cabinet

3. The focused or directed sound travels much faster in a straight line than

conventional loudspeaker.

4. Dispersion can be controlled – very narrow or wider to cover more listening areas.

5. Can reduce or eliminate the feedback from microphones.

6. Requires same power as required for regular speakers.

7. There is no lag in reproducing the sound.

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CHAPTER 08

8.1 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.

“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”

So we can conclude- Audio Spotlighting really “put sound where you want it” and

will be “A REAL BOON TO THE FUTURE.”

8.2 FUTURE SCOPE

"So you can control where your sound comes from and where it goes," says Joe

Pompei, the inventor of Audio Spotlight. Pompei was awarded a “Top Young Innovator”

award from Technology Review Magazine for his achievements.

The targeted or directed audio technology is going to tap a huge commercial

market in entertainment and in consumer electronics, and the technology developers are

scrambling to tap into that market. Analysts claim that this is possibly the most dramatic

change in the way we perceive sound since the invention of the coil loudspeaker.

Continuing to improve on the commercial success of the Audio Spotlight sound

system, Holosonics has announced that its next generation laser like sound system, with

improved performance and lower cost, is now actively in production. These new systems

are being exhibited at the 2004 Consumer Electronics Show in Las Vegas alongside MIT

Media Lab technology.

The performance and reliability of the Audio Spotlight have made it the choice of

the Smithsonian Institution, Motorola, Kraft, and Cisco Systems etc.

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Holosonics

put in four

individual

Audio Spotlights into the Daimler Chrysler MAXXcab prototype truck to let all

the passengers enjoy their own choice of music. Boston Museum of Science - as

well as the United States military.

There is an even bigger market for personalized sound systems in entertainment

and consumer electronics.

Holosonic Labs is working on another interesting application at the Boston

Museum of Science that allows the intended listeners to understand and hear

explanations, without raising the ambient sound levels. The idea is that museum

exhibits can be discretely wired up with tiny speaker domes that can

unobtrusively, provide explanations.

There are also other interesting applications that they are looking at, such as

private messaging using this system without headphones special effects at

presentations as well as special sound theme parks that could put up animated

sound displays similar to today’s light shows.

22

Holosonic has installed their Audio Spotlight system at Tokyo’s Sega Joyopolis

theme park.

The US Navy has installed sound beaming technology on the deck of an Aegis-

class Navy destroyer, and is looking at this as a substitute to the radio operator’s

headphones.

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REFERENCES

www.silentsound.co.za – silent sound

www.techalone.com – Audio Spotlighting

www.wikipedia.org – sound from ultra sound

www.holosonics.com

www.howstuffworks.com

www.seminarprojects.com

www.spie.org

Engineering Physics by B.Premlet

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