Audio spotlighting

AUDIO SPOTLIGHTING 2015-16

CHAPTER 1

INTRODUCTION

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

woofers which generally rely on circuits ant large enclosures to produce quality sound,

whether it dynamic, electrostatic or some other transducer – based design. Engineers have

struggled for nearly a century to produce a speaker design with the ideal 20Hz – 20,000Hz

capability of human hearing and also produce a narrow beam of audible sound.

Audio spot lighting is a very recent technology that creates focused beams of sound

similar to light beams coming out of a flash light. Specific listeners can be targeted with sound

without others nearby hearing it, i.e. to focus the sound into a coherent and highly directional

beam. It makes use of non-linearity property of air.

The Audio spotlight developed by American Technology Corporation uses ultrasonic

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

spotlight exploits the property of non-linearity of air. A device known as parametric array

employs the non-linearity of the air to create audible by products from inaudible ultrasound,

resulting in extremely directive and beam like sound. This source can projected about an

area much like a spotlight and creates an actual specialized sound distant from a transducer.

The ultrasound column acts as a airborne speaker, and as the beam moves through the air

gradual distortion takes place in a predictable way. This gives rise to audible components

that can be accurately predicted and precisely controlled.

DEPT. OF MTE, ACIT Page 1


CHAPTER 2:

THEORY

The regular loudspeakers produce audible sound by directly moving the air molecules. The

audible portions of sound tend to spread out in all directions from the point of origin.

They do not travel as narrow beams. In fact the beam angle of audible sound is very wide, just

about 360 degrees. This effectively means that the sound you hear will be propagated through

the air equally in all directions. Conventional loudspeakers suffer from amplitude

distortions, harmonic distortion, inter - modulation distortion, phase distortion, crossover

distortion, cone resonance etc. Some aspects of their mechanical aspects are mass, magnetic

structure, enclosure design and cone construction.

In order to focus sound into a narrow beam, you need to maintain a low beam angle that

is dictated by wavelength. The smaller the wavelength, less the beam angle and hence, the

more focused the sound. The beam angle also depends on the aperture size of the speaker. A

large loudspeaker will focus the sound over a smaller area. If the source loudspeaker can

be made several times bigger than the wavelength of the sound transmitted, then a finely

focused beam can be created. The problem here is that this is not a very practical solution, thus

the low beam angle can be achieved only by making the wavelength smaller and this can be

achieved by making use of ultrasonic sound.

FIG 1 : F.JOSEPH POMPEI AT THE MIT LAB. PROPAGATION OF SOUND BEAM

FROM AUDIO SPOTLIGHTING DEVICE



CHAPTER 3:

TECHNOLOGY OVERVIEW

The technique of using a nonlinear interaction of high – frequency waves to generate low –

frequency waves was originally pioneered by researchers developing underwater sonar

techniques in 1960’s. In 1975, an article cited the nonlinear effects occurring in air. Over the

next two decades, several large companies including Panasonic and Ricoh attempted to develop

a loudspeaker using this principle. They were successful in producing some sort of sound

but with higher level of distortion (>50%). In 1990s, Woody Norris a Radar Technician

solved the parametric problems of this technology.

Audio spotlighting works by emitting harmless high frequency ultrasonic tones that human

hear cannot hear. It uses ultrasonic energy to create extremely narrow beams of sound that

behave like beams of light. Ultrasonic sound is that sound which have very small wavelength

– in the millimeter range. These tones make use of non-linearity property of air to produce

new tones that are within the range of human hearing which results in audible sound. The

sound is created indirectly in air by down converting the ultrasonic energy into the frequency

spectrum we can hear.

In an audio spotlighting sound system there are no voice coils, cones or enclosures. The result

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

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

conventional speakers in homes, movie theaters and automobile – everywhere.



FIG 2: CONVENTIONAL SPEAKERS

FIG 3: AUDIO SPOTLIGHTING



CHAPTER 4:

RANGE OF HEARING

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

human hearing is expressed as a percentage of shift from the lowest audible frequency to the

highest it spans a range of 100,000 percent. No single loudspeaker element can operate

efficiently over such a wide range of frequencies.

Using this technology it is possible to design a perfect transducer which can work over a wide

range of frequency which is audible to human hear.

FIG 4: RANGE OF HEARING



CHAPTER 5:

WORKING

The original low frequency sound wave such as human speech or a music is applied into an

audio spotlight emitter device. This low frequency signal is frequency modulated with ultrasonic

frequencies ranging from 21 kHz to 28 kHz. The output of the modulator will be the modulated

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

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

the beam angle will be around 3 degree, as a result the sound beam will be a narrow one with a

small dispersion.

FIG 5: AUDIO SPOTLIGHTING EMITTER



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

comes into action which slightly changes the sound wave. If there is a change in a sound wave,

new sounds are formed within the wave. Therefore if we know how the air affects the sound

waves, we can predict exactly what new frequencies (sounds) will be added into the sound

wave by the air itself. The new sound signal generated within the ultrasonic sound wave will

be corresponding to the original information signal with a frequency in the range of 20 Hz

to 20 kHz will be produced within the ultrasonic sound wave. Since we cannot hear the

ultrasonic sound wave we only hear the new sounds that are formed by non – linear action of the

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

ultrasonic envelope acts as the airborne speaker.

FIG 6: DIRECTIVITY



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

reproduction of sound is freed from bulky enclosures. There are no woofers or

crossovers. This technology is similar in that you can direct the ultrasonic emitter towards

a hard surface, a wall for instance and the listener perceives the sound as coming from the spot

on the wall. The listener does not perceive the sound as emanating from the face of the

transducer, but only form the reflection of the wall. For the maximum volume (sound

level) that trade show use demands, it is recommended that the Audio Spotlight speaker,

more accur ately called a tr ansducer, is mounted no more than 3 meters from the average

listeners ears, or 5 meters in the air. The mounting hardware is constructed with a ball joint so

that the Audio Spotlights are easily aimed wherever the sound is desired.

FIG 7: COMPUTER SIMULATION OF SOUND BEAM



CHAPTER 6:BEAM DISPERSION

FIG 8: DISPERSION OF SOUND BEAM

Figure shows the dispersion of sound beam from an audio spotlighting emitter. Even

after traveling a distance of 10m the beam covers only an area of 3.2 meter square.



CHAPTER 7:

BLOCK DIAGRAM

COMPONENTS

1. Power Supply.

2. Frequency oscillator.

3. Modulator.

4. Audio signal processor.

5. Microcontroller.

6. Ultrasonic amplifier.

7. Transducer.

FIG9: BLOCK DIAGRAM OF AN AUDIO SPOLIGHTING SYSTEM



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

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

microcontroller unit and other process management.

2. Frequency oscillator: The frequency oscillator generates ultrasonic frequency signals

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

information signals.

3. Modulator: In order to convert the source signal material into ultrasonic signal a

modulation scheme is required which is achieved through a modulator. In addition, error

correction is needed to reduce distortion without loss of efficiency. By using a DSB modulator

the modulation index can be reduced to decrease distortion.

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

where equalization and distortion control are performed in order to produce a good quality sound

signal.

5. Microcontroller: A dedicated microcontroller circuit takes care of the functional

management of the system. In the future version, it is expected that the whole process

like functional management, signal processing, double side band modulation and even

switch mode power supply would be effectively taken care of by a single embedded IC.

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

frequency modulated wave in order to match the impedance of the integrated transducers.

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



7. Transducer: It is 1.27 cm thick and 17” in diameter. It is capable of producing

audibility up to 200 meters with better clarity of sound. It has the ability of real time sound

reproduction with zero lag. It can be wall, overhead or flush mounted. These transducers ar e

arranged in form of an array called parametric arr ay in order to propagate the ultrasonic

signals from the emitter and thereby to exploit the nonlinearity property of air.

FIG10: PARAMETRIC LOUDSPEAKER



CHAPTER 8:

MODES OF LISTENING:

There are two modes of listening:

1. Direct Mode.

2. Projected Mode.

FIG11: DIRECTED AUDIO AND PROJECTED AUDIO

Direct Mode: Direct mode requires a clear line of approach from the sound system unit

to the point where the listener can hear the audio. To restrict the audio in a specific area

this method is appropriate.

Projected or Virtual mode: This mode requires an unbroken line of approach from the

emitter of audio spotlighting system, so the emitter is pointed at the spot where the is to

be heard. For this mode of operation the sound beam from an emitter is made to reflect

from a reflecting surface such as a wall surface or a diffuser surface. A virtual sound

source creates an illusion of sound source that emanates from a surface or direction



where no physical loudspeaker is present.

CHAPTER 9:

ADVANTAGES

1. Can focus sound only at the place you want.

2. Ultrasonic emitter devices are thin and flat and do not require a mounting cabinet.

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

loudspeakers.

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

5. Can reduce or eliminate the feedback from microphones.

6. Highly cost effective as the maintenance required is less as compared to conventional

loud speakers and have longer life span.

7. Requires only same power as required for regular speakers.

8. There is no lag in reproducing the sound

DISADVANTAGES 1. Lack of mass production. i.e, each unit must be hand made.

2. The most common form of distortion is clipping



CHAPTER 10:

APPLICATIONS

1. Automobiles: Beam alert signals can be directly propagated from an announcement device in the dashboard to the driver. Presently Mercedes – Benz buses are fitted with audio spotlighting speakers so that individual travelers can enjoy the music of there on interest.

2. Retail sales: Provide targeted advertising directly at the point of purchase.

3. Safety officials: Portable audio spotlighting devices for communicating with a specific person in a crowd of people.

4. Public announcement: Highly focused announcement in noisy environments such as subways, airports, amusement parks, traffic intersections etc.



5. Emergency rescue: Rescuers can communicate with endangered people far from reach.

6. Entertainment system : In home theatre system rear speakers can be eliminated by the

implementation of audio spotlighting and the properties of sound can be improved.

7. Museums: In museums audio spotlight can be used to describe about a particular object to a

person standing in front it, so that the other person standing in front of another object will not be

able to hear the description.

8. Military applications: Ship – to – ship communications and shipboard announcements.

9. Audio/Video conferencing: Project the audio from a conference in four different languages,

forma single central device without the need for headphones.

10. Sound bullets: Jack the sound level 50 times the human threshold of pain, and an offshoot of

audio spotlighting sound technology becomes a non-lethal weapon.



CHAPTER 11:

FUTURE OF AUDIO SPOTLIGHTING : Even the best loudspeakers are subject to distortion and their omni directional sound is

annoying to the people in the vicinity who do no wish to listen. Audio spotlighting system

holds the promise of replacing conventional speakers. It allows the user to control the

direction of propagation of sound. The audio spotlight will force people to rethink their

relationship with sound. Audio spotlighting really “put sound where you want it”.

CHAPTER 12:



CONCLUSION :

Audio spotlighting is really going to make a revolution in sound transmission and the

user can decide the path in which audio signal should propagate. Due to the unidirectional

propagation it finds application in large number of fields. Audio spotlighting system is going to

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

REFERENCE



1. F. Joseph Pompei. The use of airborne ultrasonics for generating audible sound beams.

Journal of the Audio Engineering Society, P. J. Westervelt. Parametric acoustic array.

Journal of the Acoustical Society of America.

2. Thomas D. Kite, John T. Post, and Mark F. Hamilton. Parametric array in air: Distortion

reduction by preprocessing. Journal of the Acoustical Society of America.

3. Jacqueline Naze Tjotta and Sigve Tjotta. Nonlinear interaction of two collinear,

spherically spreading sound beams.

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

5. www.techalone.com – Audio spotlighting

6. www.howstuffworks.com

7. www.holosonics.com

8. Electronics For You – Vol. 40 January 2008
