Directional speaker

ABSTRACT
Directional speaker is very recent technology that creates focused beams of sound
similar to light beams coming out of a flashlight. By ‘shining’ sound to one location, specific
listeners can be targeted with sound without others nearby hearing it. To focus sound
into a coherent and highly directional beam, it uses a combination of non-linear acoustics and
some fancy mathematics. But it is real and is fine to knock the socks of any
conventional loud speaker. The Audio Spotlight & Hyper Sonic Sound
Technology(developed by American Technology Corporation), uses ultrasonic energy to
create extremely narrows beams of sound that behave like beams of light. Directional
speaker 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.
It gives the meaning of Enjoy your music quietly i.e. without disturbing others. Secret
home theatre is an application of Audio spot lighting. Specific listeners can be targeted with
sound without others nearby hearing it. It makes use of non linearity property of air. It can be
either directed at a particular listener or to a point where it is reflected. This acoustic device
comprises a speaker that fires inaudible ultrasound with very small wavelength which acts in a
manner very similar to that of a narrow column. The ultra sound beam acts as an airborne
speaker. Being the most recent and dramatic change in the way we perceive sound.
i

INDEX
1. Introduction
2. Theory in to the depths of directional speaker technology
3. Non-Linearity property of air
4. Application of Directional speaker – Towards the future
5. Conclusions and future perspectives
6. References (Bibliography)
ii

LIST OF CONTENTS
Chapter
No.
Description Page
No.
ABSTRACT i
INDEX Ii
LIST OF CONTENT iii
LIST OF FIGURES v
1 INTRODUCTION 1
1.1. What is sound? 1
1.1.1 Perception of sound 2
1.1.2 Terminology of sound 3
1.1.3 Classification of sound 3
1.1.4 Basic Principles of sound 6
1.1.5 Interference of sound 6
1.2. Principles of Directional speaker 8
2 THEORY IN TO THE DEPTHS OF DIRECTIONAL
SPEAKER TECHNOLOGY
11
2.1 Technology Overview 12
2.2 Components and Specifications 12
2.2.1 Sound beam amplifier 13
2.2.2 Directional speaker Transducer 15
3 NON-LINEARITY PROPERTY OF AIR 18
3.1. Modulation schemes for getting Directional sound 20
3.2. Direct audio and Projected audio 21
4 APPLICATIONS OF DIRECTIONAL SPEAKER –
TOWARDS THE FUTURE
22
4.1. Advantages of Directional speaker over Normal speaker 23

5 CONCLUSIONS AND FUTURE PERSPECTIVES 25
6 REFERENCES (BIBLIOGRAPHY) 25
iv

LIST OF FIGURES
v
Figure No. Description Page No.
1.1 Classification of sound based on frequency 4
1.2 Directional sound wave front vs Spherical wave front 9
2.1 Block diagram of Directional speaker 12
2.2 Construction of the piezoelectric transducer used for the
octagonal array
14
3.1 Model diagram of Directional speaker 19

DIRECTIONAL SPEAKER
S V COLLEGE OF ENGINEERING, DEPT.OF E.C.E Page 1
CHAPTER - 1
INTRODUCTION
Directional Sound refers to the notion of using various devices to create fields of sound
which spread less than most (small) traditional loudspeakers. Several techniques are available to
accomplish this, and each has its benefits and drawbacks. Ultimately, choosing a directional
sound device depends greatly on the environment in which it is deployed as well as the content
that will be reproduced. Keeping these factors in mind will yield the best results through any
evaluation of directional sound technologies. Generally, any sound from the speaker is isotropic
which means they emits sound in all directional due to they operate in lower frequency (20 to
20,000HZ). This is an idea to create the directional sound emitting device.
Generally, the audible sound frequency is the range from 20 Hz to 20 kHz; however,
ultrasound is sound pressure with a frequency greater than the upper limit of human hearing i.e.
20 kHz. Recently the highly directional audible sound has been investigated for a few years. The
audible sound has the characteristics of spreading, however the ultrasound is directional.
Traditional speaker arrays can be fabricated in any shape or size, but a reduced physical
dimension (relative to wavelength) will inherently sacrifice directivity in that dimension. The
larger the speaker array, the more directional, and the smaller the size of the speaker array, the
less directional it is. This is fundamental physics, and cannot be bypassed, even by using phased
arrays or other signal processing methods.
1.1. WHAT IS SOUND?
In physics, sound is a vibration that typically propagates as an audible wave of pressure,
through a transmission medium such as a gas, liquid or solid. In human physiology and
psychology, sound is the reception of such waves and their perception by the brain. Humans can
hear sound waves with frequencies between about 20 Hz and 20 kHz. Sound above 20 kHz is
ultrasound and below 20 Hz is infrasound. Animals have different hearing ranges. Sound can
propagate through a medium such as air, water and solids as longitudinal waves and also as a

DIRECTIONAL SPEAKER
transverse wave in solids. The sound waves are generated by a sound source, such as the
vibrating diaphragm of a stereo speaker. The sound source creates vibrations in the surrounding
medium. As the source continues to vibrate the medium, the vibrations propagate away from the
source at the speed of sound, thus forming the sound wave. At a fixed distance from the source,
the pressure, velocity, and displacement of the medium vary in time. At an instant in time, the
pressure, velocity, and displacement vary in space. Note that the particles of the medium do not
travel with the sound wave.
The behavior of sound propagation is generally affected by three things:
 A complex relationship between the density and pressure of the medium. This relationship,
affected by temperature, determines the speed of sound within the medium.
 Motion of the medium itself. If the medium is moving, this movement may increase or
decrease the absolute speed of the sound wave depending on the direction of the
movement. For example, sound moving through wind will have its speed of propagation
increased by the speed of the wind if the sound and wind are moving in the same direction.
If the sound and wind are moving in opposite directions, the speed of the sound wave will
be decreased by the speed of the wind.
 The viscosity of the medium. Medium viscosity determines the rate at which sound is
attenuated. For many media, such as air or water, attenuation due to viscosity is less
The speed of sound is the distance travelled per unit time by a sound wave as it propagates
through an elastic medium. In dry air at 0 °C (32 °F), the speed of sound is 331.2 meters per
second (1,087 ft/s; 1,192 km/h).
1.1.1. Perception of sound
A distinct use of the term "sound" from its use in physics is that in physiology and
psychology, where the term refers to the subject of perception by the brain. The field of

DIRECTIONAL SPEAKER
psychoacoustics is dedicated to such studies. Historically the word "sound" referred exclusively
to an effect in the mind.
The physical reception of sound in any hearing organism is limited to a range of
frequencies. Humans normally hear sound frequencies between approximately 20 Hz and 20,000
Hz (20 kHz). The upper limit decreases with age.
Sometimes sound refers to only those vibrations with frequencies that are within the
hearing range for humans or sometimes it relates to a particular animal. Other species have
different ranges of hearing. For example, dogs can perceive vibrations higher than 20 kHz.
1.1.2. Terminology of sound
Pitch is perceived as how "low" or "high" a sound is and represents the cyclic, repetitive
nature of the vibrations that make up sound. For simple sounds, pitch relates to the frequency of
the slowest vibration in the sound (called the fundamental harmonic). In the case of complex
sounds, pitch perception can vary. Sometimes individuals identify different pitches for the same
sound, based on their personal experience of particular sound patterns.
Loudness is perceived as how "loud" or "soft" a sound is and relates to the totalled
number of auditory nerve stimulations over short cyclic time periods, most likely over the
duration of theta wave cycles. This means that at short durations, a very short sound can sound
softer than a longer sound even though they are presented at the same intensity level.
Noise is a term often used to refer to an unwanted sound. In science and engineering,
noise is an undesirable component that obscures a wanted signal.
1.1.3. Classification of sound
Sound mainly classified by their frequency of sound waves. Sound waves can be classified
into following three classes:

DIRECTIONAL SPEAKER
 Audible waves
 Infrasonic waves
 Ultrasonic waves
Figure 1.1: Classification of sound based on frequency
Audible waves:
The waves which can be heard by human ears are called audible waves. Their frequency
range extends from 20 Hz to 20 KHz but it may vary from person to person in accordance to his
age. Children and youth can hear sounds of up to 20 KHz frequency whereas the audible range of
old persons is lesser than 20 KHz.
The generally accepted standard range of audible frequencies is 20 to 20,000 HZ, although the
range of frequencies individuals hear is greatly influenced by environmental factors. Frequencies
below 20 Hz are generally felt rather than heard, assuming the amplitude of the vibration is great
enough. Frequencies above 20,000 Hz can sometimes be sensed by young people. High
frequencies are the first to be affected by hearing loss due to age and/or prolonged exposure to
very loud noises.
Infrasonic waves:
The study of such sound waves is sometimes referred to as infrasonic, covering sounds
beneath 20 Hz down to 0.1 Hz and rarely to 0.001 Hz. People use this frequency range for

DIRECTIONAL SPEAKER
monitoring earthquakes, charting rock and petroleum formations below the earth, and also in
ballistocardiography and seismocardiography to study the mechanics of the heart.
Infrasound is characterized by an ability to cover long distances and get around obstacles
with little dissipation. In music, acoustic waveguide methods, such as a large pipe organ or, for
reproduction, exotic loudspeaker designs such as transmission line, rotary woofer, or traditional
subwoofer designs can produce low-frequency sounds, including near-infrasound. Subwoofers
designed to produce infrasound are capable of sound reproduction an octave or more below that
of most commercially available subwoofers, and are often about 10 times the size.Waves having
a frequency of less than 20 Hz are called infrasonic waves. These waves cannot be heard by
human ears. These waves are produced by the vibration of huge bodies like the earth.
Ultrasonic waves:
Ultrasound is sound waves with frequencies higher than the upper audible limit of human
hearing. Ultrasound is no different from 'normal' (audible) sound in its physical properties, except
in that humans cannot hear it. This limit varies from person to person and is approximately 20
kilohertz (20,000 hertz) in healthy, young adults. Ultrasound devices operate with frequencies
from 20 kHz up to several gigahertzes.
Ultrasound is used in many different fields. Ultrasonic devices are used to detect objects
and measure distances. Ultrasound imaging or sonography is often used in medicine. In the
nondestructive testing of products and structures, ultrasound is used to detect invisible flaws.
Waves having frequency of more than 20 KHz are called ultrasonic waves. These waves
also cannot be heard by human ears, but can be heard by bats. The bat can hear waves of
frequencies up to 50 to 60 KHz and can produce such waves even.
These waves have proved to be very useful to mankind. These are used for
communications and for the determination of depth of sea. Besides it, these are used for
increasing agricultural yields, for improving the quality of seeds, for protection against insects
and in the field of treatment especially surgery.

DIRECTIONAL SPEAKER
1.1.4. Basic principles of sound
In all wave-producing sources, the directivity of any source, at maximum, corresponds to
the size of the source compared to the wavelengths it is generating: The larger the source is
compared to the wavelength of the sound waves, the more directional beam. The specific
transduction method has no impact on the directivity of the resulting sound field; the analysis
relies only on the aperture function of the source, per the Huygens–Fresnel principle.
In 1678, Huygens proposed that every point to which a luminous disturbance reaches
becomes a source of a spherical wave. The sum of these secondary waves determines the form of
the wave at any subsequent time. He assumed that the secondary waves travelled only in the
"forward" direction and it is not explained in the theory why this is the case. He was able to
provide a qualitative explanation of linear and spherical wave propagation.
1.1.5. Interference of sound
When two waves meet, there can be two kinds of interference patterns; constructive and
destructive. Constructive interference is when two waveforms are added together. The peaks add
with the peaks, and the troughs add with the troughs, creating a louder sound. Destructive
interference occurs when two waves are out of phase (the peaks on one line up with troughs on
the other). In this, the peaks cancel out the troughs, creating a diminished waveform. For example,
if two waveforms that are exactly the same are added, the amplitude doubles, but when two
opposite waveforms are added, they cancel out, leaving silence. In acoustics, a beat is an
interference pattern between two sounds of slightly different frequencies, perceived as a periodic
variation in volume whose rate is the difference of the two frequencies.
When tuning instruments that can produce sustained tones, beats can be readily
recognized. Tuning two tones to unison will present a peculiar effect: when the two tones are
close in pitch but not identical, the difference in frequency generates the beating. The volume
varies like in a tremolo as the sounds alternately interfere constructively and destructively. As the
two tones gradually approach unison, the beating slows down and may become as slow as to be
imperceptible.

DIRECTIONAL SPEAKER
This phenomenon is best known in acoustics or music, though it can be found in any
linear system. "According to the law of superposition, two tones sounding simultaneously are
superimposed in a very simple way: one adds their amplitudes". If a graph is drawn to show the
function corresponding to the total sound of two strings, it can be seen that maxima and minima
are no longer constant as when a pure note is played, but change over time: when the two waves
are nearly 180 degrees out of phase the maxima of one wave cancel the minima of the other,
whereas when they are nearly in phase their maxima sum up, raising the perceived volume.
The two waves are in phase and they interfere constructively. When it is zero, they are out
of phase and interfere destructively. Beats occur also in more complex sounds, or in sounds of
different volumes, though calculating them mathematically is not so easy.
A harmonic is any member of the harmonic series, a divergent infinite series. Its name
derives from the concept of overtones, or harmonics in musical instruments: the wavelengths of
the overtones of a vibrating string or a column of air (as with a tuba) are derived from the strings
(or air columns) fundamental wavelength. Every term of the series (i.e., the higher harmonics)
after the first is the "harmonic mean" of the neighboring terms. The phrase "harmonic mean"
likewise derives from music.
The extent to which nonlinear acoustical effects are strong or even significant depends on
the competing influences of energy loss, frequency dispersion, geometric spreading, and
diffraction. When conditions are such that nonlinear effects are strong, acoustic signals may
experience substantial waveform distortion and changes in frequency content as they propagate,
and shock waves may be present. Nonlinear acoustical effects occur in gases, liquids, and solids
and they are observed over a broad range of frequencies. Shock waves present in sonic booms
and thunder claps are in the audio frequency range. Principles of nonlinear acoustics form the
basis for procedures at megahertz frequencies used in medical ultrasound and nondestructive
evaluation of materials. Nonlinearity can also induce changes in nonfluctuating properties of the
medium. These include acoustic streaming, which is the steady fluid flow produced by the
absorption of sound, and radiation pressure, which results in a steady force exerted by sound on
its surroundings

DIRECTIONAL SPEAKER
The term harmonic is employed in various disciplines, including music, physics, acoustics,
electronic power transmission, radio technology, and other fields. It is typically applied to
repeating signals, such as sinusoidal waves. A harmonic of such a wave is a wave with a
frequency that is a positive integer multiple of the frequency of the original wave, known as the
fundamental frequency. The original wave is also called the 1st harmonic, the following
harmonics are known as higher harmonics. As all harmonics are periodic at the fundamental
frequency, the sum of harmonics is also periodic at that frequency. For example, if the
fundamental frequency is 50 Hz, a common AC power supply frequency, the frequencies of the
first three higher harmonics are 100 Hz (2nd harmonic), 150 Hz (3rd harmonic), 200 Hz (4th
harmonic) and any addition of waves with these frequencies is periodic at 50 Hz.
In music, harmonics are used on string instruments and wind instruments as a way of
producing sound on the instrument, particularly to play higher notes and, with strings, obtain
notes that have a unique sound quality or "tone color". On strings, harmonics that are bowed have
a "glassy", pure tone. On stringed instruments, harmonics are played by touching (but not fully
pressing down the string) at an exact point on the string while sounding the string (plucking,
bowing, etc. This allows the harmonic to sound, a pitch which is always higher than the
fundamental frequency of the string.
Harmonics may also be called "overtones", "partials" or "upper partials". The difference
between "harmonic" and "overtone" is that the term "harmonic" includes all of the notes in a
series, including the fundamental frequency (e.g., the open string of a guitar). The term
"overtone" only includes the pitches above the fundamental. In some music contexts, the terms
"harmonic", "overtone" and "partial" are used fairly interchangeably.
1.2. PRINCIPLE OF DIRECTIONAL SPEAKER
There are two principles are need to follow in order to get directional speaker effect they
are: First, sound waves are directional if the width of the wave front is larger than the wavelength.
Second, ultrasonic sound waves will demodulate in air. The resulting audible sound is much
quieter than the ultrasound that generates it.

DIRECTIONAL SPEAKER
The ultrasonic devices achieve high directivity by modulating audible sound onto high
frequency ultrasound. The higher frequency sound waves have a shorter wavelength and thus
don't spread out as rapidly. For this reason, the resulting directivity of these devices is far higher
than physically possible with any loudspeaker system. However, they are reported to have limited
low-frequency reproduction abilities. See sound from ultrasound for more information.
Figure 1.2: Directional Sound wave front vs. Spherical wave front
Nonlinear effects in ultrasound propagation can be used for generating highly
directive audible sound. In order to do so, we can modulate the amplitude of the audio
signal and send it to an ultrasound transducer. When played back at a sufficiently high
sound pressure level, due to a nonlinear behavior of the medium, the ultrasonic signal
gets self-demodulated. The resulting signal has two important characteristics: that of
becoming audible; and that of having the same directivity properties of the ultrasonic
carrier frequency.
If one sends out two frequencies with high frequency and amplitude into an nonlinear
medium, in our case air, a third frequency can be heard, namely the difference frequency. In this

DIRECTIONAL SPEAKER
thesis this phenomenon will be shown both theoretically and by measurement on a speaker,
which was constructed within the project. There are many advantages of creating sound this way
instead of the ordinary way. One of the advantages is that the sound that is created is very
directed even of low frequencies. The directivity of sound is a problem in conventional speaker.
The problem is that the low frequencies, is spreading in almost all directions in the room, and the
higher frequencies are more directed. If one instead creates sound by sending out ultrasonic
frequencies the nonlinearly created audible sound get the same directivity as the ultrasonic
frequencies, which have a very narrow spreading beam. A simile can be done with a light bulb
and a torch, the conventional speaker radiates the sound like a light bulb is radiates the light, the
ultrasonic speaker is on the other hand radiating the sound more like a torch or a spotlight.
The directivity of a speaker that creates sound using ultrasound can be a huge advantage
in for example a museum where you only want the people in front of a particular painting to hear
the information of that painting, and the rest of the visitors can concentrate on the other parts of
the exhibition. Another interesting advantage is that the speaker can be built very thin and that
can be of commercial interest in these days of flat screen TVs.

DIRECTIONAL SPEAKER
CHAPTER - 2
THEORY IN TO THE DEPTHS OF DIRECTIONAL SPEAKER
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 are 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 in
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 cm 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 “DIRECTIONAL SPEAKER”

DIRECTIONAL SPEAKER
invented by Holosonics Labs founder Dr. F. Joseph Pompei (while a graduate student at MIT),
who is the master brain behind the development. 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.
2.1. TECHNOLOGY OVERVEIW
The Audio Spotlight & Hyper Sonic Sound Technology (developed by American
Technology Corporation), uses ultrasonic energy to create extremely narrows beams of sound
that behave like beams of light. Ultrasonic sound is that sound that has very small wavelength—
in the millimeter range and you can’t hear ultrasound since it lies beyond the threshold of human
hearing.
Figure 2.1: Block diagram of directional speaker
2.2. COMPONENTS AND SPECIFICATION
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

DIRECTIONAL SPEAKER
(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.
2.2.1. Sound beam amplifier
Sound beam processor/Amplifier is a circuit that can enhance the audio signal to the array
of transducer.
 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 e.g. Multichannel.
2.2.2 Directional speaker transducer
The construction of the piezoelectric transducers used for the octagonal array is shown in
Figure. This type of transducer depends on the resonance properties of the piezoelectric material
itself (the PZT layer in the figure), the radiating cone (which is needed to match the high
impedance of the PZT material to the much lower impedance of air), and the air cavity. Correctly
used, this approach results in a fairly wide-band transducer (typically about 5 kHz), depending on
the choice of resonance frequencies.

DIRECTIONAL SPEAKER
Figure 2.2: Construction of the piezoelectric transducer used for the octagonal array.
 17.5”/445mm diameter, 1/2”/12.7mm thick, 4lbs/1.82kg.
 Wall, overhead or flush mounting, Black cloth cover standard, other colors 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 real-time sound reproduction - no processing lag
 Compatible with standard loudspeaker mounting accessories Due to continued
development, specifications are subject to change.

DIRECTIONAL SPEAKER
CHAPTER - 3
NON-LINEARITY PROPERTY OF AIR
A sound wave propagates through a material as a localized pressure change. Increasing
the pressure of a gas or fluid increases its local temperature. The local speed of sound in a
compressible material increases with temperature; as a result, the wave travels faster during the
high pressure phase of the oscillation than during the lower pressure phase. This affects the
wave's frequency structure; for example, in an initially plane sinusoidal wave of a single
frequency, the peaks of the wave travel faster than the troughs, and the pulse becomes
cumulatively more like a saw tooth wave. In other words, the wave self-distorts. In doing so,
other frequency components are introduced, which can be described by the Fourier series. This
phenomenon is characteristic of a non-linear system, since a linear acoustic system responds only
to the driving frequency. This always occurs but the effects of geometric spreading and of
absorption usually overcome the self distortion, so linear behavior usually prevails and nonlinear
acoustic propagation occurs only for very large amplitudes and only near the source. Additionally,
waves of different amplitudes will generate different pressure gradients, contributing to the non-
linear effect.
The extent to which nonlinear acoustical effects are strong or even significant depends on
the competing influences of energy loss, frequency dispersion, geometric spreading, and
diffraction. When conditions are such that nonlinear effects are strong, acoustic signals may
experience substantial waveform distortion and changes in frequency content as they propagate,
and shock waves may be present. Nonlinear acoustical effects occur in gases, liquids, and solids
and they are observed over a broad range of frequencies. Shock waves present in sonic booms
and thunder claps are in the audio frequency range. Principles of nonlinear acoustics form the
basis for procedures at megahertz frequencies used in medical ultrasound and nondestructive
evaluation of materials. Nonlinearity can also induce changes in no fluctuating properties of the
medium. These include acoustic streaming, which is the steady fluid flow produced by the
absorption of sound, and radiation pressure, which results in a steady force exerted by sound on
its surroundings.

DIRECTIONAL SPEAKER
The wave equations, which are usually used in solutions to acoustical problems, are valid
only when the signal propagation is relatively small. In the derivation of these formulas the
maximum displacement of the air particles is assumed to be small compared to the wavelength.
This makes the density appear to be a linear function of the pressure. When these assumptions are
no longer valid the wave will change shape as it propagates in the medium. Each part of the wave
travels with a velocity that is the sum of the signal velocity and the particle velocity. In other
words the peaks travel with a higher velocity than the rest of the wave. This makes the wave
deforming as it propagates. In this thesis the fact that the non-linearity in air creates new
frequencies if at least two frequencies are sent in to air is very important.
Directional speaker 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 specialized 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. 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 range of human hearing is expressed as a percentage of shifts from
the lowest audible frequency to the highest, it spans a range of 100,000%. No single loudspeaker

DIRECTIONAL SPEAKER
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. (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. For example, if a loudspeaker only needed to operate from 1000 to 1100 Hz
(10%), an almost perfect transducer could be designed.
This is similar to 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.
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.

DIRECTIONAL SPEAKER
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 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.
3.1. MODULATION SCHEMES FOR GETTING DIRECTIONAL SOUND
Standard amplitude modulation has always played and still plays a major role in
parametric array studies. Among the modulation schemes, AM is one of the simplest to
understand and implement. It is well known that AM can be achieved by multiplying the
sinusoidal carrier by a modulating (information-carrying) signal, which in our case is the audio
signal. The spectrum of the modulated signal has two sidebands, symmetric with respect to the
carrier frequency, and the carrier itself. The AM envelope can be thought of as the audio
modulating signal. The receiver of the AM modulated signal is as simple as a peak detector. Two
things can be inferred from this. First of all, it is reasonable to use Berktay’s work based on the
envelope of the primary signal to have a simple and basic model for the difference frequency
pressure; in AM, the envelope is the difference pressure signal since the envelope is a base band
(i.e. audio band) signal.
Second, more important for commercial applications, nonlinear interaction happens
between all the frequency components of the AM signal causing distortion.
We should distinguish between two types of distortion. One can be considered an intra-sideband
distortion and the other inter-sideband distortion. The intra-sideband distortion is caused by
different frequency components that subtract each other within a specific sideband. Although its
impact is not negligible, this type of distortion has not been studied in this work. Inter sideband

DIRECTIONAL SPEAKER
distortion, on the other hand, is the interaction between the frequency components of two
different sidebands. The two sidebands interact and more distortion is added to the demodulated
signal. This inter sideband distortion can be reduced. Propose a pre-processing algorithm to
reduce the inter sideband distortion. This algorithm is used in most published applications of the
parametric array loudspeaker. It is interesting for the goals of this study to understand what
distortion this algorithm reduces and how it does this. Kite’s algorithm is based on Berktay’s
model [2,6], as it simply applies the opposite operations present in Berktay’s model. According to
the model, a collimated wave consisting of amplitude modulated wave of pressure.
Figure 3.1: Model diagram of directional speaker
In the Directional speaker application one needs to add the carrier to generate the
difference frequencies in the audio band. Thus we used a so-called SSB-WC signal (single-
sideband with carrier), which means we added the carrier (acoustically or electrically) just after
the standard SSB modulation. Having just one sideband, we do not need to be as concerned with
inter-sideband distortion, therefore we do not need to use
Kite’s pre-processing. Moreover it may be interesting to be able to choose which sideband to use
according to the frequency response characteristic of the transducer array and the absorption of
the transmitting channel. One more rather obvious advantage of a
SSB approach is that it uses the available bandwidth more efficiently than the double sideband
approach. In the next section we will show some measurements done to compare AM and SSB
performance.

DIRECTIONAL SPEAKER
3.2. 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.
Hyper Sonic Sound technology 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. 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.
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.

DIRECTIONAL SPEAKER
CHAPTER - 4
APPLICATIONS OF DIRECTIONAL SPEAKER -TOWARDS THE
FUTURE
"So you can control where your sound comes from and where it goes," says Joe Pompei,
the inventor of Directional speaker (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. The technology that the Holosonics
Research Labs and the American Technology Corporation are lining up may seem to be a novelty
of sorts, but a wide range of applications are being targeted at it.
Continuing to improve on the commercial success of the directional speaker 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 directional speaker have made it the choice of
the Smithsonian Institution, Motorola, Kraft, and Cisco Systems etc. 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. Holosonic has installed their directional
speaker system at Tokyo’s Sega Joy polis theme park. The US Navy has installed sound beaming

DIRECTIONAL SPEAKER
technology on the deck of an Aegis-class Navy destroyer, and is looking at this as a substitute to
the radio operator’s headphones.
4.1. ADVANTAGES OF DIRECTIONAL SPEAKER OVER NORMAL SPEAKER
 Sound pollution can be reduced
 Can focus sound only at the place we want.
 The directed sound travel much faster.
 Dispersion can be controlled.
 The speaker can be build very thin and that can be of commercially in these days of flat
screen TV’s.
 Longer life span
 Requires same power as required for regular speaker.
 There is no latch when reproducing the sound.

DIRECTIONAL SPEAKER
CHAPTER - 5
CONCLUSIONS AND FUTURE PERSPECTIVES
Directional speakers can be used to create spatially limited local audio environments
without the acoustic isolation and mechanical stress pressing the ears caused by the traditional
headphones. Currently directional speakers are planar or parabolic-shaped or they are based on
modulated ultrasound. However, as even highly directional speakers radiate some sound outside
the desired area, they are most suitable for environments with enough ambient noise masking the
leaking sound. The directivity of speakers based on audible sound improves as the diameter of
the speaker is increased. Thus, either the directivity or the compact size of the speaker has to be
prioritized. Ultrasonic speakers enable improving the speaker’s directivity while maintaining a
compact size by increasing frequency of the signal transmitted. Currently, the main obstacles in
effectively adapting ultrasonic speaker technology are the speakers’ distortion due to sidebands
created in the modulation, poor low-frequency performance and high power consumption.
Possible areas of application for local audio include information and advertisement audio in
commercial spaces, guiding and narration in museums and exhibitions, office space
personalization, control room messaging, proactive rehabilitation environments, and
entertainment audio systems. However, more research and product development is still needed to
further improve the sound quality and directivity of the speakers as well as their compactness and
adaptability to various installation environments. The theoretical advantages of single-sideband
(SSB) modulation versus a standard amplitude modulation (AM) are shown to hold in practice.
The use of standard, commercially available piezoelectric transducers leads to problems of
narrow bandwidth, distortion, and large side lobes. Future work must focus on better adapted
transducers, arrays, and beam steering methods to circumvent these problems, and will require a
multidisciplinary approach scientifically and technologically.
To implement the parametric array loudspeaker algorithm, a possible solution already
investigated is the use of field-programmable gate-arrays (FPGAs), digital logic chips with some
interesting features. These are based on parallel signal processing, they are reprogrammable, they
can change their functions from time to time, and they have a shorter time to market. In 2004

DIRECTIONAL SPEAKER
successfully implemented an AM-based parametric loudspeaker system in a FPGA, using Kite’s
algorithmic distortion reduction.
In our proposed system the FPGA would be used to perform both the SSB-WC
modulation and the array beam steering. As mentioned previously, no distortion reduction
algorithm is needed distortion if SSB-WC is used. For the beam steering many different solutions
are possible. These can be roughly divided into two categories, implementation of amplitude
shading and time delays 1) by DSP, as described in the previous section, or 2) by mechanical
techniques. The first solution for beam steering requires a matrix of transmitting elements that are
addressable and algorithmically controlled. Piezoelectric or electrostatic transducers can be
adapted to these needs.
The second solution can be itself further divided into two subgroups, depending whether
we work on the transducer or on the sound beam. So, a) with mechanical means it would be
possible to move the surface on which the transducer is built, or b) it would be possible to have a
mirror that reflects the sound beam to a chosen direction.

DIRECTIONAL SPEAKER
CHAPTER - 6
REFERENCES (BIBLIOGRAPHY)
1. www.holosonics.com
2. https://en.m.wikipedia.org/wiki/Directional_sound
3. https://en.m.wikipedia.org/wiki/Sound
4. https://en.m.wikipedia.org/wiki/Sound_from_ultrasound
5. https://en.m.wikipedia.org/wiki/Beat_(acoustics)
6. https://en.m.wikipedia.org/wiki/Auditory_masking
7. https://en.m.wikipedia.org/wiki/Nonlinear_acoustics
8. https://hackaday.io/project/9085/logs
9. http://asa.scitation.org/doi/abs/10.1121/1.389414
10. https://www.homemade-circuits.com/making-ultrasonic-directive-speaker/
11. https://www.google.com/patents/US6577738
12. http://www.zao.jp/radio/parametric/index_e.php
13. http://gbppr.dyndns.org/~gbpprorg/mil/speechjam/index.html

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