TABLE OF CONTENT

1.0 INTRODUCTION 1 The concept of sound 1

2.0 GENERAL PROPERTIES OF SOUND 3 2.1 frequency 3 2.2 Wavelength 4 2.3 Amplitude and intensity 5 2.4 Speed of sound in various media 6

3.0 DECIBEL LEVELS 7

4.0 SOUND QUALITY 8

5.0 BEHAVIOR OF SOUND WAVES 9 5.1 Reflection 9 5.2 Refraction 9 5.3 Diffraction 10 5.4 Echo 10 5.5 Reverberation 11

6.0 PRODUCTION OF SOUND WAVES 12 6.1 Musical instruments 12 6.2 Electronic amplification 12 6.3 The human voice 12

7.0 TYPES OF ORDINARY SOUND 13 7.1 Speech 13 7.2 Noise 13 7.3 Music 13

8.0 CONCLUSION 13

9.0 REFERENCES 13

Analysis of Sound ii

1.0 INTRODUCTION

THE CONCEPT OF SOUND

Sound is a disturbance of mechanical energy that propagates through matter as a longitudinal wave; it is a mechanical wave because it is characterized by these three attributes.

First, there is a medium which carries the disturbance from one location to another. Typically, this medium is air; though it could be any material such as water or steel. The medium is simply a series of interconnected and interacting particles.

Second, there is an original source of the wave, some vibrating object capable of disturbing the first particle of the medium. The vibrating object which creates the disturbance could be the vocal chords of a person, the vibrating string and sound board of a guitar or violin, the vibrating tines of a tuning fork, or the vibrating diaphragm of a radio speaker.

Third, the sound wave is transported from one location to another by means of the particle interaction. If the sound wave is moving through air, then as one air particle is displaced from its equilibrium position, it exerts a push or pull on its nearest neighbors, causing them to be displaced from their equilibrium position. This particle interaction continues throughout the entire medium, with each particle interacting and causing a disturbance of its nearest neighbors.

Humans perceive sound by the sense of hearing. By sound, we commonly mean the vibrations that travel through air and can be heard by humans. However, scientists and engineers use a wider definition of sound that includes low and high frequency vibrations in air that cannot be heard by humans, and vibrations that travel through all forms of matter, gases, liquids and solids. The scientific study of sound is called acoustics.

Analysis of Sound 1 The result of such longitudinal vibrations is the creation of compressions and rarefactions within the air. Regardless of the source of the sound wave - whether it be a vibrating string or the vibrating tines of a tuning fork - sound is a longitudinal wave. And the essential characteristic of a longitudinal wave which distinguishes it from other types of waves is that the particles of the medium move in a direction parallel to the direction of energy transport.

A propagating sound wave consists of alternating compressions and rarefactions which are detected by a receiver as changes in pressure. Structures in our ears, and also most man-made receptors, are sensitive to these changes in sound pressure (Richardson et al.1995, Gordon and Moscrop 1996).

Since a sound wave consists of a repeating pattern of high pressure and low pressure regions moving through a medium, it is sometimes referred to as a pressure wave. Sound is characterized by the properties of sound waves, which are frequency, wavelength, period, amplitude, and speed.

If a detector, whether it be the human ear or a man-made instrument is used to detect a sound wave, it would detect fluctuations in pressure as the sound wave impinges upon the detecting device. At one instant in time, the detector would detect a high pressure; this would correspond to the arrival of a compression at the detector site. At the next instant in time, the detector might detect normal pressure. And then finally a low pressure would be detected, corresponding to the arrival of a rarefaction at the detector site. Since the fluctuations in pressure as detected by the detector occur at periodic and regular time intervals, a plot of pressure vs. time would appear as a sine curve. The crests of the sine curve correspond to compressions; the troughs correspond to rarefactions; and the "zero point" corresponds to the pressure which the air would have if there were no disturbance moving through it (see figure 3)

Analysis of Sound 2 2.0 GENERAL PROPERTIES OF SOUND

Sound as a longitudinal wave is characterized by several features which are esoteric to longitudinal waves.

Any simple sound, such as a musical note, may be completely described by specifying three perceptual characteristics: pitch, loudness (or intensity), and quality (or timbre). These characteristics correspond exactly to three physical characteristics: frequency, amplitude, and harmonic constitution, or waveform, respectively.

2.1 FREQUENCY.

The frequency of a sound wave is the rate of oscillation or vibration of the wave particles (i.e. the rate amplitude cycles from high to low to high, etc.) The hertz (Hz) is a unit of frequency equaling one vibration or cycle per second (1 Hertz = 1 vibration/second).

The Audible frequency range: the human ear is capable of detecting sound waves with a wide range of frequencies, ranging between approximately 20 Hz to 20 000 Hz. Any sound with a frequency below the audible range of hearing (i.e., less than 20 Hz) is known as an infrasound and any sound with a frequency above the audible range of hearing (i.e., more than 20 000 Hz) is known as an ultrasound. Such vibrations reach the inner ear when they are transmitted through air.

The frequency of a wave refers to how often the particles of the medium vibrate when a wave passes through the medium. This frequency is measured as the number of complete back-and-forth vibrations of a particle of the medium per unit of time. If a particle of air undergoes 1000 longitudinal vibrations in 2 seconds, then the frequency of the wave would be 500 vibrations per second.

As a sound wave moves through a medium, each particle of the medium

vibrates at the same frequency. Subsequently, a guitar string vibrating at 500 Hz will set the air particles in the room vibrating at the same frequency of 500 Hz which carries a sound signal to the ear of a listener which is detected as a 500 Hz sound wave.

Analysis of Sound 3 Sound Frequency and Pitch:

The sensations of these frequencies are commonly referred to as the pitch of a sound. A high pitch sound corresponds to a high frequency and a low pitch sound corresponds to a low frequency. Amazingly, many people, especially those who have been musically trained, are capable of detecting a difference in frequency between two separate sounds which is as little as 2 Hz.

When two sounds with a frequency difference of greater than 7 Hz are played simultaneously, most people are capable of detecting the presence of a complex wave pattern resulting from the interference and superposition of the two sound waves. Certain sound waves when played (and heard) simultaneously will produce a particularly pleasant sensation when heard, they are said to be consonant.

2.2 WAVELENGTH

Wavelength (represented by the symbol λ, the Greek letter lambda) is the distance between a crest and the adjacent crest, or a trough and an adjacent trough, of a wave (see figure 4).

A wave of very high frequency would produce a corresponding short wave length while a wave of low frequency would produce a large wavelength. Thus, a frequency of 20 Hz, at the bottom end of human audibility, has a very large wavelength: 56 ft (17 m). The top end frequency of 20,000 Hz is only 0.67

inches (17 mm).

The wavelengths of sounds in the range of human audibility are comparable to the size of ordinary objects. To block out a sound wave, one needs something of much greater dimensions—width, height, and depth—than a mere cloth curtain. A thick concrete wall, for instance, may be enough to block out the

Analysis of Sound 4 waves. Better still would be the use of materials that absorb sound, such as cork, or even the use of machines that produce sound waves which destructively interfere with the offending sound.

2.3 AMPLITUDE AND INTENSITY

Amplitude is critical to the understanding of sound, though it is mathematically independent from the parameters so far discussed. Amplitude is defined as the maximum displacement of a vibrating material from its mean or rest position, amplitude is the "size" of a wave. The greater the amplitude, the greater the energy the wave contains: amplitude indicates intensity, commonly known as "volume," which is the rate at which a wave moves energy per unit of a cross-sectional area.

The greater the amplitude of the wave, the harder the molecules strikes the eardrum and the louder the sound that is perceived. The amplitude of a sound wave can be expressed in terms of absolute units by measuring the actual distance of displacement of the air molecules, the changes in pressure as the wave passes, or the energy contained in the wave.

Intensity of a sound wave is the amount of energy which is transported past a given area of the medium per unit of time. The greater the amplitude of vibrations of the particles of the medium, the greater the rate at which energy is transported through it, and the more intense that the sound wave is. Intensity is the energy/time/area; and since the energy/time ratio is equivalent to the quantity power, intensity is simply the power/area.

Intensity can be measured in watts per square meter, or W/m2. A sound wave of minimum intensity for human audibility would have a value of 10−12, or 0.000000000001, W/m2. As a basis of comparison, a person speaking in an ordinary tone of voice generates about 10−4, or 0.0001, watts. On the other

Analysis of Sound 5 hand, a sound with an intensity of 1 W/m2 would be powerful enough to damage a person's ears.

While the intensity of a sound is a very objective quantity which can be measured with sensitive instrumentation, the loudness of a sound is more of a subjective response which will vary with a number of factors. The same sound will not be perceived to have the same loudness to all individuals.

Age is one factor which affects the human ear's response to a sound. Quite obviously, your grandparents do not hear like they used to. The same intensity sound would not be perceived to have the same loudness to them as it would to you. Furthermore, two sounds with the same intensity but different frequencies will not be perceived to have the same loudness. Because of the human ear's tendency to amplify sounds having frequencies in the range from 1000 Hz to 5000 Hz, sounds with these intensities seem louder to the human ear. Despite the distinction between intensity and loudness, it is safe to state that the more intense sounds will be perceived to be the loudest sounds.

2.4 THE SPEED OF SOUND IN VARIOUS MEDIA

People often refer to the "speed of sound" as though this were a fixed value like the speed of light, but, in fact, the speed of sound is a function of the medium through which it travels. What people ordinarily mean by the "speed of sound" is the speed of sound through air at a specific temperature. For sound traveling at sea level, the speed at 32°F (0°C) is 740 MPH (331 m/s), and at 68°F (20°C), it is 767 MPH (343 m/s).

The speed of sound for aircraft is given at 660 MPH (451 m/s). This is much less than the figures given above for the speed of sound through air at sea level, because obviously, aircraft are not flying at sea level, but well above it, and the air through which they pass is well below freezing temperature.

The speed of sound through a gas is proportional to the square root of the pressure divided by the density. According to Gay-Lussac's law, pressure is directly related to temperature, meaning that the lower the pressure, the lower the temperature—and vice versa. At high altitudes, the temperature is

Analysis of Sound 6 low, and, therefore, so is the pressure; and, due to the relatively small gravitational pull that Earth exerts on the air at that height, the density is also

low. Hence, the speed of sound is also low.

It follows that the higher the pressure of the material, and the greater the density, the faster sound travels through it: thus sound travels faster through a liquid than through a gas. This might seem a bit surprising: at first glance, it would seem that sound travels fastest through air, but only because we are just more accustomed to hearing sounds that travel through that medium. The speed of sound in water varies from about 3,244 MPH (1,450 m/s) to about 3,355 MPH (1500 m/s). Sound travels even faster through a solid—typically about 11,185 MPH (5,000 m/s)—than it does through a liquid.

3.0 DECIBEL LEVELS

For measuring the intensity of a sound as experienced by the human ear, we use a unit other than the watt per square meter, because ears do not respond to sounds in a linear, or straight-line, progression. If the intensity of a sound is doubled, a person perceives a greater intensity, but nothing approaching twice that of the original sound. Instead, a different system— known in mathematics as a logarithmic scale—is applied.

In measuring the effect of sound intensity on the human ear, a unit called the decibel (abbreviated dB) is used. A sound of minimal audibility (10−12 W/m2) is assigned the value of 0 dB, and 10 dB is 10 times as great—10−11 W/m2. But 20 dB is not 20 times as intense as 0 dB; it is 100 times as intense, or 10−10 W/m2. Every increase of 10 dB thus indicates a tenfold increase in intensity. Therefore, 120 dB, the maximum decibel level that a human ear can endure without experiencing damage, is not 120 times as great as the minimal level for audibility, but 1012 (1 trillion) times as great—equal to 1 W/m2, referred to

above as the highest safe intensity le vel.

Of course, sounds can be much louder than 120 dB: a rock band, for instance, can generate sounds of 125 dB, which is 5 times the maximum safe decibel level. A gunshot, firecracker, or a jet—if one is exposed to these sounds at a sufficiently close proximity—can be as high as 140 dB, or 20 times the maximum safe level. Nor is 120 dB safe for prolonged periods: hearing experts indicate that regular and repeated exposure to even 85 dB (5 less than a lawn mower) can cause permanent damage to one's hearing.

Analysis of Sound 7 Intensity # of Times Source Intensity Level Greater Than Threshold Of Hearing

Threshold of Hearing (TOH) 1*10-12 W/m2 0 dB 100 Rustling Leaves 1*10-11 W/m2 10 dB 101 Whisper 1*10-10 W/m2 20 dB 102 Normal Conversation 1*10-6 W/m2 60 dB 106 Busy Street Traffic 1*10-5 W/m2 70 dB 107 Vacuum Cleaner 1*10-4 W/m2 80 dB 108 Large Orchestra 6.3*10-3 W/m2 98 dB 109.8 Walkman at Maximum Level 1*10-2 W/m2 100 dB 1010 Front Rows of Rock Concert 1*10-1 W/m2 110 dB 1011 Threshold of Pain 1*101 W/m2 130 dB 1013 Military Jet Takeoff 1*102 W/m2 140 dB 1014 Instant Perforation of Eardrum 1*104 W/m2 160 dB 1016

Table1. List of some common sounds with an estimate of their intensity and decibel levels.

4.0 SOUND QUALITY

“Sound Quality is a perceptual reaction to the sound of a product that reflects the listener’s reaction to how acceptable the sound of that product is: the more acceptable, the greater the Sound Quality.” (R. H. Lyon) another definition states “The term Product Sound Quality refers to the adequacy of the sound from a product. This is evaluated on the basis of the totality of the sound’s auditory characteristics, with reference to the set of desirable product features that are apparent in the user’s cognitive and emotional situation.” (C. L. Fog and T. H. Pederson)

Generally speaking most working definitions include the concept of the audible suitability of a product when compared with a user’s expectation. Sound quality testing is an important design concept in the automobile and audio industries. Marketing studies in these areas can demonstrate a relationship between sound and non-auditory concepts e.g. luxury, power, speed, safety, expense making the sound of a product an important design consideration. Sound quality development itself should be an integral part of the design process and test methods should be part of the overall decision making process for product suitability.

Analysis of Sound 8 5.0 BEHAVIOR OF SOUND WAVES

Sound as a wave exhibits certain behaviors when subjected to certain conditions. These various behaviors are a function of the properties of sound waves which have been discussed in the previous sections. Like every other wave, sound does not stop or disappear when it gets to the end of a medium or when it encounters an obstacle. The subsequent sections will give a succinct analysis of the behaviors of sound in media.

5.1 REFLECTION

Reflection, in physics, is a phenomenon of wave motion, in which a wave is returned after impinging on a surface.

To reflect a wave train, the reflecting surface must be wider than one-half the wavelength of the impinging waves. For example, a pile rising above the surface of the ocean may reflect ripples, but long waves pass around it. Shrill noises, which have very short wavelengths, are reflected by a thin windowpane, but sounds of longer wavelength pass through it. Small particles of dust in the atmosphere may reflect only the shorter blue wavelengths in sunlight.

5.2 REFRACTION

Refraction of waves involves a change in the direction of waves as they pass from one medium to another. Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. So if the medium (and its properties) are changed, the speed of the waves is changed. Thus waves passing from one medium to another will undergo refraction.

Refraction of sound waves is most evident in situations in which the sound wave passes through a medium with gradually varying properties. For example, sound waves are known to refract when traveling over water. Even though the sound wave is not exactly changing media, it is traveling through a medium with varying properties; thus, the wave will encounter refraction and change its direction.

Since water has a moderating effect upon the temperature of air, the air directly above the water tends to be cooler than the air far above the water. Sound waves travel slower in cooler air than they do in warmer air. For this

Analysis of Sound 9 reason, the portion of the wave-front directly above the water is slowed down, while the portion of the wave- fronts far above the water speeds ahead. Subsequently, the direction of the wave changes, refracting downwards towards the water. This is depicted in the diagram at the right.

5.3 DIFFRACTION

Diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path.

Water waves have the ability to travel around corners, around obstacles and through openings. The amount of diffraction (the sharpness of the bending) increases with increasing wavelength and decreases with decreasing wavelength. In fact, when the wavelength of the waves is smaller than the obstacle or opening, no noticeable diffraction occurs.

Diffraction of sound waves is commonly observed; we notice sound diffracting around corners or through door openings, allowing us to hear others who are speaking to us from adjacent rooms. Many forest-dwelling birds take advantage of the diffractive ability of long-wavelength sound waves. Owls for instance are able to communicate across long distances due to the fact that their long- wavelength hoots are able to diffract around forest trees and carry farther than the short-wavelength tweets of song birds. Low-pitched (long wavelength) sounds always carry further than high pitched (short wavelength) sounds.

Reflection of sound waves off of surfaces can lead to one of two phenomenon - an echo or a reverberation.

5.4 ECHO

An echo is a reflected sound wave. The perceptible gap between the emission and repeat of the sound represents the time it takes waves to travel to an obstacle and back. The echoed sound is often fainter because not all of the original waves are reflected. Generally, echoes such as those heard in the mountains are caused by sound waves striking large surfaces 30 m (99 ft) or more away from their source. An echo in a different medium, such as a steel

Analysis of Sound 10 pipe, may be created and observed by rapping the metal when the ear is against it.

5.5 REVERBERATION

A reverberation often occurs in a small room with height, width, and length dimensions of approximately 17 meters or less. Why the magical 17 meters? The effect of a particular sound wave upon the brain endures for more than a tiny fraction of a second; the human brain keeps a sound in memory for up to 0.1 seconds. If a reflected sound wave reaches the ear within 0.1 seconds of the initial sound, then it seems to the person that the sound is prolonged. The reception of multiple reflections off of walls and ceilings within 0.1 seconds of each other causes reverberations - the prolonging of a sound. Since sound waves travel at about 340 m/s at room temperature, it will take approximately 0.1 s for a sound to travel the length of a 17 meter room and back, thus causing a reverberation

Time (t) = velocity (v)/distance (d) = (340 m/s)/ (34 m) = 0.1 s).

This is why reverberations are common in rooms with dimensions of approximately 17 meters or less. Perhaps you have observed reverberations when talking in an empty room, when honking the horn while driving through a highway tunnel or underpass, or when singing in the shower. In auditoriums and concert halls, reverberations occasionally occur and lead to the displeasing garbling of a sound.

Reflection of sound waves in auditoriums and concert halls do not always lead to displeasing results, especially if the reflections are designed right. Smooth walls have a tendency to direct sound waves in a specific direction. Subsequently the use of smooth walls in an auditorium will cause spectators to receive a large amount of sound from one location along the wall; there would be only one possible path by which sound waves could travel from the speakers to the listener. The auditorium would not seem to be as lively and full of sound. Rough walls tend to diffuse sound, reflecting it in a variety of directions. This allows a spectator to perceive sounds from every part of the room, making it seem lively and full. For this reason, auditorium and concert hall designers prefer construction materials which are rough rather than smooth.

Analysis of Sound 11 When a sound is produced in a room, sound waves spread from the source in spherical waves. When these waves strike a surface, some will be reflected. This reflected sound continues spreading until it strikes another surface which reflects it again and so on. This continues even after the actual source has ceased producing sound. However, some of the sound is absorbed at every reflection and the sound energy reduces progressively until the sound becomes inaudible. Reverberation time is the number of seconds required for the energy of the reflected sound in a room to diminish to one millionth of the original energy it had. It can also be defined as the number of seconds required for the sound pressure level to diminish to 60 decibels below its initial value.

6.0 PRODUCTION OF SOUND WAVES

6.1 Musical Instruments

Sound waves are vibrations; thus, in order to produce sound, vibrations must be produced. For a stringed instrument, such as a guitar, harp, or piano, the strings must be set into vibration, either by the musician's fingers or the mechanism that connects piano keys to the strings inside the case of the piano.

6.2 Electronic Amplification

Sound is a form of energy, hence it implies that it can be converted to other forms of energy, and this is precisely what a microphone does: it receives sound waves and converts them to electrical energy. These electrical signals are transmitted to an amplifier, and next to a loudspeaker, which turns electrical energy back into sound energy—only now; the intensity of the sound is much greater.

6.3 The Human Voice

Speech is essentially a matter of producing vibrations on the vocal cords, and then transmitting those vibrations. The sound of a person's voice is affected by a number of factors: the size and shape of the sinuses and other cavities in the head, the shape of the mouth, and the placement of the teeth and tongue. These factors influence the production of specific frequencies of sound, and result in differing vocal qualities. Again, the mechanisms of speech are highly complicated, involving action of the diaphragm (a partition of muscle and tissue between the chest and abdominal cavities), larynx, pharynx, glottis, hard and soft palates, and so on. But, it all begins with the production of vibrations.

Analysis of Sound 12 7.0 TYPES OF ORDINARY SOUND

7.1 Speech

Speech contains a complex mixture of sounds, some (but not all) of which are in harmonic relation to one another. A person's speech/voice is affected by a number of factors: the size and shape of the sinuses and other cavities in the head, the shape of the mouth, and the placement of the teeth and tongue. These factors influence the production of specific frequencies of sound, and result in differing vocal qualities. The complex mechanism of is still tethered to the production of vibrations.

7.2 Noise

Noise is simply unwanted or damaging sound. Noise consists of a mixture of many different frequencies within a certain range; it is thus comparable to white light, which consists of a mixture of light of all different colors. Different noises are distinguished by different distributions of energy in the various frequency ranges.

7.3 Music

A musical note contains, in addition to a fundamental frequency, higher tones that are harmonics of the fundamental frequency. It is a subjective kind of sound as one’s music could be noise to another.

8.0 CONCLUSION

A comprehensive understanding of Sound and its concomitant properties is an inevitable aspect of architecture and “Science” in general. It applications in everyday life can’t be overstated. Ranging from design of buildings structures (auditoriums, lecture halls, music studios) to product design (auto-mobiles, machines), to oceanography (study of life in the seas and their means of communication) and down to musical instruments (the Guitar, piano etc.) the analysis of sound has always proved crucial.

9.0 REFERENCES

Diamant, R. M. E. (1986) Thermal and Acoustic Insulation. Butterworths, London. Microsoft ® Encarta ® 2007. © 1993-2006 Microsoft Corporation http://www.wikipedia.com, http://www.oceanexplorer.noaa.gov,

Analysis of Sound 13