18 SOUND AND NOISE

S. Visalakshi Rajeswari

epgp books

 

 

Introduction

 

Human beings are bombarded with sounds of various types from the moment one wakes up. People are at all times surrounded with hundreds of various sounds which are also distinctly identifiable.

 

1.          Objectives

 

·         Impart knowledge on how sound is perceived

·         Factors contributing to sound transmission

·         Concern for control of sound in the interior

 

2.          Perception of sound

 

All species have a different range of hearing and a purpose when sound is perceived

 

  • Perception as a vibration: Dogs can perceive vibrations, much above the maximum for human beings (20 KHz), but cannot hear below 40 Hz.
  • Perception as a signal: As a cue sound is perceived by the ear, a major sense organ for communication. It is used by animals and birds as danger signal; aids for movement, locating preys, and as a mode of inter communication.
  •  Perception of nature and natural events: Natural occurrences in the atmosphere, all physically evident phenomena, such as forest fire, torrential rain, whirls of wind, tides, or volcanoes, produce their unique sounds which are very much characteristic about them.
  •  Perception through special organs: Other living organisms such as frogs, birds, reptiles, aquatic and terrestrial mammals, are gifted with specially developed organs to produce specific audible sounds. In some species like parrots these organs help them to sing and speak too.

Overriding all these, human beings have developed different cultures and technology (such as musical notes, telephones and systems) that allow them to generate, communicate, distinguish, document, and transmit and to broadcast sound. Man’s success by perception of this sense is indeed unique.

 

3.    Sound – What is it?

 

For Physicists, propagation of vibrations as mechanical waves which move in varying pressure and displacement, which are passed through different med iums (air, water etc) and which are audible refers to sound. Scientific disciplines of Physiology and Psychology, regard this phenomenon to be specifically related to aural reception of such waves and the brain’s attribute to perceive it as a sound. The field of psychoacoustics is a dedicated branch of science that deals with studies of the above phenomena. In all organisms which have a hearing sense the physical reception of sound is limited to certain frequencies (ranges). Sound frequencies which human beings can normally hear fall approximately between 20Hz and 20 KHz (20,000 Hz) though they are best heard from 1 KHz to 5 KHz. This is the range where human speech features. The upper limits as everybody knows decreases with age as people may endure deafness or at least a mild reduction in hearing, described as a condition where the range of frequencies a person hears gets reduced.

 

4.1 Sound as waves

 

Anything which vibrates, always create a wave and a wave thus formed in turn always moves through a medium, such as air, and basically displaces the air particles in an oscillating pattern, typical of the material and the medium. Vibration causes the object to exert pressure on the air molecules around it. These in turn push on other molecules around them, thus, creating a wave that moves and ripples away from the source of the vibration.

 

Precisely, sound is a wave of energy travelling from a source; that is, surging back and forth, alternately squeezing and stretching the air as though in vibration or oscillation, to one’s ears. Rooms where air is lacking, spaces devoid of air or a vacuum can hinder travel of sound. Hearing difficulty expressed when people are in space is because of this reason. Science distinguishes the congested parts of the air as compressions and the stretched parts as rarefactions.

 

4.1.1 Wave propagation

 

In air at normal temperatures the speed of sound wave transmission reported is approximately 340 m/s. The sound vibrating from any source causes a sort of disturbance to the molecules of air surrounding the area, causing them to bombard and bounce off each other. The force with which they do so is proportional to the disturbance that is affected.

 

This radial movement at equal speed forms a spherical ‘wave front’ which expands to the boundaries of an enclosed space and fills the entire space with the rapidly moving spherical sound wave fronts.

 

Consider a point source emitting waves. If the emitter is placed in the centre of a hollow sphere of one foot radius, the total emission of the source will fall on the whole surface of the sphere, that is, on 4 or 12.57 Sq.ft. Change in the radius (over short distances) does not alter the frequency of waves which give sound its characteristic tone.

 

4.1.2 Wave propagation in the interior

 

Considering sound wave fronts in an interior, they normally strike a wall, floor or ceiling and are reflected in various directions. The reflection process continues until all the energy released through vibration to the original waves is absorbed and the sound fades away.

 

4.1.3 How do we hear?

 

Here is a wave in two dimensions. Imagine the dots in reds are air molecules. When animation is applied and “played,” the dot at the center (yellow) will suddenly expand. Sequel to its expansion, it pushes on the air molecules that are adjacent and thereby closely surround it. It is at this point that “the wave” begins, which will ultimately reach an ear nearby. There lies the secret of hearing.

 

These actions and displacements are affected by the interaction that takes place among the molecules of air causing ripples. The impact is generation of energy, whereby the air molecules are transformed into those displaying pressures above or below normal atmospheric pressure. Hence they appear as denser or less dense molecules (ripples) respectively. In the natural sequence two types of density areas occur, causing compression and rarefaction. Hence, the back and forth oscillation of pressure is said to produce what is called ‘sound waves’. What do you understand from this?

 

4.1.4 Point to ponder

 

Displacement of air with change in pressure produces a sound. Then how do we hear?

 

4.  Sound waves and sound pressure

 

A rapid variation caused in the density of air molecules differing from existing or ambient atmospheric pressure which also happens in a sequence is hence said to produce sound. This sort of pressure fluctuations cause human beings eardrums’ to vibrate which is ultimately perceived as sound. How is it explained? There exists a difference. When referring to sound, scientists generally discuss these minute changes in pressure usually occurring in atmosphere as sound pressure and the actual fluctuations evidenced in pressure, per se, as sound waves. To be more precise, anything that vibrates fundamentally produces sound waves. It is understandable, therefore that sound like light is also a perception by all organisms with hearing ability.

 

 

Precisely, dual aspects related to sound, enable effective perception: one relates to a physical process that initially produces sound energy and sends it shooting through the air, and the second relates to a separate psychological process, essentially an internal process which happens not only within one’s ears and brains, but which also assume the major role of converting the incoming sound energy into sensations one interprets as noises, speech, and music. The tiny hairs inside the ear get vibrated by the vibrating air molecules which stimulate the nerve cells. They in turn send signals to the brain. Reception and perception of these signals as sounds is actually done by the brain. So hearing is a wonderful process. It is no wonder that people find some unique features with sound.

 

5.1 Features of sound waves

 

Like light, sound also emerges from a definite source (a musical instrument or a noisy automobile). The similarity ends here. They differ in a major way. Light can travel through a vacuum. Sound, however, cannot travel through a vacuum: it always has to have something to pass through (generally known as a medium), such as air, water, glass, or metal. Allen has estimated sound to travel at one of the fastest rates through Aluminum, at about 6,320 meters per second. The next- fastest speed for sound he adds is 4,600 meters per second in copper.

 

5.1.2 Self check exercise

 

A pioneering discovery that sound needs a medium was indeed demonstrated by the brilliant English scientist Robert Boyle , which all students would have experimented in their schoo l days (Woodford, 2015). Try the experiment now for a better comprehension.

 

5.1.3 Inte resting facts you would have known

 

A.     The term sound has different connotations in different disciplines

B.     Sound is a mechanical wave- exerts force to push air molecules for transmission

C.     Hearing involves physical. Physiological and psychological processes

D.    The tiny hair follicles in the ear and brain share an important role in the hearing process

E.     Source of sound and space in which the waves disperse have a decisive role in sound propagation. Hence their importance in designing spaces

 

5. Secrets of sound

 

Sound waves are the vibrations of an elastic medium which provide the stimuli for hearing. In air sound waves travel in a speed of about 1,100 feet per second or 760 mph. The speed of transmission through water is about four times greater than this. Contrarily, sound waves do not pass through a vacuum.

 

It is evident therefore that sound always has its origin from some source. Such vibrations get transmitted through multiple media; but the basic concern rests with those transmitted through the atmosphere to the ear. The natural world is filled with sounds of varied types, produced from nature herself. This is even truer of the man- made, artificial world; in the combined state in fact it is fit to cause a multiplier effect. Human beings and all organisms are surrounded with objects and things made of various materials. Whenever an object vibrates enabling a person to hear, that is, at frequencies between 20 and 20,000 c/s, sound energy is produced. Carriers of the vibrations are the medium, while vibrations are effected by some form of energy like mechanical, electrical etc. These actions make the energy produced radiate as sound. This is an important aspect to be considered in space designing.

 

6.1 Points to ponder

 

Energy released from different sources are heard as different sounds; for instance, sound energy from water falling and hitting a beach is what one hears as surf; heated air from lightning is heard as thunder. Objects set into vibration make noise because they are hit by the wind produced by heat from the Sun, but the same wind can cause gusts when they howl against it. Wonderful nature!!

 

All of us enjoy, yet do we pause for a second to think how these happen, possible impacts and our concern to monitor the effects? Stand in the open, over a hill, on the seashore, a palm grove, a meadow, an industry, welding workshop, sawmill and notice the multifarious sounds that emerge. Do you hear any of these within your house? How do you manage to prevent such sounds enter inside? An understanding of ‘how sound is described’ will be of help.

 

6.2 How do people describe sound?

 

A sound can be explained as loud against soft; differently pitched as low/ high, whisper, shout or a shrill. These words describe the way people express sound perceptions. For Scientists, sound has measurable characteristics that can be measured using instruments. An understanding of the physical qualities of sound is therefore necessary.

 

Generally speaking, people can draw relationships between such measurable characteristics to the descriptions given colloquially to the sounds heard. For example, when laymen describe a sound as heard louder or softer, scientists discuss them in terms of the sound’s intensity (amplitude). When he talks about the pitch in which it is heard, scientists call it frequency. As stated, comprehension of the difference between the perceived characteristics (Loudness and pitch) and the physical characteristics (intensity and frequency) of sound becomes imperative especially for designers of space, because they only decide the nature of the space.

 

6. How are sound waves explained?

 

A sinusoidal plane wave, characterized by certain generic properties is the popular method used to explain a sound wave:

  •   Wavelength
  •    Frequency, or its inverse, the time scale
  •   Amplitude
  •   The attributes of sound
  •    Wave number
  •    Sound pressure
  •   Sound intensity
  •    Speed of sound
  •    Direction

7.1 Wavelength: A wavelength refers to the length of one wave from the beginning of its oscillation to the end. Wavelength determines the frequency of a sound wave.

 

 

7.2 Attributes of sound

 

Like other wave forms (light and water) sound can be defined in terms of its frequency and amplitude. So the two primary attributes of sound are frequency and intensity (amplitude). While the single sound or pure tone can be represented as a sine wave, the complex tones are made up of a mixture of superimposed waves.

 

Frequency (high or low pitched) indicates just how often the waves occur during a particular period of time. Sound waves form a recurring design, a wavy pattern. One such wavy pattern is known as a wave cycle. Frequency in sound indicates the count of cycles of sound waves recurring in one second in Hertz.

 

Human hearing interprets frequency as pitch, which is heard as low or high. Increase in sound frequency will show more cycles per second and that is when sound is described as higher pitched. An action in the opposite produces a lower pitched sound. Loudness on the other hand is a sensation in human hearing and is well explained as the reception by the ear and its interpretation by the brain, attributed to the sound wave’s amplitude and its frequency. Loudness describes how people perceive sound.

 

As the sound wave passes by they cause a change in pressure which is defined as the wave’s amplitude. Greater the amplitude, greater the pressure transmitted by them and this is called as Sound Pressure (SP). The amount of energy it carries is said to be related to its amplitude. The quantum of energy passing through a specific area in a specific time interval in a specified direction is called the intensity of the wave. Higher the intensity ‘louder’ is the perception. Sound intensities are referred to in units called decibels (dB). To summarize, perception of sound is attributed to these two aspects.

6.2.1 Inte resting facts

  •   Frequency: determines the tone.  The sensation perceived is pitch
  • Amplitude: determines the intensity The sensation perceived is loudness

By virtue of these obvious reasons, a sound can become a noise. A sound becoming a noise is therefore dependent on its source and sound level.

 

6.2.1 Points to ponder

 

Do we ever wonder or bother about the various sound levels that surround us. Try to find out the noise levels emerging from different sources and identify those which people will designate as noise or unwanted sound from those you hear now. Probably you will also agree that unless control is practiced all sounds can become noise which can affect our well being and our active life. Though we don’t think about the characteristics of sound, we show great concern to avoid noise, especially in interiors. This need becomes all the more necessary if there are elderly residents, convalescing patients or infants and toddlers “Sound and noise” – how do they differ?

 

7.   Noise

 

Colloquially speaking, noise is unwanted sound.

The mixtures of sounds are known as noise, which can be expressed as a sound spectrum in which the amplitude of the component frequencies is plotted against the frequency. An example is differentiating or identifying use of varied musical instruments in a song.

 

7.1 Types of noise

 

Noise is the term used for referring to any unwanted sound. There are two types of noise

  •  Broad band or white nose (cause deafness and reduce work efficiency)
  • Meaningful noise (interferes with efficiency and makes communication difficult)

The risk of damage to the ear is not uniform over the whole frequency spectrum, but appears to be greatest for sounds between 2400 and 4800 cycles per second. In addition to any damage caused by noise, hearing loss, known as Presbycusis, can also occur naturally with age. Arrangements need to be made to prevent this condition happen to the inmates.

 

The 20t h Century was named as the ‘century of noise’, because it has become a major stress factor in the environment of man. The maximum loudness (limit) recommended for man is 85 dB (decibels). When designing an interior, the designer has to be doubly careful to see that the areas permit only the acceptable noise levels expressed in dBA.

 

Acceptable noise levels in interiors

 

 

To sum up, one can describe sound to appear in different wave forms – mechanical, longitudinal and pressure related traversing through various media. Sound from the exterior cannot be controlled unless the source and the receiver are controlled, but sound produced in an enclosed space can be controlled with sound absorbents.

 

Conclusion

 

Scope of this module was to familiarize you with the various attributes of sound which have to be understood, permitted and or prevented in an interior of a building to make living more comfortable and pleasant. Lack of concern for these issues may end up creating an interior which would hinder not only with one’s physical comfort but also with their mental balance. Impaction can be felt in one’s temperament, self control a nd work productivity. An interior therefore has to be created which will only evoke sensations of enthusiasm, calmness and being proactive. You need to know about a few more aspects related to light and sound to emerge successful in designing such interiors. The following sessions will introduce you to those factors.

 

you can view video on SOUND AND NOISE

 

WEB LINKS

  • http://en.wikipedia.org/wiki/File:Spherical_pressure_waves.gif
  • http://www.drgeorgehearingaids.com/node/27 (How we hear) on youtube
  • http://www.drgeorgehearingaids.com/how-we-hear
  • http://www.dosits.org/images/dosits/compositb-intensit1.gif
  • http://davidjarvis.ca/dave/gallery/sm/sine -wave-frequency_tn.png
  • http://www.dosits.org/images/dosits/1x.gif
  • http://www.dosits.org/images/dosits/compositb-frequenc.gif
  • http://www.physicsclassroom.com/Class/sound/u11l1c2.gif
  • http://www.slideshare.net/cartlidge/8-l-sound-hearing-boardworks