Noise monitoring & evaluation Study Module 1
Assessment details
Purpose
This subject covers the ability to site and set up basic ‘ground level’ meteorological equipment and collect and record reliable data. It also includes the ability to assess data quality, interpret significant data features and use the data to ensure the validity of air and noise monitoring measurements.
Instructions
◗ Read the theory section to understand the topic.
◗ Complete the Student Declaration below prior to starting.
◗ Attempt to answer the questions and perform any associated tasks.
◗ Email, phone, book appointment or otherwise ask your teacher for help if required.
◗ When completed, submit task by email using rules found on last page.
Student declaration
I have read, agree to comply with and declare that;
◗ I know how to get assistance from my assessor if needed… ☐
◗ I have read and understood the SAG for this subject/unit… ☐
◗ I know the due date for this assessment task… ☐
◗ I understand how to complete this assessment task… ☐
◗ I understand how this assessment task is weighted… ☐
◗ I declare that this work, when submitted, is my own… ☐
Details
Student name / Type your name hereAssessor / Marker’s use only
Class code / NME
Assessment name / SM1
Due Date / Speak with your assessor
Total Marks Available / 30
Marks Gained / Marker’s use only
Final Mark (%) / Marker’s use only
Marker’s Initials / Marker’s use only
Date Marked / Click here to enter a date.
Weighting / This is one of six formative assessments and contributes 10% of the overall mark for this unit
Introduction
Unless you’re unfortunate enough to be deaf, sound is such a common part of everyday life that we rarely appreciate all of its functions. It provides us with pleasure - such as that obtained by listening to music or the gentle sounds of a rain forest. It allows us to communicate with other human beings and animals. It can be used to alert or warn us - for example a ringing telephone means that someone wished to talk to us, or a wailing siren signifies danger.
Sound being one of our principle senses also permits us to make quality evaluations and diagnoses. We can hear when our car engine misfires telling us it needs tuning, a squeaking valve on an instrument means it needs lubrication; a heart murmur tells us we are sick; and so on.
Not all sounds are associated with pleasure. Many of the sounds associated with our modern society annoy us. This is of course a subjective judgement. For example some people enjoy “heavy metal music”, whilst others think that its only function is to kill the neighbours grass if it is played loud enough. Any sound that is unpleasant or unwanted is called noise.
The level of annoyance of noise depends not only on the quality of the sound, but also our attitude towards it. The sound of a jet aircraft taking off may be pleasant to the ears of the pilot and passengers, but will be ear-splitting agony for the people living near the end of the runway. Sound doesn't need to be loud to annoy. A rattling window on a quiet night, or a dripping tap can be just as annoying as a jet aircraft. The Chinese water torture used repetitive quiet sounds from a dripping tap.
Loud sounds can damage and destroy. A sonic boom can shatter windows and shake plaster off walls. But the most unfortunate case is when sound damages the delicate mechanism designed to receive it the human ear. When this happens our hearing is impaired. The loss may be temporary, or permanent depending on how often and for how long we are exposed.
The difference between sound & noise
When an object moves backward and forward in a repetitive motion it is said to vibrate or oscillate. If this occurs in a medium such as air the particles near the object are affected and start vibrating at the same rate, producing variations in the normal air pressure. This disturbance spreads, and eventually may reach a human ear, which translates these vibrations into a sensation that we call sound.
The simplest definition of sound is therefore any pressure variation or oscillation in a conductive medium that may be detected by the human ear. The most common conductive media are air or water, although sound may be conducted directly through solid structures such as metal pipes etc. This definition does not include any oscillation that cannot be detected by the human ear.
An example of this would be fluctuations in air pressure caused by weather changes. These can be accurately measured by a barometer, but are too slow to be picked up by a normal human ear, with the exception of when we move rapidly from one height to another, such as in an aircraft. In this instance we do not hear sound but rather experience a slow pressure build up in the ear.
Figure 1.1 – Example of a sound pressure wave with inferences of sounds and noise. Source unknown
Noise is characterised by a lack of order or regularity in its sound wave. This generally (but not always) results in tones that are less pleasing to the human ear. Musical instruments by contrast produce regular patterns in the waveforms that they generate.
A reasonable definition of noise is therefore a complex sound that lacks regularity or order in its waveform. It may also be defined more simply as any unwanted or undesired sound, or even as any sound not native to the environment although this last definition would make all musical instruments noise – a view with which many would not concur.
What this unit will teach you
By the end of this unit, you will know enough knowledge and have enough skill to engage in the practice of occupational (workplace) and environmental noise monitoring for the purposes of both;
◗ compliance based monitoring (e.g. licenses & OHS) and
◗ environmental impact assessments
The next step is applying what you know in the workplace.
Outside of specific legislative requirements, the need for noise evaluation has two major stems;
◗ Protection of hearing
◗ Protection of amenity (or from annoyance)
Protection of hearing
First of all, let there be a distinction between hearing and listening. Hearing is the transduction of sound pressure into perceived sound (or mechanical energy into electrical energy), which is done via the ears. Listening is hearing with interpretation of what is heard. To understand what is in need of protection, we need to understand the basics of the hearing process itself.
How we hear
The human ear is constructed of three main sections;
◗ the outer ear,
◗ the middle ear,
◗ and the inner ear.
The outer ear consists of a fleshy outer section called the Auricle or pinna and the auditory canal, the hole in the side of our head through which the sound waves enter. The outer ear is responsible for collecting the sound waves.
Figure 1.2 – The outer ear. From http://www.virtualmedicalcentre.com/anatomy/ear/29.
The middle ear, on the inner side of the eardrum, is responsible for conduction of sound waves to the internal ear. This process is often referred to as modulation. It is a narrow passage, extending vertically for about 15 mm and then about 10-15mm horizontally. There is a special tube called the Eustachian tube which allows the middle ear direct communication with the back of the nose and throat. This allows air into and out of the middle ear.
The middle ear also contains three small, movable bones the hammer (malleus), the anvil (incus), or anvil; and the stapes, or stirrup, collectively called the ossicles. These connect the eardrum acoustically to the fluid-filled internal ear.
Figure 1.3 – The middle ear. From www.medicalook.com
The inner ear is the part of the temporal bone containing the organs of hearing and balance. It is directly connected to the filaments of the auditory nerve. It is separated from the middle ear by the or oval window (fenestra ovalis).
The inner ear consists of membrane bound canals housed in the temporal bone and is divided into the cochlea, the vestibule, and three semicircular canals. All these canals communicate with one another and are filled with a gelatinous fluid called endolymph.
Figure 1.4 – The structure of the human ear. From learningthroughlistening.org
The whole process is one of the best examples of how nature uses biology as an effective transducer, in this case, transferring sound pressure into electrical signals. A summary of the process is as follows;
1. Soundwaves are created
2. The sound wave is collected by the outer ear
3. The wave travels down the ear canal
4. The force of the wave is absorbed by the ear drum
5. The ear drum vibrates
6. The vibrations cause the three middle ear bones to vibrate
7. The middle ear vibrations are transferred to the fluid filled cochlea
8. The fluid vibrations cause the cilia to vibrate
9. Movement of the cilia cause electrical impulses in the nerve endings of the cilia
10. The nerve signals travel along the auditory nerve to the brain
11. The brain processes these signals into the sounds we hear
The process of hearing
Sound waves are carried through the external auditory canal to the eardrum (also known as the tympanic membrane), causing it to vibrate. These vibrations are transferred by the hammer, anvil and stirrup in the middle ear through the oval window to the fluid in the inner ear. This disturbs the fluid in the cochlea and stimulates the movement of thousands of very sensitive fine hair-like projections called hair cells. Collectively these projections are called the Corti.
The hair cells transmit vibrations directly to the auditory nerve, which changes them into impulses, which carry information to the brain. The response of the hair cells to vibrations of the cochlea provides information about sound in a way that is interpretable by the brain's auditory centres.
The range of human hearing
The range of hearing, like that of vision, varies in different persons. When describing the range of human hearing, we don’t use the volume or ‘loudness’ in decibels alone, but rather the spectrum of the frequency (reciprocal of seconds per cycle (period), or c/s, commonly called Hertz (Hz)), all of which is described in later chapters.
The maximum range of human hearing includes sound frequencies from about 16 – 28,000 Hz, but the average healthy person has a normal hearing range of about 20 – 16,000 Hz. This may be extended to 20 – 20,000Hz in young people.
The least noticeable change in tone that can be picked up by the ear varies with pitch and loudness. A change of vibration frequency (pitch) corresponding to about 0.03 per cent of the original frequency can be detected by the most sensitive human ears in the range between 500 and 8,000Hz. The ear is less sensitive to frequency changes for sounds of low frequency or low intensity.
The sensitivity of the ear to sound intensity (loudness) also varies with frequency. Sensitivity to change in loudness is greatest between 1,000 to 3,000Hz, where a change of one decibel can be detected—and becomes less when sound-intensity levels are lowered.
Figure 1.5 – Range of human hearing – dB vs Frequency. From http://sound.westhost.com.
What specifically is being protected?
The hair cells. Prolonged exposure to loud sounds can damage the hair cells, which may result in hearing impairment. Initially damage may only occur to a few hair cells – which is hardly noticeable as the brain can compensate for the loss, but as more are damaged it cannot make up for the loss of information and noticeable changes in hearing occur.
Figure 1.6 – The hair cell and its movement response. From www.nlm.nih.gov.
Most commonly speech and background cannot be distinguished, whilst some words may mix together. By the time this begins to occur it is likely that irreparable damage to the ear has occurred. Hearing loss due to noise exposure is generally greatest at those frequencies where the human ear is most sensitive – around 4000Hz.
Protection against loss of amenity
Another reason that noise monitoring occurs is due to loss of amenity, which refers to any feature of the community or residence that provides comfort, convenience, or pleasure, where that pleasure is lost due to the ingress of noise.
Loss of amenity is the most difficult aspect of noise to measure, as it is purely subjective, and as such requires significant resources (in terms of calculations, indices and ranking systems) to be employed to generate a system of loss calculation that is both relevant and fair to all stakeholders involved.
Figure 1.7 – Images depicting noisy environment (left) and noise creep (right). You should notice that noise creep continuously rises and is difficult to detect the change over time. Source unknown.
Apart from obvious noise transgression by construction activities and the like, most loss of amenity is a slowly occurring process and is referred to as noise creep. This adds to the complexity of the analytical determinations. It is for this reason that this course, and subsequently these notes do not delve heavily into this awkward area of noise assessment. We’ll leave that to the experts.
Legislation, regulations, standards & codes of practice
Although law is not the most interesting subject, considering it is the sole reason for the job description of environmental technician being in existence, its discussion is more than warranted. What follows is a summary of the laws, regulations, standards and codes of practice that were in place in each state and territory accurate to the time of writing.
Workplace & occupational laws