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Noise monitoring & evaluationFor Technicians

Study module 4Measuring noise

Environmental Monitoring & Technology Series

Noise monitoring & evaluation Study Module 4

Assessment details

PurposeThis unit of competency covers the ability to monitor noise using handheld sound level meters and fixed sound monitoring stations with either data logging or telemetry. It includes the ability to perform noise surveys, process data and report results in accordance with enterprise standards.

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 declarationI 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… ☐

DetailsStudent name Type your name here

Assessor Marker’s use only

Class code NME

Assessment name SM4

Due Date Speak with your assessor

Total Marks Available 59

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

Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net/env] Course Notes for delivery of MSS11 Sustainability Training Package Page | 1


Introduction

So far, we have learnt what sound is, the physical properties of sound, how we hear sound, how sound travels and how we represent sound through the different stages of sound propagation and travel from the source to the receiver. But how exactly do we measure it?

A quick recap of what we know;

The source of the sound, or emission, is measured absolutely as sound power in unit Watts, but expressed as a sound power level relative to the 1E-12 Watts reference.

The travelling sound waves, or immission, is measured absolutely as sound pressure in unit Pascal but expressed as a sound pressure level relative to the 2E-5 Pascal reference.

The surface of the immission sound wave field is measured absolutely as intensity in Watts per meter squared but relatively as sound intensity level relative to 1E-12 W reference.

The sound pressure received by the ear, exposure or dose, is measured absolutely as Pascals squared times time (Pa2.h), but expressed as sound exposure level as decibels.

This is a lot of information, fortunately for the environmental technician, we can (in most cases) either get away without measuring all of these aspects, or we can use just one or two pieces in equipment.

Types of sound measurement devicesThe different types of measuring device are classified based on what they actually measure but generally speaking, we have Sound Level Meters (SLM), Sound Intensity Probes (SIP) and personal sound exposure meters (PSEM). Of key importance to this unit of competence is the Sound Level meter.

Sound Level Meters (SLM)

The SLM is the key device used by environmental and WHS field technicians (in conjunction with a data logging versions for field studies). These devices form the major part of these notes so won’t be discussed here in any great detail.

Data loggers

A data logger is a device that captures data. For our purposes, it is an ugly computer that requires another computer to read it! The point of a data logger is space, as in space for the data, they also need to be very rugged to put out in the field.

Data loggers are designed to monitor noise levels in remote or unattended environment for long periods of time (say, for periods of up to 2 weeks). The internal computer of the data logger will typically compute the same measurements as the handheld instruments including percentile noise statistics as well as the equivalent noise levels for time intervals ranging from one minute to one hour (typically 15 minutes). Modern data loggers can also



operate as a sound level meter as they display the current noise level on either the loggers LCD screen or a connected PC. You will explore data loggers more in later modules.

Sound Intensity Probes (SIP)

These are very specific probes that are used to determine many qualities of sound such as sound power requirements emitted from machinery, or to determine the source of a noise.

Although, formally speaking, sound intensity is the product of sound pressure and particle velocity, we have ignored the particle velocity concept as it has little relevance to the field technician, but massive relevance to the overall filed of acoustics.

Commonly, there are two different probe set-ups used in sound intensity measurements, but all set-ups use probes that measure the sound intensity using two microphones.

The p-p type of sound intensity probe measures the sound intensity using two phase-matched microphones positioned face-to-face with a known distance between them. These microphones determine a pressure gradient, from which the particle velocity is calculated. The sound pressure is determined from the average from both microphones output.

The p-u type of sound intensity probe measures both the sound pressure with a microphone and the particle velocity directly with a particle velocity probe.

Figure 4.1 – Example of a SIP [source]

Personal Sound Exposure Meters (PSEM)

Another common sound or noise measurement device is the Personal Sound Exposure Meter or PSEM. The latest version of these things are literally tiny little ‘badges’ that people wear during their working day.

The PSEM has, like all technology, undergone significant change throughout its relatively short history, and they used to be clunky devices hooked on to your belt, with a microphone on a cable was pinned to your collar to receive noise as close to your ear as possible.

You will learn more about the PSEM in the next module where noise studies are applied to the Workplace Health & Safety environment.


http://www.bksv.com/Products/handheld-instruments/sound-level-meters/sound-level-meter-kits/sound-intensity-2270-g?tab=services


Industry standardsThe practice of noise measurements is both heavily regulated and standardised. As mentioned several times, the reason for the regulation is to protect human hearing and loss of amenity. Standardisation (i.e. the use of the same techniques worldwide) is a result of the physical nature of sound (it is a universal property) and is and the requirement for results to be reportable in similar units worldwide.

Sound measurements can be done for a variety of reasons, but generally they can be qualitative (informative) or quantitative (legal). For this reason, different classes or types of noise measurement equipment have been developed.

Australian & International StandardsIn Australia, we use the Australian Standard series of documents (from Standards Australia) which cover three main areas of implementation and monitoring;

Compliance requirements of equipment

All acoustic equipment is designed in accordance with the International Electrotechnical Commission (IEC) specifications (or equivalent). The IEC develop the ‘overarching’ electrical standards for most of the electrical equipment used worldwide and is heavily involved in standardising the electrical function and calibration of noise monitoring equipment.

Workplace health and safety

The series of standards that apply in Australia for workplace monitoring of noise is the AS/NZS1269:2005 series, with standard 1 being the most significant as it deals with the operational aspects of the monitoring. This forms the majority of the next module.

Environmental

The Australian Standard for environmental monitoring of noise is covered by the AS 1055:1-3 series. Note that there are many other non-regulatory documents used in environmental monitoring but these are dealt with by module 6.

Legal categories of instrumentUnfortunately even with standardisation, there is a multitude of different terms for the same thing as a result of ‘sovereign differences’, but the only two legal classifications we need to worry about is the qualitative and quantitative classes, which are explained below;

◗ Type 0 equipment (factory calibration and the like)◗ Class 1 / Type 1 SLM (high accuracy and precision, for legal use)◗ Class 2 / Type 2 SLM (lower accuracy and precision, for common use)



The Integrated Averaging Sound Level Meter (IASLM)

What is a Sound Level Meter (SLM)?A Sound Level Meter (SLM) is a measurement device used to measure various properties of sound waves that enables us to relate the measured property for either the protection of hearing (WHS applications) or the protection of loss of amenity (community and environmental applications). A typical Class 1 / Type 1 SLM can be seen in figure 4.2 below;

Figure 4.2 – Typical Sound Level meter (SLM). This is a Bruel & Kjaer model.

These types of meters are typically classified as Class 1 / Type 1 sound level meters. We know it is a SLM, so it measures the sound pressure from a source, but what do the other terms mean?

Integration is a mathematical term which implies that the area under a curve is calculated. In our case, the curve is created as a graph of the sound pressure versus frequency, so it is the frequency domain that is integrated. The specific area calculated varies depending on how the frequency octaves are used (1/1 octave or 1/3 octaves).



Averaging is applied to the decibels in the time domain (from a graph of decibels versus time or frequency) and is typically performed early in the electrical process by use of a Root Mean Square (RMS) circuit. You will learn about this circuit later. The typical electrical ‘process’ that occurs in a IASLM can be seen in figure 4.5 below;

Figure 4.3 – Construction of a typical Sound Level Meter (Rion NA 27 SLM).

Admittedly, this looks a little confusing, but the whole process can be broken down into its key constituents (which are listed below and explained in the following sections);

◗ Microphone receives sound pressure and converts to electrical signal◗ Signal is pre-amplified (sometimes more than once, depending on the instrument)◗ Frequency weighting is applied (or not, if linear pass (un-weighted) is requested)◗ Analogue to digital signal conversion occurs◗ Digital signal processing to determine RMS sound pressure occurs◗ Digital signal processing of frequency analysis occurs◗ Displaying the final information on the readout



The microphoneWhen an object vibrates in the presence of air, the air molecules at the surface will begin to vibrate, and this vibration will travel through the air as oscillating pressure waves at frequencies and amplitudes determined by the original sound source power. Microphones are mechanical transducers that are designed, like the human ear, to transform pressure waves into useful electrical signals which we can use to determine the properties of the sounds. Like the human ear, microphones are designed to measure a very large range of amplitudes, typically measured in decibels (dB) and frequencies in hertz (Hz).

Microphone type & construction

Measurements of sound pressure level can be carried out with a variety of microphone types. Most IASLM’s employ the condenser microphones because they are compact and delivers stable and reliable response, but other microphone types (such as resistance) are sometimes used.

A condenser microphone is a type of ‘capacitance’ microphone. The housing of a condenser microphone utilises basic transduction principles to transform the sound pressure to capacitance variations, which are then converted to an electrical voltage. This is accomplished by taking a small thin diaphragm and stretching it a small distance away from an insulated stationary metal backplate. A voltage is applied to the backplate to form a pre-polarised capacitor by using an electret plate with permanently charged particles attached to the backplate.

In the presence of oscillating pressure, the diaphragm will move which changes the gap between the diaphragm and the backplate. Using a load resistor, this produces an oscillating voltage from the capacitor, proportional to the original pressure oscillation.

Figure 4.4 – Construction of a typical SLM condenser microphone (RION NA 27)



Microphone characteristics

The key operational characteristics of microphones used for SLM’s define the responses of the microphone and are directly related to the quality of the transduced sound pressure. The key characteristics for IASLM include the frequency response characteristics, the directional characteristics, the thermal characteristics and the humidity characteristics.

The frequency response as well as the temperature and humidity characteristics of a pre-polarized microphone depend considerably on the type and properties of the materials used. The frequency range is determined by the resonance frequency of the diaphragm assembly.

Voltage AmplificationThe voltage generated from the microphone is incredibly small, so small in fact that it has little practical purpose, and therefore it requires ‘enlarging’ so that a practical voltage is achieved for use by later componentry. This process is called amplification.

Preamplifier

Since the condenser microphone is a small-capacity transducer, it has high impedance, especially at low frequencies. Therefore a very high load resistance is required to ensure uniform response extending to the low frequency range. The relationship between the microphone capacitance and the low-range cut-off frequency can be expressed as follows.

If the output of the microphone were directly routed through a long shielded cable, the capacitance between the cable conductors would cause a sharp drop in sensitivity, as is evident from the following equation.

For the above reasons, a preamplifier is connected directly after the microphone, to provide a low-impedance output signal. To reduce measurement deviations due to refraction effects and the acoustic influence of the operator, the microphone/preamplifier assembly can be detached from the main unit and connected via an extension cable.

Figure 4.5 – Microphone and pre-amplifier detached from the body of the SLM by use of an extension cable. Rion NA 27.



Other amplification

From the pre-amplification, the signal can undergo other amplification processes based on what the signal is going to be used for such as RMS or frequency analysis.

Insert more information form the manual

Frequency weightingYou learnt in earlier modules that the human ear ‘hears’ sound differently to the absolute sound pressure the ear receives. If the noise meter was not adjusted to accommodate for this difference, it would be hard to relate the measured value to the effect on hearing or amenity, and as such, the signal undergo a small transformation so that it represents human hearing more accurately. This transformation is referred to as weighting.

The weighting is conducted early in the signals lifetime, and is simply an ‘arithmetic’ adjustment based on the frequency (via a circuit). The weightings are determined by the international standard, which are shown in the table below;

This table can be graphed to show the observable effect on the flat signal received by the

microphone, as shown in the figure below;



Figure 4.6 – Graph showing the effect of weighting networks on noise signal.

Analogue to digital conversionThe transduction of the sound pressure wave to the electrical signal at the microphone is referred to as an analogue process. Analogue basically means ‘a continuous signal’, which is great, but provides way too much information (because it is continuous).

Unfortunately, the rest of the instrument is a computer, which means that it operates as a digital process and requires 0’s and 1’s to work with. Ultimately this means that the continuous analogue signal needs to be chopped up or sampled and used in discrete packages of information for further processing.

An analogue-to-digital converter (abbreviated ADC, A/D or A to D) is a device that converts a continuous physical quantity (usually voltage) to a digital number that represents the quantity's amplitude. The result is a sequence of digital values that have converted a continuous-time and continuous-amplitude analogue signal to a discrete-time and discrete-amplitude digital signal. This concept is represented in the figure below;

Figure 4.6 – Electrical symbol for ADC. http://en.wikipedia.org/wiki/Analog-to-digital_converter

Digital signal processingNow that we have the signal in the digital form, we can use this to work with the data and produce an enormous amount of information that wasn’t previously (or conveniently) available to us by using the analogue signal alone.

Root Mean Square (RMS) circuit

How many averages are there? Most students state 'three, the mode, the mean and the median", and they would be correct, if applied to the theory of central tendency. In terms of averages, there are in fact many more than three - theoretically, you could even invent your own - but we shall mention four, so we can highlight one in particular;

◗ Arithmetic mean◗ Harmonic mean◗ Geometric mean◗ Root Mean Square (rms)

The RMS is how the sound level meter derives the value you see on the screen. Remember that the measured value is called the LAeq, the ‘L’ means level, the ‘A’ is the weighting and the ‘eq’ refers to equivalent. The RMS calculates the equivalent (RMS average) sound pressure level over a specified time frame (which will be slow, fast or impulsive).



The sound pressure level meter uses RMS detection to determine the continuous equivalent sound pressure. The particular steps involved in evaluating the RMS signal are simple;

◗ The voltage, E, which changes over time is raised to the power of 2, ◗ Integration of the signal for the time interval T is performed. ◗ The result is divided by T ◗ The square root is extracted.

Just for kicks, the following figure attempts to illustrate the different types of average on a data set of noise signals (decibel versus time). The rms will always be the highest value and is equivalent to the AC/DC conversion factor of 0.707 (i.e. DC is ~70 % of the maximum AC signal).

Figure 4.7 – Example of different average showing the rms. From the Nosie theory spreadsheet.

Time weightings and constant

During sound pressure level measurements, the level often fluctuates drastically, which would make it difficult to evaluate readings if some kind of averaging is not applied. Sound pressure level meters therefore provide the capability for index weighting (index averaging) using the RMS circuit. The parameters of this weighting process are called the dynamic characteristics and are determined by the time weighting.

Sound pressure level meters usually have a "Fast" and "Slow" setting for the time weighting. The time range that is considered for averaging is narrow in the "Fast" setting and wide in the "Slow" setting. In the "Fast" setting, the instantaneous level has a larger bearing on the displayed value than in the "Slow" setting. From the point of view of the measurement objective, the "Fast" setting is more suitable to situations with swiftly changing sound pressure level, whereas the "Slow" setting yields a more broadly averaged picture.

The "Fast" setting is more commonly used, and sound pressure level or sound pressure level values given without other indication are usually made with "Fast" characteristics.

The "Slow" time weighting setting is suitable for measuring the average of noise with fairly constant levels. Aircraft noise and high-speed train noise is usually transient noise with high



fluctuation, but here the "Slow" setting is used to determine the maximum level for each noise event.

The "10 ms" setting of the NA-27 results in a very short time weighting, enabling the meter to closely follow noise fluctuations.

The "Imp (Impulse)" setting enables the meter to track noise bursts of very short duration. In the "Peak (Peak Hold)" condition, no averaging is carried out, and the peak value of the frequency-weighted sound pressure waveform is displayed.

Frequency analysis

In order to be able to correctly weight sounds to the perception levels of the human ear, or to get more detailed information about complex sounds it is necessary to divided the frequency range of audible sound (20 – 20,000Hz) up into bands. This is done by using electronic filters that reject all sound with frequencies outside the selected band. These bands normally have widths of 1/3 of an octave or 1 octave.

For those not familiar with music an octave is a doubling of frequency (i.e. going from 260 to 520Hz is one octave). On a piano this means moving up eight white keys (hence the term octave). On a sound frequency graph it means a frequency band where the higher frequency is twice the lower frequency.

The spectrum analyser is the most commonly used analyser and offers the best features of parallel and swept filter analysers. Modern dynamic signal analysers rapidly sample the input signal, digitize the samples and store them in memory. The sampling rate, which is generally 2.5 times the upper frequency limit of the analyser, sets the upper analysis limit. The time record is converted to the frequency domain using the Digital Fast Fourier transform (DFFT) algorithm. Analysers generally use either 1024 or 2048 sample points in the time domain to give a 400-line or 800-line spectrum in the frequency domain.

Within the range of the analyser, the upper bound of the frequency analysis may be selected, but the lower the upper frequency selected, the longer will be the required time to acquire the 1024 (or 2048) samples. Each record of 1024 (or 2048) samples is processed while the next record is being acquired.

In sound measurement, the values stated for frequency bands are normally centre frequencies. This means that a range of sounds is allowed through the sound filter with the frequency stated being the centre. An example of this is the 1000Hz centre frequency. In this band a filter allows all sound of frequencies between 707 – 1414Hz through, but rejects all others.

This process of dividing complex sound up into bands is called frequency analysis, and the results of a frequency analysis are presented on a chart called a spectrogram or a frequency histogram. Figure 4.10 shows the spectrogram of a complex waveform.



Figure 4.10 – Spectrogram of a complex waveform. Brüel and Kjær.



Measurement modes & functions

It is important to realise that the type of noise measurement made depends on the purpose of the measurement. For example narrow frequency band determinations may be required to identify the noise from a particular machine in a factory, or maybe only the dB(A) level is required to find out whether the factory noise level exceeds the allowable levels according the legislation. In the former case the machine may put out noise in a particular frequency band, and narrow band frequency analysis would allow estimation of its contribution to total noise only. In the latter case only the total noise in the area would be determined, and no specific noise sources examined.

The type of noise source will also determine the type of noise measurement made. For example steady noise sources require different types of measurement to impulsive noise sources. The appropriate types of measurement for different types of noise sources are summarised in the table below.

Modes of measurementThe sound pressure level (Lp, Leq or LE)

Statistical analysers also allow measurement of cumulative noise doses over time. Where noise levels fluctuate in an unpredictable fashion over time, they are best represented by the equivalent noise level which has the same acoustic energy (or noise dose) as the original



fluctuating levels for the same period of time T. All measurements of this type are A-weighted, and so are sometimes represented by the symbol LAeq,T. Here the “A” represents an A-weighting, the “eq” tells us that it is an equivalent noise or sound level, and the T is the time is it averaged over. A single LAeq,T value can for example be used to represent the fluctuating noise levels from an industrial workshop, which can then be compared with the 85dB(A) standard. This indicates whether there is a danger of exceeding the allowable Australian 100% noise dose for an 8 hour day of 85dB(A) LAeq,8hr if the noise fluctuations continue. Noise doses over 10 hours L10hr, and 18 hours L18hr are also commonly determined.

SPL weightings (A, C or Flat)

These are as explained above on page 9.

Sound Exposure Level (SEL, LE)

The levels of many sounds change from moment to moment. This variation must also be accounted for when measuring noise levels. High quality sound integrating level meters have a setting that allows for this – a measure referred to as the sound exposure level or SEL. It is also given other symbols such as (LS) or (LEA,T). The sound exposure level is defined as that level which lasting for 1 second has the same acoustic energy as a given noise equivalent lasting for time T – hence the term (LEA,T).

Max, Min and Peak

Lmax is the maximum sound pressure level and Lmin the minimum sound pressure level encountered during a measurement. In the NA-27, the sampling interval for A/D conversion is 10 ms (100 samples per second), and the Lmax and Lmin values since the start of the measurement are stored. Therefore the Lmax and Lmin readings up to the current point can be displayed already during measurement.

The term peak refers to the measurement mode of Lpeak and is the waveform peak sound pressure level for a given measurement interval that can be measured.

Percentile measurements, Lx

These are instruments that measure the distribution of fluctuating noise with time for the purpose of assessing community noise and its potential to cause hearing damage. In addition to providing energy averaged noise levels (such as Leq and LAeq) they also provide information on how often certain sound levels are exceeded. For example they provide values such as L1, L10, L50 and L90, which are the sound pressure levels exceeded 1%,10%, 50% and 90% of the time respectively. When these are used with A weightings these values become LA10, LA50 and LA90 values which are commonly used by the NSW EPA for investigating sound levels.



Day-Night Sound Level (LDN)

The Day-Night Sound Level is the A-weighted equivalent sound level for a 24-hour period with an additional 10dB weighting imposed on the equivalent sound levels occurring during night time hours (10pm to 7am). Hence, an environment that has a measured daytime equivalent sound level of 60 dB and a measured night time equivalent sound level of 50 dB, can be said to have a weighted night-time sound level of 60 dB (50 + 10) and an LDN of 60 dB.

Operational functions

These include items such as memory functions. Each meter purchased will have a different level of functionality in regards to its operational performance.

Operational consideration

Background noiseWhen measuring a certain sound in a certain location, all other sounds present at that location except the measurement target sound are background noise (also called ambient noise or dark noise). Since the sound pressure level meter will display the combination of target sound and background noise, the amount of background noise must be taken into consideration when determining the level of the target sound.

If the difference between the meter reading in absence of the target sound and the reading with the target sound is more than 10 dB, the influence of background noise is small and may be disregarded. If the difference is less than 10 dB, the values shown in the table below may be used for compensation, to estimate the level of the target sound.

If for example the measured sound pressure level when operating a machine is 70 dB, and the background sound pressure level when the machine is not operating is 63 dB, the compensation value for the difference of 7 dB is -1 dB. Therefore the sound pressure level of the machine can be taken to be 70 dB + (-1 dB) = 69 dB.

The above principle for compensating the influence of the background noise assumes that both the background noise and the target sound are approximately constant. If the background noise fluctuates, and especially if it is close in level to the target sound, compensation is difficult and will often be meaningless.

EnvironmentalNoise meters are precision instruments and as such must be protected from shocks and vibrations. Take special care not to touch the microphone diaphragm. The diaphragm is a very thin metal film which can easily be damaged.

Common ambient conditions for operation of noise meters are as follows;

◗ temperature range -10 to +50ºC, ◗ relative humidity 30 to 90%.



Protect the unit from;

◗ water, ◗ dust, ◗ extreme temperatures, ◗ humidity, and,◗ direct sunlight◗ air with high salt or sulphur content, gases, and stored chemicals.

CalibrationFactory electronic calibration

Factory calibrations are designed to check an instrument over its entire frequency range. This is very time consuming, and the procedure involves specialized staff and equipment dedicated to that purpose. As the term implies, the calibration is performed at a NATA accredited laboratory, and most standards require recalibration every two years for the data gathered by the noise meter to be legal.

Electrical calibration

Calibration of the meter can be performed electronically in a similar fashion to the factory calibration but over a shorter range or using a single calibration point. It is performed by using a externally or internally generated electrical signal of known amplitude and frequency which is run into the microphone amplifier circuit, and checked against known reference values and any deviation from the reference can be corrected by adjustment of a preset control on the meter.

Although this calibration can check the amplifier, and the weighting networks and filters, the microphone sensitivity is not checked. Thus, it is important to supplement this form of calibration with regular acoustic calibration

Acoustic calibration

A tonal acoustic signal of known sound pressure level is applied to the microphone and the meter reading is compared with the reference level. Any error outside the quoted calibrator tolerance may be adjusted by the preset gain control (if available). Modern devices use 1000 Hz as the calibration frequency (at 94dB), as the same result is obtained with the A-weighting network switched in or out. Calibrators operating at other frequencies require all weighting networks to be switched out during the calibration process.



Figure 4.9 – Example of a pistonphone used for acoustic calibration of noise meters in the field.

The noise generating device is called a pistonphone and care should be taken to ensure that there is a good seal between the microphone housing and calibrator cavity.

During calibration, the sensitivity adjustment on the sound level meter is adjusted to make it read whatever the value equal to the sound pressure level generated by the pistonphone calibrator. Calibration is accurate to ±0.5 dB for most instruments intended for use in the field (general purpose sound level meters) and ±0.2 dB for precision instruments for laboratory use. Large errors may indicate damage to either the sound level meter or the calibrator, and in such cases both should be returned to the manufacturer for checking.



Assessment task

After reading the theory above, answer the questions below. Note that;

Marks are allocated to each question.

Keep answers to short paragraphs only, no essays.

Make sure you have access to the references (last page)

If a question is not referenced, use the supplied notes for answers

Answer the following questions1. List, and briefly describe, the difference between the four types of noise meter. 4mk

Type your answer here

Leave blank for assessor feedback

2. Which standard dines the electrical aspects of noise meters? 1 mk



3. Identify the standards associated with WHS and environmental monitoring. 2 mk



4. What are the three categories/class/type of instrument? What is the primary difference between them? 3 mk





5. What is an IASLM? 1 mk



6. What do the term integrating and averaging mean in relation to an IASLM? 2 mk



7. What does the microphone do? 1 mk



8. Which type of microphone is commonly used in Class 1 noise meters? 1 mk



9. Identify the three key operational characteristics of a condenser microphone. 3 mk



10. What does the process of amplification do to a signal? 2 mk





11. What is the meant by the term frequency weighting? 2 mk



12. What is the difference between A, C and flat weightings? 3 mk



13. What is meant by the term RMS? How does it relate to the noise signal and the measurement of LAeq? 6 mk



14. Identify the four common time constants. How does a slow setting differ from a fast setting in terms of what is averaged? 4 mk



15. Briefly describe the term frequency analysis. 4 mk





16. Explain the meaning of the term impulsive sound, and give one example. Why are impulsive sounds potentially more damaging to human hearing than normal sounds? 4 mk



17. Explain the meaning of the following terms with respect to sound/noise level measurement LA10, LA50 and LA90. 6 mk



18. Explain the difference between an equivalent sound level, a day night sound level and an A-weighted sound exposure level. 6 mk



19. Why is correcting for background level so important? 2 mk



20. How is the background correction achieved? 2 mk




Assessment & submission rules

Answers◗ Attempt all questions and tasks◗ Write answers in the text-fields provided

Submission◗ Use the documents ‘Save As…’ function to save the document to your computer using

the file name format of;name-classcode-assessmentname

Note that class code and assessment code are on Page 1 of this document.

◗ email the document back to your teacher

Penalties◗ If this assessment task is received greater than seven (7) days after the due date (located

on the cover page), it may not be considered for marking without justification.

Results◗ Your submitted work will be returned to you within 3 weeks of submission by email fully

graded with feedback.◗ You have the right to appeal your results within 3 weeks of receipt of the marked work.

Problems?If you are having study related or technical problems with this document, make sure you contact your assessor at the earliest convenience to get the problem resolved. The name of your assessor is located on Page 1, and the contact details can be found at;

www.cffet.net/env/contacts

Resources & referencesReferences

(NSW), E. P. (2000). NSW Industrial Noise Policy. Sydney: Environmental Protection Authority (NSW).

(NSW), R. &. (2001). Environmental Noise Management Manual. Sydney: Roads & Traffic Authority (NSW).

Australia, S. (1997). AS 1055.1-3. Homebush: Standards Australia.

Australia, S. (2005). OCcupational Noise Management, Part 1: Measurement and Assessment of Noise Immission and Exposure. Homebush: Standards Australia.

Australia, S. (2011). Methods for the sampling & analysis of ambient air: Part 14: Meteorological monitoring for ambient air quality monitoring applications. Homebush: Standards Australia.

Bies, D. &. (2003). Engineering Noise Control, 3rd Ed. London: Spon Press.

Kester, W. (2004). Analogue-Digital Conversion. United States: Analogue Devices.


http://www.cffet.net/env/contacts


Maltby. (2005). Occupational Audiometry: Monitoring & protecting hearing at work. London: Elselvier.

NOHSC. (2000). National Standard for Occupational Noise [NOHSC: 1007(2000), 2nd Ed. Canberra: Australian Government.

Organisation, W. H. (1995). Occupational Exposure to noise: Evaluation, prevention & control. Geneva: WHO Publishing.

Rossing, T. (2007). Handbook of Acoustics. New York: Springer.

South, T. (2004). Managin Noise & Vibration at Work. London: Elselvier.

Workcover, N. (2004). Code of Practice: Noise Management & Protection of Hearing at Work. Sydney: Workcover NSW.

Workplace Health and Safety Regulation 2011. (n.d.).

Further reading and online aids

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