noise mike breslin

8/2/2019 Noise Mike Breslin

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BASELINE NOISE MEASUREMEDifferent Techniques Different Re


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Assessment Type & Methodolog


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Individual Methodologies:BS 4142PPG 24

BB93CRTN/DMRB/Road Noise Insulation RegulationsCRN/Railway & Guided Transport Systems Insulation Reg

Wind Farm Noise (ETSU-R-97)Noise ActAnnex 2 of MPS 2


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Multiple Methodologies Required:Environmental Statements

Nuisance Investigations

World Heath Organisation Guidelines

BS 8233


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No Established Methodology:

Construction Noise

AL-72 Perhaps?


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Baseline Assessment of Critical Importance Comparative as opposed to Absolute

Assessment Criteria


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Individual Methodologies:BS 4142: Almost Exclusively Comparative

PPG 24: Absolute

BB93: AbsoluteCRTN/DMRB/Road NIR: Elements of BothCRN/Railway NIR: Elements of Both

Wind Farm Noise (ETSU-R-97): Elements of BotNoise Act: Elements of BothAnnex 2 of MPS 2: Elements of Both


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BS 4142

Index: LA90,T measured using time-weighting F expressed to the nea

Ensure Time Interval sufficient to obtain a representative va

May be necessary to repeat the measurements on a number of ocobtain a representative sample (especially if meteorological factors pote

Background to be measured at a time typical of that when source will


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BS 4142 continued

Index: LA90,T measured using time-weighting F expressed to the ne

Clear? Yes

In reality consultants often reluctant to round LA90s & LAeqs where the assessm

Both LAeq and LA90 rounded in BS 4142 (see 3.1 and 3.10)

e.g. Rating Level 49.5 & Background 45.4 is the margin 5 dB (rounded) o


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BS 4142 continued

Ensure Time Interval sufficient to obtain a representative v

Under 6 Specific Noise Level, clear Reference Time Intervals are g

- 1 Hour during the day and 5 minutes during the night for the Spec

There is no similar guidance on the Reference Time Interval for Backgro

In the absence of any specific guidance it Reasonable to Use the LA90 1

And the LA90, 5 minutes at night?

In the absence of guidance many people assume the same Reference TIs appropriate for both the Specific Noise Level and the Background Noi


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Measurement Period and LA90

Not Established Industry Practice to do Long Measurement Periods (e

No Analytically Correct Way of Combining Percentiles

In practice 1 hour, 15 minute or 5 minute LA90

measurements generally

Average or Minimum 1 hour, 15 minute or 5 minute used for assessmen


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Measurement Period and LA90

8 hour LA90 significantly lower than Average (shorter period) LA90s

Minimum shorter period LA90s significantly lower than 8 Hour LA90

The shorter the measurement period, the higher the average LA90

(~ 1d

The shorter the measurement period, the lower the minimum LA90

The shorter the measurement period, the higher the maximum LA90


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Conclusions: Measurement Period and LA90

No Clear Quantitative Guidance on Measurement Period in BS 4142

The Measurement Period for LA90 affects the results

Shorter Measurement Periods Give Higher Average LA90s and Lower M


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BS 4142 continued

May be necessary to repeat the measurements on a number of ocobtain a representative sample (especially if meteorological factors pote

PositionWind

DirectionLAeq

LAmax

F

LA10 LA90

W 66.3 71.3 67.5 64.6

5 SE 57.0 62.5 58.1 55.7

Difference 9.3 8.8 9.4 8.9

PositionWind

DirectionLAeq

6

W 67.7

SE 57.3

Difference 10.4


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BS 4142 continued

Background to be measured at a time typical of that when source will b

Figure 2: Long-Term Noise Measurement Results

30

40

50

60

70

80

90

100

12:00

14:00

16:00

18:00

20:00

22:00

0:00

2:00

4:00

6:00

8:00

10:00

12:00

14:00

16:00

18:00

20:00

22:00

0:00

2:00

4:00

6:00

8:00

10:00

12:00

LAeq

Lamax F

LA10

LA90

Thur

9/9/04

Fri

10/9/04

Sat

11/9/04


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BS 4142 continued

Background to be measured at a time typical of that when source will b

Whats Typical when Background Levels Vary with:

Time of Day Weather Day of the Week

Time of the Year Time Interval Chosen for LA90 Measurements

At no point does BS 4142 advise on the use of minimum rather than typ


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BS 4142 continued

Measured at the assessment position(s) or other positions assumed

Positions that are Outside Buildings

Representative of the noise level at buildings where people likely to be af

Free-Field

Preferred Measurement Height 1.2 1.5mWhere measurements above ground floor necessary - 1 metre from faca

Apart from measurements having to be made outside buildings there is co

latitude for interpretation


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BS 4142 continued

Does the uncertainty regarding background measurement position

Is the free-field level representative of the background level at the bui

Receptor

1

2Bu

sy

Road


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BS 4142 continued

Does the uncertainty regarding background measurement position

Is the free-field level representative of the background level at the build

Diffuse Field Equal

Probability of

SoundArriving fromany Direction

Background Noise -Many Distant Sources

Predominantly

From a

SpecificDirection

Specific Noise

Facade removes 50% of Soundfield

3 dB reduction in background

Reflection gives up to 3 dB Increase

Facade Background Lower than Free-Field

Reflection give

Facade Rating Level High


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Baseline for BS 4142: Summary

Critical Element of the Assessment Methodology

Considerable Variation Can be Obtained in a Specific Location due to:

Measurement Position

Measurement Time Interval

Weather Conditions

The way the Results are Processed and Interpreted


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PPG 24 ASSESSMENT FOR RESIDENTIAL DEVE

More Straightforward than BS 4142 Principally Uses LAeq

Difficulty Arises with Specified Measurement Position in Urban Locations

Measurements Often Have to be Taken in Elevated Positions (security)

3 dB Facade Correction can Result in Apparently Low Free-Field Levels

Likely level at the time of application andany increase that may reasonably be expected in the foreseeable future

to be determined

Measured Noise Levels should be representative of typical conditions


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Measured Noise Levels should be representative of typical conditio

Usually taken to mean mid-week

Usually taken to mean dry with light or no windNo Specific Guidance on Measurement Duration

Para 8 of Annex 1 confuses some people (the arithmetic average o

readings should be rounded up)I take this to mean the average of several days readings (not the arof short-term LAeq noise levels to be arithmetically averaged to give tLAeq, 07:00 23:00 and LAeq, 23:00 07:00)


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Additional Requirements

NEC noise bands source-specific

Must be able to identify principle influences on daytime & night-time Need to know how many events exceed 82 dB LAmax S at night

Unless dominant noise sources indisputable, requires either:

Attended daytime and night-time measurementsor periodic audio recordings to enable the principle noise sources to

and the capturing of events which exceed 82 dB LAmax S at night

Question: should the 82 dB LAmax S criterion be applied to emergencysirens in urban locations?


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STRATEGIES FOR BASELINE ASSESSMEN

Calculations/Modelling

Measurements

Combination of Measurements & Calculations

Most Baseline Assessments Need an Element of both Measuremen


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CALCULATING BASELINE NOISE LEVEL

Requires the Availability of:

Source Information

A validated model

Most Applicable to Transportation Noise


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CALCULATING BASELINE NOISE LEVEL

Limitations:

Availability/validity of traffic data

Models generally predict only LAeq or LA10 (no LAmax for PPG 24

Most applicable where receptors abut a road or railway for insta

Difficult to apply to complex situations (multiple sources/traffic l

Doesnt take into account other sources which may affect ambi


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BASELINE NOISE MEASUREMENTS

Most Reliable Longterm Attended Measurements

Attended Samples Reliable but only a Very Limited Snapshot

Unattended Longterm Measurements Better Picture of Data over aDoubt Over Identification of Sources


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A Practicable Compromise

Establish the Diurnal Pattern of Noise Levels with a Long-Term Unatte(preferably with periodic and event audio recording)

Take sample measurements simultaneously at satellite locati

Apply the Diurnal Variation from the Long-Term Measurements to the S

Measurement Results to obtain an Estimate of the Daytime & NighNoise Levels at each Satellite Location


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Period Mon 23 Tue 24 Wed 25

LAeq, 07:00 23:00 - 57.1 55.9

LAeq, 23:00 07:00 51.1 51.7 51.3

Table 3.1: Daytime and Night-time LAeq Noise Levels at the Long

Time LAeq LAmax S LA10 LA90Sample Long-

Term Position LAe q

12:15 54.8 60.5 57.1 51.9 -1.9

Table 3.2: Noise Levels at Position 1 at a Height of 1.5m


Term Position LAe q

12:45 54.4 61.7 56.0 51.6 -1.6


Time LAeq LAmax S LA10 LA90 Sample Long-Term Position LAe13:20 54.7 60.3 56.3 52.6 -1.5



Term Position LAe

14:00 54.6 59.8 56.4 52.3 -1.4



Term Position LAe q

15:00 54.5 58.6 55.8 52.6 -1.6



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Long-Term Plus Satellites Implicit Assumptions & Cautionary No

The same noise sources must be the principal influence on the indices be

The danger of there being extraneous noise events at the unattenden.b. Birdsong can play havoc with A-weighted SPLs

Be aware of the different attenuation rates of different indice

Consider a Road:-


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LAeq/LA10 Line Source

- 10 log (distance)

i.e. 3 dB per doubling of distance

LAmax/(LA1?) Point So

- 20 log (distance)

i.e. 6 dB per doubling of dist


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Levels ~ 20m from A-Road Levels ~ 100m from A


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As you get further from a Line Source (e.g. Road)

The Noise Indices get Closer Together

The Diurnal Variation of the LA90 Decreases

The diurnal pattern of the other indices less distinct (influence of loca

Long-term Position and Satellite Positions should therefore ideally be cdistances from the main noise source

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