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Brian Marston
science forum beginner

Joined: 13 May 2005
Posts: 25

Posted: Fri Jul 14, 2006 7:02 am    Post subject: Re: Measuring Background Noise

Hello in Ireland <www.pateltonra.com>

Define operating hours. It looks like the bare minimum will be 24 hours
of measurement, if you're in a fully urban area. From what you say, and
without knowing the area, I'd recommend nothing less than 24 hours. It
can take years of measurement before you get the feel for the daily /
weekly fluctuations.

Averaging is a debate that can go on for years - logarithmic average,
arithmetic average, absolute lowest LA95,15min or average of lowest
LA95,15min values over a number of days, statistical trimming of each
periods LA95,15min values or a combination.

Talk to the authority who set the conditions, and get a copy of the
policy those conditions are based on. Talk through what measurements
they expect and how and where they expect them to be measured. If you
get it wrong, you are playing with the the livelihood of that company so
it can't be taken lightly.

Doug wrote:
 Quote: I have just got myself involved in some noise measurement work and have some received basic training. (I plan to do more training) However, in the meantime I need some advice on measuring background noise. The situation: A local factory/ warehouse has a planning condition that the LAeq (15 minutes) between 0800 and 2200 must must not exceed the background noise (defined as L95) by more than 5dB(A) and from 2200 to 0800 must not exceed by more than 3dB(A). To establish the backgrond noise I am assuming that I need to get an L95 reading for at least 15 minutes during the day and another reading during the night, at times when the factory is not operational. My question is - do I just take one 15 minute reading for day time background and one for night time or do I need to take readings at different times - as the backgound may vary e.g. noise at 8.00 in the morning may not be the same at say 20.00 in the evening. If I do take reading at more than one time - what do I do with the results. Average them? Advice would be appreciated. Doug
Kev
science forum beginner

Joined: 29 Aug 2005
Posts: 3

 Posted: Thu Jul 13, 2006 11:11 pm    Post subject: Re: Measuring Background Noise Doug, Where are you located? Your state/country should have an environmental body that sets the industrial noise policy, and this document will guide you when carrying out noise assessments. BACKGROUND NOISE To get a genuine L95 reading it will generally be necessary to measure noise levels (for example at 15 min intervals) over a period of a week with an unattended noise logger. If you were being thorough with the assessment, you would then match this data against meteorological data to exclude periods of high winds and/or heavy rain. How you then determine the background noise level from these measurements will vary according the noise policy, however it will involve something like sorting the L95(15min) values in ascending order and selecting the 10th percentile value. FACTORY NOISE To determine the LAeq from the factory, you should make attended 15 minute measurements, so that you can exclude extraneous nosie sources such as aeroplanes, lawn mowers and so on. The number of measurements you make should be based on your assessment of the factory opertations - i.e does the factory equipment operate consistently, or does it vary throughout the day? SEASONS It is true that the background level will vary with the season due to insects, and if possible you should avoid measuring noise during the periods (the insects would be classed as extraneous noise). I don't want to complicate things too much for you mate, but you should also be aware that in rural areas, meteorological phenomena such as temperature inversions (which occur in some areas during winter) will also affect noise levels. Kev
Noral Stewart

Joined: 23 May 2005
Posts: 77

Posted: Thu Jul 13, 2006 10:40 am    Post subject: Re: Measuring Background Noise

First, I do not like the idea of mixing measurement methods and basing the
limit on an leq exceeding an L95 by some amount. The existing leq may
already be 10 or 20 dB higher than the L95. However, it is the regulators
and not you who have set that method and you have to live with it. I think
with vary with different 15 minute periods. You really need to have some
idea how the local authorities will interpret the situation. However, they
could easily say that you must meet the limit for the quietest 15 minutes of
the day on the quietest day of the year. Did you catch that, the sound will
vary from day to day and possibly seasonally as well. In our area, the L95
is often higher in the summer and early fall due to insects, and then lower
in the winter and early spring. If you do not have nearby sound sources at
night, you will find the nighttime levels are often dominated by distant
sources, and levels due to these sources can vary strongly with atmospheric
conditions.

"Doug" <doug.corrie@pateltonra.com> wrote in message
 Quote: I have just got myself involved in some noise measurement work and have some received basic training. (I plan to do more training) However, in the meantime I need some advice on measuring background noise. The situation: A local factory/ warehouse has a planning condition that the LAeq (15 minutes) between 0800 and 2200 must must not exceed the background noise (defined as L95) by more than 5dB(A) and from 2200 to 0800 must not exceed by more than 3dB(A). To establish the backgrond noise I am assuming that I need to get an L95 reading for at least 15 minutes during the day and another reading during the night, at times when the factory is not operational. My question is - do I just take one 15 minute reading for day time background and one for night time or do I need to take readings at different times - as the backgound may vary e.g. noise at 8.00 in the morning may not be the same at say 20.00 in the evening. If I do take reading at more than one time - what do I do with the results. Average them? Advice would be appreciated. Doug
Doug
science forum beginner

Joined: 02 Apr 2005
Posts: 15

 Posted: Wed Jul 12, 2006 12:53 pm    Post subject: Measuring Background Noise I have just got myself involved in some noise measurement work and have some received basic training. (I plan to do more training) However, in the meantime I need some advice on measuring background noise. The situation: A local factory/ warehouse has a planning condition that the LAeq (15 minutes) between 0800 and 2200 must must not exceed the background noise (defined as L95) by more than 5dB(A) and from 2200 to 0800 must not exceed by more than 3dB(A). To establish the backgrond noise I am assuming that I need to get an L95 reading for at least 15 minutes during the day and another reading during the night, at times when the factory is not operational. My question is - do I just take one 15 minute reading for day time background and one for night time or do I need to take readings at different times - as the backgound may vary e.g. noise at 8.00 in the morning may not be the same at say 20.00 in the evening. If I do take reading at more than one time - what do I do with the results. Average them? Advice would be appreciated. Doug

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