From July 2007 onwards residents of Anick and Oakwood have experienced unacceptable levels of noise from the new Egger plant. These have been moderated by actions taken by Egger following intervention by Tynedale District Council, but noise levels remain too high – and above the levels permitted by the planning conditions for the plant. However, the outcome is still awaited of further actions beginning 1 October to implement the recommendations of a survey by noise consultants employed by Egger and the effect of finally closing down the old plant, currently expected during October.

If you would like to read it the Tynedale District Council Planning approval for the new Egger factory can be downloaded from [here]

You can log any noise intrusions online by clicking this link [Log it!]

Decibels for Dummies!
Posted by Administrator (admin) on Oct 03 2007 at 10:47 pm
Noise levels >>

DECIBELS EXPLAINED: a simple guide

This guide has been compiled from various sources to help the author – a complete layman – understand the meaning of decibel readings from a noise meter.

What is sound/noise?

Noise is broadly defined as unsought or unwelcome sound.

Sound is a construct by the ears and brain to interpret pulses or waves of higher air pressure which are caused by vibrations from a remote source.

Why is measuring sound complex?

Measuring sound is more complicated than I expected for many reasons, of which four are given below.

1. Any measurement made by a noise meter or microphone directly measures the force, frequency, etc of waves of air pressure, not the sound perceived by a human being. The human hearing system does not hear all pitches of sound with equal success: we hear low-pitched and high-pitched sounds less well than middle-range sounds, so raw meter results have to be adjusted to reflect this.

2. The air pressures vary rapidly and constantly. Issues arise about how long the slice of time used for each measurement, and therefore the frequency of measurements, should be. Also of whether to record the peak force or the average force.

3. The variation in force of the air pressures which we can hear is gigantic. The air pressures which overpower and harm our hearing apparatus are about one million times more powerful than the gentlest air waves we perceive. The range to be measured is too large for a simple arithmetical scale, with the same physical “distance” between adjacent points throughout the scale, to be useful.

4. The lower threshold of human hearing varies from person to person and there are air pressure waves too gentle to register. So a realistic, but essentially arbitrary, standard benchmark has to be established to approximate to the lower threshold of human hearing and act as a base point for comparisons of air pressure / volume of sound.

The decibel system and computer-managed noise meters cunningly taking these and other complications into account and provide an accurate and practical means of comparison between different sound levels as we perceive them. The broad meanings can be grasped without going through any of the sophisticated calculation involved. And there are widely accepted international standards, which allow the use of handy short-hand terms.

How is measurement achieved?

1. The noise meter applies a standard “correction” to the air pressures for differently pitched sounds to replicate the varied sensitivity of the human ear to different pitches of sound. The most common standard is simply called “A”, usually written as “dBA”.

2. Standard time-slices of 125 milliseconds and 1 second have been adopted to define the duration of the instant of time for each measurement. These time-slices are known as “Fast” or “F” and “Slow” or “S”. Meters will also record either the maximum noise level in an instant or the average noise level (or “equivalent continuous sound level”) in that instant, and will display either the highest level recorded since the meter was last reset or the ongoing sequence of sound levels.
 
3. To cope with the wide possible variations in force, a “logarithmic” scale is used. For each 10 decibels of increase, the perceived noise doubles. So 10 decibels is twice as loud as 0 decibels, 20 decibels is four times as loud as 0 decibels, 30 decibels is eight times as loud … etc. (The air pressures actually double with every 3 decibels added but our hearing system is itself scaled to reduce the amount of variation perceived.).

4. The most frequently used benchmark level, taken as equal to 0 decibels, approximates to the lower threshold of human hearing and increasing noise is shown by higher dB. On this basis, human hearing is damaged when a level of 120 decibels is reached. Quietness might be about 30 dB, distant road noise shows up as about 45 dB, wind in a tree as 55 dB, a car passing close by at 30 mph as 65 dB, and an airliner taking off as 75dB plus.

What then does the term “decibel” mean?

A decibel reading is simply defined as the ratio between the benchmark force of air pressure and the force of air pressure recorded. The word “decibel” is written as “dB” rather than “Db” because technically a decibel is one tenth of a larger, less used unit called a “Bel”. The benchmark force is most frequently set at the assumed threshold of human hearing.

But one can also set the benchmark level at the highest relevant level or the mid-point, provided the benchmark level is defined. This is how otherwise puzzling displays calibrated in “-dB” (minus decibels signifying a lower volume) or showing both plus and minus decibel readings are arrived at. They are all valid because the decibel is an abstract concept – a ratio between two calculated results. There is no such thing as an unchanging physical quantity called a decibel.

A cheap meter claims to be accurate to within +/- 1.5 decibels. More sophisticated instruments can record direct to computer and include other options and features.

What do the maximum dB levels prescribed in the Egger planning conditions mean?
The planning conditions talk about “Ambient noise levels”, by which is meant the perceived noise levels. These levels are to be measured at the nearest boundary to the plant of designated residential properties (including “Fairfield” Oakwood). The levels shall not exceed “LAeq 1 hour (0700 to 2300 hours) 50 dB”, “LAeq 15 minutes (2300 to 0700 hours) 42 dB” and “LAmax fast (2300 to 0700 hours) 60 dB”. There are also other proscriptions about “no tonal or impulse character”.

1. “LAeq 1 hour (0700 to 2300 hours) 50 dB”

“LAeq” stands for “equivalent continuous sound level” or average noise level , where

L = “the level”
A= using the “A” correction algorithm mentioned above to reflect human hearing
eq= equivalent

The time period “1 hour” is the period over which the sound level is averaged.

The time period in brackets indicates the hours of the day for which this standard applies.

So this means that average noise levels during the day should not exceed 50 decibels for any period of 1 hour.

50 decibels is just below the level of noise (55 dB) at which noise becomes intrusive. The World Health Organisation recommends a maximum daytime level of 55 dB.

2. “LAeq 15 minutes (2300 to 0700 hours) 42 dB”

This is the equivalent limit for night-time. Average noise levels should not exceed 42 dB for any period of 15 minutes or longer. 42 dB is below the level of distant road noise.

3. “LAmax fast (2300 to 0700 hours) 60 dB”

This sets a maximum night-time noise level in any time-slice of 125 milliseconds (one eighth of a second) of 60 dB. 60 dB is the level of normal conversation at 1 metre.

Further Information
The best source I have found is a UK Government publication which is available free of charge over the internet: “Planning Policy Guidance Note 24: Planning and Noise”, especially its Glossary and Annexes 1 and 2, which define and explain terms.

IW 14.9.07 rev.30.9.07