A good example of how one needs to be very careful quoting
statistics. It is very easy to fall afoul of Twain's Law if you do
not qoute them in full context.
Carl Clifford
On 06/09/2006, at 9:58 PM, Paul Taylor wrote:
Andrew Taylor wrote:
I found part of the EES for Bald Hills at:
http://www.wind-power.com.au/news/BaldHills_pdfs/
BH_APPENDIX_11_part1.pdf
The turbines they were proposing to install are said by their
manufacturer
to produce at 106dbA in high wind speeds. This is not quiet.
You neglected to include the units; "106dBA" is meaningless otherwise.
dBA is short for A-weighted decibels: the *relative* loudness in air
as perceived by the human ear. The units are important: relative to
what? ("Decibels ain't decibels, Sol.")
In this case, it is 106dBA sound _power_ level (PWL). That's not the
same as the sound _pressure_ level (SPL), which is what people normally
associate with "decibels".
The paper goes on to calculate the predicted sound pressure levels at
seven sites - presumably neighbouring properties. These range from
34 to 42 dbA SPL - approximately quiet talking from 1 metre away.
("Normal" talking from 1 metre away is 40 to 60dBA.) That's very
different to 106 dBA SPL - a loud jackhammer from 1 metre away!
Again, I used Wikipedia as the source for this information:
http://en.wikipedia.org/wiki/Sound_power_level
http://en.wikipedia.org/wiki/Sound_pressure_level
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Paul Taylor Veni, vidi, tici -
I came, I saw, I
ticked.
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