Hot air and OBP's

To: Birding-aus <>
Subject: Hot air and OBP's
From: Paul Taylor <>
Date: Wed, 06 Sep 2006 21:58:34 +1000
Andrew Taylor wrote:
I found part of the EES for Bald Hills at:
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:


   Paul Taylor                                  Veni, vidi, tici -
                           I came, I saw, I ticked.

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