Subject: Sound Article: The Elusive Decibel (fwd)

Mike Williamson (
Thu, 3 Sep 1998 11:28:44 -0400 (EDT)

---------- Forwarded message ----------
Date: Thu, 3 Sep 1998 09:01:57 -0300
From: "David M.F. Chapman" <>
Reply-To: Marine Mammals Research and Conservation Discussion
Subject: Recent Article: The Elusive Decibel

Hello from Nova  Scotia, Canada

MARMAM subscribers may be interested to learn of a recent 3-page Technical
Note by David M.F. Chapman and Dale D. Ellis, entitled "The Elusive
Decibel: Thoughts on Sonars and Marine Mammals", published in Canadian
Acoustics 26(2) 29-31 (June, 1998).  There is no abstract, but the
introductory paragraph reads...

"A few years ago, there was considerable controversy over the effects of a
proposed global acoustic experiment designed to measure the temperature of
the world's oceans . The focus of concern was the possible effect of the
acoustic signals on whales and other marine life. There is continued
interest in the effects of underwater sound on marine animals, according to
a recent news item in The Economist  based on related scientific
correspondence in Nature . The thesis is that loud signals from
experimental sonars harm marine mammals, or at least harass them enough to
unacceptably alter their behaviour patterns. In the various discussions of
this important issue that can be found in the press and on the internet,
one often sees questionable comparisons being made, such as the acoustic
output of a naval sonar being compared with the noise from a jet aircraft.
Some misunderstandings between professionals in different fields can be
traced to the multiple uses of the term "decibel". Acoustical terms can be
confusing, even for experts. It is not at all surprising that
well-intentioned articles sometimes fail to present situations clearly. By
definition, the decibel is a relative unit, not an absolute unit with a
physical dimension; unless the standard of comparison is cited, the term
"decibel" is to all intents and purposes useless. The confusion is not
helped by the use of the decibel to specify distinctly different physical
quantities, or the same physical quantity with different reference levels.
Some reporters-and even some scientists-are getting their "apple" decibels
mixed up with their "orange" decibels, as it were."

Those with no access to Canadian Acoustics may request a copy from the
authors by writing to

David M.F. Chapman
Defence Research Establishment Atlantic
PO Box 1012
Dartmouth, Nova Scotia
Canada B2Y 3Z7

or  by sending email to

Please specify your preference for a paper reprint or an electronic version
in .pdf format readable using Adobe Acrobat.


Dave Chapman
DREA (902) 426-3100  x 228