On Fri, 2007-08-31 at 14:59 +0200, Jens M Andreasen wrote:
Late one friday afternoon, a sound-engineer was
sitting in his chair
admiring a brand new pair of flat frequency response monitors. He then
observed the following:
For two frequencies represented by sine-waves and an octave apart to
have the same relative loudness, the higher octave will need to have its
amplitude adjusted to half of that of the lower octave.[1]
Both frequencies will then force a membrane to travel the same distance
within a given timeframe - the higher will go half as far but twice as
often than the lower - and they will also both have the same speed or
steepness at the zero-crossing.
Surprisingly, the lower frequency consumes four times as much energy
than the higher[2], although it is apparently not doing any more actual
work.
At a lower frequency the magnet has to work against the tension of the
membrane for a longer time - I'm sure a speaker cone doesn't obey a
perfect Hooke's law, but it may have something to do with it.
--ll