"dorothy.bradbury" wrote:

small audible reduction of 3 dB require a 50% reduction in sound
energy.

o The letter after dB is the Weighting applied
---- (A) is used for humans - poor at 25dB(A) since it is an approximation
-------- qualitative nature of the noise becomes important
-------- for fans bearing choice, vibration, resonance, blade-to-housing gap
---- (A) is really aimed at industrial noise
-------- hence there is a new ISO standard aimed at super-silent noise
levels

o A reduction of 10dB(A) is a 50% reduction in sound energy
---- 3dB(A) is the margin most people can detect
---- however this too depends on the noise level re 20s or 70s

I have to correct your science here.

A doubling of absolute signal power represents an increase in dB of 3dB.
Reference http://ccrma-www.stanford.edu/~oded/M151/decibels.html ,
but this is also generally known from any textbook.

Applying a profile as in db(A) makes no difference since dB reduction is
about relative level differences; putting in a profile will preserve ratios.

( Profile * signal_1 )/(Profile * signal_2) = signal_1/signal_2

"3dB(A) is the margin most people can detect" This is correct.