On 11/22/2010 7:41 AM, Adrian Tuddenham wrote:
The convenient shortcut dB formula relating voltages is often taught
with insufficient emphasis being placed on the conditions for which it
is valid.
This is why it's only been used over the last 30 or maybe 40
years, while the "power dB" goes back 80 years or so. It's
only been since the adoption of the nearly universal
voltage-not-power scheme of interfacing. This is primarily a
result of the use of solid state electronics which
characteristically have nearly zero output (source)
impedance but without the ability to supply any significant
amount of current. It's just how things work now.
After a while, people begin to believe that the voltage
formula is the true representation of dB until a situation arises where
it generates nonsense results
Not a lot of confusion, because, in general, audio people
TODAY work with dB of gain or voltage levels, and absolute
(not relative) watts when dealing with power levels. Someone
will understand a 100W or 200W amplifier, but won't think of
one having 3 dB more (power) gain than the other.
--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson
http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff