A U
D I O... P A P E R
DYNAMIC
RANGE NOVEMBER 2001 by Steve
Deckert
It doesn't
matter if your listening to ten or a hundred watts, the most dynamic
range occurs in the first watt of playback. It calculates
out to around 30dB of dynamic range in the first watt. The
second watt adds another 3 dB. The power must be doubled for
each 3dB of increase. In audio, power comes with diminishing
returns.
A typical
noise floor in a small apartment is around 45dB during the day. The softest
tone the human ear hears at 1000 Hz is about 5 dB. (a tone that is just audible
at 30 Hz must be a at least 60
dB.)
In a 600,000 cubic feet concert hall a full symphony orchestra can reach an spl
of 120 dB at the listeners ear. The original power required to reach this level
by the orchestra is staggering. However to transpose this down to a say 4800
cubic foot listening room the power required to reach the same spl would be much
less. Assuming the listener sits about 8 feet away from the speakers, if his
goal was to reach an spl of 120 dB he would need approximately 40 acoustical
watts. There are speakers today with efficiencies as low as 0.1 percent. The
most efficient speakers available are close to 40 percent. The 0.1 percent
would require 400 times more power than the 40 percent efficient speaker. In
fact to reach 120 dB at 8 feet from the 0.1 percent would require 40,000 watts,
where the 40 percent speaker would need only 100 watts.
You might think
there is a huge difference between a 2 watt Zen triode amp and say a 120 watt solid state
amplifier but in reality its only 20dB difference. On a 100 dB efficient
speaker, 2 watts is 103dB and the bigger amps 128 watts is 121 dB. If you set
the volume dial for a peak level of 100 dB (way louder than the average listening
level in the home) there is no difference between the 2 watt amps and the 120
watt, 250 watt, or 40,000 watt amps. Gotta have that extra 20 dB of dynamic
range, turn down the noise floor  listen at night. This will sound far
superior to the same dynamic window during the day with a larger amp since there
is 20 dB less ambient noise polluting the sound you hear.
For what it's
worth.
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