HOW TO UNDERSTAND DIFFERENT IMPEDANCE RATES?!!!

John Fields starship at freeside.fc.net
Thu Jun 5 08:55:09 EST 1997


Arny Krüger (arnyk at pop3.concentric.net) wrote:


: Luc.vanHoye at ping.be wrote in article <33935466.1CC at ping.be>...
: > I am trying to figger out if the impedance of an audio device has
: > something to do with how loud its signal can go...

: It does not.

: Impedance and sensitivity are separate specifications.
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It does.

Consider an amplifier with an 8 ohm output impedance feeding 8 volts into 
a speaker with an 8 ohm impedance.  The speaker will be dissipating 8 
watts of power and will generate a specific sound pressure level.

Next, consider the same amplifier putting 8 volts into a 16 ohm load.
Since P = E^2 / R, the power being pumped into the load is 8^2 / 16, or 4 
watts, which will yield a lower sound pressure level.

The assumption, of course, is that both speakers have the same efficiency 
and are, in fact, identical except for their impedances.

John Fields
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