HOW TO UNDERSTAND DIFFERENT IMPEDANCE RATES?!!!

Brian McAllister mcallister at mindspring.com
Fri Jun 6 13:28:30 EST 1997


starship at freeside.fc.net (John Fields) wrote:

>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.
>--------------------------------------------------------
>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
>-----------
I think that the fallacy here is that you are comparing impedance
matched components to mismatched components.

If the test amplifer was a tube amp with a multiple impedance output
transformer, and each speaker was connected to its matching impedance
tap, the voltages would increase correspondingly and the power output
and therefore the sound pressure level would remain the same for
either speaker.

Even in your amplifier, the sound output would be the same for any
given amplifier power output.

Brian McAllister



More information about the Audiolog mailing list