Date: Thu Mar 12 08:24:07 2009 Back to Contents ------------------------------------------------------------------------

Author: Zani, Gerald

Subject: Re: stereo speakers


The question about impedance matching and the resistance of stereo
speakers is an excellent question.

The question itself displays critical thinking about impedance matching.
It shows that most people think of a speaker as a resistive load and
assumed that selecting the output impedance of an amp is an application
of impedance matching.

People use audio systems their whole lives but are commonly unaware that
conventional impedance matching does not apply.

Selecting the right amplifier output impedance does not mean the speaker
impedance is being matched.

Thanks to Anthony and his students for broaching the question. - J

-----Original Message-----
From: [] On
Behalf Of Anthony Lapinski
Sent: Monday, March 09, 2009 8:18 PM
Subject: [tap-l] stereo speakers

I was discussing Ohm's law today, and a few students were asking about
stereo speakers and their resistance. Textbooks do few problems
speakers. From my understanding, a typical speaker is 8 ohms. This will
get a certain amount of current and voltage, providing a power (P = IV)
the speakers. If one replaces the speaker with one that has a lower
resistance, does this mean that the current (and power) will increase
a given voltage? Or is it that for a given power (volume), the current
will increase while the voltage will decrease (since R is now less)? And
the implication is that when the volume is turned up (P increases), an
amplifier must have a better power rating to supply the sound if the
speaker resistance is lower.

Is this correct? Can anyone provide some "basic" physics information
speakers, amplifiers, and Ohm's law?

From Thu Mar 12 08:24:07 2009