Date: Mon Mar 9 20:18:27 2009

Author: Anthony Lapinski

Subject: 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 involving
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) to
the speakers. If one replaces the speaker with one that has a lower
resistance, does this mean that the current (and power) will increase for
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 about
speakers, amplifiers, and Ohm's law?