Speaker's efficiency, sensitivity and impedance

I'll admit, I only completed freshman college calculus and I'm no math wizard, but I can't follow the author's math. I wish he'd explain how he arrives at the following:

Let’s say the loudspeaker has an efficiency of 90 dB for one watt at one meter and the desired maximum sound pressure level during peaks is 110 dB (that’s really loud). This will require 100 watts. If the signal source is 1 volt maximum, how much amp gain is required?

100 watts into 8 ohms requires 28 volts. So the amp needs to provide a voltage gain of 28 times which is 29 dB.

Tvad- Read Robert Harley's "Complete Guide to High End Audio" available from Amazon=8>) The sections on "How Much Power Do I Need?" and "The dBW Power Rating" may lend some clarity. The only aspect Mr Harley leaves out is converting volts to dBW.(pages 159 through 162 in the Third Edition) I had skipped over the part you sited, and concentrated on the section right after when reading the Transcendent article. The writer forgot to say, "Trust me!"

Audiokinesis Duke, Thank you for the first complete explanation of this commonly misleading conundrum, I’ve heard..

Happy Listening!

Is it safe to conclude that the impedance of a speaker gives an indication of the current demand on the amp? It seems that as impedance falls there would be more current drawn to keep the equation in balance. If the amp is not able to supply the current we get clipping.

Is it safe to conclude that the impedance of a speaker gives an indication of the current demand on the amp

That would be very safe! That IS what the impedance actually tells you. It just doesn't tell you the whole story -- but it's a good part of the story!