Speaker's efficiency, sensitivity and impedance

YES- semantic gymnastics seems the most popular sport in the audio industry, and these forums. You can see by the definition for "sensitivity/efficiency" given by a company some of you MAY be familiar with(after all the years they've been manufacturing for the sound industry), that even JBL considers the two terms synonymous- second question on this site: (http://www.jbl.com/home/product_support/JBL_contactus.aspx). The difference between the two terms lies in the input being measured in volts for sensitivity, and watts for efficiency(as mentioned), and that depends on the semantic application that the manufacturer or rater chooses to observe. Another professional view: (http://www.projectsunlimited.com/audioProducts/MovieClips/TechNotes/Glossary.asp?articalID=29) This site offers a caveat regarding the use of 2.83v as a reference, and how the result's affected by a system's impedance: (http://www.transcendentsound.com/amp_input_sensitivity_and_gain.htm) So much obfuscation found in here!

Jeff- View the last site(URL) in my last post. There's a brief treatise on how impedance, amp output and sensitivity affect a system's SPL(just past the halfway point of the article).

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!"