Speaker efficiency vs. power requirements

Hello great information and thanks for the input - just to clarify - the information I posted at the top is NOT my conclusion. This is however what *I* was told by someone who claims to know this stuff. As I pondered the statement, I grew unsatisfied with the logic and chose to post for discussion.

To clear some things up for some of you:
The mention of 90db is in regard to the speaker efficiency. I believe this number was selected since it was the rating of my speakers.

Another couple questions to further enhance this discussion:

1) Given the rated efficiency of a speaker - how does the Ohms rating effect power requirements? For example, a 90db speaker at 6Ohms.

2) Depending on which speaker, isn't it true that different frequency requirements may have more or less efficiency at varying ohms? What does this do to the overall power requirements?

And to top it off, what about impedance?

Just to further complicate the issue... a 3 db increase doubles the power (wattage). To double VOLTAGE, it takes a 6 db increase.

Drjjpdc: Your comment "Therefore a 200 watt amp has twice the wattage of a 100 watt amp and is only 3 db louder, which is about the limits that you can detect by ear." is WAY off base. I use a dB meter on a daily basis at work and differences of less than 1 dB are easily discernable on my less than "hi resolution" test bench using a 4" communications grade speaker and test tones. Some people have demonstrated hearing differences down into the millibel range under test conditions.

Herman: 100 dB's is too quiet. I would say that a system should be able to do at least 110 dB's at the seated listening position. This is not too hard to accomplish so long as you have enough amplifier for the size room that you are in and relatively efficient speakers that don't go into massive compression when fed some juice. Obviously, using more efficient speakers in a smaller room would put most people WAY ahead of the game. Sean
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Sorry Sean I did not mean to say that nobody can hear less than 3db differences. I meant to say that in the context of our discussion on amplifiers, a 3db difference and doubling amp power is barely discernible as hearing a loudness difference in the 2 amps. That is different than perceiving loudness changes in sound during decibel testing. That is why in audio circles if we have a 100 watt amp, we need to buy at least a 200 watt one to hear a noticeable difference in power as opposed to hearing subtle differences.

I was just reading Robert Harley's chapter on amplifiers in his book, "The Complete Guide to High-End Audio," last night. He explains all this fairly clearly. He makes it pretty easy to understand and calculate an amps potential versus speaker requirements, how to determine the dBW power rating, what it means, and why it is useful. Give it a read. You'll get all you need.