Speaker db rating?

Groundhog- Read this before you get too confused between amplifier output power, SPL and perceived loudness levels: (http://www.audioholics.com/education/frequently-asked-questions/relationship-between-watts-and-dbs) You'll notice that it actually takes 10 times the amplifier power to produce an SPL that SOUNDS twice as loud to our ears. That is an important factor to consider with your goals.

This site is a bit more in depth in it's presentation of the facts: (http://www.analogrules.com/dbwatts.html) The tool that Hemihorn posted takes these factors into consideration.

For simplicity:
Assuming 92db speakers
1 watt = 92db
2 watts = 95db
4 watts = 98db and so on...

Takes double the wattage to increase 3db
Takes 10 db to have perceived doubling of volume

Please forgive me for getting a bit off topic, but, with all due respect to JohnK; it doesn't make the case for hi-eff horns for me.

Hi: Other thing to take in count is how much power do we need for transients ?, maybe we can be safe about with an amplifier headroom of 5-6db for distortion free performance.

Regards and enjoy the music.
Raul.