You are closing in on what you need to know very well. Let me expand upon the dB vs perceived loudness vs power relationship.
First, you already know that a 3 dB change will double or half the power required from an amp. You also need a few more things to know.
First, a 3 dB change in volume is perceived as only a small change in volume. In fact, it is considered the smallest change that we as normal people can detect as a volume change. Smaller changes are perceived as being fuller or somehow less full, or some other subjective description.
Next: To be perceived as being twice as loud a sound has to be 10 dB louder then the quieter one. Thus, 86 dB is twice as loud as 76 dB and half as loud as 96 dB.
Third: A 10 dB change in volume is a change in amp power of a factor of 10. To get from the 86 dB to 96 dB you need 10 times the power.
Forth and last: Music has dynamics, loud, soft and average levels. The speaker sensitivity specs combined with output power can get you to a average volume number but the music is going to peak out louder then that. The amp must be capable of producing those peaks without distorting. There is no "standard" for how much louder a peak is then the average for any piece of music. There are some good rules of thumb however. The two I use are: a) assume peaks are 10 dB above the average and b) size the amp to have 3 dB of headroom above your expected peak.
So how does this act in practice:
Assume speakers of 89 dB /watt/meter. (Somewhere between the higher efficiency spec of 92 and the lower one of 86). I've take some readings in my living room and have come to the conclusion that for me, LOUD is a average of about 86 dB. In this example, to reach my average listing level, since I am 3 dB BELOW the 89 dB spec, I only need 1/2 watt. (3 dB less is half the power.) But now I need to accommodate the peaks which are 10 dB above that average. That's 10 times the power, so I need 5 watts. We want 3 dB headroom above that so that doubles and you are now at 10 watts per channel.
Lets take a look at another example, this one the speakers are at 86 dB and you are a LOUD junkie looking for 89 dB average level.
To get to the average level you want, you need 3 dB more power then 1 watt. Increase volume 3 dB and you double the power. So instead of 1/2 watt, you now need 2 watts. To handle the peaks you need another 10 dB, that's a multiple of 10 so you are now at 20 watts. Add that 3 dB of headroom and that doubles to 40 watts.
If you try to drive those 86 dB speakers to averages in the low 90's things get drastic. Lets use 92 dB average. That an increase of 6 dB, so you quadruple the power needed at average or 4 watts. Factor in the peaks at 10 dB (10 times the power) and you are now at 40 watts and add the 3 dB headroom to protect against clipping and you are now at 80 watts per channel.
I hope this is understandable and helps you get a feel for how your listening habits and speaker sensitivity can interact to effect the amount of power you are going to need.
Shelly_D
