kenjit
You asked about how an amp can be designed toward a particular speakers driver. As I'm sure you know impedance changes due to frequency, a very low frequency signal at a loud volume creates a low impedance. Not all amps are designed to be a one size fits all answer. Sub amps have dozens of signal filters to try to match the signal to the amplifier, a compromise of the music, and low frequency amps are the easiest to design because they only have to deal with a very small frequency range. The reason why every sound system needs a sub is because amps can't be all things to all speakers but an amp designed for low impedance loads can do a better job than and amp designed for 10Khz. The perfect speaker would have an amp for every frequency but 15 thousand amps in our living rooms is a little much. Matching a curve is very hard and if music was a sign wave it would be easier but music is very complex and impedance and many other factors in a music signal reproduction show themselves to amps at the same time which makes amplifying those signals a compromise when heard on the speaker. Amps that are at least designed to amplify the best guesses of the complex signals created by recordings in a narrow frequency band are better than brute force amps that are huge and can handle a .5 ohm load created by a synth but can't at the same time reproduce the triangle. This is why no matter how expensive the speaker and amplifier it never sounds like a real instrument.
Once I was mixing an orchestra at a church and the conductor asked a violinist with a Stradivarius to come and play for me at the mixing console, well she did and tears came to my eyes the sound was so beautiful, I've never heard a recording half that good.
