... why are amplifiers not built as a high impedance current source?Mainly because speakers are designed to be driven by a low impedance voltage source. When amps and speakers are co-designed though there exists the possibility to use current drive - I believe Bruno Putzeys has done this on his actives (Kiis) over at least part of the frequency band.
Are all amps being built wrong?
The power amplifiers that drive our loudspeakers are mostly built as a low impedance voltage source. They have always been ... but why?
Loudspeakers have a (greatly) varying impedance over the frequency range. A current drive amplifier would eliminate the issues that stem from this varying impedance, and at the same time make discussions about esoteric speaker cables that strive for optimal R, C, L superfluous. Although there still would be these un-measurable ’this (very expensive) cable sounds better’ debates and opinions ... and that’s OK, that’s part of the fun. :)
So ... why are amplifiers not built as a high impedance current source?
This is an interesting read: https://www.current-drive.info/
Loudspeakers have a (greatly) varying impedance over the frequency range. A current drive amplifier would eliminate the issues that stem from this varying impedance, and at the same time make discussions about esoteric speaker cables that strive for optimal R, C, L superfluous. Although there still would be these un-measurable ’this (very expensive) cable sounds better’ debates and opinions ... and that’s OK, that’s part of the fun. :)
So ... why are amplifiers not built as a high impedance current source?
This is an interesting read: https://www.current-drive.info/