Who in their right mind needs an 8Ω speaker anyway?
Cables must be thick.
As of writing this, Time - Alan Parsons is being played in a far away room. Sound arriving at pristine quality. Speaker is a baffle Zeis Ikon with DEW drive unit of 12Ω. The 12Ω are steped up by a big auto transformer to 58.5Ω. A one transistor Pleiades BD139 transistor feeds those 58.5 ohms. Sound is big if not huge. The power into the speaker should be much less than 1W. Quiescent transistor current has just been measured to be 70mA! Impedance matching does the volume trick. No negative feedback gives a relaxed big sound. With no distortion to listener's brain.
Why not sticking with nice impedances for speakers such as 50Ω, 200Ω of 600Ω as used in studio microphones?
Output transformers if (or unlikely by then needed) would be low turn ratio maximizing quality and ease of construction (or minimizing cost).
Higher impeadnce speakers can be directly connected to a transistor or an electron tube. (At your risk, take all safety, life saving precautions).
A disadvantage of higher Z is possibly danger from a higher voltage. Not in the case of a Pleiades one transistor amplifier operating with just 12V (through safety fuse) and at say 100mA quiescent current through transistor operating in class A (electrons flowing all the time).
An advantage is possibly unneeded negative feedback.
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