Based on the circuit of K. Jones.
It is connected directly to the headphone out of portable devices.
It uses one active device only per channel. For example a 2N3055 bipolar transistor.
The full range speaker for each channel is connected to the collector being itself the load resistor.
The emitter is connected to ground.
A few KΩ resistor from collector to base provides bias.
The signal is applied to the base through a capacitor. If the music source output capacitor can withstand the DC voltage this capacitor can be omitted. So it is just a power amplifier with 3 components per channel including the speaker.
Battery (+) is applied through a fuse to the other speaker terminal.
Battery (-) is connected to ground.
The value of the base biasing resistor is determined experimentally by arranging with a variable resistor a not excessive DC displacement of the speaker cone.
The transistors should be used with a heat sink to minimize the risk of thermal runway.
Everything is in the same cabinet with both speakers and a 12V battery.
Or it can be made to an active speaker for each channel.
This is the Pleiades power amplifier.
Only 2 components per channel.
It operates in class A meaning electrons flow all the time through the active device. It sounds smooth, dynamic, loud. frightening realistic with no noise, no hiss and natural sweet sound.
Electrons flow all the time through each speaker too.
All protection should be exercised including a fuse next to the battery terminals for example.
A special version can be made for vocals, echo chamber use etc or for electric bass or guitar.
Pleiades concepts, designs, schematics are open source for anyone wanting to improve, build, sell.
Reference:
Audio Amplifiers - J. R. Davies - Data Publications LTD. London - chapter 7 - page 41 - 2 transistor miniature A.F. amplifier by K. Jones
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