Creating a "perfect" portable monitoring amplifier speaker

It is difficult to have :


Small size and at the same time great bass


and at the same time a small, class A single ended power amplifier with perhaps one only transistor


and at the same time low battery consumption


and at the same time sounding correct to listener' brain.


But so far results are promising. An output transformer greatly helps improving efficiency or playing time or loudness. See for example the Pleiades BD139 one transistor amplifier with a custom made output transformer.


As of writing the Zeis Ikon baffle speaker plays which is more efficient than the Pleiades cube. But listing is an adjacent room.