speaking of volume.. every device I've ever used is obscenely loud. On my phone (with headphones) even just 1 increment on the volume is too much at times; on my windows PC I basically never go above 10/100. How are these things calibrated exactly
Evidently there isn't much standardization between devices. Personally I don't find it that annoying - devices remember what volume I last set them to.
But how about complex impedance? The phone could measure that instead. A perfectly inefficient speaker -- one where you're holding the diaphragm in place with your fingers, maybe, or where you've removed the magnet with a hammer -- will have a reactive component. It'll look like an inductive load if it's an old-school speaker with a voice coil, or a capacitive load if it uses a piezo transducer.
In either case, a perfectly efficient element that radiates all of the incoming energy would look more like a pure resistance, much like a properly-matched antenna at RF. So there might be some room to implement your suggestion, given a bit of R&D effort.