Let’s try some actual numbers.

A fancy passive IEM quotes:

> Sensitivity: 114 dB-SPL (@ 0.1V)

That’s on the high side for an IEM. Let’s be conservative and say it’s actually 100dB SPL at 1mW (which is on the low side) and that the user has hearing loss and the IEM is actually outputting 90dB continuously (I’m not an expert but this seems high. Certainly I would not set an active IEM anywhere near that loud, even at a concert). That’s 0.1mW of electrical power to each IEM, for 0.2mW total. This part could run for days on a small battery pack.

A modern amplifier might as well be 100% efficient, although that body pack could easily be some wildly efficient Class A design.

Let’s suppose the DSP is processing 96kSPS (might as well minimize latency and the need for a complex antialiasing setup and let’s assume it’s using a duper-high-fidelity FIR filter that’s a whole 100ms long, i.e. 9600 taps, and that the FIR implementation is pure brute force, so there are 9600 times 96k FMAs per second. That’s about 2 billion FMAs per second for both ears. (Again, this is a ridiculous way to do this.) The fancy nonlinear compression stuff will be negligible in comparison.

From some quick Googling, you could easily spend a whole watt on the DSP. And there’s where all that battery charge goes :)

I bet that someone who really cared about optimizing this could put some software engineering into getting DSP power down below 50mW. Either use an FFT to optimize the filter or use a much lower complexity filter bank.