I'm n gauge too, and was reading down this thread with the idea of 'consisting' some of these under the base board with bigger-than-loco-sized-speakers, as static sound decoders. I may have some larger locomotives in the future, that could take speakers (e.g. Farish WD), but I'll also always have some small tank engines that won't ever take a speaker, and I think the mix of sound an non-sound would be worse than no sound at all. With static sound decoders, all the space in the engines can then be used for capacitors.
I'm not a purist, and as long as it sounds OK-ish, it is probably better value for my needs. Does anyone know if there are issues with e.g. these econamai in consist mode without a motor connected? I saw in another thread someone had rigged up a motor and gearbox to provide a load under the board.