rickman wrote in :

You are aware that a standing wave still moves up and down, no?

Sorry about this.. even after my last post, I have a thought I can't drop
easily. A few years ago someone showed me a speaker cone in a video, driven
by AC current, and it had ferrofluid on it, but I think there was soem
comment that any thixotropic fluid will do. It had peaks and troughs, in a
sort of semi-random 2D form across the cone that held it. These peaks and
troughs did not oscillate up and down on the spot, they stood rigid as
merings peaks after drying in an oven. (Actually they did shift a little, but
not a lot, and that was mainly due to erratic vibrations in the whole
doings.) Anyway, would that effect not also be called a standing wave?