I need to replace the loudspeaker in our Kundt’s tube. It’s homemade and some of the homemade things are so ancient or esoteric that like for like replacement is impossible or too expensive, and I need to work out what a suitable replacement is. There was also a “colourful character” a few years ago whose legacy is somewhat erratic!

Things didn’t get off to a good start when I needed a metric Allen key and imperial socket to remove the bolts holding it in.

So I was very relieved to find not only can I buy the exact same speaker but it’s available from a usual supplier and less than a tenner.