There is a current trend within the Woodchuckers Facebook group for turning passive speakers for smartphones. I made my attempt yesterday.
This is my version. Timber is ash for the horn, beech for the base, and oak for the phone stands. Sound travels through a piece of 22mm copper pipe.
The horn part still needs to be glued on, and there is no finish on it yet. I will take some photographs when it is 100% finished.