Have a block of wood cut to size with a surface area of approx. 20x30 cm, so that you can place a loudspeaker on it. The thickness should be at least 5 cm (estimated), possibly more. Choose the colour and type of wood so that it matches the loudspeaker, or paint, spray, etc..
Now for the hard part. You might be able to do this at a DIY store. Drill a hole in the middle of the block ("from below") with the diameter of the rod (6.5 cm); but not through. Only in such a way that you can put the wooden block over the rod and the construction is stable. It may be better if the hole is offset so that it coincides (approximately) with the centre of mass of the speaker. (Glue/glue, as needed...). It's best to ask at the DIY store if this is a good idea ... or if they have a better idea :-)

https://teufel.de/standfuss-...
https://d2um2qdswy1tb0.cloudfront.net/product-sp...