Thanks - yes good advice. The CD is temporary. I'm planning to make a wooden soundhole cover in the future with some 1x8 white pine I have in the garage. The pine is soft and easy to shape with a jigsaw and a small router/trimmer towards a Lutehole-type shape.I'm curious how the sponge can dampen overtones when it's past the nut and most often the fretted string too. Seems like a dead part of the string past the nut. I've heard about this but havent tried it and don't understand how it could work. I suggest spraying the cd black or some other solid color.
Maybe an oil rub to add some colour.
Regarding the sponge above the nut - I did a test with it on and off, and it clearly kills some wolf notes. There are so many sounds that come from this sweet lovely acoustic bass. The sponge cleans it up a bit. I had to do the same thing with my baritone - the thicker strings bring some overtones.

