Most slapping bass players close both F-holes of their double basses....I think, to avoid feedback.
But unplugged the bass sounds dead then.
What does that mean to the amplified sound......?
Is it a difference to your sound amplified, when you close F-holes?

If it´s not necessary and I have no feedback with open f-holes.......should I close them or not...what gives a better sound amplified??????

If it ain't broke, why mess with it?

I had horrible issues with feedback, I'd have loved to have seen the closed hole setup. Has anyone got a pic?

Personally, I'd say, if it doesn't currently feedback, don't mess with it as moles said. On the other hand, if it is feeding back, then block it up. If works well for acoustic guitars. :)

There are ALOT better ways to avoid feedback. Do a search over on Rockabillybass.com, tons of good info on that and on this site too.

Closing the F-holes is strictly a feedback reduction trick.

If you're bass isn't howling like a moose in rut, leave them alone.