Want to add Horn to bass amp

[olddawg]

A single 12" and 60/80W is the absolute minimum you can use if you donīt play alone.
Some customers ask for smaller amps claiming "we rehearse in a very small room" ... but the problem is the drummer, even if playing carefully and with a small kit he produces a certain sound pressure level around him, even in a closet, which you must match or at least approach.
If you dare, I suggest you build a powered cabinet, so you add an extra speaker, extra cabinet volume and extra power when you add it when needed, and keep the original combo as is for smaller gigs or rehearsal.
Not too complex, you get any used cabinet, even a dead one or a dead combo, or buy some cut to size wood (even particle board) and cook a simple one, then fit 2 x 10" or a single 12" or 15" , cut the back for a ready made plate amp and you are done.
No need for hardware or tolexing, just paint it flat black, onstage it will look like a tolexed cabinet anyway from a few feet away.

Depends on the drummer, genre, and situation. I have an old Gorilla SS 30 watt bass amp that I picked up for nothing. It originally had a 10" in it that I replaced with an old 12" JBL I had laying around. It's a sealed cab. People love it in my home studio and I and others have used it live. I like it because I'm old too and it's small and light. It's right on the edge of being practicle too. Rehearsals for my cover band, the bass player just plugs into the PA. Sounds fine. He has an active/passive option on his expensive bass. Never uses the active mode. At first he had some fancy expensive preamp/DI box. One day I got sick of him fussing with it and one day I said just plug the damn straight into the board. Sounded better. Now he doesn't bring it. Amazing what you can get by with if you can actually play and have a possibly decent instrument.