Hi,

Without knowing what guitar amp you have, I can just tell you one thing. If the guitar amp is open-back, it probably won't make a very good bass amp. That might be OK for relatively quiet practice or studio use, but probaby won't have enough punch to play on a stage in a band without a tuned enclosure. Matching the right speaker to a cabinet requires a certain amount of math or at least the measurements, to figure the cubic feet of the cabinet and match it with a suitable speaker. And also you have to take into consideration that a guitar amp generally does not have a high-wattage output (compared to a proper bass-rig).

There might come a point where you consider selling the guitar amp as-is and shopping for a good deal on a bass combo.

If you decide to proceed- Eminence speakers are the brand I'd say are most commonly found in a bass amp. They're available in a lot of different styles/models and reasonably priced. If you're looking for something a little more upscale - E-V, JBL, BlackWidow, Celestion, (to name a few) might be worth investigating.

I hope that helps.

Thanks dvdhawk. I bought a bass amp. Still sitting pretty with the ole' guitar amp. You're input was very insightful.