So I recently got a VOX AC4 to mess around with at home and in the studio. Wanting to throw in a new speaker for sure. Im trying to find a high quality speaker that I could throw in. Also any other simple mod suggestions I'm not aware of?

Thanks, Jon
Godin Passion RG-3
Gibson SG Standard
Egnater Tourmaster 4100
Fender Blues Deluxe Reissue
Marshall JVM215C
JHS Sweet Tea V2
Guyatone WRM5
TC Flashback Delay
Get a properly sized 1x12 cab with a greenback or a Weber blue or silver bell. I was never able to get my AC4 to sound great with the tiny stock cab. I don't think a simple speaker swap is enough.

After that, JJ tubes seemed to work great in the preamp and power, a nice CTS pot or two for the controls, and swap the smaller caps out for Mallory 150s. That's probably less than $50 and lets the amp breathe a lot more, far less stuffy when pushed. It doesn't have too many parts so upgrading is cheap. If it turns into your favorite recording amp I'd look into upgrading the output transformer. It's too expensive to be worth it for casual playing but I bet it would be the difference between a good cheap amp and a great low watt amp.