And I was doing 12volts thinking it would be easier to keep it 12v since I'd be starting with 12v. But if its going to take more, then it'd be good to get +/-15 to 18v or so.
A TDA2030 amp chip produces only 10W into a 4 ohm speaker with a supply of positive and negative 12V. It produces 14W with a positive and negative 14V supply.
Why not use a TDA2005 bridged amp IC that is used for car radios? It produces 14W into a 4 ohm speaker with a 14V single supply.