First time I post a thread on this site. Not sure if I have it on the right section so I apologize in advance if I don't. I own a Crate BT220 combo amp. 220 watts at 4ohm into a single 15" speaker. It has a external out put jack to add an external cab and it clearly states it connects it in SERIES and it recommends a 4ohm cab. I am currently building a custom 12" cabinet and am planning on putting in a 12" 4ohm speaker. From my research I know in the end it will make the output to both the internal speaker and the external cab lesser wattage and 8ohm to each. My initial problem is it just doesn't seem loud enough as is so wanted to expand into adding more speakers. My question is would it even be worth it to continue this project knowing my end results is more volume overall? A high end 12" speaker would be bought so assume quality of speaker doesn't matter here. I was told overall having the 2 speakers (1x15 and 1x12) at 8ohm wouldn't be louder and in fact might be at a lesser volume then running the single built in 15" at 4ohm like manufactured. I rather ask fellow bass players who have probably mixed and matched and have experience running these different setups.