If your amp has plenty of power spare, then the series cable will work fine. The biggest snag is that the actual result is unpredictable, however, if you already have the other cab, it's a cheap experiment. If you are thinking of buying a new cab, then it could be an expensive mistake. Electrically, it's not an issue to run in series. The problem is that it always seems to make one cab louder than the other. One will sound out, and overshadow the other. When I tried it for an experiment, with a big 18" in one and my 4x10" in the other, all I could here was the 4x10 cab. The 18" driver may as well have not been there. On it's own it takes a lot of power to get it going, and the other cab is much more able to convert power into volume.