I have a 65 Amps London combo that sounds stellar with it's Celestion Blue and G12H30. Being open back, naturally, the bass was not as robust as if it were closed-back. That's OK, as I really like the swirlly-open sound the open back provides. Dan with 65 Amps said that the closed back cab they offer had more bass, but was more directional. I like the sound of the older Celestions, so when Jim cloned them and came out with his Scumbacks, it occured to me that a 55hz cone Scumback might just add enough bass to give the combo some more bottom, without loosing what I like about open backed speakers. I had asked the question here to see if anyone else had done it, talked to Jim about it, and decided to go for it. Yowwzah! A home-run! I like the combo even better. Both the "color" channel and the trem channel have more character than before (an unexpected side benefit!). The trem channel, in particular has gotten even more guts and girth. It has caused the channels to be even more distinct/different from each other, in a really good way. The Scumback hasn't had days of break-in time, but despite that, still has that "smooth" character that the more modern (I've not heard the newest reissues) Celestions lack...they just sound "harder", somehow, to my ears. Well, that's it...the 55hz cone in the open backed cab (with a blue) is a winner for me. Of course, YMMV, etc.