Acme Low B2-II
Andy Lewis came up with a seriously great line of cabinets which he released as the Acme Low B series. These are available as the B1 with 1x10", the B2 with 2x10" and the B4 with (you guessed it) 4x10" custom drivers. I chose the Low B2-II cabinets and a modular approach where I could use anywhere from one to four of these cabinets, depending on the stage, PA setup and venue.
In general you can pick any two of the following three attributes when designing a bass cabinet:
Light / small - a convenient size and/or weight
Low - great low frequency response down where it counts
Loud - more efficient designs that require less power
Andy chose the first two design elements for the Low B2, so the box is small, not overly heavy and delivers smooth even bass response down to low B (31hz) on a five-stringed bass instrument. These cabinets really deliver the goods and have such a nice even response throughout their range that they are suitable for PA use and even full-range audio playback.
The only minor downside to this approach is that these cabinets require a generous amount of amplifier power, although most modern bass amplifiers are capable of driving these cabinets to the required levels. To state this as clearly as I possibly can, the expectation has to be reasonable with regards to the amount of volume you're going to get out of these small cabinets with a given amount of amplifier power. For the mid-sized venues I'm currently playing in, 400watts does the job nicely with some amplifier headroom still available. For larger clubs I routinely use more power to get higher volume levels and still have plenty of amplifier headroom available.
While I have tried a number of other bass cabinets over the last few years, I keep returning to the Acmes for their unbeatable accuracy.
There is simply no question that I wish for more venues where I could actually put all four of my Acme cabinets to use. Depending on the size of the room, two or even a single Acme Low B2 cabinet will provide more-than-adequate coverage. These are truly amazing, accurate cabinets for the low price of admission and for that reason are nearly unbeatable.