Hi jmone,
Interesting question. You can actually go smaller than the 3-inch woofer in the M0 (Accent) or Audiobyte--IF you are willing to trade off other variables, output being one of the big trade-offs.
For example, I don't know if you have ever heard a tiny radio made by Tivoli Audio, called the PAL (Portable Audio Laboratory). It uses a 2-inch long-excursion full-range driver and a lot of electronic equalization to force the driver to reproduce a wide frequency range, including audible bass to about 50 Hz. BUT its major limitation is you cannot turn it up loud because the tiny woofer is already moving near the limits of its back-and-forth excursion so as to produce audible bass at a moderate listening level.
The Tivoli Audio PAL was developed by Henry Kloss (the original "K" of KLH), the founder of Advent, who also invented the first domestic video projector. The PAL was based on a high-quality table radio first offered by KLH in the 1960s. The KLH Model One used a slightly larger driver, about 3 inches, and extensive EQ. Kloss was also one of the early partners in Acoustic Reseach in the 1950s with Edgar Villchur, when they developed the first really good relatively compact acoustic suspension speaker that had deep bass output, the AR-1.
The 2-inch woofer in the Tivoli Audio PAL is the smallest driver in a speaker that I'm aware of that has effective bass output. Kloss decided that most listeners would be sitting quite close to the PAL, within a couple of feet, so high volume output wasn't needed. He traded that off for decent bass output at very moderate playback levels.
Regards,
Alan
