Actually, many of the Lowther and Fostex eight inch drivers share similar Thiele/Small parameters. The Fostex FE-206E and FE-207E and most of the eight inch Sigma drivers along with almost all of the Lowther drivers are fairly close. They tend to have light cones with large magnets producing low Qts and high SPL for 1 w at 1 m.

I swap my Lowthers (PM6C, PM2C, PM6A, PM2A, and the DX series) in and out of my ML TL design every few weeks. A quick adjustment of the variable BSC to get the SPL balanced and I sit back and listen. All of them sound slightly different with different strengths and weaknesses. Typically one trades bass response for high frequency response as the magnet gets bigger. Many other people have used the Fostex FE-206E and FE-207E in the same enclosure with slight changes to the port length tuning and the correction circuit.

Most of the time, swapping a full range driver requires small adjustments like the amount of stuffing, different postions in the room, or different filter components. A lot of the enclosure designs can accomidate many different, yet similar, full range drivers. Also, one needs to keep in mind that the enclosure produces the bass and adds its own baffle step signiture. But once you get above say 400 Hz, the sound is all from the driver and the enclosure is not so important. Swapping full range drivers in a box impacts the bass produced from the box and then the mids and highs are from the driver itself.

Martin