In the 1989 Stereophile review of the RSTL, there was some technical data I hadn’t run across before:
- The midrange line is not intended to increase output at all, but rather completely absorb the rear wave. Note the midrange line is completely stuffed, whereas the woofer lines are not
- The output of the midrange line is claimed to be 40dB down from the main output
- The midrange transmission line does lower the resonance frequency of the driver (to 40Hz), moving it away from the crossover point and hence (potentially) simplifying the crossover
- The crossover slopes are 3rd order. It is not clear to me if this is stated in the literature or observed in the measurements. It is also not clear if this is electrical, acoustic, or both
- The design mounts the two 6″ midrange units on a 5″ wide front baffle 😉
Point #1 is not surprising given the mids are crossed over at 200Hz in the RSTL, so there is no need for any bass augmentation from the mids.
Point #5 shows just how creative John Wright is!