The best way to explain the differences between R-series mics (R-121, R-122 MKII, R-122V) and SF-series mics (SF-12, SF-24, SF-1) is to take a look at their ribbon transducers (the transducer is the magnetic frame or assembly that the ribbon element is housed in). This is the R-121 transducer (also used in R-122 MKII's and R-122V's). It has a long, wide, thick (2.5 micron) ribbon element. The transducer is a "flux frame" design; basically one frame that the magnets are secured to and the ribbon element sits in. It's a tough ribbon design that can handle sound pressures that would blow most ribbon mics (135 dB SPL at 20 Hz). This design makes the R-series mics tough enough to use in live applications (see Are ribbon mics recommended for live use?) The R-series transducer has a slight upper midrange rise (see frequency response) that gives it a little extra presence and "character." Our R-series mics have become "must haves" for the recording of rock, pop, jazz, and country music. This is the SF-12 transducer (also used in SF-24's and SF-1's). Compared to the R-series transducer, it has a shorter, narrower, thinner (1.8 micron) ribbon element. The transducer is a more "classic" design, utilizing separate magnets at the four corners and two pole pieces that the ribbon sits between. While SF-series mics can handle 130 dB SPL (at 40 Hz), they are not recommended for extremely loud applications. The SF-series transducer gives a warm, flat response and extends a few kHz further into the high frequencies than our R-series mics. Its more purist sound lends itself to strings, woodwinds and other classical applications. The stereo imaging and realism of the SF-12 and SF-24 is uncanny - excellent for ensambles, drum overheads, choirs, acoustic groups, etc.