Since 1925, Keilwerth has concerned itself with creating saxophones that allow the musician to shape their own sound and style. With this in mind, Keilwerth took the technical advantages and improvements of the SX 90, and added some extra features to truly make the musician's instrument their own. The result was the SX 90 R (the R standing for tone hole rings), a saxophone reminiscent of the old Conn and Buescher saxophones of the 1940s.
The most striking feature of this saxophone is its tone holes. The SX 90 R uses tone hole rings which are soldered on to the standard drawn tone holes. The tone hole rings give the pads a longer life, and the rings themselves are easier to replace if necessary, because they are a piece separate from the tone hole. The production of darker, more immediate, less focused sound is an added benefit of the tone hole rings, which allow the musicians to form their own individual voice.