growing popularity in the audiophile community of single-ended valve (vacuum tube) amplifiers has sparked renewed interest in the Klipschorn and other highly sensitive Klipsch models. Utilizing the room walls and floor boundaries as extensions of the bass horn helps extend the speaker's frequency response down into the 35 Hz range, considerably lower than would be possible otherwise. Because of the folded horn, the woofer cone moves no more than a few millimeters. As the only speaker in the world to be in continuous production for 70 years, the Klipschorn has remained relatively unchanged since its inception. Circa 1970, diode overload protection was added across voice coils to prevent burnout from clipping produced by an overdriven amplifier. The midrange horn was originally made entirely from formed wood. Some fibreglass bells were used on the midrange horn, as well as metal, in the late 1950s. Eventually the midrange horn was changed from metal to braced fiberglass, and the tweeter was front mounted in the 1980s. Both of these changes reduced the already low distortion. In 2005, the company made some minor cosmetic and functional revisions to this legendary speaker, including the elimination of the inset collar, or spacer, between the upper and lower cabinets for a cleaner appearance. A horizontal wall seal was added to improve the low frequency horn's connection to the wall. The crossover, which includes some equalization, was revoiced in the early 2000s. In 2006, Klipsch offered the 60th Anniversary Klipschorn, a separate model from the standard Klipschorn. In 2016, Klipsch released the 70th Anniversary Klipschorn with a fully enclosed horn. The release was limited to 70 pairs. Other legacy speakers Among Klipsch's legacy models, the La Scala and the Klipsch Belle, are fully horn-loaded and have extremely high sensitivity similar to the Klipschorn, but their "W"-shaped folded bass horns do not require corner placement in the listening room. The La Scala II, which uses the same drivers as the Klipschorn but has a smaller bass chamber and less bass extension, was voted into Stereophile magazine's "Recommended Components" in the "A" class for speakers with restricted extreme low frequency. Other models, including the Cornwall and Heresy, use horn tweeters and midranges in conjunction with direct-radiating woofers and also have unusually high sensitivity (although not as high as the fully horn-loaded models). All of the models cited above feature separate horn-loaded tweeter and midrange. As of 2006, the majority of