This piano, which has a one-piece, "double-iron" frame with struts in front _and behind_ the soundboard, also features a "resonator" (US patent #55,385 by William Steinway, June 5, 1866), a whole-perimeter soundboard-compression mechanism. Another interesting feature is the "unifying bridge," which extends to the left from the bass bridge to the long bridge and slightly past it "for the purpose of equalizing the transition from the steel strings to the covered bass strings, thus preventing any break in tone" (from the patent). Note that in the patent the word "string" is misspelled as "spring" in at least two spots.#vertical #upright #Steinway #doubleiron