Tunable Duplex Scaling
Both Fazioli and Mason and Hamlin (of Haverhill, Massachusetts) employ tunable duplex scaling. The idea behind duplex scaling, invented by Theodore Steinway in 1872, is that the non-speaking portion of the string, located between the non-speaking bridge pin and the hitch pin (formerly considered the "waste end" and damped with a strip of cloth), resounds in sympathy with the vibrating portion of the string. Steinway & Sons' earliest employment of the duplex scale made use of aliquots, individually positionable (hence tunable) contact points, where each note of the duplex scale bears a perfect harmonic, intervallic relationship to its speaking length, i.e., an octave or fifth whether doubled or tripled. Because it was time-consuming to correctly position each aliquot, Steinway abandoned individual aliquots for continuous cast metal bars, each comprising an entire section of duplex bridge points. Their feeling was that with an accurately templated bridge and carefully located duplex bar, the same result would be achieved with far less fuss.
Mason & Hamlin, however, embraced Theodore Steinway's original idea. They felt that the tuning of these short stretches of free string can be achieved with greater accuracy than can be attained with a duplex bar. With the fixed points of a duplex bar, small variations in casting are liable to produce imperfections in the duplex string lengths. Furthermore, since variations in humidity can cause duplex scales to move in pitch more rapidly than the speaking scale, manual readjustment of the string tension on the non-speaking side of the bridge, and/or a readjustment of the duplex position to better accommodate humidity fluctuation, is feasible with individual aliquots.
More recently, Fazioli has modified Theodore Steinway's original idea by creating a stainless-steel track, fixed to the cast iron plate, on which aliquots slide. This system improves the ease with which aliquots can be adjusted, both during manufacture and during subsequent service.