I remember seeing a piano from the early XX century that had a fourth string, however it was sympathetic (never struck) and there was no fine control of how man

I remember seeing a piano from the early XX century that had a fourth string, however it was sympathetic (never struck) and there was no fine control of how many strings were being struck. EDIT: found it! https://www.pianostreet.com/blog/piano-news/bluthner-and-the-aliquot-fourth-string-system-4711/ https://www.pianostreet.com/blog/piano-news/bluthner-and-the...