Southwell, William (c.1756–1842), musical instrument maker, was born in Dublin but little is known about his early life or family except that he had one brother, Nicholas. Educated locally, he became (1772) the apprentice of Ferdinand Weber (1715–84), the highly regarded German keyboard maker. Impressing with his ear for music and excellent craftsmanship, he soon established a reputation as a talented maker of quality musical instruments; in 1784 he was referred to as ‘the celebrated Southwell of this city’ (quoted in de Valera, 127). In 1782 he set up his own shop at 26 Fleet St., and began work on various improvements for the piano, which he patented in London. He had a flair for decoration, and made instruments that were far more elaborate than those of his contemporaries. In the 1780s he crafted some demilune table pianos, at least three of which are still extant; they combine mechanical virtuosity with exquisite cabinetwork. Part of Southwell's genius lay in his vast knowledge of piano-making techniques on the Continent; thus he was able to refine English and Irish designs, and incorporate improvements from Germany and Vienna. In 1794 he patented his greatest invention: a square piano with an extended compass, which he made by running the extra half-octave under the soundboard. This major breakthrough was soon copied by all other designers of square pianos. Moving to London, he made pianos for Longman and Broderip, and there is evidence that Joseph Haydn was so impressed with the craftsmanship and design that he purchased one of Southwell's models. In 1798 Southwell took out a new patent, which included improvements to his 1794 piano and a design for a harp with pedals. Working at Marlborough St. in London, Southwell also published music, imported instruments, and repaired damaged instruments. His business thrived, and in 1804 he entered into a partnership with his brother Nicholas and his own two sons. In 1807, after giving a speech in Dublin on improvements to the piano, he took out a new patent for an upright or ‘cabinet piano’, and this improvement helped make the instrument stronger and more durable. Continuing to work on refining his inventions into old age, he took out new patents in 1821 and 1837. Thereafter he disappeared from view, although it is believed that he returned to Dublin, where he died at Rathmines in 1842.
He married while in Dublin, and although other details of the marriage are unknown he had at least three sons and a daughter. His sons John and Francis assisted him in his work as a piano maker into the 1820s.