Virtual “slack” strings are designed for and employed by the Laptop Orchestra of Louisiana. These virtual strings are “slack” in the sense that they can be very easily displaced, bent, tugged upon, etc. This enables force-feedback control of widely ranging pitch glides, by as much as an octave or more, simply by bending the virtual string. To realize a slack string design, a virtual spring with a specific nonlinear characteristic curve is designed. Violin, viola, and cello-scale models are tuned and employed by the Laptop Orchestra of Louisiana in Quartet for Strings.