Synthesised acoustic guitar sounds based on a detailed physical model are used to provide input for psychoacoustical testing. Thresholds of perception are found for changes in the main parameters of the model. Using a three-alternative forced-choice procedure, just-noticeable diff erences are presented for changes in frequency and damping of the modes of the guitar body, and also for changes in the tension, bending stiff ness and damping parameters of the strings. These are compared with measured data on the range of variation of these parameters in a selection of guitars.