This experiment explores how changes in soundpost height affect the perceptual qualities of the violin and whether there is a threshold of change below which players and luthiers do not perceive differences. A violin installed with a height-adjustable carbon fibre soundpost was employed. The experiment was designed as a sequence of playing tests. An experimenter was present to change the soundpost height. Thirteen professional violinists and six luthiers participated. The experiment involved two phases. During the first phase, subjects played and described their feelings about the violin with different soundpost settings in order to find their optimal soundpost height. During the second phase, the experimenter randomly increased, decreased or did not change the soundpost height in ten trials within a range of approximately ±0.1 mm around their optimal height. For each trial, subjects were asked to play the violin, comparing it with the previous setting, and to decide whether they were the same or different. Initial results indicate that each subject's optimal soundpost height varies within an interquartile range of 0.3 mm and the smallest height variation that could be recognized above chance level is about 0.04 mm.