This paper reports recent progress towards the development of a spatial ear trainer. A study into the perceptual construct of 'ensemble width' (i.e. the lateral spacing of the outer sources contained within an auditory scene) was conducted. With the help of a novel surround panner, exemplary stimuli were created. Changes were highly controlled to enable unidimensional variation of the intended qualitative effect. To assess the success of the simulation, a subjective experiment was designed based on Multidimensional Scaling (MDS) techniques and completed by an experienced listening panel. Additional verbal and non-verbal data were collected so as to facilitate analysis of the perceptual (MDS) space. Results show that unidimensionality was achieved, thus suggesting the stimuli to be suitable for training purposes.