Judgment of musical instrument quality is a complex process that implies criteria relating to the nature of the sound produced (accuracy, timbre, ...) but also sensations closely linked to the contact between the instrument and the musician (ease of playing,...) byt also sensations closely linked to the contact between the instrument and the musician (ease of playing, ...). From this viewpoint, a set of trumpets was studied (Causse and al, (1995) ): from playing tests carried out by professional trumpet players, attempts were made, on the one hand, to define subjective factors they used in their judgments and, on the other hand to correlate these factors with geometrical or acoustical parameters. This preliminary study led to three notions implied in this judgment process, among which was the sound volume, and to propose, for each of them, a significant physical interpretation. Following this study, the sound volume, which is an important component of the trumpet player's vocabulary and which seems to be associated with a broader notion of openness, was focused on. Different possible interpretations of openness, through a questionnaire, followed by an experimental procedure (playing and hearing tests), were explored. In addition, complementary measurements were done in order to propose a more precise physical interpretation. The first results obtained from the second study will be presented and discussed.