This paper deals with sonic perception in entries and exits of underground spaces. My purpose is to describe sonic qualities or sonic failures in these spatial transitions which are very important in the global appreciation of subterranean spaces. This paper shows how a specific methodology can be used to develop a catalogue which connects spatial forms, sonic sources and social practices. Firstly observations of the same place but with different sonic sources and different practices will take place. Secondly, observations of the same practices and the same sonic sources will be executed but in different places chosen to value the effects of built up spaces, materials used, architectural devices used to come in or out. For all of these configurations, sociological, acoustical and architectural surveys will lead to the understanding what users feel in these transitions. Sonic quality is approached through the development of new protocols of measurement between acoustical criteria and subjective evaluation of listening. This research will focus on entries and exits in the Parisian subway (Paris - Gare du Nord ; Paris – Gare Montparnasse ; Eole). Data collected are recaptured around interdisciplinary tools such as the concept of the Sound Effect ;Augoyard, 95= in order to exactly describe sensitive transitions (sonic qualities) between two ambiences, an outside one and an underground one. Architects could use this methodology to improve the predictability of the sonic quality in their underground spaces projects.