Virtual reality has demonstrated successful outcomes for treating social anxiety disorders, or helping to improve social skills. Some studies showed that various factors can impact the level of participants' anxiety during public speaking. However, the influence of sound design on this anxiety has been less investigated, and it is necessary to study the possible impacts that it can have. In this paper, we propose a model relating sound design concepts to presence and anxiety during virtual reality interactions, and present a protocol of a future experimental study aimed at investigating how sound design and in particular sound distractions can influence anxiety during public speaking simulations in virtual environments.