Two speakers are set up d$=17\mathrm{.}7$md$=17\mathrm{.}7$m apart and facing one another. They then play identical tones in phase with each other. A student stands at the exact midpoint between the two speakers and begins walking towards one of them, stopping at the first point where she hears the volume reach a minimum. She then measures that her stopping point is r$=6\mathrm{.}5$mr$=6\mathrm{.}5$m away from the closer of the two speakers.