Deep-sea divers often breathe a mixture of helium and oxygen to avoid getting the "bends" from breathing high-pressure nitrogen. the helium has the side effect of making the divers' voices sound odd. although your vocal tract can be roughly described as an open-closed tube, the way you hold your mouth and position your lips greatly affects the standing-wave frequencies of the vocal tract. this is what allows different vowels to sound different. the "ee" sound is made by shaping your vocal tract to have standing-wave frequencies at, normally, 270 hz and 2300 hz. what will these frequencies be for a helium-oxygen mixture in which the speed of sound at body temperature is 750 m/s? the speed of sound in air at body temperature is 350 m/s.