Consider two such tubes at 20°C. One is filled with air, in which the speed of sound is 343 m/s. The other is filled with helium, in which the speed of sound is 1.00 × 103 m/s. To see the effect of helium on voice quality, calculate the ratio of the nthnatural frequency of the helium-filled tube to the nth natural frequency of the air-filled tube.
A few friends are goofing around with some left-over helium party balloons, taking turns to witness how helium alters the pitch of one’s voice. A simplified model of how your voice is generated by your vocal cords, is to consider it as cords vibrating above a gas-filled cylindrical tube that is open only at one end. The quality of the voice depends on the harmonic frequencies generated by the tube; larger frequencies lead to higher-pitched voices. Consider two such tubes at 20°C. One is filled with air, in which the speed of sound is 343 m/s. The other is filled with helium, in which the speed of sound is 1.00 × 103 m/s. To see the effect of helium on voice quality, calculate the ratio of the nthnatural frequency of the helium-filled tube to the nth natural frequency of the air-filled tube.
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