08a - 8A: SOUND WAVES IN TUBES-PART II C. STANDING WAVES IN...

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8A: Standing Waves In Tubes-part 2 - 1 8A: S OUND W AVES IN T UBES - PART II C. S TANDING W AVES IN A T UBE C LOSED AT O NE E ND 1. Introduction Last week we discussed standing waves in tubes open at both ends. Today we will investigate generation of standing waves in “close” tubes. We use the term closed tube when discussing a tube with one closed end and one open end. A periodic sound wave, generated by a small speaker near the open end, travels down the tube, reflects from the closed end of the tube and is superimposed on the original wave. One would expect a standing wave or resonance to occur if the next wave to start down the tube reinforces the waves already bouncing up and down the tube. When a positive pressure pulse hits a closed tube end, it is reflected as a positive, not a negative, pulse (no phase shift). If a positive pulse is started at an open end, it travels down the tube, reflects back as a positive pulse, reflects at an open end as a negative pulse, reflects at the close end as a negative pulse and finally, after two round trips, ( 4L ), reflects down the tube again as a positive pulse, reinforced by the next pulse from the speaker. The fundamental frequency, f 1 , is thus: f 1 = v / 4L
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This note was uploaded on 01/20/2012 for the course P 109 taught by Professor Staff during the Fall '08 term at Indiana.

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08a - 8A: SOUND WAVES IN TUBES-PART II C. STANDING WAVES IN...

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