Module4 - Physics 434 Autumn 2007 Module 4 Impulse Response...

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Autumn 2007 Module 4 Impulse Response of the Kundt’s Tube and Analysis by Fourier Transformation Introduction Previously, you developed an automated system to characterize the response of the Kundt’s tube to sound waves driven by a known frequency. You generated a transmission spectrum of the tube by scanning the frequency of sound sent to a speaker at one end of the tube and measuring the average of the absolute value of the time varying amplitude of the sound recorded for a known time interval using a microphone at the other end of the tube. You noted a series of peaks in the spectrum occurring at frequencies (very roughly) approximating the ideal f n = n (c s /2L), for a tube closed at both ends, where L is the length of the tube, c s is the speed of sound and n is an integer. Now, you will reconfigure the Kundt’s tube to measure its response to an impulse. You will observe that the tube exhibits a “ring down” behavior, something akin to the sound a bell makes when struck with a sharp blow. Fourier transformation analysis of the ring down will generate the same spectrum of frequencies you’ve seem from the Kundt’s tube. The impulse response experiment is a specific case of the stimulus response experiment. Here, you will generate the impulse using the timer-counter facility of the DAQ board to produce a logic pulse of a software selectable time duration. Then, at the end of the pulse you will acquire the sound-wave (pressure) response of the system using a microphone connected to the ADC. The response from the data acquisition is given in Figure 1, for an ideal tube, with perfect reflection of the pulse, and a slight decay. Because the experiment is over so quickly, and so readily repeated, you will develop a facility in your VI to add many experiments together to improve the signal to noise ratio. Figure 1. Response from impulse in ideal tube
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Module4 - Physics 434 Autumn 2007 Module 4 Impulse Response...

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