Acoustic Experiments with a Sound Card

Hermann Hoever

A sound card is not only useful for computer games. Here, I demonstrate that it can replace an expensive storage oscilloscope. I have used it for many acoustical experiments, from measuring frequencies of sinusoidal sound waves to the more complicated Doppler effect and measuring the speed of sound. For example, I have been able to measure the frequency of the sound that accompanies the Telecom's test image (channel S04). Furthermore, I used my sound card to visualize the waves associated with different sounds and vowels. I define the term "noise" and explain its consequences. In this context, I have demonstrated the risks associated with headphones experimentally, by demonstrating that they can be substantially louder than normal speakers. Resonant excitation of a body with its eigenfrequency is particularly interesting: I have recorded the sound of an oscillating wine glass and used it to excite the resonant vibration of the glass. I studied the beating produced by two sinusoidal sound waves of different frequencies, i.e. the oscillation of the resulting sound volume between loud and quiet. The Doppler effect allows the calculation of the speed of a sound emitting object that passes the receiver and I conducted such a measurement using my sound card. Finally, I measured the speed of sound. These experiments have taught me a lot about acoustics as it is much easier to understand these concepts by exploring them experimentally.

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