Sound Waves

As you know, sound is a longitudinal pressure wave that travels in air, at approximately 344 m/s at the room temperature, 20 degrees Celsius under one atmosphere.  In Lab 2A, we will study the physical properties of sound by changing its frequency and amplitude, allowing us to both visualize the waveform and hear sound as it comes from various sources (waveform generators, pianos, guitars, etc.). In Lab 2B, we will log the waveform using a microphone and further analysis will be conducted. Lastly, in Lab 2D, you will study a more complex property of waves known as interference. 
  • Lab 2A - Generator and Observation of Sound Waves 
  • Lab 2B - Complex Sound and Fourier Analysis
  • Lab 2C - Sound Interference

Lab 2A -  Generation and Observation of Sound Waves

Pre-Lab 2A - Operating Waveform Generator and Oscilloscope

For this Pre-Lab,  become acquainted with how a waveform generator and an oscilloscope work. It is crucial that you learn how to operate these 2 tools proficiently in order to complete the rest if this course and become successful further in your career. 
  • A waveform generator is, as the name implies, a device that is able to produce a waveform. These can be in the form of a sinusoid, square wave, triangle, etc.. 
  • An oscilloscope is a device that allows you capture a waveform in the form of voltage vs time.
Please refer to Electronics Resources page to learn in detail how to operate these tools before coming to class.
Download the Tektronix oscilloscope software, OpenChoice Desktop.

Fill in the slides in the Pre-lab assignment and submit it to gradescope. The Pre-lab is due 1 hour before your lab session.

Lab 2A - Generation and Observation of Sound Waves

For this lab, we will generator a sinusioidal waveform using the waveform generator and listen to that signal through a set a speakers. Then, we will use an oscilloscope, to see if the waveform that we created is in fact a sinusoid with the frequency that we outputted from the waveform generator. Following, we will capture the sound through al microphone and display the signal on the oscilloscope in parallel to the signal going directly to the speakers. Lastly, we will use the microphone again to capture the resonant frequency of an Aluminium bar and determine the speed of sound within that medium. ​

Lab 2B -  Complex Sound and Fourier Analysis 

Pre-Lab 2B - Introduction of Fourier Analysis

Now that we have determined that our microphone is indeed capturing the proper waveform of a sound signal, we will capture various sounds and analyze them through a method called Fourier Analysis. 

Please watch the following video to gain an understanding of what Fourier Analysis is and what a Fourier Transform does.
​After you gain a visual understanding of what a Fourier Transform is, complete the following Pre-Lab assignment. The sound .wav files are located in the sounds folder.

Lab 2B - Acquiring Sound and Fourier Analysis

We will now record complex wave forms using the Arduino/Microphone combination. First you will generate a pure tone that will be used to calibrate your data acquisition device (DAQ) and then you will record major and minor chords from a Piano and Guitar. After that you will record a damped oscillation from a single note. Finally, you will perform Fourier analysis on your data.

Lab 2C -  Sound Interference

Pre-Lab 2C - Interference

Interference is defined as "​the combination of two or more waveforms to form a resultant wave in which the displacement is either reinforced or canceled." Therefore, if two sound waveforms are observed and they are in certain configuration, they will cause an interference pattern to occur which could results in either a constructive or destructive pattern. For this pre-lab, you will theoretically simulate interference of two waveforms coming from points sources separated some distance apart.

Lab 2C - Sound Interference and Fourier Analysis

 In this lab, this phenomena will be observed by two methods. The first will rely on observing a pattern as you scan space with your detector (microphone). The second method will displace the two "point" sources by some amount that equates to a phase shift in their waveform. 

Unit 2 Report - Sound
edited August 1, 2024 by Mingda He