Chapter 2 Sound Waves: Section 2.1 & 2.2 (2.2.1 – 2.2.2) - Anqi

Section 2.1 Concepts

This section introduces the readers the physical perspective of sound waves. The whole section is very organized, going from the basic idea of sound waves, sine waves, to the phenomenon of resonance. As a science person, I feel this section is easy to follow. But I would suggest that since this section talks a lot about frequency and harmonic frequencies, a figure of sine waves of different frequency would help the readers to visualize the relations between, say a wave of frequency f₁ and another one with frequency f₂, where f₁ = n*f₂ (n is an integer). Also, at the end of 2.1.5.2 Resonance of a Transverse Wave, I understand that given lambda = v/f, we can get f = v/lambda, but I think some readers might find it sudden jumping from an equation v = sqrt(Fm/L) to f = sqrt(Fm/L)/2L.

The only part I found very confusing was the statement on the case of a closed pipe in 2.1.5.3 Resonance of a Longitudinal Wave, “air pressure is at its maximum at the closed end, so the closed end corresponds to the crest of the fundamental wavelength,” while in Figure 2.20 there exists a node, which is a fixed point instead of a maximum or minimum, at the closed end. From my understanding, as the molecules at the closed end cannot move, it has to be a node, while the molecules at the open end vibrate and thus form the crest of this sound wave.

· Learning Supplements:

The flash and video tutorials in this section well summarize the materials covered and the quizzes are closed related to the content. MAX was a little bit difficult to navigate at first, but mostly minor problems. There is so much to explore about this software. Hope I will feel more comfortable with it soon.

· Section 2.2 Applications (2.2.1- 2.2.2)

This section links the physics talked about in previous section to the real life applications and gives specific examples. 2.2.1 Ear Testing and Training is very intuitive and seemingly short compare with other parts of 2.2. I feel something is missing, but I am not sure what it is, and I think the music students might have better views on it. The first part of section 2.2.2 explains the importance of using tools for analyzing frequency, and introduces sound analysis system, including analysis microphone, one which is given an example later. However, I feel “The sine wave generates all frequencies equally, so the frequency response graph, in the ideal, should be flat,” where the word “equally” is quite confusing. It would make more sense if rephrased as “The sine wave generates all frequencies of the same amplitudes.” As human ears are sensitive to frequencies from 20Hz to 20,000Hz, why should the analysis microphone, mocking human ear, get a graph that is flat? Is it because the analysis microphone should be equally sensitive to sounds of all frequencies? From my understanding, the reason why we want the frequency response graph to be flat is not because “the sine wave sweep generates all frequencies equally” but probably the fact that the sounds of comparatively similar amplitudes sound more pleasant to the audiences.

· Learning Supplements:

- 2.2.1 Ear Training for Frequencies

This learning supplement shows how sound changes along with the frequency. Nothing too much to say about it.