Experiment 5: Introduction to Sound

Introduction

                The purpose of this experiment is to understand the sound waves by examining their characteristics such as their wave pattern, frequencies, amplitudes, periods, and wavelengths. Simple relationships between these characteristics are used to compute and confirm the experimental results.

                This experiment was conducted using a tuning fork, a microphone, and a Lab Pro. The experiment was set up as shown in figure 1. For the first part of this experiment, a pressure vs. time graph of a person saying “AAA” into the microphone was constructed using Logger Pro. This procedure was repeated with a different person saying “AAA.” Once the graphs were constructed, a comparison between these graphs were made and analyzed. As a second part, a pressure vs. time graph of a tuning fork stricken by a soft object was constructed, and this was repeated with the same tuning fork with a different loudness. The graph was analyzed, and a comparison was made. Finally, the sound waves produced by a human voice and a tuning fork were compared and were analyzed.

Figure 1: Experimental set-up

Data and Analysis

Table 1: Comparison between the sound waves produced by first and second person

Person	Period(s)	Frequency(Hz)	Wavelength(m)	Amplitude	# of waves in 0.03s
1	0.0085 ± 0.0005	118 ± 6.9	2.9 ± 0.17	0.850 ± 0.005	3.5
2	0.0075 ± 0.0005	133 ± 8.9	2.6 ± 0.17	0.078 ± 0.005	4

Table 2: Comparison between the sound waves produced by a tuning fork with different loudness

Person	Period(s)	Frequency(Hz)	Wavelength(m)	Amplitude	# of waves in 0.03s
1	0.0040 ± 0.0005	250 ± 31.3	1.4 ± 0.17	0.101 ± 0.005	7.5
2	0.0040 ± 0.0005	250 ± 31.3	1.4 ± 0.17	0.012 ± 0.005	7.5

Figure 2: Sound Pressure vs. Time of a human voice (1) 

Figure 3: Sound Pressure vs. Time of a human voice (2)

Figure 4: Sound Pressure vs. Time of a tuning fork (1)

Figure 5: Sound Pressure vs. Time of a tuning fork (2) 

Figure 6: Sound Pressure vs. Time of a human voice with a time frame of 0.3s

Summary

               The sound wave produced by human voice in this experiment was a periodic wave because the same pattern was repeated in a measured time frame. For instance, as shown in figure 2, the wave pattern from 0.0s to 0.0085s repeatedly showed up for 3 and a half times in 0.03s. This was confirmed by dividing the total time taken by the period, and it also resulted in 3.5 waves. Since one complete wave pattern was seen in the first 0.0085s, it was taken as the period of these waves. Hence, frequency turned out to be 118Hz since the frequency was the reciprocal of the period. The wavelength was also computed to be 2.89m, where v was equal to the speed of the sound. Besides, figure 2 showed that the power was changing from minimum 1.8 to 3.5 units. Therefore, the power amplitude was determined to be half of the difference between these 2 values, which was 0.85. If the sample was 10 times as long, these characteristics would probably not change. Perhaps 10 times as many waves would be shown in 0.3s. In figure 6, the sound wave of the human voice in 0.3s time frame was recorded. However, the voice loudness, tones, and frequencies had all changed.

In comparison to figure 2 and 3, figure 2 had larger period since the period in figure 3 was about 0.0075s and that in figure 2 was 0.0085s. Therefore, the frequency of the first person was smaller, hence, smaller pitched. Since they had different frequencies, their wavelengths also differed as shown in table 1. Their amplitude differed because they had different loudness. The first person’s voice was louder than the second one; hence, the first one had higher amplitude. In addition, figure 3 showed 4 waves in 0.03s whereas figure 2 showed only 3 and a half waves in the same period of time. All of these differences were shown in table 1.

In figure 4 and 5, both of the graphs were created by a sound from the same tuning fork but with different loudness. Since both of these were of the same tuning fork, they were expected to produce the same wavelength and frequencies. This was confirmed by these experimental results shown in figure 4 and 5. However, they produced amplitudes with a difference in the order of 10 as shown in table 2. This was because the loudness of the sound was dependent on its amplitude. In the second trial with the tuning fork, the sound was made softer by simply striking it softer, so it produces lower sound. Since the first trial created louder voice than the second, it should have larger amplitude. Therefore, the experimental results were consistent.

By comparing all of the graphs in figure 2 to 5, it was seen clearly that human voice was not a simple sinusoidal wave, and it was not smooth. However, the tuning fork was. No matter the sound of the tuning fork was made louder or softer, it produced the same frequency and wavelength, but this was not true for human voice. The time frame 0.03s used in this experiment was very short. This revealed that sound waves were really small. In real life, perhaps only the images from television screen can show several frames in this time frame.