Cavity Resonance

The purpose of this experiment is to explore the resonant behavior of acoustic cavities (a coke bottle and your voice). Recall that a resonant frequency is defined as a natural frequency of vibration which is determined by the physical properties of the vibrating object. In this case the physical properties which affect the natural frequency of the cavity are its volume, area of opening, and length of opening port. In this experiment, only the effects of changing volume will be explored since the other factors are not easily changed.

本实验的目的在于探索声腔的共振行为（一个可乐瓶和你的声音）。请回忆，共振频率被定义为振动物体的自然振动频率，该频率由振动物体的物理性质决定。在此情况下，影响腔体自然频率的物理性质包括其体积、开口面积和开口端的长度。在本实验中，仅会探讨改变体积的影响，因为其他因素不容易改变。

The apparatus consists of a coke bottle, a graduated cylinder, and a digital computer interface with which to produce a digital image of the sound made by blowing over the coke bottle. The computer interface can also be used to collect data on your voice.

该装置包括一个煤油瓶、一个量筒以及一个数字计算机接口，用于产生吹奏煤油瓶发出的声音的数字图像。计算机接口还可用于收集你的声音数据。

程序：计算机接口的设置：

2. Scroll down the "Sensors" menu to "Sound Sensor" and click-and-drag t hat icon to the image of the port where your microphone is connected.

向下滚动“传感器”菜单到“声音传感器”，并将该图标拖动到麦克风所连接插孔的图像上。

1. Click on "Scope" under the "Displays" menu to display an oscilloscope screen. Click the "Start" button and produce a sound to confirm that you can display a sound waveform. You may need to adjust the V/div(sensitivity) and/or Offset (vertical position) controls until get a satisfactory waveform with no clipping of the peaks. Experiment with starting and stopping the display.

1. 在“显示”菜单下点击“示波器”以显示示波器屏幕。点击“开始”按钮并发出声音以确认可以显示声音波形。可能需要调整V/div（灵敏度）和/或偏移（垂直位置）控制，直到获得一个没有波峰 clipping 的满意波形。尝试开始和停止显示。

2. Click the "Start" button and blow over the coke bottle close to the microphone, but do not blow directly on the microphone. Once you are producing a satisfactory waveform, click the "Stop" button to hold the display. You can repeat this part if you like to get a better waveform.

2. 点击「开始」按钮，将嘴唇靠近麦克风吹气，但不要直接对着麦克风吹。一旦你产生了一个满意的波形，点击「停止」按钮以保持显示。如果你想获得更好的波形，可以重复这个步骤。

3. Click the data storage button to store that trace of the sound waveform. This button looks like pincers picking up a ball. Then double-click on "Graph" under the "Displays" menu to put a graph on the screen. Drag the icon for your data set over onto the graph to display it. It will appear cluttered with their cute symbols for data points, but you can clean it up by going to the Display/Settings and taking off the "Show data points" and "Show Legend Symbol" options.

3. 点击数据存储按钮以存储该声音波形的轨迹。这个按钮看起来像钳子夹起一个球。然后双击“图形”选项，位于“显示”菜单下，以在屏幕上显示一个图形。将你的数据集图标拖到图形上以显示它。它会显得杂乱，因为有那些可爱的数据点符号，但你可以通过进入显示/设置，取消勾选“显示数据点”和“显示图例符号”选项来清理它。

4. Measure the time associated with the first clear peak on the waveform. Then move the cursor to the last clear peak to the right and record that time as "End Time". You can just read the numbers off the graph, or go Display/Measure to display a set of crosshairs on the screen to make measurements. Try both ways to see which you like best. Record the number of periods spanned and calculate the period and frequency of the wave.

测量波形上第一个明显的峰值对应的时间。然后将光标移动到右边最后一个明显的峰值，并将该时间记录为'结束时间'。你可以直接从图上读取数字，或者通过Display/Measure菜单在屏幕上显示一组十字线以进行测量。尝试两种方法，看看哪种更符合你的喜好。记录所跨越的周期数，并计算波的周期和频率。

5. Repeat the process after adding 50 ml (same as cm³) of water from a graduated cylinder. Repeat for added volume 100, 150 and 200 ml.

再加入50毫升（相当于立方厘米）水，从量筒中取水。重复此过程，加入体积分别为100、150和200毫升的情况。

6. Plot your data with frequency in Hz on the vertical axis and the added volume on the horizontal axis.

将频率（单位：Hz）作为纵轴，增加的体积作为横轴绘制你的数据。

7. From your graph, predict the frequency which should be produced if 125 cm³ is added to the empty bottle. Then measure that frequency by the procedure outlined above for comparison.

从你的图中，预测如果向空瓶中加入125 cm³气体后应产生的频率。然后用上述 outlined 的程序进行测量，以作比较。

125 cm³ 加入后预测的频率 _________。

测得的频率 _________

双击 DataStudio 图标以启动数据采集软件。

8. Now record your voice for three vowel sounds, "AH" as in "father", "EE" as in "heed", and "OO" as in "who". As you record each, sketch the waveform in the space provided and determine the frequency. Then click on the FFT option and drag it onto the work area and display the FFT (Fast Fourier Transform) of the sound. It gives you the intensity as a function of frequency. Do a rough sketch of that FFT on the sketch of the inner ear's basilar membrane to represent how that frequency pattern would be detected by the inner ear. The point is to see how different the patterns are and to give some impression of how the human ear distinguishes these sounds.

8. 现在录制三个元音声音，'AH' 如 'father'，'EE' 如 'heed'，和 'OO' 如 'who'。在录制每个声音时，绘制出波形图，并确定其频率。然后点击FFT选项，将其拖到工作区域，并显示该声音的FFT（快速傅里叶变换）。它会给出频率的强度分布。在内耳基膜的草图上大致画出该FFT图，以表示内耳如何检测这种频率模式。重点是观察这些模式之间的差异，并对人类耳朵如何区分这些声音有所印象。