Experiment P32: Sound Waves (Sound Sensor)

Transcription

1 PASCO scientific Vol. 2 Physics Lab Manual P32-1 Experiment P32: (Sound Sensor) Concept Time SW Interface Macintosh file Windows file waves 45 m 700 P32 P32_SOUN.SWS EQUIPMENT NEEDED Interface musical instrument Power Amplifier Speaker Sound Sensor Tuning Forks (optional) PURPOSE The Interface can produce output signals and monitor input signals at the same time. This activity uses the interface to explore musical tones produced through the interface, sounds produced by a musical instrument, and sound waves that YOU produce. Try the suggested activities to become familiar with the Sound Sensor. THEORY Most of the sounds we hear are noises. The impact of a falling object, the clapping of hands, the sound of traffic, and most of human speech are noises. Noise corresponds to an irregular vibration of the eardrum produced by some irregular vibration source. The sound of music has a different characteristic, having more or less periodic tones produced by some regular vibration source. (Of course, musical instruments can make noise as well!) A graph representing musical sounds has a shape that repeats itself over and over again. Such graphs can be displayed on the screen of an oscilloscope when the electrical signal from a sound sensor is measured. Pythagoras found that notes played together on musical instruments were pleasing to the ear when the ratios of the string lengths were the ratios of whole numbers. Galileo introduced the concept of frequency. A sequence of notes of increasing frequency make up a musical scale. Many different scales exist. The simplest musical scale in many Western cultures is the just major scale (for example, do-re-mi-fa-so-la-ti-do ). In this scale, the ratio between frequencies of two successive notes is 9:8, 10:9, or 16:15. For example, the ratio of re (297 Hz) to do (264 Hz) is 9:8 (or 1.125). Most music written in the Western world uses the even-tempered scale, which has thirteen notes and twelve intervals. The ratio between all successive notes is exactly the same ( ). PROCEDURE This activity has three parts. In the first part, the program generates output signals that are amplified by the Power Amplifier and played through a speaker. In the second part, the Sound Sensor measures sounds from a musical instrument such as a harmonica or recorder. In the third part, the sound sensor measures sounds from a human voice. The program monitors and displays the output signals sent to the Power Amplifier and the input signals measured by the Sound Sensor. dg 1996, PASCO scientific P32-1

2 P32-2: Physics Lab Manual Vol. 2 PASCO scientific A: GENERATE MUSICAL TONES PART IA: Computer Setup 1. Connect the interface to the computer, turn on the interface, and turn on the computer. 2. Connect the Power Amplifier DIN plug to Analog Channel A. 3. Open the document titled as shown: Macintosh P32 Windows P32_SOUN.SWS The document will open with a Scope display, a Fast Fourier Transform (FFT) display, and a Signal Generator window. Note: For quick reference, see the Experiment Notes window. To bring a display to the top, click on its window or select the name of the display from the list at the end of the Display menu. Change the Experiment Setup window by clicking on the Zoom box or the Restore or Maximize button in the upper right hand corner of that window. P , PASCO scientific dg

3 PASCO scientific Vol. 2 Physics Lab Manual P32-3 PART IIA: Sensor Calibration and Equipment Setup You do not need to calibrate the Sound Sensor or the Power Amplifier. 1. Connect the speaker to the output jacks on the Power Amplifier. Power Amplifier Speaker Sound Sensor To Interface 2. Arrange the Sound Sensor in front of the speaker so the sound sensor can detect the signal. 3. Turn on the Power Amplifier switch on the back panel. PART IIIA: Data Recording Generate Musical Tones 1. Click the MON button ( )to begin monitoring data. The data should appear in the Scope and FFT displays. Measuring Frequencies 2. The first Signal Generator frequency is 264 Hz ( do on the just major scale ). Hold the Sound Sensor near the speaker. Examine the FFT display. Compare the value of the fundamental frequency in the FFT to the output frequency in the Signal Generator. 3. Use the Smart Cursor ( )to measure the fundamental frequency in the FFT more accurately. (Note, to improve the resolution of the Smart Cursor, expand the size of the FFT display.). Adjusting Frequencies The frequency and amplitude can be adjusted by larger/smaller increments by pressing modifier keys while clicking on the up/down arrows as shown in the table, or by clicking on the displayed value and typing in a new one. When using the cursor and mouse button to click on the up-down arrows next to the frequency value, the default change is 10 Hz per click. Use modifier keys (Control, Option and Command or CTRL and ALT) to increase or decrease the amount of change per click. (See the table.) dg 1996, PASCO scientific P32-3

4 P32-4: Physics Lab Manual Vol. 2 PASCO scientific Macintosh Key Windows Key (s) frequency Shift key Shift key 100 Hz No modifier key No modifier key 10 Hz Control key Ctrl key 1 Hz Option key Alt key 0.1 Hz Command key Alt + Ctrl keys 0.01 Hz 4. Enter the next frequency on the first musical scale and hit enter. Measure the frequency in the FFT display for each note as before. 5. Repeat the process for the rest of the frequencies in the first musical scale. Note Letter name Frequency (Hz) do C 264 re D 297 me E 330 fa F 352 so G 396 la A 440 ti B 495 do C(octave higher) 528 Diatonic C Major scale (just major scale) 6. Repeat the process for the second musical scale (even-tempered scale). 7. Click STOP to stop monitoring data. 8. Turn off the Power Amplifier. Note Letter name Frequency (Hz) do C 262 C Sharp 277 re D 294 D Sharp 311 me E 330 fa F 349 F Sharp 370 so G 392 G Sharp 415 la A 440 A Sharp 466 ti B 494 do C(octave higher 524 Equal-tempered Chromatic scale P , PASCO scientific dg

5 PASCO scientific Vol. 2 Physics Lab Manual P32-5 ANALYZING THE DATA: Generate Musical Tones 1. How do the notes in the diatonic scale sound compared to the notes in the chromatic scale? 2. Do any of the notes in either scale have harmonic frequencies? B: MUSICAL INSTRUMENT PART IB: Computer Setup Use the same computer setup as in Part A. However, you will not need to use the Power Amplifier. (This part may be easier to do with a partner who can run the computer while you play the musical instrument.) PART IIB: Sensor Calibration and Equipment Setup You do not need to calibrate the Sound Sensor. 1. Arrange the musical instrument so you can play musical tones into the Sound Sensor. PART IIIB: Data Recording Musical Instrument 1. Click the MON button ( )to begin monitoring data. The data should appear in the Scope and FFT displays. 2. Play a single note (for example, middle C) into the Sound Sensor. 3. Examine the waveform of the musical sound in the Scope display. 4. Measure the fundamental frequency in the FFT display. If the waveform has harmonic frequencies, use the Smart Cursor to measure and record them as well. 5. Repeat the process for a different note. 6. Click STOP to stop monitoring data. ANALYZING THE DATA: Musical Instrument 1. Describe the waveform of a single note on the musical instrument. Does it have harmonic frequencies? 2. If the note has harmonic frequencies, how does the value of each harmonic compare to the value of the fundamental frequency? dg 1996, PASCO scientific P32-5

6 P32-6: Physics Lab Manual Vol. 2 PASCO scientific C: VOICE PART IC: Computer Setup Use the same computer setup as in Part B. PART IIC: Sensor Calibration and Equipment Setup You do not need to calibrate the Sound Sensor 1. Arrange the Sound Sensor so it will be able to record your voice. PART IIIC: Data Recording Voice 1. Click the MON button ( )to begin monitoring data. The data should appear in the Scope and FFT displays. 2. Sing a single tone into the Sound Sensor. 3. Examine the waveform of your singing in the Scope display. Experiment by trying different vowel sounds at approximately the same pitch. For example, switch from OO to EE to AH to UU to AY. Try other mouth shapes. 4. Measure the fundamental and harmonic frequencies in the FFT display. 5. Whistle a single note into the sensor. Examine the waveform in the Scope and measure the fundamental and harmonic frequencies in the FFT display. 6. Change the pitch of your whistle. Examine the waveform and measure the frequencies. 7. Click STOP to stop monitoring data. ANALYZING THE DATA: Voice 1. Describe the waveform of one of your singing tones. Does it have harmonic frequencies? How does it compare to the waveform of a single note from the musical instrument? 2. If the tone has harmonic frequencies, how does the value of each harmonic compare to the value of the fundamental frequency? 3. Which vowel sounds have the least complex waveform? The most complex? P , PASCO scientific dg