Objectives
Introduction
A wind instrument is an instrument that produces sound by manipulating air through varying the wind pressure passing through the air outputs of the device (Berg and Stock, 27). These devices are heavily dependent on pressure as well as the size and shape of the instrument (pg. 28). A good example of a wind instrument is the organ pipe. It is a tool that produces a specific pitch when pressurized air is driven through it. Organ pipes usually exist in sets, where each is confined to produce a specific tune. Normally, it is a keyboard device that is played using pedal boards and manuals (Backus, 59). Wind moves through the vibrating air columns constantly while a respective key is pressed.
Working mechanism
Disturbances caused near or even at the end of an enclosed air column result into vibrations that in turn lead to sound. The frequency of this sound is in turn determined by varying the flow rate of air and also changing the length of the wedge distance and the orifice (pg. 45). Therefore, the frequency is generally dependent on the length of the pipe, the flow rate of air and whether the pipe is open or closed.
Apparatus
2 ranks of organ pipes
Microphone or a microphone amplifier
Hoses and valves
Thermometer
Ruler
Connectors
Printer
Rubber gloves
Cables
Air compressor
Oscilloscope
Frequency spectrum analyzer
Procedure
The students were assisted in familiarizing with the equipment, where all instruments were cross-checked to see if everything was in order
4 pipes from the two ranks were selected. Their lengths were then measured and recorded. The oscilloscope and spectrum analyzer were also setup
The room temperature was measured and recorded. The compressor hose was then connected, and the pipes were sounded with the ends either open or closed.
The pipes were blown into using the air compressor, where a steady airflow was produced. Each pipe was then connected to a microphone at the outlet. The microphones were in turn connected to the oscilloscope and the frequency spectrum analyzer.
The oscilloscope then produced waveforms of the sound while the frequency spectrum analyzer created a frequency spectrum
The oscilloscope was connected to a printer, and a sample of each of the waveforms of the different pipes was printed.
The spectrum analyzer compared the frequency spectrum of the pipes for both open and closed states, where the frequency and the relative amplitudes were recorded.
Results
The pictures below are printouts of the waveforms of the sounds produced by the microphone as a result of the pipes. Furthermore, the tables contain the frequency values and the relative amplitudes of the sounds produced by the pipes. The frequency is represented in Hertz (HZ) while the relative amplitude is measured in decibel milliwatts (dBm).
closed small pipe F
Closed large pipe C
Closed large pipe G
Closed small pipe B
Length in centimeters
Length uncertainty: ±0.05 cm.
Data Analysis
Fractional uncertainty = least count / actual value.
Percentage uncertainty = fractional uncertainty x 100.
Relative amplitude’s least count = 0.005dBm
As per the above results, the pipes had a higher pitch when open than when closed. For example, pipe b recorded a frequency of 1143.8 Hertz compared to the 1073 Hertz of the closed state. However, the closed pipes were louder compared to the open pipes. This is due to a higher relative Amplitude in decibel Milliwatts in closed pipes compared to open pipes. As per the existing theory, open pipes increase the air flow rate, which in turn increases the wave frequency. This is because the frequency is directly proportional to the flow rate of air. Thus, the results of this experiment were successful, since they concur with this theory.
Conclusion
In conclusion, the loudness in closed pipes is higher than in open pipes due to the higher relative amplitude in closed pipes than in open pipes. Besides, the pitch in open pipes is more than in closed pipes due to higher air flow rate.
Work Cited
Backus, The Acoustical Foundations of Music, W. W. Norton & Co Inc, 2nd Revised edition, 1977.
Berg and Stock, The Physics of Sound, Addison-Wesley; 2nd edition, 1994.
White and White, Physics and Music: The Science of Musical Sound, Dover Publications; Reprint edition, 2014.
