Concrete Drill Sitting in a faculty office during a quarter break, enjoying the quiet, a faculty member was launched about a meter into the air by the sudden sound of a loud concrete drill directly above his office. After a brief and loud burst, there was again quiet for long enough for him to settle down to work and then another sudden loud burst of noise. After several such episodes removed the possibility of concentration, he decided to measure the sound and collected the following data: Measurement A Contour Flat to 20 kHz Drill on 58 dBA 68 dB Background 34 dBA 64 dB Excess over bkg. 24 dBA 4dB Analysis

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Analysis, Concrete Drill Sound Sound measurement in decibels inside of buildings can be so misleading as to be worthless since it gives equal weighting to low frequency building sounds to which the human ear has minimal response. This example shows that the use of an A Contour filter gives a much better representation of what the ear hears. Besides the conceptual difference between sound loudness and sound intensity, this example employs the idea of the just noticeable difference in sound level. It also makes use of the rule of thumb for loudness for comparing the before and after loudness, although in this case that is a questionable application since the added sound of the drill is quite different in nature than the background sound to which it is being compared. Statement of example

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Fire Alarm Measurement Periodic testing of the fire alarm in the physics building provided the opportunity for measurement of the sound level with different filter contours. Measurements were made inside a faculty office down the hall from the alarm. The following data was collected: Measurement A Contour Flat to 20 kHz Fire Alarm on 65 dBA 71 dB Background 38 dBA 70 dB Excess over bkg. 27 dBA 1 dB Analysis

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Analysis, Fire Alarm Sound Sound measurement in decibels inside of buildings can be so misleading as to be worthless since it gives equal weighting to low frequency building sounds to which the human ear has minimal response. This example shows that the use of an A Contour filter gives a much better representation of what the ear hears. Besides the conceptual difference between sound loudness and sound intensity, this example employs the ideas of the just noticeable difference in sound level and the "rule of thumb" for adding loudness. As suggested with the drill example above, this is not a good application for the rule of thumb for loudness because it is reasonable only if the sounds being compared are similar, whereas the fire alarm and the background noise field are very different in nature. Statement of example

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