Victory for the ACT Student Text 15e

298 • S CIENCE

PASSAGE IV In 1933, Dr. Fletcher and Dr. Munson of Bell Labs discovered that the sensitivity of the human ear varies with frequency. The Fletcher-Munson equal-loudness contours (Figure 1) show how the human ear’s sensitivity to sound pressure level (SPL) varies with frequency. Each contour represents the loudness level as perceived by the human ear. Loudness is subjective but related to sound pressure level as measured by a sound level meter.

The Cambridge Edge How can you recognize a data representation item? Here are some sample items to help you recognize what these questions ask: 1. Select a conclusion that can be supported by Figure X. 2. Determine what the slope of a given line represents in Figure X. 3. Predict the results given an assumption or a new situation. 4. Select a statement that is best supported by the data represented in Graph X. 5. Determine the results based on the difference of time or location. 6. Determine the relationship between the two variables. 7. Determine which conclusion is NOT consistent with the information given in Graph X. 8. Select an explanation for a given outcome. 9. Identify the LEAST •‹‰‹ϔ‹…ƒ–

The bottom contour (minimum audible) represents the hearing threshold of the human ear, that is, the minimum SPL of a pure tone that the average human ear with normal hearing can hear with no other sound present. The top contour (120 phons) represents the pain threshold of the human ear, that is, the SPL beyond which sound becomes unbearable to the average listener. Prolonged exposure to sound pressure levels in excess of the pain threshold can cause physical damage. Figure 1

15. The Fletcher-Munson contours indicate that the human ear is: A. equally sensitive to all frequencies. B. less sensitive to low and high frequencies and more sensitive to mid-range frequencies. C. most sensitive to low and high frequencies and less sensitive to mid-range frequencies. D. capable of hearing sounds below 20 hertz.

16. The threshold of human hearing: F. does not depend on sound frequency. G. is sometimes equal to the threshold of pain. H. is based on an average ear with normal hearing. J. is represented by the 10-phon Fletcher-Munson contour.

assumption made when determining a particular outcome.