1. Sound in everyday life Pitch: related to frequency. Audible range: about 20 Hz to 20,000 Hz; Ultrasound: above 20,000 Hz; Infrasound: below 20 Hz Loudness: related to amplitude of the sound wave There are two different ways to measure loudness: 1. Using the subjective sensation of a human being; 2. Using the physically measurable quantity “intensity” of sound;

2. Common misconception There are two different types of sound detectors: 1. All available electronic devices/detectors use linear scales to measure sound intensity “I”. The most sensitive sound detector is the human ear. It can detect sounds with intensity as low as 10 -12 Watt/m 2 (called the threshold of hearing I 0 ) and as high as 1 Watt/m 2 (called the threshold of pain). 2. The human perception of loudness is based on a logarithmic scale and is called the sound level “  ”  Sound level is measured in decibels (dB) and is defined in terms of its intensity “I”, as I 0 is taken to be the threshold of hearing: http://www.youtube.com/watch ?v=3oZPPIVC8MU&feature=r elmfu

3. Intensity of Sound: Decibels Example 1. Find the sound level at the threshold of hearing. Ex. 2. Find  corresponding to I=3*10 -6 W/m 2 (comfortable level of two people talking). Ex. 3. What about 21 student talking? Ex. 4. The sound level is 70 dB, what is the intensity? Ex. 5. By how many dB will the sound level increase if the “I” triples?

4. Sound level is given by  = 10 log( I / I 0 ) with I 0 = 10 -12 W/m 2. The usual threshold of human hearing is defined as sound level of  = 0 dB. What does this actually mean in terms of sound intensity? 1) intensity is undefined at that level 2) intensity is 10 0 W/m 2 3) intensity is 0.0 W/m 2 4) intensity is 10 -12 W/m 2 5) intensity is 1.0 W/m 2 Decibel Level III

5. When Mary talks, she creates a sound level of 60 dB at your location. Alice talks with the same volume, also giving 60 dB at your location. If both Mary and Alice talk simultaneously from the same spot, what would be the new sound level that you hear? 1) more than 120 dB 2) 120 dB 3) between 60 dB and 120 dB 4) 60 dB 5) less than 60 dB Decibel Level I

6. 1) about the same 2) about 10 times 3) about 100 times 4) about 1000 times 5) about 10,000 times A quiet radio has a sound level of about 40 dB. Busy street traffic has a level of about 70 dB. How much greater is the intensity of the street traffic compared to the radio? Decibel Level II