1. Sound “A sound man…”

2. Frequency The frequency of a sound wave is perceived as the pitch (note) –High frequency → high pitch → high note –“Middle C” has a frequency of 256 or 262 Hz Each octave has a different frequency by a factor of 2 An octave above middle C is 512 or 524 Hz An octave below middle C is 128 or 131 Hz

3. Notes × 2

4. Amplitude The amplitude of a sound wave is also (more commonly) called intensity –Intensity refers to the amount of energy carried by the wave We detect intensity as loudness (or volume) –High intensity → High volume → Loud –Low intensity → Low volume → Soft Measured on the decibel scale (dB)

5. Decibels Due to the way our ears work and the way our brain interprets the signals from our ears… Twice the intensity does not exactly sound twice as loud Sound is measured on a logarithmic scale We define the “threshold of hearing” as 0 dB If a sound wave has an amplitude of 10× this threshold, we add 10 dB 20 dB is 100 times as much +3 dB is approximately double

6. Decibel Scale

7. Decibel Reduction

8. The Doppler Effect A change in pitch due to a moving wave source –Or a moving observer Examples –Sirens –Ice Cream Truck –Doppler Radar –Astronomy

9. Example, page 409 Professional driver on a closed course. Do not attempt.

10. Another Example A local fire station has a roof-mounted siren that has a frequency of 975 Hz. If you are on a bicycle moving away from the station at a speed of 6 m/s, what will be the frequency of the sound waves reaching your ear? 958 Hz

11. Practice Chapter 15, 6-10