Sound propagation 2

1. Sound propagation 2 Review Questions

2. Review • Reflection: • a sharp change of direction at solid obstacles with no change in speed • Refraction: • A gradual change of direction due to inhomogeneous speed • Diffraction: • A change of direction (bending) of rays at solid obstacles Chapter 2.3 in text book

3. Review Questions • We can understand a person who is not talking directly at us, even outside on a field. This is an example of • Reflection • Refraction • Diffraction • Resonance • Beats

4. Review questions • You sit in the back of a DC-10 (airplane). The rhythmic swelling and diminishing of the engine noise is an example of • Reflection • Refraction • Diffraction • Resonance • Beats

5. Review questions • You blow across the opening of a bottle. The sound you hear is an example of • Reflection • Refraction • Diffraction • Resonance • Beats

6. Review questions • In clear nights, you can hear the train from a greater distance than during the day. This often is an effect of • Reflection • Refraction • Diffraction • Resonance • Beats

7. Review questions • The pizza is ready, and you call everybody for dinner. You can be heard in every room of the house. This works due to • Reflection • Refraction • Diffraction • Resonance • Beats

8. Review questions • You are sitting behind a pillar in a concert. How will this influence your musical experience? a) You won’t hear all the treble sounds. b) You won’t hear all the bass sounds. c) The pillar really muffles all sound for you. d) You will hear everything fine due to reflections from the walls. e) Reflections from the walls will get all frequencies to you, but muffled.

9. Diffraction and Reflection • Long wavelengths (low frequencies) are diffracted stronger. • Pillar: 50 cm diameter • Bass: > 1m wave length • Treble: < 50 cm wave length • Reflection involves absorption of sound energy: reflected wave has less amplitude than the incoming wave