Questions and Problems

Author: N.H. Crowhurst

1. What are the differences between echo and reverberation?

2. How does the standing wave pattern in a room or auditorium differ from that in an organ pipe?

3. Explain what causes sound waves to reflect when they encounter the surface of a different material.

4. When sound is reflected, is all of the wave reflected, or does some of it into the reflecting material?

5. What is the reverberation time of a building or auditorium?

6. What is the inverse-square law? Explain when it applies to sound waves.

7. What makes listening to anything outdoors different from listening to the same thing indoors?

8. Explain how the principle of masking applies (a) to trying to hear a conversation at a noisy airport, and (b) in getting the full benefit of listening to high fidelity.

9. Does wind stop sound waves? If not, why is it more difficult to hear any distance up-wind than down-wind?

10. Explain why you think a reproduction of violin playing through a loudspeaker with a metal horn would not sound very realistic.

11. What is the connection or relationship between frequency and wavelength in sound waves? What would be the wavelength corresponding to a note whose frequency is 250 cycles, if the speed of sound is 1100 feet per second?

12. Listening to a particular high fidelity setup, the following facts are noticed: (a) an organ note of 41 cycles is equally audible anywhere in the room; (b) a power-line hum (that proves to have a frequency of 180 cycles) seems quite strong in places and almost inaudible at others; (c) the sound of a snare drum played with a wire brush on a certain recording is audible in front of the loudspeaker, but not toward the sides of the speaker enclosure. Explain these differences.

13. What does the word transient mean, but to what is its meaning restricted (a) musically, (b) in audio?

14. Why do instruments or other sources of sound with "impact" transients (a) attract attention, and (b) give a good indication of their direction, which smooth-starting tones do not?

15. Why does a sound of particular intensity only seem to carry a certain distance? How can a megaphone help sound to carry further?

16. Do the following devices amplify sound: a megaphone; a speaking tube; the reflecting board over a speakers platform? If so, why? If not, why not?