SOUND a range of compression wave frequencies to which the human ear is sensitive

2. SOUND a range of compression wave frequencies to which the human ear is sensitive

3. Theaudio spectrum extends from approximately 20 Hzto20,000 Hz.

4. Range of Some Common Sounds

5. Intensity Range for Some Common Sounds

6. Sounds are produced byvibrating matter. 1. reeds 3. membranes 4. air columns 2. strings Sound is a mechanical wave (longitudinal). It will not travel through a vacuum.

7. Sounds possess the characteristics and properties that are common to all waves.

8. Just like all longitudinal (compression) waves, sound waves possess a velocity, frequency, wavelength, phase, period, and amplitude. Sound waves also reflect, refract, diffract, and interfere.

9. The velocity of sound in air depends on the air temperature. The speed of sound in dry air is 331.5 m/s at 0 ºC. This speed increases with temperature: about 0.6 m/s for every 1 ºC increase in temperature.

10. Sound generally travels fastest in solids and slowest in gases, but there are some exceptions. Medium Velocity (m/s) Medium Velocity (m/s) Air 330 Carbon dioxide 260 Helium 930 Hydrogen 1270 Oxygen 320 Water 1460 Sea water 1520 Mercury 1450 Glass 5500 Granite 5950 Lead 1230 Pine wood 3320 Copper 3800 Aluminium 5100

11. The human ear relates amplitude to loudness and frequency to pitch.

12. Listen to various sound frequencies here and mixtures of sound waves here. Click here to make your own sound waves. You should hear that frequency relates to pitch and amplitude relates to loudness (for a given frequency).

13. Sound waves refract. Click here to view a simulation of the refraction of sound waves.

14. The interference of sound waves can cause “beats” Click here and here to run computer simulations of interfering sound waves that result in discernable beats. View interference “beats” here and here. What are evidences of reflection and the diffraction of sound?

15. *Fact* All objects have a natural frequency of vibration. Resonance- the inducing of vibrations of a natural rate by a vibrating source having the same frequency “sympathetic vibrations”

16. Famous Bridge Collapses: Evidences of Resonance? Tacoma Narrows link Others link

17. A resonant air column is simply a standing longitudinal wave system, much like standing waves on a string. closed-pipe resonator tube in which one end is open and the other end is closed open-pipe resonator tube in which both ends are open

18. A closed pipe resonates when the length of the air column is approximately an odd number of quarter wavelengths long. l = {(1,3,5,7,…)/4} * l • With a slight correction for tube diameter, • we find that the resonant wavelength of a • closed pipe is given by the formula: • = 4 (l + 0.4d), where  is the wavelength of sound, l is the length of the closed pipe, and d is the diameter of the pipe.

19. An open pipe resonates when the length of the air column is approximately an even number of quarter wavelengths long. l = {(2,4,6,8,…)/4} * l • With a slight correction for tube diameter, • we find that the resonant wavelength of an • open pipe is given by the formula: • = 2 (l + 0.8d), where  is the wavelength of sound, l is the length of the closed pipe, and d is the diameter of the pipe.

20. Click here to see a simulation of standing waves in a resonant tube (closed and open). Learn more about resonance here.

21. Why aren’t there “black keys”between every two “white keys”on a piano keyboard?

22. Can you look at this chart of notes and frequencies for the “white keys” and decide where “black keys” should be placed?

23. Now look at a graph of those values. Does this graph help you decide?