Properties of sound Sound is a longitudinal wave Longitudinal waves travel at different speeds depending on the medium (air @ 25oC 346m/s, water 1490 m/s) Denser the medium, the faster it travels, energy can transfer faster through molecules closer together. Loudness of a sound depends on intensity (the amplitude of the wave. Higher amplitude … louder sound) Measured in deciBels (dB), talking is about 50 dB over 120 dB is painful.

Loudness/intensity

Properties of sound Pitch (high or low) is directly related to frequency. Higher frequency = higher pitch (Also related to wavelength, indirectly. Bigger wavelength = lower pitch) Humans hear between 20 Hz and 20,000 Hz. Below that range is infrasound, above is ultrasound.

Musical Instruments Rely on standing waves to make sound Only certain wavelengths are made by instruments, depending on the size of the instrument Fundamental frequency: the lowest frequency standing wave made by the instrument.

Stringed Instruments The wavelength of the fundamental frequency is twice the length of string. Changing the size of the string changes the wavelength and the frequency. Changing the tension on the string changes the medium (density) and the wave speed

Wind/Brass Instruments Change size of wave by opening closing holes, changes size of tube that standing wave is made in. In a tube open at both ends, you get ½ the wavelength, so multiply by 2 to find the wavelength for the fundamental frequency In a tube closed at one end, you get ¼ the wavelength, so multiply by 4 to find the wavelength for the fundamental frequency

Musical Instruments Strings make ½ wave, so mult. by 2. Open tubes make ½ wave so mult. by 2 Closed tubes make ¼ wave so mult. by 4.

Resonance and Harmonics Vibrations can cause other parts of the instrument and other objects to vibrate … called resonance. The other standing waves created are called harmonics. That’s why everyone’s voice sounds different and why instruments sound different when they play the same note. The have the same fundamental frequency (note), but different harmonics because of resonance Waves interfere, called beats

How we hear Outer ear focuses waves, passes them to ear drum (middle ear) which passes them to three bones (hammer, anvil, stirrup) to the cochlea (inner ear) which resonates at certain frequencies. Hair cells pick that up and transmit to brain.

Ultrasound and Sonar Use speed of sound in medium and time to figure out how far away something is (e.g. bottom of ocean floor) Ultrasound...frequencies beyond our hearing used in medicine (babies).