Chaps 19-20

 Produced by vibrating material objects ◦ e.g. vibrating piano string, vibrating tuning fork, vibrating saxophone reed, vibrating column of air at flute mouthpiece ◦ Demonstrate  Pitch = our (subjective) impression of the frequency of a sound Pitch = our (subjective) impression of the frequency of a sound ◦ High pitched sounds = high frequency, small wavelength ◦ Low pitched sounds = low frequency, large wavelength ◦ Demonstrate  Humans hear in the range of 20 – 20,000 Hz Humans hear in the range of 20 – 20,000 Hz

 Sound waves are produced by compression and rarefaction of air ◦ Compression = area of compressed, higher density air ◦ Rarefaction = area of lower pressure, lower density air  Compression areas equate to peaks of a transverse wave, rarefaction areas equate to troughs of transverse waves  The air itself does not travel with the wave, only the wave energy travels through the air

 Any substance that is elastic can transmit sound – it needs to be able to compress and rarefy  Elasticity does not mean stretchiness  Elasticity = ability of a substance to resume its initial shape, once it has been deformed by an applied force, as the applied force is removed

 Sound travels faster in water than in air ◦ water is more elastic than air  Sound speed in air depends on humidity and on temperature TempSpeed 0ºC330 m/s 20ºC340 m/s Sound speed in dry air

 Demonstration: ◦ tuning fork in air, tuning fork on table ◦ Why is it louder when touching the table?  Forced vibration = one object is made to vibrate by contact with another, vibrating object  Can occur at any frequency

 Natural frequency = set of frequencies at which an elastic object vibrates when disturbed ◦ Depends on elasticity and shape of the object ◦ Not usually just one frequency!  Resonance = the vibratory response that occurs when an object is forced to vibrate at it’s natural frequency  Demonstration: ◦ Two different-frequency tuning forks ◦ two equal-frequency tuning forks

 Pitch depends on frequency, or on the lowest frequency component if a sound is a composite of multiple frequencies ◦ A = 440 Hz ◦ C = 256 Hz  Loudness ◦ Intensity is a measure of how much energy the sound wave carries ◦ enery α A², f², v ◦ Loudness is a physiological sensation, is subjective

 Quality ◦ Most musical sounds are composed of superposition of tones of a variety of frequencies - “partial tones” ◦ Fundamental frequency (first harmonic) = lowest frequency vibration in the sound ◦ Fundamental frequency determines the pitch of the note ◦ Harmonics or overtones = whole number multiples of the fundamental frequency

Fundamental (say, 440 Hz): + Harmonic (say, 880 Hz): = the actual sound produced by the instrument: The adding of waves like this is called Fourier analysis

 Produce standing transverse waves on the strings  The note you play is the 1 st harmonic (fundamental frequency) ◦ There are 2 nodes on the string; nodes are at the ends of the string In the 2 nd harmonic there are 3 nodes on the string In the 3 rd harmonic there are 4 nodes on the string, etc.

 The fundamental frequency of a string is its (fundamental) resonant frequency  Fundamental frequency depends on the characteristics of the string ◦ Density of the string ◦ Tension in the string ◦ Length of the string

 Produce standing longitudinal waves ◦ Standing waves occur in the air inside the body of the instrument  Resonant (fundamental) frequency depends on ◦ Length of the pipe/body of instrument ◦ Density of air in the instrument

 Ends can be open (antinode) or closed (node)  Both ends open ◦ Fundamental frequency occurs when the standing wave has one node (in the middle)  One end closed ◦ Fundamental frequency occurs when the standing wave has one node (at closed end) ◦ Only odd harmonics occur Air density distance

 ral-tour

In 1909, a 27 rank electro-pneumatic organ was built and installed by the Kimball Company of Chicago. It was rebuilt by Schoenstein of San Francisco in By the mid 1980's, this organ had come to the end of its natural life and was replaced in 1992 by a new 77/79 rank mechanical action English-style organ built by Kenneth Jones and Associates of Bray, Ireland. The organ, which has 4,066 pipes, stands in a Gothic case designed to match the woodwork installed in the Comes interior of A notable element of the organ is the Fanfare Trumpet that extends from the front of the choir gallery. The organ serves both liturgical and concert purposes.