CN2 - Acoustics and Ear Review

I) Acoustics and sound

A) Pitch

-Started with Pythagoras and his hammers <500 B.C. as an expression of ratios and then moved to strings. 2:1 = an octave. etc.

-The scientific description of rate of vibrations. One complete vibration is a cycle. 

- frequency = cycles per second. A=440 is standard for western tuning.

-human ear can detect 20-20K cycles per second!

- higher frequency = higher pitch - 880, 1760 etc.

- string is a good example of wavelength, also: bottle, vocal chords, room, anything which can resonate.

-Sine wave is a perfect wave along a length of a string e.g.piano

-Every tone is made of partials [1/8/, 1/4, 1/2 length] and overtones [8ve, 5th, 15ve, 3rd] which make up the timbre or nature of the sound. A flute is very pure, whereas violins have many partials and overtones which 'color' the sound. 

-Volume is a factor of amplitude

drawing of sine wave:

B) Review of Ear and transmission

- vibrations are collected by the auricle or pinna

- travels down the tube to the tympanum oreardrum

-tympanum is in contact with the three ossicles : malleus [hammer], incus[anvil] and stapes [stirrup]. 

-These communicate with the cochlea, a snail-like structure which is in ennervated by Cranial Nerves: V [mandibular], the Vestibulocochlear nerve [VIII] and Vagus [X]. These are part of the autonomic nervous system, meaning they are always monitoring the outside world. Vagus is very important Cranial Nerve. It also ennervates the gastric and cardiac systems. 

-Interpretive activity goes on in the temporal lobe of the brain.

terms: 

sine wave - basic tone which has a wavelength and nodes

node - spot on wave where it passes the ì0î

frequency - # of cycles per second of a sound wave

overtone - a resonant partial of any sound

pitch - frequency of fundamental tone

partial - a constituent part of and unpure tone

octave - 12 scale degrees above or below = ësame note different placeí

cycle - one complete path of a wave

resonation - the transmission of a wave through material

auricle, pinna - external collector of sound

tympanic membrane or tympanum - eardrum

ossicles: malleus, incus and stapes - three bones of ear which transmit information

Facial & Vestibulocochlear nerves [V,VIII] - nerves which go to brain with sound info.

meatus - hole in the head

Cochlea - snail-like hearing structure which ëinterpretsí vibration.