PH 105 Dr. Cecilia Vogel Lecture 20
OUTLINE • Keyboard instruments • Piano • action • strings • soundboard • pedals • Organ • flue vs reed • pipes
Piano • Sound of the piano • is due to three factors: • the source of the sound • string hit by hammer • the resonators • bridge and soundboard • the radiation of sound • directly from the string and soundboard
Piano Action • When a key is pressed • a mechanical wonder called the “action” • causes a small hammer to strike a string. • The sound of hammer striking string • is an important component of the attack portion of the envelope. • Different timbre from being struck by something hard vs soft. • If hammer is old and hard, sounds tinny.
Piano Action • Important point: • Hammer does not get pushed all the way to the strings. • If it did, the hammer would be in the string’s way. • Pushed part way to get it moving, • then continues to move freely (inertia) • and bounces off the string. • String vibrates freely.
Soundboard • The string is struck • at about 1/8 its length • (varies from one to next) • so many harmonics are present. • The string does not sound loud, • but bridge transmits vibrations to soundboard, • soundboard resonates like plate. • Large soundboard creates large sound.
Sustain & Release • The sustained sound of piano • is due to the string continuing to vibrate. • Can last several seconds. • When a key is released, • a damper (small pad) touches the string • stops strings vibration. • Soundboard continues to vibrate for a short time (release).
Piano Strings • The pitch of the string • depends on length, density and tension • Piano strings vary • in length (longer is lower) • and density (heavier is lower)
Harmonics? • The partials of an ideal string • are all the harmonics of the fundamental: • 1, 2, 3, etc. • The partials of a stiff rod • are not harmonic: 1, 2.76, 5.4, etc. (lab) • The partials of a stiff string, • are somewhere in between • almost harmonic. • Maybe 1, 2.029, 3.065, etc. • For string instruments, that’s close enough.
Stretch Tuning • Piano, however, plays several octaves, • & over that range the differences multiply. • Ex: 16th harmonic may be 16.94 instead of 16 • this would be 4 octaves plus a semitone • (2)(2)(2)(2)(1.059) • instead of perfect 4 octaves (16) • Stretch tuning of piano means • octave increase is more than a factor of 2. • So that high note matches overtone of low note • & there won’t be beats between them.
String Wrapping • The thicker a string is, • the more it acts like a rod than an ideal string • & the worse the inharmonicity. • This is because they get harder and harder to bend as they get thicker • For low notes, don’t use thick strings • To make them low, must be heavy. • Use thin strings • which bend easily • & wrap them. • the wrap acts like a coil, which bends easily
Unisons • Heavier strings push the air harder, • tend to be louder. • To keep all notes of similar loudness • use two or three strings of same pitch • or unison.
Inside a Piano • In video observe: • lever action • string’s length, diameter, wrapping • hammer doesn’t strike if key pressed slowly • hammer flies freely, bounces back • strings run over bridge, attached to soundboard
Grand Piano Pedals • Sustain pedal pushes the dampers away, • so sustain continues after key released. • Also, unplayed strings may resonate. • Maybe a pedal • which sustains only the notes that are being played when you depress pedal. • Una corda pedal shifts the action sideways • not all unison strings are struck. • attack sound is softer, but sustain is not, • because unstruck string resonates, too.
Organ • Sound source • air blown through pipes • Many, many, many pipes • can play several notes, like piano • can play various harmonics at different levels to produce desired timbre • like a synthesizer
Organ Pipes • Timbre (spectrum) of individual pipe depends on many factors, including: • shape and size of bore • reed vs. flue • like reed vs air reed woodwind • mouth, lips, ears, languid • cylinder vs. cone • chimney or not • short cavity, resonates at a harmonic • open vs. closed
Allen 320 Renaissance Organ at St. James Lutheran Church • http://helios.augustana.edu/~dr/105/allen-renaissance-organ.html
Summary • Piano • Hammer, string, soundboard, and damper determine envelope • String pitch determined by length and density • Inharmonic overtones lead to stretch tuning and wrapping. • Organ • different pipes have different timbre • synthesis of sound