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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

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ph 105
PH 105

Dr. Cecilia Vogel

Lecture 20

slide2

OUTLINE

  • Keyboard instruments
  • Piano
    • action
    • strings
    • soundboard
    • pedals
  • Organ
    • flue vs reed
    • pipes
piano
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
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 action5
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
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
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
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
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
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
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
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
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
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
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
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
Allen 320 Renaissance Organ at St. James Lutheran Church
  • http://helios.augustana.edu/~dr/105/allen-renaissance-organ.html
slide18

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