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: 16 th harmonic may be 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

 len-renaissance-organ.html Allen 320 Renaissance Organ at St. James Lutheran Church

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