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PH 105 Dr. Cecilia Vogel Lecture 20
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OUTLINE Keyboard instruments Piano action strings soundboard pedals Organ flue vs reed pipes
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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
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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.
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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.
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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.
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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).
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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)
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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.
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Stretch Tuning Piano, however, plays several octaves, & over that range the differences multiply. Ex: 16 th 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.
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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
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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.
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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
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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.
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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
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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
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http://helios.augustana.edu/~dr/105/al len-renaissance-organ.html Allen 320 Renaissance Organ at St. James Lutheran Church
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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
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