PH 105

Dr. Cecilia VogelLecture 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)

1

1

2

Tf

L

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

http://helios.augustana.edu/~dr/105/allen-renaissance-organ.html

Allen 320 Renaissance Organ at St. James Lutheran Church

SummaryPiano

Hammer, string, soundboard, and damper determine envelopeString pitch determined by length and densityInharmonic overtones lead to stretch tuning and wrapping.

Organdifferent pipes have different timbre synthesis of sound