Physics of Musical Instruments
Strings viola da gamba cello guitar harpsichord piano electric guitar
Strings vibrate with a frequency depending on its length, weight and tension length tension mass per unit length
The length of the part of the string actually vibrating can be changed quickly by the fingers fretless fret
The main problem with all string instruments is: How to make a skinny string move a large amount of air (impedance matching) ? Solution: The string moves a board, the board moves the air
not useful in a hot day very useful in a hot day
Acoustic guitar String vibration body vibration Resonances of the body (and air inside) help transfer the energy from the strings to sound at some frequencies, like the formants in the voice
Some resonances free guitar
Some resonances
Chladni patterns of some resonances
Luthiers try to control the frequencies of these resonances using braces
Plucking the strings at different points changes the timbre See it yourself at
Violin main difference: bowed, not plucked
resonances
Helmholtz (air) resonance
Loudness when playing different notes
Aging of violins: fact or fiction setwins.html
Piano harpsichord
“gravicembalo col piano e forte” (Bartolomeu Cristoforo, 1709) The piano has a hammer instead and it’s possible to control intensity
The sound of the piano is loud AND sustained one single string, overtones filtered out change in decay rate
vertical mode excited initially by the hammer sounding board “gives” faster dumping horizontal mode not initially present sounding board is rigid slower dumping One reason for the two decay rates
Big range in pitch is accomplished by using string of varying thickness thickness length length tension tension Thick string lead to inharmonicities: f, 2f, 3f, 4f, 5f, …, 16f, … f, 2f, 3f, 4f, 5f, …, 16f, … shifted more and more ½ tone higher
F F stretching stretching and deforming
Consequences for tuning f 2.001f... 2f 4f... beating
Consequences for tuning f 2.001f f 4.002f... “stretched octave” tuning
Soundboard
Soundboard
Modes of the soundborad:
Wind instruments oboe flute saxes tuba organ
How to generate oscillation (sound) from continuous blowing ? fipple fipple reed reed
fipple
Simplified, theoretical flute L/2L/2 open end holes closed holes open
Simplified, theoretical flute
embouchure machinery to open/close tone holes metal Modern Boehm flute
semitone mistuning
Reeds
The reed is like the vocal chords and the strings, NOT ! The resonances of the reed are irrelevant, it vibrates with the frequency of the resonances of the column of air
material is irrelevant Boehm fingering
flute, recorder clarinet saxophone, oboe
basssaxophone