The Physics of Electromechanical Keyboard Instruments
Edward Daw
11/12/07
Abstract In the history of western music, the birth of new musical styles has almost always been precipitated by the invention of new instruments. For example, the invention of the piano played an important part in the transition from baroque music to the classical style of Beethoven and Mozart. In the 20th century, jazz, blues, rock, gospel and many other new music forms changed our culture and our society. In this lecture I will discuss the Hammond organ and the Rhodes piano. I will discuss how these instruments work, and some of the beautiful music they were ‘instrumental’ in producing.
– Typeset by FoilTEX – Ed Daw 11/12/07 A Crude Classification Scheme for Keyboard Instruments • PIANOS – key stroke applies a sharp impulse – subsequent tone decays naturally – key velocity controls intensity, tone – one oscillator per key – tonal quality may vary throughout note
• ORGANS – continuous excitation of oscillator – note continues while key depressed – no effect of key velocity on sound – one key can control many oscillators – each oscillator produces a fairly ‘flat’ tone
1 Ed Daw 11/12/07 Waves
Figure 1: LIGO experiment site, Livingston, Louisiana
A typical piano or organ oscillator consists of a vibrating string, pipe, or other metal object. How do you translate vibrations of metal objects in to electrical signals?
2 Ed Daw 11/12/07 Helmholz’s Synthesizer
Figure 2: Helmholz’s experimental apparatus for the synthesis of tones
3 Ed Daw 11/12/07 Pickups
PERMANENT COPPER MAGNET IC MAGNET COIL FIELD LINES SS NN
VV
SS NN (S) (N) ST EEL BECOMES MAGNET IZED IN FIELD OF PERMANENT VV MAGNET
Figure 3: Magnetic fields in a pickup
4 Ed Daw 11/12/07 Faraday’s Law - For More than Just Generators
MAGNET IC FLUX T HROUGH COIL
VOLT AGE ACROSS COIL
Figure 4: Faradays law of induction as a metal object is bought close to the pickup
5 Ed Daw 11/12/07 Bring On the Music
MAGNET (NOT MOVING)
MOVING ST EEL OBJECT
VOLT AGE ACROSS COIL
Figure 5: Multiple cycles of motion of the string or bar result in oscillations in the voltage across the pickup coil.
6 Ed Daw 11/12/07 The Rhodes Piano
Figure 6: Harold Rhodes (1910 - 2000)
Figure 7: Rhodes Stage 2a
7 Ed Daw 11/12/07 Tuning Forks
CONTACT HOLD WITH HERE PRONGS OF WOOD FORK VIBRATE IN OPPOSITE DIRECTIONS
Figure 8: Vibrations in a tuning fork
8 Ed Daw 11/12/07 A Piece of the Action...
Figure 9: Rhodes Stage 2 action
Figure 10: Tuning a rhodes tine
9 Ed Daw 11/12/07 Pickup Location and Tonal Quality
Figure 11: Pickup location instructions from manual
10 Ed Daw 11/12/07 Hammond Organs
Figure 12: Laurens Hammond ( 1895 - 1973 ). The first hammond was designed and built by Laurens in 1935.
11 Ed Daw 11/12/07 A Nice Example of a Hammond B3
Figure 13: A Hammond B3
12 Ed Daw 11/12/07 Tonewheels
TONEWHEEL
PICKUP
VV
MAGETIZABLE METAL
Figure 14: Tonewheel driving a pickup
13 Ed Daw 11/12/07 Actual Hammond Tonewheels
Figure 15: Actual tonewheels and pickups http://theatreorgans.com/hammond/keng /kenhtml/HammondEricb.htm
14 Ed Daw 11/12/07 Drawbars
tonewheels drawbars
FREQUENCY F
FREQUENCY 2F ++ out FREQUENCY 3F
FREQUENCY 4F
Figure 16: Drawbars combine oscillators at different harmonics of the fundamental frequency to generate the overall sound
15 Ed Daw 11/12/07 Leslie Cabinets Invented by Don Leslie
Figure 17: Inside a Leslie speaker cabinet
16 Ed Daw 11/12/07 Conclusions
• Electromechanical keyboards are fabulously ingenious applications of classical physics to our art and culture
• Their continued popularity alongside more modern alternatives such as waveform and digital synthesizers is a fitting testament to the ingenuity and skill of their inventors.
• I wish I had longer to play the music. Thank you for coming !
• I will round off this talk with a tune called ‘Yaba Funk’, courtesy of Captain Yabaa
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