Strings: Guitar, Harp, Piano and Harpsichord

Transcription

1 Strings: Guitar, Harp, Piano and Harpsichord 80/20 A stringed instrument uses standing waves on a string to provide the frequency generation. f 1 f 2 f 3 f 4 ~ ~ String Standing Waves f n A Standing Wave results from interference of counter-reflecting reflecting waves. Fundamental Mode Node L = 2 /₄ λ 1 f 1 = v string / λ 1 = v string / 2L Antinode λ 1 /4 λ 1 /4 Node 80/20 The distance between neighboring nodes & antinodes is ¼ λ.. [ N-A A d = ¼ λ ] Second Harmonic f 2 = v string Node Antinode L = 4 /₄ λnode 2 string / λ 2 = v string / L Antinode λ 2 /4 λ 2 /4 λ 2 /4 λ 2 /4 Node

2 Physics 1251 Unit 2 Session 21 Scales and Strings 80/20 Frequency of n th harmonic: The Vibrating String Demonstration f n = [2n/(4L)] v string f n = [n/(2l)] (T/ μ)] 80/20 The modes that will be present are those that are excited. 80/20 The modes that will be present are those that are excited. ~ ~ f 1 f 2 f 3 f 4 Energy source can excite selected modes f n Example: Guitar Overtones (Harmonics) Plucking, strumming, damping

3 The Guitar is a fretted stringed instrument that is plucked or strummed. Neck Strings (6) Body Tuning pegs Frets Density of strings sets range of each string Denser wire: lower pitch Less dense wire: higher pitch Frets shorten the string to raise the pitch. The tuning pegs change the string tension. L o L 1 Fret L o / L n Tuning Pegs

4 The strings are attached to the body and sound board by a flat bridge. 80/20 The coupling of the string to the sound board will accentuate or attenuate various frequencies. Strings ~ ~ f 1 f 2 f 3 f 4 Sound Board and Acoustics filter harmonics f n The response of the body and air cavity determine the filtering of the harmonics. Guitar in cross section Sound hole Neck Truss rod Body Vibration Modes of Guitar Body: Holographic vibration images of Guitar body

5 80/20 A Harp is a stringed instrument that is plucked. Its strings are of various lengths. Strings The principal pitch of each string in a Pedal Harp is determined by its length. Pedal Harp Strings Traditional Irish Harp Sound Board Pedals However, depressing a pedal shortens or lengthens the string length, raising (or lowering) the pitch incrementally. The principal pitch of each string in a Pedal Harp is determined by its length. 80/20 A Harpsichord is a keyboard stringed instrument whose strings are plucked. However, depressing a pedal shortens or lengthens the string length, raising (or lowering) the pitch incrementally.

6 80/20 A Harpsichord is a keyboard stringed instrument whose strings are plucked. 80/20 A Harpsichord is a keyboard stringed instrument whose strings are plucked. 80/20 A Harpsichord is a keyboard stringed instrument whose strings are plucked. 80/20 A Harpsichord is a keyboard stringed instrument whose strings are plucked. Harpsichord Action String Plectrum Jack Damper Key

7 The jack plucks in one direction, then retracts in the opposite. 80/20 A Piano is a keyboard stringed instrument whose strings are hammered. Each string is used for one pitch only. Fortepiano Strings Piano Key Board Sound Board The Piano strings are hammered by a felt hammer, actuated by the action. action. The Piano strings are hammered by a felt hammer, actuated by the action. action. String and Damper Hammer Jack Key

8 80/20 A Piano has multiple strings (in the treble) to provide a more powerful sound. Piano strings are tensioned by tuning pins in a strong frame. Multiple Strings Frame Bass Strings Sound Board Frame Tuning Pins Piano hammers are made of felt and wood. Hammer Head Back Check Felt Wood The timbre of the piano sound is affected by the hardness of the hammer felt. Felt hard or soft? Pivot hinge