Musical Acoustics
Supplementary podcasts highlighting aspects discussed in the 'Musical Acoustics' course from the School of Physics and Astronomy at the University of Edinburgh.
Episodes
February 13, 2010 • 8 mins
In singing, air pressure from the lungs is used to set the vocal folds into periodic oscillation producing a pitched sound source at the base of the vocal tract. By changing the positions of the jaw, lips and tongue the resonances of the air in the vocal tract, called vocal formants, can be altered. We perceive the different tone qualities produced as the vowel sounds used in everyday communication. Vocal tract resonances can also...
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February 11, 2010 • 10 mins
The important acoustical characteristic common to members of the musical brass instrument family is not the material of construction, but the way in which the note is sounded by vibrating the lips against the rim of a mouthpiece. The lips act as a valve, open and closing periodically to modulate the flow of air into the instrument. The resulting pressure changes in the mouthpiece set up standing waves in the air column contained by...
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February 11, 2010 • 10 mins
Almost all brass instruments have air column resonances which are close to forming a harmonic series; this gives rise to the familiar pattern of “bugle call†natural notes. In the upper register the harmonics are close enough together to allow a diatonic scale to be played without modifying the tube length, although certain harmonics have to be modified in pitch by lipping or hand-stopping. The much larger pitch intervals betwe...
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November 24, 2008 • 10 mins
The original Hammond used rotating tone wheels to generate harmonics which were added using drawbars; not true harmonics though. The principle is known as additive synthesis. The organ is usually played through a Leslie speaker which utilizes the Doppler principle to produce chorale and tremolo effects. Modern digital synthesizers such as the Nord Electro simulate both the drawbars and the Leslie speaker. In subtractive synthes...
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November 21, 2008 • 9 mins
In concert halls it’s desirable that the time between the arrival of the direct sound and the first reflection is not greater that 20ms. Highly reflecting parallel walls may cause undesirable flutter echo. The distance from the source where the intensity levels of the direct and reverberant sound are the same is known as the Room Radius; a typical value for a large hall is 5m. Closer than the room radius you hear mostly direct...
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November 17, 2008 • 8 mins
Sound rays obey Snell’s law of reflection. When they strike a surface the fraction of sound energy absorbed is known as the absorption coefficient, which varies with frequency. The time for the reverberant sound in a room to drop by 60dB is known as the reverberation time R. This can be calculated from the formula R = 0.16 V/A where V is the volume in cubic metres and a is the total absorption in metric Sabin i.e. the sum of t...
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November 10, 2008 • 10 mins
In Pythagorean tuning the 5ths are true i.e. in the frequency ratio 3/2. In 1/4 Comma Mean Tone the major 3rds are true i.e. in the frequency ratio 5/4. Both tunings give rise to the wolf which restricts the number of playable keys to 6 major and 3 minor. In Equal Temperament all keys are playable but neither the 3rds or 5ths are true. In circular temperaments the total reduction in all 5ths round the circle is one comma; all k...
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October 31, 2008 • 15 mins
The Boehm flute has a cylindrical body and a tapered headjoint, which is required to compensate for the flattening effect of increased lip cover over the embouchure hole in the upper register. Like the saxophone, the clarinet has a mouthpiece and a single reed. It has distinctive tone qualities in the low (Chalumeau) register and higher (clarinet) register. The tone quality of the oboe and bassoon, which both have double reeds, i...
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October 27, 2008 • 10 mins
In a woodwind the sound is generated by the resonating air column within the instrument, the material of construction being of secondary importance. To a first approximation the flute can be considered as a cylindrical tube open at both ends, the clarinet as a cylindrical tube closed at one end and the saxophone, oboe and bassoon as conical tubes closed at one end. All these instruments generate a complete harmonic series and over...
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October 17, 2008 • 10 mins
This podcast is about the modern grand piano. A full size piano usually has a compass of 7 1/4 octaves, from A0 to C8. For the notes A0 to A1 there is only one string per note, for the octave above (Bb1 to Bb2) two strings per note and for the notes above these three strings. All strings up to Bb2 are overwound to increase their mass per unit length. The plane and overwound strings have separate treble and bass bridges which a...
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August 25, 2008 • 15 mins
Rudiments
There are twelve semitones to a complete octave, two semitones making a tone. The major diatonic scale has seven notes separated by the intervals of a tone (T) and semitone (S) in the sequence TTSTTTS. Each note has a separate letter name. In the scale of C major the most important intervals are C-E (major third), C-Eb (minor third), C-F (perfect fourth), C-G (perfect fifth); the triad CEG is referred to as chord I, c...
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