Keys in woodwind- the physical cut off frequency

When a tone is produced on a wind instrument, the bore of the instrument works as a resonator, to produce a pitch, but the internal surface of the bore is not a perfect smooth parallel surface. In woodwind, the keyholes even in a closed situation, still add (drill tone hole) or attach a little bit some space (plug/attach tone hole)in the bore. The rough and uneven surface of the bore causes energy loss, especially the high frequencies with short wavelengths. Diffraction refers to various phenomena that occur when a wave encounters an obstacle or opening. The tone hole, the lattice rough surface, is the obstacle to the sound wave. When covering most and all tone holes of the woodwind instrument, short-wavelength in high frequency have trouble the get around corners and obstacles by traveling the whole length of the pipe, while the high frequencies (>1000Hz) are lost (Benada,1990). 

For fingering in woodwind instrument, it creates different patterns of open and close holes,The calculation tone-hole cutoff freqency, around this frequency is basically weaken, f = 0.11*(b/a)*v*sqrt(1/(s*(t+1.5*b))). (Benada,1990)

b = diameter of the tone hole; a = diameter of a pipe; v = volocity of air; s = the distance between holes; t = thickness of the wall.

Based on the formula above, we can explain that in a woodwind octave key or when playing the second octave of an instrument, the top hole is always released. The top key released and a series of closed tone holes makes the distance between two-tone holes is high in value, resulting in a low cut-off frequency. The dampen first partial makes the second partial stand out. For fork fingering, the complex fingering with different lengths of distance between holes provides more combinations of various cut-off frequencies. For baroque flutes without a lot of harmonic partials, the sound is duller; for double reed instruments with rich harmonic partials of the reeds, the sound is balanced back with a clearer and crispier sound.

  Benade, A. H. (1990) Fundamentals of musical acoustics. 2nd. rev. ed. New York: Dover.


Comments

Post a Comment

Popular posts from this blog

Post-spectralism influence on tuning

According to Helmholtz (2011), a musical note is due to the fundamental frequency and the quality of a musical sound is due to the presence of upper partials. For traditional western music, pitch perception is mainly fundamental, rather than the frequencies in the spectrum which Teodorescu-Ciocanea (2003) describes as a “note proper” tradition. The spectralism composers shifted the domain from absolute pitches, intervals and chords to the spectrum. Spectral music is a complex approach to timbre, Teodorescu-Ciocanea (2003) classified 9 tendencies and their possibilities in spectral music. To conclude the techniques, tuning the frequencies according to the harmonic series is the major approach; while working with noise, generated digitally and/or extended techniques on instruments, is a sort of timbral dissonance which dilutes the pitch perception of a musical sound. Teodorescu-Ciocanea describes inharmonicity as the combination of frequencies that are not integral multiples of the funda
Read more

Haba's field shifting - and the expansion of traditional functional harmony

Image
Hába characterizes the quarter-tone gamut as separated into two fields, one half comprising the twelve conventional pitches, and the other half, shifting all the twelve notes by a quarter-tone, the twelve quarter-tone pitches. In harmony, Passages occur in which chords composed purely of conventional pitches alternate with chords composed purely of quarter-tone pitches. Two fields are not always rejecting each other when he equally divided a perfect 4th (5 semitones)into 2 equal intervals, equal 2.5 for each, the 0.5 quartertones always step into the other field. Sometimes, this fourth interval can be further divided into 2.5+2+0.5 or other permutations. This kind of splitting a fourth can be traced to ancient greek tetrachord, a scale of four notes, bounded by the interval of a perfect fourth. A chord across both fields, the chord spell like a flatter dominant 7th chord. the 7th harmonic on harmonic series is quite flat (-31cents). This chord combines both fields sounds better accordi
Read more

Temperament, Tuning, and Timbre -- the underrated trinity in music

 The trinity here is not about the Christianity faith, but similar to the idea of the Christian doctrine of it defines God as being one God existing in three coequal, the core and fundamental definition, temperament, tuning, and timbre (TTT) are the basic building blocks of music, yet, underrated and even neglected in our music education system. TTT correlates with each other. A note is played, it carries out a series of frequencies, the harmonic series. The series multiples from the fundamental frequency with a series of integers (1f 2f 3f 4f 5f 6f 7f 8f 9f 10f 11f 12f 13f...). The loudness of individual particles, and different patterns, creates different timbres. View the series in a different way, the combination of the integers creates intervals. The combination of the beginning of the series sounds more harmonious and vice versa; simple ratios sound pure and vice versa. The pure perfect 5th interval is based on the ratio of 2:3 (2nd and 3rd harmonics at the same time), Pytheogoro
Read more