Knut Guettler

Acceptance limits for the duration of pre-Helmholtz transients in bowed string attacks

The attack of most bowed notes shows an initial part before Helmholtz triggering occurs (the pre-Helmholtz transient), during which the stick-slip interaction promotes frequencies other than that of the string’s fundamental. Depending on the particular combination of bowing parameters, this state is characterized either by periods that are prolonged, or by a division of the period into two or more parts, multiple flyback. An onset with perfectly periodic motion (Helmholtz triggering) directly from the very start is also possible. A sample of violin tones representing these three classes of attacks, and with different duration of the pre-Helmholtz transient, has been collected by the use of a computer-controlled bowing machine. The tones were evaluated by 20 advanced string students and professionals in a listening test, judging the acceptance and quality of the attacks. The maximum acceptable duration of the pre-Helmholtz transient was estimated to 50 ms (⩽10 nominal periods, open G string, violin) for attacks with prolonged periods, and 90 ms (⩽18 periods) for multiple-flyback attacks. These values refer to a neutral start in a neutral context, such as when practicing a scale. A playing test, in which the performances of two professional violinists were analyzed, confirmed these results, and showed that the same limits apply to a larger group of bowing styles as well.

An empirical investigation of bow-force limits in the Schelleng diagram

An experimental study of the upper and lower bow-force limits for bowed violin strings is reported. A bowing machine was used to perform bow strokes with a real violin bow on steel D and E strings ...

Anomalous low‐pitched tones from a bowed violin string

With a bow force greater than the Schelleng maximum and careful control, it will be demonstrated that it is possible to produce sounds on a violin of definite pitch ranging from approximately a musical third to a twelfth or more below the normal pitch. The lowered pitch is in agreement with the fundamental frequency of the observed harmonic series. The fundamental itself is very weak if the sounds are produced on the open G string. Mari Kimura has utilized the effect in performances [New York Times, 21 April 1994, p. B3, and Strings, Sept./Oct. 1994, 60–66]. These anomalous low frequencies (ALF) occur when the bow force is great enough to prevent the Helmholtz kink from triggering the normal release of the string from the bow hair. As a result of pronounced bow‐nut and bow‐bridge reflections there is at the bow a very complex string waveform, some portion of which regularly triggers the slipping of the string. ALF can also be produced on a bowed string mounted on a steel beam, where the motion is detected...

On the interaction between double basses and the stage floor

Double bassists unanimously claim the importance of a compliant stage floor for producing a warm and nuanced orchestra sound. However, in the limited number of reports studying the stage floor’s contribution to radiated sound no clear conclusion has been reached. The present study, based on measurements of three concert halls and three double basses, points at some measurable features that should be considered when trying to settle the question: (1) With a compliant floor the velocity transfer between the bass bridge and floor is often higher than 0 dB in the low-frequency range. In these cases the bass largely acts as a mass (viewed from the end pin) while the floor acts like a spring. (2) The floor properties aect the bridge mobility in the low-frequency range. (3) Below the Helmholtz resonance, around 60 Hz, the radiation of the bass corpus falls about 40 dB within one octave while the ratio between the input power at the bridge and the power transferred to the floor via the end pin has been observed to boost from 3 to 40% in the same range. (4) The eect of a compliant floor may be more pronounced for the player than for the audience.

Quality aspects of violin bows

The string player’s test of a bow includes four major aspects: (1) the bow should be ‘‘well balanced’’ with an appropriate total weight; (2) the bow should have a good grip of the string over the entire length of the bow stroke; (3) the ‘‘timbre of the bow’’ should be pleasing; and (4) the bow should bounce easily in advanced bowing patterns like rapid spiccato and ricochet. A poor bow will: fatigue the player by demanding too much physical effort (in particular in string crossings); tend to lose the grip of the string when approaching the tip; disguise the tonal quality of a fine instrument; and be sluggish and scratchy in rapid bouncing sequences. Some plausible physical properties which govern these four quality aspects will be presented, focusing on the last, the bouncing bow. [Work supported by School of Electrical Engineering, Royal Institute of Technology, Stockholm.]

Some aspects of bow resonances—Conditions for spectral influence on the bowed string

The resonant bow seems to some extent capable of modifying the power spectrum of the bowed string, even during a steady‐state Helmholtz motion, where only one slipping interval occurs during a fundamental period. Longitudinal resonances in the bow hair, strongly coupled to the transverse vibrations of the stick, are being excited by the changes of the frictional force which occur during each individual period. In general, these velocity fluctuations—superimposed on the steady bowing velocity—show small amplitudes compared to those of the string under the bow. In certain frequency regions however, dependent on the bow/bridge distance, impedances, etc., their energy content is sometimes great enough to cause noticeable modification of the string velocity. Such spectral changes would at any rate be small, but may still bear some acoustic significance. The present analysis is based on measurements on a violin bowed by a computer‐controlled bowing machine, and supported by computer simulations. [Thanks are ext...

Stage floor vibrations and bass sound in concert halls

The double bass and cello sections in the orchestra transmit vibrations to the stage floor through the end pins. Whether or not these vibrations may contribute to the perceived sound in the hall has been investigated since the 1930s. In this study the conditions for an efficient transfer of instrument vibrations to the floor, as well as the radiation from the floor to the audience area, are investigated. The study includes measurements of the impedance matching between bass and stage floor, the vibration velocity transfer to the floor via the endpin, and radiation from point-driven bending waves in the stage floor well below the coincidence frequency. The impedance conditions and radiation properties of the stage floors of five concert halls were investigated. In the two most promising halls, full-scale experiments were run with an artificially excited double bass supported via the end pin on the stage floor and on a concrete support below, respectively. The contribution from the stage floor radiation to the sound level in the audience area was 5 dB or more between 30 and 60 Hz. This range covers the fundamental frequencies over one octave starting from the lowest note (B0) of a five-string bass.

Double basses on the stage floor: Tuning fork–tabletop effect, or not?

The question whether or not double basses can benefit from a compliant and radiating stage floor in the low end of their tonal register, similar to the well-known tuning fork-tabletop effect, was examined through field experiments in five concert halls. The topic comprises several aspects: (1) How well the mechanical impedances of double basses and the stage floor match, (2) amount of vibration velocity transmitted to the floor through the end pin of the bass, and (3) radiation efficiency of point-excited bending waves in the stage floor far below the coincidence frequency. Each aspect represents a prerequisite for the tuning fork-tabletop effect to take place. The input impedance at the end pin was measured for three representative double basses. The stage floors of five orchestra halls were measured with respect input impedance and damping, while sound radiation to the audience area was measured for two of them. In Lindeman Hall, Oslo, all conditions for the tuning fork-tabletop effect to take place were clearly met. The contribution from the stage-floor radiation to the sound pressure level in the audience area was found to be about 5 dB between 40 and 60 Hz, and even higher between 30 and 40 Hz.

A concise overview of present knowledge of bowed‐string gestures and their acoustical consequences

During the few years of our young millennium the picture of what happens acoustically when the bow is drawn across the string has become considerably more complete. A few surprises emerged along the way: the bows position on the string does not seem to influence the spectral envelope‐and different from what Schelleng predicted‐there seems to be no clear correlation between minimum bow force and the bow speed. The intention of this presentation is to give a brief survey of related studies and their results, as well as pointing out some of the blank spots still remaining on the canvas.

Method for time‐domain localization of stochastic noise in quasiperiodic signals

In order to establish knowledge on the sources of noise in nearly periodic signals, it is essential to apply methods that give the best possible resolution in the time domain. Of particular importance is this kind of analysis when attempting to synthesize low‐pitched bowed string instruments, where most of the noise appears in pulses. The present method isolates the noise from the signal without the use of any nonrectangular window or zero padding. This can conveniently be done by combining FFT with the Bluestein filter [L. I. Bluestein, Nerem Record, 218–219 (1968)], which allows the number of elements under analysis to be arbitrarily chosen as an exact integer product of the signal period. The suggested method minimizes leakage to neighboring elements when returning to the time domain after the deterministic/stochastic signal separation, thus providing a very reliable separation between the two signal components in both domains. Sound examples will be given for several instruments.