In order to investigate the physical processes involved in the build-up of the sound signal in a labial organ pipe a pipe foot model has been developed. The main important parameters, such as positions of the lower and upper lips, the wind pressure in the pipe foot, and the width of the flue, can be adjusted by means of this model. Moreover, different types of languids and pipe bodies (resonators) can be attached to the model. For the reason of corresponding to a real metal organ pipe these parts of the model are made of a typical alloy used in organ building. The reproducibility of measurements is provided by the micrometer screws applied for the adjustments. Flow and edge tone measurements are carried out with the help of this model. Velocity measurements with different flue widths show that the exit velocity of the jet corresponds to the Bernoulli-velocity and is asymmetrically contracted. At larger distances (>5 mm) the velocity distribution can be described by a Gauss-function having linearly increasing width. A mathematical relation of the centerline velocity as a function of the cut-up height L is found. The results of edge tone measurements show differences between previous studies and the present one. No frequency stages (and hysteresis phenomena) are found within the investigated pressure and cut-up range; the frequency modes of the edge tone coexist. The measured frequencies can be described by theoretical models.
An optimization method, based on an acoustic waveguide model of chimney and resonator, was developed and tested by laboratory measurements of experimental chimney pipes. The dimensions of the chimney pipes are modified by the optimization algorithm until the specified fundamental frequency is achieved, and a predetermined harmonic partial overlaps with an eigenfrequency of the pipe. The experimental pipes were dimensioned by the optimization method for four different scenarios and were built by an organ builder. The measurements show excellent agreement between the measured sound spectra and calculated input admittances. The developed optimization method can be used for sound design of chimney pipes.
Vibrations of plucked and blown reeds of lingual organ pipes without the resonators have been investigated. Three rather surprising phenomena are observed: the frequency of the reed plucked by hand is shifted upwards for large-amplitude plucking, the blown frequency is significantly higher than the plucked one, and peaks halfway between the harmonics of the fundamental frequency appear in the spectrum of the reed velocity. The dependence of the plucked frequency on the length of the reed reveals that the vibrating length at small vibrations is 3 mm shorter than the apparent free length. The frequency shift for large-amplitude plucking is explained by the periodic change of the vibrating length during the oscillation. Reed vibrations of the blown pipe can be described by a physical model based on the assumption of air flow between the reed and the shallot. Aerodynamic effects may generate and sustain the oscillation of the reed without acoustic feedback. The appearance of subharmonics is explained by taking into account the periodic modulation of the stress in the reed material by the sound field. Therefore, a parametric instability appears in the differential equation of vibration, leading to the appearance of subharmonics.
Although sulfuryl fluoride (SO2F2) is an efficient fumigant that does not react with the surface of indoor materials and does not reduce the stratospheric ozone shield, there are some concerns about its use. It is a toxic gas that attacks the central nervous system, and its global warming potential (GWP) value is 4780 for 100 years’ time. Therefore, it is a clear necessity of implementing detection methods for tracing such a molecule. In this work a sensitive photoacoustic setup was built to detect SO2F2atconcentrations of parts per billion by volume (ppbv). The symmetric S–O stretching mode was excited by a continuous-wave quantum cascade laser with radiation wavenumber ranging from 1275.7 to 1269.3 cm−1. The photoacoustic signal was generated by modulating the laser wavenumber at the first longitudinal mode of the photoacoustic cell with amplitude depth of 5 × 10−3 cm−1. The detection of a minimumSO2F2concentration of 20 ppbv was achieved
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