Ewa Skrodzka

Modal parameters of two incomplete and complete guitars differing in the bracing pattern of the soundboard

Similarities and differences in vibrational behavior of two guitars having a symmetric Torres bracing pattern and an asymmetric pattern forming a lattice on a soundboard are investigated by means of the modal analysis technique and laser Doppler vibrometry (LDV) measurements. Instruments are investigated before and after a bridge and strings assembling (i.e., they are incomplete or complete). The bracing pattern and the absence/presence of the bridge and strings have some effect on modal frequencies and mode shapes. The bracing pattern does not affect the sequence of at least first three low frequency mode shapes of incomplete/complete instruments but affects their modal frequencies. Depending on frequency, the bridge behaves either as a rigid or a flexible structure.

Mechanical and optical investigation of dynamic behavior of violins at modal frequencies

Two main aims of our investigation are to show differences in natural vibrations between two violins that differ in the thickness of the back plate and to determine whether they are linear systems. Two experiments were performed on the top and back plates. The first experiment was a mechanical modal analysis in a version with a fixed response point. In the second experiment optical measurements of the plates velocities in modal frequencies obtained from the first experiment were performed by use of laser Doppler vibrometry. The second experiment was a simplified modal analysis experiment with a fixed excitation point. Changes in the thickness of the back plate caused changes in certain modal frequencies of both plates. However, no important differences in mode shapes were found in both experiments. Thus, violins can be treated as linear systems but with great care.

COMPARISON OF SINGLE AND DUAL-PHASE LOCK-IN AMPLIFIERS FOR PHOTOACOUSTIC SPECTROSCOPY

Dual phase lock-in is usually used in photoacoustic research because it allows precise projection of the measured spectra. In this article, double and single phase lock-in amplifiers were used and the advantages and disadvantages of both were compared. Two liquid crystals were studied in this work: ethylo- and penthylo-cyanobiphenyl in cyclohexane, tetrahydrofuran, and acetonitrile. The red-shift of the maximum related to the polarity of solvents and a bigger shift for 4-penthylo-4′-cyanobiphenyl relative to 4-ethylo-4′-cyanobiphenyl were observed. In order to investigate the usefulness of the single-phase device, compared to the more expensive double-phase device, the frequency dependence measurements and photoacoustic spectra were recorded and compared. Small differences were observed (within the limit of error) in spectra obtained using the single and the double lock-in amplifier. The simpler single-phase lock-in device can be used to reliably measure frequency spectra without any loss of information.

Photo-acoustic and ultrasonic investigation of the mixtures of water and several glycols

In the paper the results of the ultrasonic velocity and absorption measurements were presented, as well as the thickness in water mixtures of some glycols. The experiments were provided in the temperature range from 291.15 to 303.15 K for whole molar fraction. Adiabatic compressibilities were calculated from Laplaces equation based on the experimental results obtained. Variations of these values with concentration and temperature were studied. Structural interactions and the formation of a compact pseudostable structure at very low concentrations of ethylene glycol and polyethylene glycols were observed. The plots of the adiabatic compressibility versus the mole fraction of PEG and EG display two characteristic points at low concentrations: the intersection of the isotherms and their minimum. Such relations between adiabatic compressibility, concentration and temperature are usually attributed to the formation of pseudo-stable molecular structures. To formulate a model of local structures present in the ...

Fitting of hearing aids with different technical parameters to a patient with dead regions

Fitting of hearing aids with different technical parameters to a patient with dead regions The purpose of the study was to determine an optimal hearing aid fitting procedure for a patient with well diagnosed high-frequency ‘dead regions’ in both cochleas. The patient reported non-symmetrical hearing problems of sensorineural origin. For binaural amplification two similar independent hearing aids were used as well as a pair of dependent devices with an ear-to-ear function. Two fitting methods were used: DSLi/o and NAL-NL1, and four different strategies of fitting were tested: the initial fitting based on the DSLi/o or NAL-NL1 method with necessary loudness corrections, the second fitting taking into account all the available functions of hearing instruments, the third fitting (based on the second one) but with significantly reduced amplification well above one octave of frequency inside dead region, and the final fitting with significantly reduced gain slightly below one octave inside dead regions. The results of hearing aids fitting were assessed using an APHAB procedure.