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Relaksacja oscylacyjna w związkach halogenopodstawnych benzenu

100%

Linde B. B. J. , Lezhnev N. B.

tom Vol. 83, nr 27

413-418

The acoustic investigations in the group of halogenated benzenes compounds and particularly research of the dependencies of acoustic parameters and the structure of the organic liquids, demonstrated some interesting regularities in the group of these compounds in gas and liquid states. In this paper the results of research in five cyclic liquids: bromo-, chloro-, fluoro- and jodobenzene were discussed in comparison to the benzene. The acoustic relaxation observed in all the compounds was found to result from Kneser's processes (vibrational relaxation). Based on investigations reported in this paper, as well as other, both experimental and literature data concerning a great number of compounds, one can draw a conclusion that almost all acoustic relaxation (Kneser-type) processes in liquids can be described using one relaxation time. It also seems that all vibrational degrees of freedom of the molecule take part in this process. It is known that arising of differences in transition probabilities could be caused by additional attraction in interaction of molecules having the dipole moments. A high value of dipole moments of halogenobenzenes with adequate benzene could be responsible for the difference of transition probabilities and changes of the relaxation times.

Effect of Bass Bar Tension on Modal Parameters of a Violin’s Top Plate

80%

Skrodzka E. B. , Linde B. B. J. , Krupa A.

tom Vol. 39, No. 1

145--149

Experimental modal analysis of a violin with three different tensions of a bass bar has been performed. The bass bar tension is the only intentionally introduced modification of the instrument. The aim of the study was to find differences and similarities between top plate modal parameters determined by a bass bar perfectly fitting the shape of the top plate, the bass bar with a tension usually applied by luthiers (normal), and the tension higher than the normal value. In the modal analysis four signature modes are taken into account. Bass bar tension does not change the sequence of mode shapes. Changes in modal damping are insignificant. An increase in bass bar tension causes an increase in modal frequencies A0 and B(1+) and does not change the frequencies of modes CBR and B(1−).

Modal Analysis of a Trapezoidal Violin Built after the Description of Félix Savart

80%

Duerinck T. , Skrodzka E. , Linde B. B. J.

tom Vol. 39, No. 4

623--628

One-dimensional experimental modal analysis of an unvarnished trapezoidal violin built after the description of F. Savart and an anonymous trapezoidal violin on display in the Music Instrument Museum of Brussels is described. The analysis has revealed ten prominent modes. A mode that may potentially play a role of the “tonal barometer” of the instrument is pointed out. The mode shapes are symmetric and of high amplitude, due to the construction of the instrument. Subjective evaluation of the sound quality demonstrated no pronounced difference between the trapezoidal violin and normal violin.