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1

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

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

Archives of Acoustics

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2014

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Vol. 39, No. 1

145--149

EN

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−).

2

Modal Parameters of Two Violins with Different Varnish Layers and Subjective Evaluation of Their Sound Quality

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

Archives of Acoustics

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2013

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Vol. 38, No. 1

75--81

EN

Two violins were investigated. The only intentionally introduced difference between them was the type of varnish. One of the instruments was covered with a spirit varnish, the other was oil varnished. Experimental modal analysis was done for unvarnished/varnished violins and a questionnaire inquiry on the instrument’s sound quality was performed. The aim of both examinations was to find differences and similarities between the two instruments in the objective (modal parameters) and subjective domain (subjective evaluation of sound quality). In the modal analysis, three strongly radiating signature modes were taken into account. Varnishing did not change the sequence of mode shapes. Modal frequencies A0 and B(1+) were not changed by oil varnishing compared to the unvarnished condition. For the oil varnished instrument, the frequency of mode B(1+) was lower than that of the same mode of the spirit varnished instrument. Our two violins were not excellent instruments, but before varnishing they were practically identical. However, after varnishing it appeared that the oil-varnished violin was better than the spirit-varnished instrument. Therefore, it can be assumed with a fairly high probability that also in general, the oil-varnished violins sound somewhat better than initially identical spirit-varnished ones.

3

Vibroacoustic investigation of a batter head of a snare drum

Skrodzka E. B., Hojan E., Proksza R.

Archives of Acoustics

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2006

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Vol. 31, No. 3

289-297

EN

The modal analysis of a batter head of a snare drum and measurements of the instrument's sound spectrum have been performed. The modal analysis results is comparable to the scarce literature reports. The analysis of the frequency maxima of the sound spectrum revealed significant discrepancies between the modal frequencies and those of the spectral peaks. It has been shown that the lowest mode (0, 1) is the strongest mode of radiation only for central excitation. For non-central excitation, the frequencies of spectral peaks differ significantly from the modal frequencies. It has been found that the batter head was not necessary the most strongly radiating element of the drum system and that the influence of other elements (the snare drum, the shell, the snares) are also very important as far as sound impression is concerned.

4

Discrimination of the amplitude modulation rate

Lemańska J., Sęk A. P., Skrodzka E. B.

Archives of Acoustics

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2002

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Vol. 27, no. 1

3-22

EN

This study examines the amplitude modulation rate discrimination for sinusoidal and noise carriers. It was shown that the discrimination of AM rates is a monotonically growing function of modulation rate. Higher values of the discrimination thresholds were observed for a narrowband carrier. It appears that in the case of a narrowband noise carrier, the spectral range of the noise envelope is similar to that of the modulation rates of the signal (up to 120 Hz). It results in a masking in the modulation rate domain and in a much higher threshold growth than that observed for a wideband noise carrier or a sinusoidal carrier. The results are consistent with the idea of the so-called second stage of filtering acting on the envelope of the acoustic signal. This hypothesis postulates the existence of a so-called modulation filter bank, (MFB), responsible for the frequency selectivity observed in the amplitude modulation rate domain. The existence of the MFB suggests that a certain form of the spectral analysis of any acoustic signal envelope may be performed in the auditory system after initial filtering in the auditory filter bank. A model of the modulation rate discrimination based either on the classical concept of the excitation patterns or on the modulation excitation patterns has not accounted for our experimental data. According to both the models, an increase in the frequency discrimination threshold versus modulation rate should be slower than that measured in the experiment.

5

Auditory filters in sensorineural hearing impaired subjects

Skrodzka E. B., Wicher A., Ozimek E., Sęk A. P.

Archives of Acoustics

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2002

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Vol. 27, no. 3

159-174

EN

The study is devoted to determination of the shape of the auditory filters in subjects with sensorineural hearing loss. Apart from the classical sensorineural hearing loss, changes in the auditory filter shapes have been analysed in the subject diagnosed with dead regions. The dead region is an area on the basilar membrane over which the functioning of the inner hair cells and/or neurones innervating them has ceased. This type of hearing impairment means that the information on the sounds whose frequencies correspond to the dead region of the basilar membrane are to a very limited degree if at all, transmitted to higher levels of the auditory path. This transmission, if happens, is performed through the auditory filters at the centre frequency other than that of the signal. This phenomenon and the fact that in the dead region the hearing loss is theoretically infinite, affect the transmittance of the auditory filters. Results of the study reported here have shown that in general, the subjects with sensorineural hearing loss develop broadening of the auditory filter accompanied by reducing of its dynamics. This fact explains a considerable decrease in speech intelligibility presented at a background of a noise. In the subject with the dead regions the broadening of the filters was the greatest in the region of the dead one. The results also indicate the lack of correlation between the shape and width of the auditory filter and the shape of the audiogram.