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2 Archives of Acoustics

2 2008

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Directional properties of the loudspeaker systems with analog and digital crossover networks

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Niewiarowicz M. , Łopacz H.

tom Vol. 33, No. 4

541-551

Directional properties of loudspeaker systems with analog and digital crossover networks have been investigated. The study has been performed for a three-way loudspeaker system subjectively classified as of average quality. The digital crossover networks have been designed in such manner that the cut-off frequencies of filters (1000 Hz and 5000 Hz) corresponded to those of the analog networks and the slopes of the amplitude characteristics were 12 and 18 dB/oct. The set of impulse responses for different angles in the whole sphere around the loudspeaker system were measured and then, applying a convolution with the excitation signals of the "tone burst" type, for some specific frequencies from the cut-off region of crossover networks, the directional characteristics have been calculated for the steady and transient states. The quantitative analyses of results, based on the values of directional coefficient, show significant differences between the characteristics in steady and transient states, as well as for the analog and digital systems.

Application of sentence tests in the investigation of speech intelligibility in quiet and noise in adult CI recipients supported with a hearing aid

80%

Niewiarowicz M. , Stieler O. , Komar D.

tom Vol. 33, No. 4

475-482

The investigations of speech intelligibility were carried out for 9 patients with a cochlear implant (CI), 1 male and 8 females, aged 18-69 (mean 41). In all cases deafness was recognized as postlingual. All patients were using the hearing aid (HA) on the ear opposite to the CI. The novelty of this work consisted in the application of new Polish sentence tests in the evaluation of the effect of supporting electrical hearing with a HA in noise conditions. The sentence tests (developed at the Institute of Acoustics, Adam Mickiewicz University in Poznań - European Union Project HEARCOM) were presented to patients in quiet and in noise conditions (speech bubble noise). The speech intelligibility was determined in two cases: when transmission was only via the CI and when the HA was also used. The presentation of tests was conducted for three angles (0°, -90° and +90°o) in relation to the patient's head. The value of SRT (Speech Reception Threshold) was determined for the tests carried out in noise conditions. The improvement of the speech intelligibility was affirmed when the process of hearing via the CI was supported with a HA. The particularly essential difference was observed for the angle of +90° (HA-side). The results obtained in the investigations show that acoustic compensation in the range of the remaining audibility field to a great degree supports electrical hearing. This conclusion can be an important contribution to the application of the HA on the side opposite to the CI, especially in the noisy environment.