The paper presents results of hearing loss measurements provided for 81 young people (from 16 to 25 years old). The main aim of the work was to find the influence of headphones of the types used (closed, semi-open, open and in-ear) on the hearing losses. The first part of the research was to answer questions about the influence of: time of listening, loudness of music, other noise exposures as well as the type of the headphones used. It turned out that all factors mentioned above influence thresholds of hearing but the found dependencies are not explicit. The greatest hearing losses were observed for people who work as sound reinforcement engineers and, moreover, no influence of the headphone types was found for them. It turned out that the use of in-ear headphones causes the greatest hearing losses for some subjects (thresholds shifted up to about 20 dB HL at 4 kHz). The daily time of a listening also affected the hearing thresholds. It was found that for users of in-ear and close headphones, an average time of musical exposure of three hours causes the hearing loss of 10-15 dB HL at higher frequencies. The use of open as well as semi-open headphones has no influence on the hearing damage. Thus it would be stated that these kinds are safety in use. Almost 15% of the investigated young people have their thresholds shifted up at higher frequencies, particularly at 4 kHz, which means that they have the first symptoms of a permanent hearing damage.

The work presents a comparison of some sound attributes perceived at a multichannel and stereo playback of musical recordings. The width of the virtual source, coherence impression, total size of sound scene, general quality and balance were the subjects of interest after the format reduction in accordance with the ITU recommendation. The results showed that evaluation of these attributes depends on the way the original audiosphere has been created in the surround system, for example, for a narrow virtual source the mix-down process causes only a small change in its size but for a broad source the observed degradation is significant. In addition, different ways of conversion from the multichannel to stereo format have been tested for compatibility.

This chapter presents results of research on influence of auditory fatigue on some aspects of listening condition measured among various groups of listeners. Three experiments have been carried out. The aim of the first one was to find the influence of the kind of headphones used by young people on their hearing loss. The second experiment was concerning the temporary threshold shift (TTS) caused by the listening of loud musical signals after several time of sound exposure. The main interest of the third experiment was the detection ability of changes in spectrum of musical samples obtained after several time of listening to the loud music. It turned out that except for frequency of 4 kHz there is no relation between the types of preferred headphones and the shift of hearing threshold while for the frequency of 4 kHz, a statistically important influence of the headphone types on the threshold values was observed. The second and third experiments were carried out under conditions which normally exist in a studio or on the stage when the sound material is recorded and/or mixed. It turned out that after several loud music listening sessions the average value of temporary threshold shift reached more than 3 dB for 1 kHz and increased up to 6-7 dB with an exposure time of 120 min. On the basis of results obtained from the third experiment, it was found that the decrease in ability to detect the spectrum changes for longer noise exposure exists particularly for lower changes (of ±1.5 dB) and at all frequency regions under investigation. It may suggest that the hearing system gets tired for the region of higher frequencies faster than for other bands after listening to loud music. The results may also be influenced by the mental fatigue which occurred after several time duration of permanently played loud sounds, together with demanding tasks. Such conditions involving the mental engagement in a noisy environment, which is referred to the natural scenery of the studio work can significantly reduce the time of exhaustion which causes the decrease of accuracy in solving several tasks. It should be also noted that the tendencies observed within young people culture in listening loud music in order to be isolated from the environment is actually causing not the TTS phenomenon but permanent threshold shift (PTS).

A relationship between the generalized Miller 61111(w; w , w , w ) coefficient and the Phillips-van Vechten ionicity in alkali halides is presented. The correlation is employed to estimate the nonlinear refractive index of these crystals.