Acoustic quality of a classroom is a term proposed to describe acoustic properties that contribute to a subjective impression received by a human, such as speech intelligibility, external noise, or vocal effort. It is especially important in classrooms, where suitable conditions should be provided to convey verbal content to students, taking into account their age. The article presents a method for assessing the acoustic quality of classrooms based on a single number global index and taking into account a number of factors affecting the outcome of the assessment. Partial indices are presented and their weights are proposed based on an analysis of factors determining whether a room meets applicable acoustic requirements. Results of the assessment of the acoustic quality carried out with the use of the developed method in selected classrooms are also presented.

The article presents results of our own research regarding acoustic properties of 110 classrooms in five typical primary schools in Warsaw. The target of the research was to assess the classrooms using established criteria. These criteria include the reverberation time and the speech transmission index. The research has shown a large diversity of acoustic properties of classrooms within each of the schools and between the schools, resulting from the classroom equipment and the school building construction. In addition, the assessment has indicated that classrooms in schools researched do not meet the established acoustic criteria (reverberation time and speech transmission index). Because the classroom equipment is different for younger forms (integrated teaching) and for older forms (subject teaching), the results have been analyzed separately for rooms for younger forms (0-III) and for rooms for older forms (IV-VI). Synthetic results prove the advisability of such division. Correlation analysis has been conducted for the speech transmission index STI and reverberation time Tmf, as well as for the speech transmission index STI and the suggested reverberation time Twf defined in a similar manner as Tmf, but in a wider frequency range. The correlation between the speech transmission index STI and Twf is higher than that between the STI index and Tmf. The reverberation time Twf can therefore be used for a more precise assessment of acoustic properties of interiors with regard to verbal communication than Tmf. In addition, the paper presents estimated analysis results of the influence of selected classroom equipment (carpets) on its acoustic properties.

Increased efficiency of production and improved quality have contributed to the development of ultrasonic technological applications, in which low frequency ultrasounds are generated to operate, accelerate as well as to facilitate technological processes. Technological ultrasonic devices (i.e. sources of ultrasonic noise in the work environment, e.g. ultrasonic washers, ultrasonic welding machines) have relatively high power and their nominal frequencies are in the range from 18 kHz to 40 kHz. In Poland, ultrasonic noise (defined as noise containing high audible and low ultrasonic frequencies from 10 kHz to 40 kHz) is included in the list of factors harmful to health in the work environment and therefore the admissible values of ultrasonic noise in the workplaces are established. The admissible values of ultrasonic noise and the new ultrasonic noise measurement method make it possible to perform the assessment of occupational risk related to ultrasonic noise. According to this method, the scope of the measurements includes the determination of the equivalent sound pressure levels in the 1/3 octave bands with the centre frequencies from 10 kHz to 40 kHz. This paper presents the description of both, i.e. the method for ultrasonic noise measurements and the method of the assessment of occupational risk related to ultrasonic noise. The examples of the results of the assessment of occupational risk related to exposure to ultrasonic noise are also discussed.

The assessment of teachers' exposure to noise in primary schools was carried out on the basis of: questionnaire studies (covering 187 teachers in 3 schools), noise measurements at the teachers' workplaces, measurements of the school rooms acoustic properties (reverberation time and speech transmission index STI in 72 classrooms), analysis of statistical data regarding hazards and occupational diseases in the education sector. The studies have shown that noise is the main factor of annoyance in the school environment. Over 50% of questioned teachers consider noise as annoying and near 40% as very annoying or unbearable. A-weighted equivalent continuous sound pressure levels measured in classrooms, teacher rooms and common rooms are in the range of 58-80 dB and they exceed 55 dB (criteria of noise annoyance). The most frequently reported subjective feelings and complaints (over 90%) are: growth of psychical and emotional tension, irritation, difficulties in concentrating, hoarseness, cough. Noise in schools is also a harmful factor. High A-weighted equivalent continuous sound pressure levels ranging from 80 to 85 dB, measured in corridors during pauses and in sports halls, can cause the risk of hearing damage among PE teachers and persons oversensitive to noise. The latter concerns both teachers and pupils. High background noise levels (55-65 dB) force teachers to raise their voice. It can lead to the development of an occupational disease - chronic voice disorders due to excessive vocal effort lasting for at least 15 years. In the education sector 785 new cases of this disease were reported only in 2008. Poor acoustics in classrooms (reverberation time ranging from 0.8 to 1.7 s, STI < 0.6 in 50% of classrooms) have an adverse influence on speech reception and make the teaching and learning processes difficult.