Attenuation of high-level acoustic impulses (noise reduction) by various types of earmuffs was measured using a laboratory source of type A impulses and an artificial test fixture compatible with the ISO 4869-3 standard. The measurements were made for impulses of peak sound-pressure levels (SPLs) from 150 to 170 dB. The rise time and A duration of the impulses depended on their SPL and were within a range of 12-400 mus (rise time) and 0.4-1.1 ms (A duration). The results showed that earmuff peak level attenuation increases by about 10 dB when the impulse's rise time and the A duration are reduced. The results also demonstrated that the signals under the earmuff cup have a longer rise and A duration than the original impulses recorded outside the earmuff. Results of the measurements were used to check the validity of various hearing damage risk criteria that specify the maximum permissible exposure to impulse noise. The present data lead to the conclusion that procedures in which hearing damage risk is assessed only from signal attenuation, without taking into consideration changes in the signal waveform under the earmuff, tend to underestimate the risk of hearing damage.
In this study, change in A-weighted and 1/3 octave sound pressure levels (SPLs) was used to assess the influence of wearing earplugs by musicians on their musical performances. Seven soloists and 3 music assembles performed 4 pieces of music with musician's earplugs donned and doffed. They used silicon custom moulded earplugs with acoustic filters designed to attenuate sound by 9, 15 or 25 dB. Results showed that the use of earplugs affected the sound level and the spectrum of played sounds. This effect was the greatest for brass players. The difference between SPLs in high-frequency 1/3-octave bands and A-weighted SPLs with and without earplugs exceeded 5 and 15 dB, respectively. Similar changes for woodwind, percussion and string instruments were less noticeable than for brass instruments; they were more than 5 dB for 1/3-octave spectra and no more than 2 dB for A-weighted SPL.
The impulse noise is agent harmful to health not only in the case of shots from firearms and the explosions of explosive materials. This kind of noise is also present in many workplaces in the industry. The paper presents the results of noise parameters measurements in workplaces where four different die forging hammers were used. The measured values of the C-weighted peak sound pressure level, the A-weighted maximum sound pressure level and A-weighted noise exposure level normalized to an 8 h working day (daily noise exposure level) exceeded the exposure limit values. For example, the highest measured value of the C-weighted peak sound pressure level was 148.9 dB. In this study possibility of the protection of hearing with the use of earplugs or earmuffs was assessed. The measurement method for the measurements of noise parameters under hearing protection devices using an acoustical test fixture instead of testing with the participation of subjects was used. The results of these measurements allows for assessment which of two tested earplugs and two tested earmuffs sufficiently protect hearing of workers in workplaces where forging hammers are used.
The aim of this study was to evaluate the absorption in a user’s head of an electromagnetic field (EMF) emitted by the Wi-Fi and/or Bluetooth module of a wearable small Internet of Things (IoT) electronic device (emitting EMF of up to 100 mW), in order to test the hypothesis that EMF has an insignificant influence on humans, and to compare the levels of such EMF absorption in various scenarios when using this device. The modelled EMF source was a meandered inverted-F antenna (MIFA)-type antenna of the ESP32-WROOM-32 radio module used in wearable devices developed within the reported study. To quantify the EMF absorption, the specific energy absorption rate (SAR) values were calculated in a multi-layer ellipsoidal model of the human head (involving skin, fat, skull bones and brain layers). The obtained results show up to 10 times higher values of SAR from the MIFA located in the headband, in comparison to its location on the helmet. Only wearable IoT devices (similar in construction and way of use to the investigated device) emitting at below 3 mW equivalent isotropically radiated power (EIRP) from Wi-Fi/Bluetooth communications modules may be considered environmentally insignificant EMF sources.
In this study, music teachers' exposure to sound was tested by measuring the A-weighted equivalent sound pressure level (SPL), the A-weighted maximum SPL and the C-weighted peak SPL. Measurements were taken prior to and after acoustic treatment in four rooms during classes of trumpet, saxophone, French horn, trombone and percussion instruments. Results showed that acoustic treatment affects the exposure of music teachers to sound. Daily noise exposure levels (L EX, 8 h ) for all teachers exceeded a limit of 85 dB while teaching music lessons prior to room treatment. It was found that the L EX, 8 h values ranged from 85.8 to 91.6 dB. The highest A-weighted maximum SPL and C-weighted peak SPL that music teachers were exposed to were observed with percussion instruments (LA max = 110.4 dB and L Cpeak = 138.0 dB). After the treatments, daily noise exposure level decreased by an average of 5.8, 3.2, 3.0, 4.2 and 4.5 dB, respectively, for the classes of trumpet, saxophone, French horn, trombone and drums, and did not exceed 85 dB in any case.
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