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Objective and Subjective Assessment of the Sound Attenuation Efficiency Obtained by Custom Moulded Earplugs with Various Acoustic Filters – a Preliminary Study0

Gołębiewski Roman, Wicher Andrzej, Kaczmarek-Klinowska Milena, Mirugalska-Handke Karina

Archives of Acoustics

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2022

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Vol. 47, No. 2

201--212

EN

Background: Hearing loss caused by excessive exposure to noise is one of the most common health risks for employees. One solution for noise reduction is the use of hearing protectors, which is a very effective method for protecting hearing from the workplace noise. In order to obtain better attenuation efficiency, custom moulded earplugs can be equipped with a suitable acoustic filter. The effectiveness of the hearing protectors’ attenuation is based on real measurement of hearing thresholds for normal hearing people with and without hearing protectors. However, this is a time consuming process, and the obtained values are characterised by quite large inter-individual variability. The optimal solution is to measure the attenuation characteristics based on the objective method (without the presence of the subject), the results of which will be in accordance with the results of subjective tests. Therefore, the main purpose of the research in this work was to measure the attenuation characteristics of the self-designed custom moulded earplugs with and without acoustic filters through the use of subjective and objective methods, and to compare the results in terms of the research methods. Methods: Measurements of the acoustic attenuation obtained by custom moulded earplugs with designed F1, F2, and F3 acoustic filters (internal diameters dF1 = 1:25 mm, dF2 = 0:85 mm, and dF3 = 0:45 mm), as well as full insert earplugs (without any acoustic filters) were carried out using two methods: objective and subjective. The objective measurements were carried out in an anechoic chamber. The artificial head (High-frequency Head and Torso Simulator Brüel & Kjær Type 5128) was located at a distance of 3 m, directly opposite the loudspeaker. The test signal in the measurements was pink noise – in the frequency range up to 12.5 kHz and the level 85, 90, and 95 dB. The hearing protectors with and without acoustic filters were mounted in the Head and Torso Simulator which was connected with Pulse System Brüel & Kjær. Five normal hearing subjects participated in the subjective measurements. A pink noise signal was used for one-third octave bands: 125, 250, 500, 1000, 2000, 4000, and 8000 Hz. The attenuation value was defined as the difference (in dB) between the hearing threshold of the test signal with a hearing protector and the hearing threshold determined without a hearing protector. Results: The results of the objective method proved that in addition to the significant impact of frequency on the attenuation values, the type of filter used in custom moulded earplugs also had a significant effect. In addition, the results of the objective method showed that in the whole frequency range the highest attenuation values are shown by the full earplugs, achieving slightly above 45 dB for frequency of 8 kHz. The attenuation values obtained from subjective measurements also confirmed that both the frequency and type of filter significantly affect the attenuation values of the tested hearing protectors. Conclusions: The results of this study did not confirm the hypothesis that the measurement method had no significant effect on the attenuation characteristics of self-designed custom moulded earplugs with different types of acoustic filters. The largest differences in attenuation values between the type of measurement methods occur for the low frequency band (250 Hz) and for higher frequencies (4000 Hz mainly). The change of the internal diameter of the F1 filter from 1.25 mm to 0.85 mm (F2 filter) did not significantly affect the attenuation characteristics.

2

Designing of quasi one-dimensional acoustic filters using genetic algorithm

Garus Sebastian, Sochacki Wojciech

Vibrations in Physical Systems

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2019

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Vol. 30, nr 2

art. no. 2019210

EN

In phononic quasi one-dimensional structures, there is a phenomenon of a phononic bandgap (PhBG), which means that waves of a given frequency do not propagate in the structure. The location and size of PhBG depend on the thickness of the layers, the type of materials used and their distribution in space. The theoretical study examined the transmission properties of quasi one-dimensional structures designed using a genetic algorithm (GA). The objective function minimized the transmission integral and integral of the absolute value of the transmission functions derivative (to eliminate high transmission peaks with a small half width) in a given frequency range. The paper shows the minimization of transmission in various frequency bands for a 40-layer structure. The distribution of multilayer structure transmission was obtained through the Transfer Matrix Method (TMM) algorithm. Structures surrounded by water were analyzed and built of layers of glass and epoxy resin.

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Substitutional transmittance function of helicoidal resonator

Łapka W.

Vibrations in Physical Systems

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2010

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Vol. 24

265--270

EN

An analytical and computational characteristics of transmission losses of the helicoidal resonator are compared in this paper. The substitutional transmittance function of helicoidal resonator was proposed based on amplitude characteristic of electrical band-stopfilter. At first approach the analytical model can be considered as valid for practical silencing systems design calculations in ducted systems.

PL

W niniejszym artykule dokonano porównania charakterystyk tłumienia przenoszenia rezonatora helikoidalnego uzyskanych na drodze obliczeń analitycznych i numerycznych. Zaproponowana została zastępcza funkcja transmitancji rezonatora helikoidalnego na podstawie charakterystyki amplitudowej elektrycznego filtru pasmowo-zaporowego. Tak wykonany analityczny model transmitancji w pierwszym przybliżeniu może być uznany za poprawny dla celów obliczeniowych praktycznego projektowania systemów wyciszeniowych w instalacjach kanałowych.

4

Zastosowanie filtrów akustycznych czynnych w układach hydraulicznych

Kollek W.

Napędy i Sterowanie

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1999

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R. 1, nr 1

4--7

PL

W maszynach roboczych jednym z głównych źródeł dźwiękotwórczych obok silnika spalinowego jest napęd hydrauliczny. W układzie hydraulicznym przyczyny hałaśliwości można podzielić na mechaniczne i hydrauliczne. W grupie przyczyn hydraulicznych powstawania hałasu, a to często jako hałasu wtórnego jest pulsacja ciśnienia powodowana okresowo zmiennym natężeniem przepływu czynnika.

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Podstawy projektowania filtrów akustycznych hydraulicznych układów napędowych

Kollek W., Kudźma Z., Rutański J.

Napędy i Sterowanie

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1999

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R. 1, nr 3/4

59--62

PL

W artykule przedstawiono przyczyny powstawania pulsacji ciśnienia w hydrostatycznych układach napędowych, która to pulsacja jest jedną z podstawowych przyczyn hałaśliwości. Podano modele tłumików pulsacji typu biernego i czynnego wykorzystanych jako filtry akustyczne układów hydrostatycznych. Przedstawiono program komputerowy obliczania parametrów tłumików. Przeprowadzono badania doświadczalne skuteczności poszczególnych tłumików w obniżaniu hałasu wytypowanych układów.