scholarly journals Objective and subjective assessment of sound attenuation efficiency by individual hearing protectors with various acoustic filters – a preliminary study

2020 ◽  
Author(s):  
Roman Gołębiewski ◽  
Andrzej Wicher ◽  
Artur Duraj ◽  
Milena Kaczmarek-Klinowska ◽  
Karina Mrugalska-Handke
Keyword(s):  
Measurement Method ◽  
Hearing Threshold ◽  
Test Signal ◽  
Objective Method ◽  
Frequency Range ◽  
Hearing Protectors ◽  
Acoustic Filters ◽  
Subjective Measurements ◽  
Attenuation Characteristics ◽  
Attenuation Values

Abstract Background: Hearing loss caused by excessive noise levels is one of the most common health risks for employees. One solution for noise reduction is the use of hearing protectors, which is one of the most effective methods for protecting hearing from noise at the workplace. In order to obtain different attenuation efficiency, individual hearing protectors 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 characterized 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 individual hearing protectors with 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 individual hearing protectors with designed F1, F2 and F3 acoustic filters, 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 Brül & 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 Brül & 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 also had a significant effect. The objective measurement method showed that different levels of stimulation of the test signal did not significantly affect the attenuation efficiency for both the full earplugs and the earplugs with the F1, F2 and F3 filters. 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. Unlike the results of the objective method, the subjective method did not indicate significant differences in attenuation when using F1 and F2 filters. Conclusions: The comparison of the average attenuation values obtained from the objective and subjective methods showed that in general the measurement method does not significantly affect the average attenuation values. In turn, the analysis of variance broken down into subgroups according to the types of filters used in the earplugs showed that the influence of the measurement method on the attenuation values is statistically significant when the F1 filter and full earplug are used. The results of this study partly confirmed the hypothesis that there is no significant impact of the measurement method on the attenuation characteristics of the earplugs with different types of acoustic filters.

scholarly journals Measurement of Earmuffs Attenuation at High Audible Frequencies

2017 ◽  
Vol 42 (2) ◽  
pp. 249-254
Author(s):  
Emil Kozłowski ◽  
Rafał Młyński
Keyword(s):  
Frequency Band ◽  
Measurement Method ◽  
Sound Attenuation ◽  
The Other ◽  
Hearing Protection ◽  
Noise Attenuation ◽  
Frequency Range ◽  
Test Fixture ◽  
Hearing Protectors ◽  
Audible Frequency

Abstract Standardised measurements of sound attenuation of hearing protectors are performed in the frequency range from 125 Hz to 8 kHz. However, noise present at many workplaces contains significant components at higher audible frequency. Therefore, the knowledge about noise attenuation with earmuffs in the audible frequency range above 8 kHz is also necessary for proper hearing protection. The aim of this study was to obtain values of the noise attenuation with 27 commonly-used earmuffs models in the 1/3 octave bands of 10, 12.5 and 16 kHz. The measurements were conducted with a real ear at threshold (REAT) method with participation of subjects. The study showed that attenuation of earmuffs ranged from 24.7 to 42.8 dB, depending on model of earmuffs and frequency band. Furthermore, the measurements were performed with the use of acoustic test fixture which is designed especially for testing hearing protectors. Results obtained with the use of acoustic test fixture indicated that this measurement method can lead to values close to attenuation measured with participation of subjects. On the other hand, values obtained with the use of acoustic test fixture may differ average up to 14 dB from REAT method.

A waveform inversion technique for measuring elastic wave attenuation in cylindrical bars

Geophysics ◽  
1992 ◽  
Vol 57 (6) ◽  
pp. 854-859 ◽  
Author(s):  
Xiao Ming Tang
Keyword(s):  
Elastic Wave ◽  
Wave Attenuation ◽  
Waveform Inversion ◽  
Finite Size ◽  
Low Frequency ◽  
Frequency Range ◽  
Multiple Reflections ◽  
Low Frequencies ◽  
The Time Domain ◽  
Attenuation Values

A new technique for measuring elastic wave attenuation in the frequency range of 10–150 kHz consists of measuring low‐frequency waveforms using two cylindrical bars of the same material but of different lengths. The attenuation is obtained through two steps. In the first, the waveform measured within the shorter bar is propagated to the length of the longer bar, and the distortion of the waveform due to the dispersion effect of the cylindrical waveguide is compensated. The second step is the inversion for the attenuation or Q of the bar material by minimizing the difference between the waveform propagated from the shorter bar and the waveform measured within the longer bar. The waveform inversion is performed in the time domain, and the waveforms can be appropriately truncated to avoid multiple reflections due to the finite size of the (shorter) sample, allowing attenuation to be measured at long wavelengths or low frequencies. The frequency range in which this technique operates fills the gap between the resonant bar measurement (∼10 kHz) and ultrasonic measurement (∼100–1000 kHz). By using the technique, attenuation values in a PVC (a highly attenuative) material and in Sierra White granite were measured in the frequency range of 40–140 kHz. The obtained attenuation values for the two materials are found to be reliable and consistent.

scholarly journals A Digital Heterodyne 2-150 kHz Measurement Method

2021 ◽  
Author(s):  
Paul Wright ◽  
Deborah Ritzmann
Keyword(s):  
Measurement Method ◽  
Power Grid ◽  
New Method ◽  
Digital Method ◽  
Frequency Range ◽  
Multi Resolution Analysis ◽  
Resolution Analysis ◽  
Conducted Emissions

This paper describes a new method for measurements of signals in the 2–150 kHz frequency range, as required to support the regulation of conducted emissions on the power grid. The digital method is based on heterodyning, decimation and multi resolution analysis.<div><br></div>

Attenuation of Earmuffs against Low Frequency Noise

1987 ◽  
Vol 6 (4) ◽  
pp. 167-174 ◽  
Author(s):  
Jukka Starck ◽  
Jussi Pekkarinen ◽  
Seppo Aatola
Keyword(s):  
Low Frequency ◽  
Peak Level ◽  
Standard Test ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Low Frequencies ◽  
Hearing Protectors ◽  
Noise Measurements ◽  
Attenuation Values ◽  
Very High

The standard test for hearing protectors cannot be applied to determine the attenuation values for low frequency noise or for noise consisting of high intensity impulses. Moreover, the aging of earmuffs and the use of spectacles may cause leakage which decreases attenuation mainly at low frequencies. To study the real attenuation of earmuffs, noise measurements were taken outside and inside the earmuffs of workers at industrial work places, and of military conscripts when shooting with different firearms. The effect of spectacles on the attenuation was measured under laboratory conditions. In industrial workplaces the average attenuation was 4 dB in the 63 and 125 Hz octave bands. For shooting noise the attenuation was found to be good for small calibre weapons but poor for large calibre weapons, which generate very high peak level impulses at low frequencies. Spectacles decreased earmuff attenuation by 9–11 dB.

scholarly journals High Frequency Modal Testing of the Multiblade Packets Using a Noncontact Measurement and Excitation System

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
C. H. Liu ◽  
C. Zang ◽  
F. Li ◽  
E. P. Petrov
Keyword(s):  
High Frequency ◽  
Measurement Method ◽  
Natural Frequencies ◽  
Spectral Lines ◽  
Modal Testing ◽  
Frequency Resolution ◽  
Mode Shapes ◽  
Finite Model ◽  
Frequency Range ◽  
Noncontact Measurement

High cycle failure of blades and vanes caused by the vibration is one of the major causes reducing the lifetime of turbomachines. For multiblade packets, the failure may occur at vibrations with high frequencies that can reach up to tens of kHz. The experimental modal testing of blades is crucial for the validation of numerical models and for the optimization of turbomachine design. In this paper, the test rig and procedure for measurements of dynamic characteristics of lightweight multiblade packets in wide and high frequency ranges are developed. The measurements are based on a noncontact excitation and noncontact measurement method, which allows the determination of the modal characteristics of the packets with high accuracy in wide frequency ranges. The responses of the multiblade packets are measured using a Scanning Laser Doppler Vibrometry (SLDV), while vibrations are excited by the acoustic excitation technique. Modal tests of the blade packet comprising 18 vane blades connected by shrouds are performed. The measurements are performed within the high frequency range of 0–30 kHz, and the natural frequencies and mode shapes are obtained for first 97 modes. To capture the complex high frequency blade mode shapes, each blade in the packet is scanned over 25 reference points uniformly distributed over the blade concave surface. In order to obtain the high frequency resolution, the frequency range used for the measurements is split into several frequency intervals accordingly to the number of spectral lines available in the used data acquisition system, and for each such interval, the test is performed separately. The finite model of the packet is created, and the numerical modal analysis is performed to compare the calculated natural frequencies and mode shapes with the experimental measurements. The comparison shows the satisfactory with those from finite element analysis. It illustrates the measurement method described in this work is effective and reliable.

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