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This paper proposes a quick and straightforward technique for estimating the insertion loss (IL) of earplugs measured on an acoustical test fixture (ATF) using a commercial impedance tube. In this method, the earplug's acoustic properties (i.e., its transmission loss and the reflection coefficient of its medial surface) are determined from its transfer matrix measured using the three-microphones impedance tube method modified here for the current application. The IL is then estimated using a one-dimensional analytical model of open and occluded earcanals based on the wavefield decomposition theory. The method is evaluated numerically and experimentally from 50 Hz to 6.5 kHz. The numerical study allows for verifying the accuracy of the proposed approach in comparison to a simplified model of an ATF earcanal excited by normal incidence plane wave and diffuse field excitation. The experimental evaluation, which involves six earplugs (including five commercially available ones) representing various earplug families, demonstrates the accuracy of the estimation method, yielding results with a maximum difference of 3 dB compared to ATF measurements, on average, among the tested earplugs.

Hearing protection devices like earplugs are largely used to protect workers against noise. The discomfort related to the use of earplugs is known to reduce their effectiveness. Since this discomfort remains difficult to evaluate, it seems necessary to improve current tools like acoustical test fixtures to help earplug manufacturers to design more comfortable devices. In this perspective, a numerical model of an artificial ear based on the finite element method is proposed. This model aims to investigate the important features needed to correctly evaluate objective indicators related to the acoustical comfort of earplugs using an artificial ear. In the present preliminary study, the ability of this numerical model to simulate the insertion loss of earplugs is tested by comparing sound pressure level transfer functions computed in both the open and occluded numerical earcanal with experimental data measured on the corresponding physical artificial ear. Results reveal that the proposed numerical model simulates well the sound pressure level in an open earcanal but fails in the occluded case above 400 Hz. Possible sources of discrepancies are investigated. In particular, the effect of various model parameters on the acoustic response in the earcanal is evaluated.

Passive and active in-ear devices (IED) occluding the ear canal are commonly used to (i) protect people from high noise levels (earplugs), (ii) assist people suffering from hearing impairment (hearing aids) or (iii) help people in listening from their sound systems (earbuds). However, the usability and/or efficiency of IEDs can be greatly affected by several discomfort components (physiological, acoustical and functional). The mechanical pressure exerted by the IED onto the ear canal walls is greatly suspected to affect the aforementioned comfort components. This physical characteristic is closely related to the displacement field induced by the IED insertion, which has to be known for a better understanding of perceived discomfort. Thus, this paper proposes to validate a method based on medical images to estimate the displacement field of the ear canal walls due to the insertion of an IED. The approach is validated on a human-like artificial ear with canal geometry deformed using two custom molded IEDs with controlled shapes. These geometries are obtained using computed tomography imaging and the displacement field is computed using a registration method. The errors due to the ear canal segmentation and to the registration steps are small enough to compute a relevant estimation of the expected displacement field. Results show that the amplitude of the displacement and its location into the ear canal can be evaluated with an accuracy of +/- 0.2 mm and +/- 0.4 mm respectively. Preliminary results on images with a degraded resolution indicate that the proposed approach used to assess the displacement field of the ear canal walls using computed tomography images could be applied on magnetic resonance images, which is a preferred method to image human subject ear canals for future investigations.

This paper compares different approaches to model the vibroacoustic behavior of earmuffs at low frequency and investigates their accuracy by comparison with objective insertion loss measurements recently carried out by Boyer et al. [(2014). Appl. Acoust. 83, 76–85]. Two models based on the finite element (FE) method where the cushion is either modeled as a spring foundation (SF) or as an equivalent solid (ES), and the well-known lumped parameters model (LPM) are investigated. Modeling results show that: (i) all modeling strategies are in good agreement with measurements, providing that the characterization of the cushion equivalent mechanical properties are performed with great care and as close as possible to in situ loading, boundary, and environmental conditions and that the frequency dependence of the mechanical properties is taken into account, (ii) the LPM is the most simple modeling strategy, but the air volume enclosed by the earmuff must be correctly estimated, which is not as straightforward as it may seem, (iii) similar results are obtained with the SF and the ES FE-models of the cushion, but the SF should be preferred to predict the earmuff acoustic response at low frequency since it requires less parameters and a less complex characterization procedure.

This paper deals with source localization techniques in time domain for broadband acoustic sources. The goal is to detect accurately and quickly the position and amplitude of noise sources in workplaces in order to prevent employees from hearing loss or safety risk. First, the generalized cross correlation associated with a spherical microphone array is used to get a raw noise source map. Then a linear inverse problem is defined. Commonly, linear inverse problem is solved with an l2-regularization. In this study, two sparsity constraints are used to solve the inverse problem, the orthogonal matching pursuit and the truncated Newton interior-point method. Synthetic data are used to highlight the abilities of such techniques. High resolution can be achieved for various acoustic sources configurations. Moreover, the amplitudes of the acoustic sources are correctly estimated. Finally, a comparison of computation time shows these techniques are suitable in real scenario.