Low Sound Levels Research Articles

High sound pressure level sound absorption in acoustic resonant metamaterials: adapting a mass-spring model for nonlinear effects

In aerospace, conventional materials as micro-perforated panels backed by cavities are used to absorb sound at high sound pressure levels. These solutions are not optimal at low frequencies compared to resonant acoustic metamaterials, which present an acoustic absorption peak with a wavelength-to-thickness ratio greater than conventional materials, i.e., a ratio>>5. Acoustic resonant metamaterials are mainly studied at low sound pressure levels (<100dB). However, they are sensitive to increasing the amplitude of acoustic excitation. The studied metamaterial is composed of a compact array of thin single-perforation panels spaced by thin cylindrical air cavities. In a previous study, a mass-spring model was developed for low sound pressure levels. The perforations are modeled by equivalent masses, whereas cavities by equivalent springs. In the perforations, high values of the acoustic velocity lead to an increase in the acoustic resistance of the material. This effect is considered by the Forchheimer parameter in the mass-spring model. To determine this parameter and to study how it is impacted by the metamaterial geometry, the computational fluid dynamic method is used. The mass-spring model is adapted with a nonlinear term. The adapted model agrees well with simulations by finite element method at sound pressure levels up to 140dB.

Fitness club adjacent to a quiet corporate office - Prototypes

There is a demand for fitness clubs in hotels, residential, and corporate buildings - sometimes adjacent to sensitive spaces. Activities involving weight drops and spinning bikes, among others, cause dynamic forces in the structure that propagate through the building's structure and radiate airborne sound. There is an effort by acousticians worldwide to establish a standardized method for measuring and rating the noise radiated by gyms into adjacent areas. This article describes the construction of a gym over a corporate office, occupying an area of 2100 m2 each. The gym's floor structure is a concrete and steel deck, and the office below has low sound levels. The goal of making gym activity inaudible in the office is undoable in practice. We tested several prototypes to arrive at a double insulation system with a floating slab with natural rubber mounts. A system of dynamic dampers was installed to reduce the movement of the floating slab with the dynamic excitation above it. The results of the prototype were auspicious. This paper presents the measurements of the natural frequency of the structure and the floating slab, the transmissibility of the system, and the differences in vibratory velocity from the floating floor to the structure.

A study on the perception of refrigerator noise in everyday life

Advancements in technology and noise control measures significantly reduced the noise emissions of refrigerators. Despite the achievement of low sound power levels in modern refrigerators, substantial efforts are still dedicated to further minimizing their noise. This initiated an examination into the need for ongoing activities to reduce noise, given the already minimal noise levels. This study aimed to evaluate the impact of refrigerator noise in everyday life, examining the circumstances and extent of individuals' exposure to noise while exploring their general perception. In an online survey, attention to refrigerator noise was explored to understand how often respondents can hear refrigerator noise in their daily lives. In addition, questions about the operating conditions of the refrigerator, in particular at the times when participants could hear refrigerator noise, were also assessed in the survey. Finally, the results of measurements that generalize the extent to which refrigerator noise can exceed background noise in normal rooms were also evaluated in this study.

Pedestrians' street-crossing decisions compared between conventional and electric vehicles

To safely cross a road before an approaching vehicle, pedestrians need to accurately judge the vehicle's motion. Recent studies from our lab demonstrated that the noise emitted by a vehicle conveys important information about its motion, particularly in the case of accelerating approaches. Here, we compared street-crossing decisions between conventional (ICEVs) and electric vehicles (EVs) with or without AVAS sounds. The experiment presented high-fidelity audiovisual VR simulations of approaching vehicles, based on recordings of real ICEVs and EVs. The presented velocity profiles included a large variation in acceleration rates, a = 0 to 4.4 m/s^2, and two velocities at the moment of the crossing decision (28 km/h versus 50 km/h). To investigate whether the lower sound level of EVs compared to ICEVs contributes to differences in crossing decisions, we additionally presented a condition in which the sound levels were matched between vehicle types. All experimental conditions were presented in two modality conditions (auditory-only and audiovisual). We compare the crossing decisions between vehicle types, velocity profiles and level profiles in terms of collision probabilities estimated from the measured psychometric functions. Preliminary results confirm differences between crossing decisions made in interaction with EVs compared to ICEVs, reduced in the level-matched conditions.

Long-term outcome of patients with Ménière’s disease following cochlear implantation: a comprehensive outcome study with validated assessment tools

PurposePatients suffering from Ménière’s disease (MD) experience vertigo, and impairments in hearing and quality of life (QoL). This study aims to investigate the impact of cochlear implantation (CI) on various aspects affecting patients with MD.MethodsA single tertiary centre’s CI database for CI recipients with MD between 2014 and 2022 was screened retrospectively. Hearing, vertigo, tinnitus symptoms, and hearing-related QoL were assessed. Pre- and postoperative hearing tests in conjunction with subjective outcome measures by visual analogue scale (VAS) and validated tools such as the Dizziness Handicap Inventory (DHI), Tinnitus Handicap Inventory (THI) and Nijmegen Cochlear Implant Questionnaire (NCIQ), as well as the assessment of the pre- and postoperative Functional Level Scale (FLS) were examined.ResultsEleven ears were included (median age: 59 years at implantation). Following implantation, there was a significant enhancement in Word Recognition Scores at sound levels of 65 dB and 80 dB compared to before treatment (preop vs. 12 months postop: p = 0.012). However, no significant enhancement was observed for 50 dB. MD-related impairments improved significantly postoperatively, as measured by the VAS (vertigo: p = 0.017; tinnitus: p = 0.042), DHI (p = 0.043), THI (p = 0.043) and NCIQ (p < 0.001). The FLS improved significantly (p = 0.020).ConclusionCI has positive effects on all areas examined in our cohort. However, discrimination of speech at low sound pressure levels remained problematic postoperatively. In patients suffering from MD, the prioritized treatment goals include not only improved hearing but also the rehabilitation of vertigo and tinnitus, as well as the enhancement of QoL. Validated instruments are useful screening tools.

Device and Fitting Protocol for a Transitional Intervention for Debilitating Hyperacusis.

This report describes a hearing device and corresponding fitting protocol designed for use in a transitional intervention for debilitating loudness-based hyperacusis. The intervention goal is to transition patients with hyperacusis from their typical counterproductive sound avoidance behaviors (i.e., sound attenuation and limited exposure to healthy low-level sounds) into beneficial sound therapy treatment that can expand their dynamic range to the point where they can tolerate everyday sounds and experience an improved quality of life. This requires a combination of counseling and sound therapy, the latter of which is provided via the hearing device technology, signal processing, and precision fitting approach described in this report. The device combines a miniature behind-the-ear sound processor and a custom earpiece designed to maximize the attenuation of external sounds. Output-limiting loudness suppression is used to restrict exposure to offending high-level sounds while unity gain amplification maximizes exposure to healthy and tolerable lower level sounds. The fitting process includes measurement of the real-ear unaided response, the real-ear measurement (REM) system noise floor, the real-ear occluded response, real-ear insertion gain, and the output limit. With these measurements, the device can achieve the prescribed unity gain needed to provide transparent access to comfortable sound levels. It also supports individualized configuration of the therapeutic noise from an on-board sound generator and adaptive output limiting based on treatment-induced increases in dynamic range. The utility of this device and fitting protocol, in combination with structured counseling, is highlighted in the outcomes of a successful 6-month trial of the transitional intervention described in a companion report in this issue.

"Every breath you take": evaluating sound levels and acoustic characteristics of various neonatal respiratory support and ventilation modalities.

Early sensory experiences have a significant impact on the later life of preterm infants. The NICU soundscape is profoundly influenced by various modalities of respiratory support or ventilation, which are often mandatory early in the care. The incubator, believed to shield from external noise, is less effective against noise originating inside. The objective of this study was to evaluate the sound levels and characteristics of frequently used respiratory support and ventilation modalities, taking into consideration the developing auditory system of premature infants. To evaluate sound dynamics inside and outside an incubator during respiratory support/ventilation, experimental recordings were conducted at the Center for Pediatric Simulation Training of the Medical University Vienna. The ventilator used was a FABIAN HFOI®. Jet CPAP (Continuous positive airway pressure), whether administered via mask or prongs, generates significantly higher sound levels compared to High-flow nasal cannula (HFNC) and to High-frequency oscillatory ventilation (HFOV) delivered through an endotracheal tube. Upon evaluating the sound spectrum of jet CPAP support, a spectral peak is observed within the frequency range of 4 to 8 kHz. Notably, this frequency band aligns with the range where the hearing threshold of preterm infants is at its most sensitive. Non-invasive HFNC and invasive HFOV generate lower sound levels compared to those produced by jet CPAP systems delivered via masks or prongs. Moreover, HFNC and HFOV show a reduced acoustic presence within the frequency range where the preterm infant's hearing is highly sensitive. Therefore, it is reasonable to speculate that the potential for auditory impairment might be more pronounced in preterm infants who require prolonged use of jet CPAP therapy during their time in the incubator.

Towards digitally programmed nonlinear electroacoustic resonators for low amplitude sound pressure levels: Modeling and experiments

Passive acoustic foams have limitations in efficiently reducing low-frequency noise below 800 Hz due to the associated wavelengths for reasonable material thickness. To address this challenge, passive or semi-active resonators are commonly employed solutions. Linear resonators are very efficient within a narrow frequency bandwidth. However, nonlinear oscillators can broaden this bandwidth, but activation of their nonlinear responses typically requires high excitation amplitudes, beyond human hearing tolerance amplitudes. Furthermore, the specific type of nonlinearity in such devices is often predetermined by the inherent properties of the resonator. In this study, we employ a novel digital control algorithm, allowing to activate the nonlinear response of the electroacoustic resonator at low excitation amplitudes. This algorithm, which relies on real-time integration, facilitates the creation of nonlinear resonators featuring polynomial or diverse non-polynomial nonlinearities within the range of low amplitudes. The nonlinear control is carried out on a loudspeaker equipped with a microphone. Our research highlights the potential to create nonlinear resonators with different, versatile and programmable behaviors. Unprecedented non-polynomial nonlinear behaviors are experimentally exhibited, we consider cubic, piece-wise linear, and logarithmic nonlinearities. These behaviors are implemented and compared to a semi-analytic model to control an acoustic mode of a tube under conditions of low excitation amplitudes and frequencies.

Characterizing inner-hair-cell specific dysfunction from spike-train-derived transduction functions using a phenomenological auditory-nerve model

The impact of outer-hair-cell damage on sensorineural hearing loss (SNHL) has been extensively studied compared with inner-hair-cell (IHC) damage (e.g., stereocilial). Pre-clinical SNHL animal models provide unique data to directly address IHC-specific deficits (e.g., carboplatin-exposed chinchillas). Spike-train data (period histograms) to low sound level tones can be used to derive IHC-transduction functions by mapping instantaneous spike rates to corresponding sinusoidal pressure values (Horst et al., 2018). However, this approach depends on sensation level and spontaneous rate, which are both affected by IHC dysfunction. To better understand the effect of these dependencies, we used a phenomenological auditory-nerve (AN) model (Bruce et al., 2018) that provides parametric control over IHC and OHC dysfunction allowing exploration of optimal experimental design. Here, we explore the utility of spike-train-derived IHC-transduction functions in capturing parametric changes in IHC dysfunction as currently implemented in the AN model. We used unsupervised methods and information-theoretic approaches to quantify the dependency of transduction functions on IHC dysfunction. We also compared model findings with AN-fiber data recorded from carboplatin-exposed chinchillas. Preliminary findings suggest that transduction functions obtained from the AN model can capture IHC-specific dysfunction within specific regimes of controllable model parameters, thus showing promise for characterizing IHC dysfunction.

A silent echo-planar spectroscopic imaging readout with high spectral bandwidth MRSI using an ultrasonic gradient axis.

We present a novel silent echo-planar spectroscopic imaging (EPSI) readout, which uses an ultrasonic gradient insert to accelerate MRSI while producing a high spectral bandwidth (20 kHz) and a low sound level. The ultrasonic gradient insert consisted of a single-axis (z-direction) plug-and-play gradient coil, powered by an audio amplifier, and produced 40 mT/m at 20 kHz. The silent EPSI readout was implemented in a phase-encoded MRSI acquisition. Here, the additional spatial encoding provided by this silent EPSI readout was used to reduce the number of phase-encoding steps. Spectroscopic acquisitions using phase-encoded MRSI, a conventional EPSI-readout, and the silent EPSI readout were performed on a phantom containing metabolites with resonance frequencies in the ppm range of brain metabolites (0-4 ppm). These acquisitions were used to determine sound levels, showcase the high spectral bandwidth of the silent EPSI readout, and determine the SNR efficiency and the scan efficiency. The silent EPSI readout featured a 19-dB lower sound level than a conventional EPSI readout while featuring a high spectral bandwidth of 20 kHz without spectral ghosting artifacts. Compared with phase-encoded MRSI, the silent EPSI readout provided a 4.5-fold reduction in scan time. In addition, the scan efficiency of the silent EPSI readout was higher (82.5% vs. 51.5%) than the conventional EPSI readout. We have for the first time demonstrated a silent spectroscopic imaging readout with a high spectral bandwidth and low sound level. This sound reduction provided by the silent readout is expected to have applications in sound-sensitive patient groups, whereas the high spectral bandwidth could benefit ultrahigh-field MR systems.

Influence of Acoustic Streams on the Efficiency of Ultrasonic Particle Agglomeration

The article is devoted to the study of ultrasonic agglomeration of PM 2.5 in homogeneous and inhomogeneous ultrasonic fields. The possibility of increasing the efficiency of ultrasonic agglomeration by initiating acoustic streams in a resonant inhomogeneous ultrasonic field is shown. A inhomogeneous ultrasonic field with zones of high and low sound pressure levels formed using a bending-oscillating disk transmitter made it possible to initiate acoustic vortex-type streaming that promotes the movement of particles into the nodal areas of a standing wave and between them. Due to the formation of a inhomogeneous ultrasonic field, the efficiency of particle collection is increased: for PM 2.5, the efficiency reaches 95%; PM 1.5—92%; PM 0.5—85%. The results were obtained under the following conditions: concentration 2 × 10−2 g/m3, sound pressure level 165 dB, flow rate 6.2 m3/h. For comparison, when a homogeneous ultrasonic field is formed in the agglomeration chamber (under similar conditions), the efficiency of particle capture by inertial gas cleaning equipment does not exceed the following: for PM 2.5—89%; PM 1.5—85%; and PM 0.5—76%. The obtained research results made it possible to propose a design for an agglomeration chamber that can greatly increase the productivity of ultrasonic flow processing.

Visualization and analysis of multi-channel dynamic range compression in hearing aids

One main functionality of hearing aids is restoring audibility. This means that low sound pressure levels are amplified above the elevated hearing threshold, and higher sound pressure levels do not exceed the individual uncomfortable loudness level (UCL). To this end, hearing aids provide frequency-dependent dynamic range compression which is denoted as hearing aid channels (HACs) in the recently published standard IEC 60118-16. As an increasing number of HACs, among other features, is one main feature to differentiate between price or technology levels, IEC 60118-16 includes a measurement procedure to verify the number of HACs. In this work, we verify this test procedure with a research hearing aid (RHA), and evaluate six commercial hearing aids of three different manufacturers and two technology levels. These results demonstrate the possibilities and limitations of the new test procedure. Furthermore, we introduced an extension of this test procedure with a channel-specific compression setting to overcome limitations and to get a deeper insight into the functionality of HACs in hearing aids. These results show that many HACs of commercial devices are coupled to neighboring frequencies, and that different strategies are used across manufacturers to adapt the number of HACs for different technology levels.

The Right-Ear Advantage in Static and Dynamic Cocktail-Party Situations.

When presenting two competing speech stimuli, one to each ear, a right-ear advantage (REA) can often be observed, reflected in better speech recognition compared to the left ear. Considering the left-hemispheric dominance for language, the REA has been explained by superior contralateral pathways (structural models) and language-induced shifts of attention to the right (attentional models). There is some evidence that the REA becomes more pronounced, as cognitive load increases. Hence, it is interesting to investigate the REA in static (constant target talker) and dynamic (target changing pseudo-randomly) cocktail-party situations, as the latter is associated with a higher cognitive load than the former. Furthermore, previous research suggests an increasing REA, when listening becomes more perceptually challenging. The present study examined the REA by using virtual acoustics to simulate static and dynamic cocktail-party situations, with three spatially separated talkers uttering concurrent matrix sentences. Sentences were presented at low sound pressure levels or processed with a noise vocoder to increase perceptual load. Sixteen young normal-hearing adults participated in the study. The REA was assessed by means of word recognition scores and a detailed error analysis. Word recognition revealed a greater REA for the dynamic than for the static situations, compatible with the view that an increase in cognitive load results in a heightened REA. Also, the REA depended on the type of perceptual load, as indicated by a higher REA associated with vocoded compared to low-level stimuli. The results of the error analysis support both structural and attentional models of the REA.

An auditory brain-computer interface to detect changes in sound pressure level for automatic volume control

Volume control is necessary to adjust sound levels for a comfortable audio or video listening experience. This study aims to develop an automatic volume control system based on a brain-computer interface (BCI). We thus focused on a BCI using an auditory oddball paradigm, and conducted two types of experiments. In the first experiment, the participant was asked to pay attention to a target sound where the sound level was high (70 dB) compared with the other sounds (60 dB). The brain activity measured by electroencephalogram showed large positive activity (P300) for the target sound, and classification of the target and nontarget sounds achieved an accuracy of 0.90. The second experiment adopted a two-target paradigm where a low sound level (50 dB) was introduced as the second target sound. P300 was also observed in the second experiment, and a value of 0.76 was obtained for the binary classification of the target and nontarget sounds. Further, we found that better accuracy was observed in large sound levels compared to small ones. These results suggest the possibility of using BCI for automatic volume control; however, it is necessary to improve its accuracy for application in daily life.

Auditory enhancement in younger and older listeners with normal and impaired hearinga).

Auditory enhancement is a spectral contrast aftereffect that can facilitate the detection of novel events in an ongoing background. A single-interval paradigm combined with roved frequency content between trials can yield as much as 20 dB enhancement in young normal-hearing listeners. This study compared such enhancement in 15 listeners with sensorineural hearing loss with that in 15 age-matched adults and 15 young adults with normal audiograms. All groups were presented with stimulus levels of 70 dB sound pressure level (SPL) per component. The two groups with normal hearing were also tested at 45 dB SPL per component. The hearing-impaired listeners showed very little enhancement overall. However, when tested at the same high (70-dB) level, both young and age-matched normal-hearing listeners also showed substantially reduced enhancement, relative to that found at 45 dB SPL. Some differences in enhancement emerged between young and older normal-hearing listeners at the lower sound level. The results suggest that enhancement is highly level-dependent and may also decrease somewhat with age or slight hearing loss. Implications for hearing-impaired listeners may include a poorer ability to adapt to real-world acoustic variability, due in part to the higher levels at which sound must be presented to be audible.

Perception-based noise assessment of a future blended wing body aircraft concept using synthesized flyovers in an acoustic VR environment—The ARTEM study

New aircraft concepts are currently being developed with the goal of less emissions of CO2 and noise. Remarkable noise reductions in long-range aircraft can only be expected from disruptive vehicle designs, new propulsion systems and specific low-noise technologies. In this paper, one such future vehicle design, a blended wing body (BWB) long-range aircraft, is described and studied with respect to sound levels on the ground, sound characteristics and noise annoyance. Virtual flyovers of different vehicle variants were synthesized and auralized in an acoustic VR environment, and investigated through psychoacoustic laboratory experiments. The applied methodology was successfully hierarchically validated by comparison with measurements of existing jet aircraft, assessing acoustical indices, time-frequency features, perceived plausibility, and induced noise annoyance. The perception-based evaluation of the BWB revealed that, while the BWB aircraft may initially be perceived as somewhat more unfamiliar, they are substantially less annoying than current tube-and-wing long-range aircraft of similar range and mission for take-offs as well as for landings. For the best BWB variant, noise annoyance was reduced by 4.3 units for departures and by 3.5 units for approaches on the 11-point scale. The main reason for these findings seems to be the acoustic shielding by the body of the extended fuselage, which was found to be an important factor in reducing sound levels in the order of 10–20 dB, and accordingly also to strongly reduce loudness. Additional low noise technologies and geared turbofan engines with a high bypass ratio further contributed to the reduction of noise annoyance of the BWB. A large part of the BWBs benefit could be explained by its lower sound levels, but additional benefits were found. The observed reduction in noise annoyance was found to be larger than what can be explained with conventional noise metrics. This benefit is probably due to more favorable sound characteristics compared to today's reference aircraft, such as less variation in time and less audible tones. The current study thus suggests that the studied BWB vehicle concept may substantially reduce noise annoyance on humans.

Shape-Configurable MXene-Based Thermoacoustic Loudspeakers with Tunable Sound Directivity.

Film-type shape-configurable speakers with tunable sound directivity are in high demand for wearable electronics. Flexible, thin thermoacoustic (TA) loudspeakers-which are free from bulky vibrating diaphragms-show promise in this regard. However, configuring thin TA loudspeakers into arbitrary shapes is challenging because of their low sound pressure level (SPL) under mechanical deformations and low conformability to other surfaces. By carefully controlling the heat-capacity-per-unit-area and thermal effusivity of an MXene conductor and substrates, respectively, we fabricated an ultrathin MXene-based TA loudspeaker exhibiting high SPL output (74.5dB at 15kHz) and stable sound performance for 14 days. Loudspeakers with the parylene substrate, whose thickness was less than the thermal penetration depth, generated bidirectional and deformation-independent sound in bent, twisted, cylindrical, and stretched-kirigami configurations. Furthermore, we constructed parabolic and spherical versions of ultrathin, large-area (20cm × 20cm) MXene-based TA loudspeakers, which displayed sound-focusing and 3D omnidirectional-sound-generating attributes, respectively. This article is protected by copyright. All rights reserved.

Model-inversion control to enforce tunable Duffing-like acoustical response on an Electroacoustic resonator at low excitation levels

The electroacoustic resonator is an efficient electro-active device for noise attenuation in enclosed cavities or acoustic waveguides. It is made of a loudspeaker (the actuator) and one or more microphones (the sensors). So far, the desired acoustic behaviour, expressed in terms of a linear-time-invariant relationship between sound pressure and vibrational motion (the acoustical impedance), has been more efficiently achieved by a model-inversion strategy which is implemented by driving the electrical current in the loudspeaker coil, based upon the measured pressure. The corrector transfer function is defined in the Laplace domain and digitally executed by the classical infinite-impulse-response technique, though a state–space representation could be employed. In this work, we are interested in enforcing a nonlinear behaviour at low sound excitation levels, where the electroacoustic resonator would normally behave as a linear-time-invariant system. Hence, in order to transform its acoustical response from linear to nonlinear, the model-inversion technique must be reformulated in time domain. The state–space representation of the relationship between the input measured pressure and the output electrical current gives the right perspective and the solution to this problem. We provide the conception of this model-inversion control algorithm capable of transforming a linear-time-invariant acoustical response to potentially any causal acoustical response of the electroacoustic resonator. Such control strategy is tested by targeting a Duffing acoustical response with tunable parameters. Both numerical simulations and experimental tests in quasi-open field validate the approach. The results provided in this contribution open the doors for conceiving non-conventional absorbers which can exploit nonlinear phenomena for noise mitigation even at low excitation amplitudes.

Sound energy-based surface contribution analysis for the vehicle interior noise problem

Booming noise is a major comfort problem in vehicle cabins occurring in lower frequencies. The method of panel or surface analysis serves as a viable tool to trace the sound emitting components on the enveloping chassis. Traditional techniques evaluate the surface contributions with respect to the sound pressure level at the driver’s position. However, using the sound pressure level as the control objective implies two major drawbacks: Firstly, the local sound pressure is highly sensitive to the position of the evaluation point. As a consequence, the predictions of the surface contributions become unreliable at frequencies or areas with low sound pressure levels. Secondly, surface contributions in existing techniques can be positive or negative, which facilitates the event of acoustic shortcircuits. This talk presents an accurate and robust contribution analysis method for the vehicle interior noise problem. For this purpose, the sound energy density is used as the control objective. A quadratic form yields energy-based contributions, which are always non-negative and thus avoiding acoustic shortcircuits. These findings demonstrate that contributing surface are effectively identified even in regions with sound pressure levels. As such, the evidence from this study suggests that the sound energy density provides an accurate and robust control objective.

High level sound transmission through cadaver human ears—On the influence of bone conduction and hearing protective devices

High level sound exposure can cause substantial injury to the auditory system, motivating efforts to predict and prevent this injury. Measurement techniques using acoustic manikins are effective for low and moderate sound levels, but nonlinear effects in the middle ear and alternate sound transmission pathways to the inner ear limit their utility at higher sound pressure levels. Here, we describe results from a series of measurements made in cadaveric human ears conducted in our laboratory over the last several years. We quantified sound transmission to the inner ear by measuring the difference in sound pressure level across the cochlear partition near the base of the cochlea, which drives basilar membrane motion. We describe measurements quantifying sound transmission through the human middle ear, which is limited by suspensory ligaments for sounds above approximately 130 dB SPL, resulting in nonlinear (harmonic) distortion of sounds in the cochlea at higher sound pressure levels. Similarly, we describe observations of sound transmission to the cochlea via bone conduction from vibratory transducers, as well as high level sound and impulse noise/blast exposures. The implications of these measurements for hearing loss predictions, effectiveness of hearing protective devices, and injury mechanisms are discussed.