External Microphone Research Articles

Noise monitoring in primary schools: comparisons between different time-dependent parameters for acoustic performance evaluation

The A-weighted equivalent sound level is commonly used to describe or regulate environmental noise over a defined time interval. Although it is very convenient and easy to compare noise limits or requirements, it does not provide summary information on how noise evolves. On the other hand, the detailed analysis of the history of the measurements over time is too burdensome in the case of long-term monitoring. As part of a large study that aims to investigate the effects of noise on the cognitive abilities of primary school children, long-term unattended monitoring was carried out using low-cost instrumentation based on smartphone apps and calibrated external microphones. From the data obtained, acoustic indices and parameters were calculated, which allowed the assessment of the time-dependent noise exposure of the students based on the type of activity carried out in class. This analysis can be useful for validating the acoustic design requirements in schools.

Soundbox-based sound insulation measurement of composite panels with viscoelastic damping

Sound transmission loss (STL), an essential index for assessing the sound insulation performance of composite laminated structures, typically relies on experimental methods to measure. The soundbox method (SBM), a straightforward technique for measuring the STL, is sensitive to microphones’ positions. Within the framework of the Chebyshev-Ritz method, a semi-analytical vibro-acoustic model extended to composite laminated panels with viscoelastic damping (VED) is proposed for the first time. Based on the developed simplified layer-wise theory, the panel is modeled using three layers: the top face layer, the VED layer, and the bottom face layer. A closed cavity is added to the model as the soundbox enclosure used in actual measurements. By employing the Hamilton's principle, the governing equation for the coupling system is derived, and the vibration and internal acoustic responses of the coupling system are calculated. A discretization strategy is introduced to address the frequency-dependent properties of the VED layer, avoiding the need to reconstruct the stiffness matrix at each frequency. To obtain the STL of the panel, sound pressures at external measurement points are calculated based on the Rayleigh integral. The proposed model is validated against numerical results from finite element analyses. The influences of the microphone position inside and outside the cavity on the measured STL are studied. Furthermore, parametric studies over the microphones' positions are performed to enhance the SBM-based evaluation of the composite panel's sound insulation performance. The optimal locations for two internal microphones and one external microphone are recommended. Finally, experimental studies are carried out to guide the implementation of the SBM.

Evaluation of a multi-function in-ear device performance in the presence of impulse noise using acoustic test fixtures

Real-time noise exposure monitoring has the potential to assess risk before damage occurs. We present on the development of an in- ear device that (1) provides hearing protection; (2) measures the noise in the ear canal to estimate exposure dose; and (3) monitors distortion product otoacoustic emissions (DPOAE) over time. To validate the device’s ability to measure impulse noise under hearing protection, we measured the response in a field test. A single AR15 was shot multiple times, and four prototypes were used in multiple acoustic test fixtures (ATFs) at different relative distances from the exit of the gun. The ATFs included a G.R.A.S 45 CB in addition to a head simulator designed to detect both air- and bone-conducted sound. We evaluated the impulse peak insertion loss (IPIL) metric of the device inserted by itself or in combination with other hearing protection (“double protection” condition) to assess attenuation of impulsive noises. We also compared the device's microphone measurements to those obtained through the ATF microphones, and to the recordings of external microphones located at or near the ear of each ATF. Results demonstrate the value of testing in-ear devices in acoustic test fixtures during development phases.

Digital assessment of speech in Huntington disease.

Speech changes are an early symptom of Huntington disease (HD) and may occur prior to other motor and cognitive symptoms. Assessment of HD commonly uses clinician-rated outcome measures, which can be limited by observer variability and episodic administration. Speech symptoms are well suited for evaluation by digital measures which can enable sensitive, frequent, passive, and remote administration. We collected audio recordings using an external microphone of 36 (18 HD, 7 prodromal HD, and 11 control) participants completing passage reading, counting forward, and counting backwards speech tasks. Motor and cognitive assessments were also administered. Features including pausing, pitch, and accuracy were automatically extracted from recordings using the BioDigit Speech software and compared between the three groups. Speech features were also analyzed by the Unified Huntington Disease Rating Scale (UHDRS) dysarthria score. Random forest machine learning models were implemented to predict clinical status and clinical scores from speech features. Significant differences in pausing, intelligibility, and accuracy features were observed between HD, prodromal HD, and control groups for the passage reading task (e.g., p < 0.001 with Cohen'd = -2 between HD and control groups for pause ratio). A few parameters were significantly different between the HD and control groups for the counting forward and backwards speech tasks. A random forest classifier predicted clinical status from speech tasks with a balanced accuracy of 73% and an AUC of 0.92. Random forest regressors predicted clinical outcomes from speech features with mean absolute error ranging from 2.43-9.64 for UHDRS total functional capacity, motor and dysarthria scores, and explained variance ranging from 14 to 65%. Montreal Cognitive Assessment scores were predicted with mean absolute error of 2.3 and explained variance of 30%. Speech data have the potential to be a valuable digital measure of HD progression, and can also enable remote, frequent disease assessment in prodromal HD and HD. Clinical status and disease severity were predicted from extracted speech features using random forest machine learning models. Speech measurements could be leveraged as sensitive marker of clinical onset and disease progression in future clinical trials.

An Implantable Piezofilm Middle Ear Microphone: Performance in Human Cadaveric Temporal Bones.

One of the major reasons that totally implantable cochlear microphones are not readily available is the lack of good implantable microphones. An implantable microphone has the potential to provide a range of benefits over external microphones for cochlear implant users including the filtering ability of the outer ear, cosmetics, and usability in all situations. This paper presents results from experiments in human cadaveric ears of a piezofilm microphone concept under development as a possible component of a future implantable microphone system for use with cochlear implants. This microphone is referred to here as a drum microphone (DrumMic) that senses the robust and predictable motion of the umbo, the tip of the malleus. The performance was measured by five DrumMics inserted in four different human cadaveric temporal bones. Sensitivity, linearity, bandwidth, and equivalent input noise were measured during these experiments using a sound stimulus and measurement setup. The sensitivity of the DrumMics was found to be tightly clustered across different microphones and ears despite differences in umbo and middle ear anatomy. The DrumMics were shown to behave linearly across a large dynamic range (46dB SPL to 100dB SPL) across a wide bandwidth (100Hz to 8kHz). The equivalent input noise (over a bandwidth of 0.1-10kHz) of the DrumMic and amplifier referenced to the ear canal was measured to be about 54dB SPL in the temporal bone experiment and estimated to be 46dB SPL after accounting for the pressure gain of the outer ear. The results demonstrate that the DrumMic behaves robustly across ears and fabrication. The equivalent input noise performance (related to the lowest level of sound measurable) was shown to approach that of commercial hearing aid microphones. To advance this demonstration of the DrumMic concept to a future prototype implantable in humans, work on encapsulation, biocompatibility, and connectorization will be required.

Investigation of characteristics and generating mechanism of wind noise on external microphone of mobile device

The multipurpose external microphone of mobile devices is exposed to the outside windy environment, which inevitably generates wind noise. The wind noise acts as noise in signal processing, like Active Noise Control and capturing voice, and damages the user's experience. This paper investigates the acoustic characteristics and generation mechanism of wind noise through experiments and numerical analysis for a commercial TWS earbuds model. The experimental results show that the wind noise has broadband characteristics with dominant low-frequency band noise (below 2500Hz), unlike general cavity flow. On the same model, the Lattice-Boltzmann method numerical analysis has been performed through powerFLOW software. The numerical result shows good agreement of +-3dB with experimental results in the 1/3 octave band spectrum for the wind noise band. Numerical results flow field investigation reveals that the disturbed flow field is induced by an interaction between the vortical structure of the inflow and separated flow field, which is governed by geometry configurations. The disturbances induce the complex pressure gradient on inflow into the microphone, measured as wind noise on the microphone. These results show that the wind noise measured by the microphone of mobile devices is a flow phenomenon caused by external excitation.

Can Smartphones with External Microphones Be Used in Place of Sound Level Meters?

Sound and noise are two sides of the same coin, around us during our daily lives. Excessive noise is listed as a public health concern and is one of the most common environmental and occupational exposures. Many municipalities in BC enacted Bylaws to regulate noise, which are enforced by Bylaw Officers and Environmental Health Officers (EHOs).&#x0D; Noise complaints are addressed by conducting measurements with approved and standardized Commercial Sound Level Meters (SLMs). Smartphone technology has progressed rapidly in the past decade, including the use of external microphones. Studies have been conducted on their use, however, the effects of their use have yet to be fully assessed.

Smartphone applications for measuring noise in the intensive care unit: A feasibility study

PurposeThis study aims to explore the suitability of using smartphone applications with low-cost external microphones in measuring noise levels in intensive care units. MethodsFour apps and two external microphones were tested in a laboratory by generating test signals at five noise levels. The average noise levels were measured using the apps and a professional device (i.e. a sound level meter). A field test was performed in an intensive care unit with two apps and one microphone. Noise levels were measured in terms of average and maximum noise levels according to the World Health Organisation's guidance. All the measurements in both tests were conducted after acoustic calibration using a sound calibrator. ResultsOverall, apps with low-cost external microphones produced reliable results of averaged noise levels in both the laboratory and field settings. The differences between the apps and the sound level meter were within ±2 dB. In the field test, the best combination of app and microphone showed negligible difference (< 2 dB) compared to the sound level meter in terms of the average noise level. However, the maximum noise level measured by the apps exhibited significant differences from those measured by the sound level meter, ranging from −0.9 dB to −4.7 dB. ConclusionSmartphone apps and low-cost external microphones can be used reliably to measure the average noise level in the intensive care unit after acoustic calibration. However, professional equipment is still necessary for accurate measurement of the maximum noise level.

Acoustic Flow Sensor Using a Passive Bell Transducer

Sensing based on a passive transducer that is wirelessly linked to a nearby data collection node can offer an attractive solution for use in remote, inaccessible, or harsh environments. Here we report a pipe flow sensor based on this principle. A transducer mounted inside the pipe generates an acoustic signal that is picked up by an external microphone. The passive transducer comprises a cavity with a trapped ball that can oscillate in response to flow. Its collisions generate an acoustic signal correlated to the flow speed. The transducer is implemented on a 6 mm diameter probe and characterized as a water flow meter. The time - average microphone voltage output is calculated by an analogue circuit, without any further signal processing. With the microphone mounted on the probe, and for flow rates in the range 0.35 m/s to 6.5 m/s, correlation between the sensor voltage output and flow rate data from a commercial flow meter is demonstrated with a worst-case accuracy of 2%. This was achieved by simple averaging of the acoustic pulse train over a 5-second time interval. Consistent correlation with the microphone mounted on the pipe wall at distances up to 150 mm from the probe location is also reported. These results demonstrate the viability of remote acoustic flow sensing using passive structures and offer a simple and minimally invasive flow monitoring method.

Are smartphones and low-cost external microphones comparable for measuring time-domain acoustic parameters?

This study examined and compared the diagnostic accuracy and correlation levels of the acoustic parameters of the audio recordings obtained from smartphones on two operating systems and from dynamic and condenser types of external microphones. The study included 87 adults: 57 with voice disorder and 30 with a healthy voice. Each participant was asked to perform a sustained vowel phonation (/a/). The recordings were taken simultaneously using five microphones AKG-P220, Shure-SM58, Samson Go Mic, Apple iPhone 6, and Samsung Galaxy J7 Pro microphones in an acoustically insulated cabinet. Acoustic examinations were performed using Praat version 6.2.09. The data were examined using Pearson correlation and receiver-operating characteristic (ROC) analyses. The parameters with the highest area under curve (AUC) values among all microphone recordings in the time-domain analyses were the frequency perturbation parameters. Additionally, considering the correlation coefficients obtained by synchronizing the microphones with each other and the AUC values together, the parameter with the highest correlation coefficient and diagnostic accuracy values was the jitter-local parameter. Period-to-period perturbation parameters obtained from audio recordings made with smartphones show similar levels of diagnostic accuracy to external microphones used in clinical conditions.

Medical Safety and Device Reliability of Active Transcutaneous Middle Ear and Bone Conducting Implants: A Long-Term Multi-Centre Observational Study

Active bone-conducting hearing devices (aBCHD; e.g., MEDEL Bonebridge® (BB)) and active middle ear implants (aMEI; e.g., MEDEL Vibrant Soundbridge® (VSB)) use radio frequency transmission to send information from an external microphone and sound processor to an internally implanted transducer. These devices potentially have an advantage over devices with percutaneous links because the skin is closed over the implantable components, which should reduce the risk of skin problems and infection. On the other hand, surgical procedures are more complex, with a greater risk of damage due to surgery. The objectives of this research were to quantify the reliability and long-term survival of MEDEL VSB and BB devices, determine the adverse and serious adverse device-related complications, and consider associated causes. A multi-center observational retrospective and prospective study was conducted at eleven auditory implant centers in the United Kingdom. Data was collected using a surgical questionnaire and audiological reports. Data were obtained from patient notes or from prospective cases that had a minimum follow-up of one year post-implant. Consecutive patient records were reviewed. Datasets from 109 BB and 163 VSB were reviewed. Of these, 205 were retrospective case note reviews, and 67 were prospective cases. The mean follow-up was 4 and 6 years, respectively, for BB and VSB. Kaplan–Meier Survival analyses indicated that the BB survival was 97% and 93.3% at 1 and 5 years, respectively, and the VSB was 92.1% and 87% at the same time points. This is a large cohort study for the field and has indicated that BB and VSB are safe interventions. Care should be taken to monitor magnet strength in the first few months. For the majority of device-related effects, there was no apparent association with etiology. However, an interesting pattern emerged for individuals who exhibited an inflammatory response, e.g., adhesions or device extrusion, and those with a history of chronic suppurative otitis media. This should be considered in future work and is not surprising given that many VSB recipients have a complicated hearing history, often associated with otitis media.

Quiet Spacecraft Cabin Ventilation Fan: Wake Measurements Results

A spacecraft cabin ventilation fan suitable for aerodynamic and acoustic ground tests was designed and two copies of the fan assembly were fabricated - designated as Quiet Space Fan. Both fans were tested for aerodynamic performance and acoustic levels in the NASA Glenn Research Center Acoustical Testing Laboratory. A new test rig for small axial flow fans was designed to accommodate the instrumentation and back-pressure adjustments. Measurements acquired were - static pressures for measuring performance, a 72-channel in-duct microphone array, external microphone measurements for acoustics, and inter-stage hot wire measurements of the fan wake. This report documents the wake velocity and turbulence measurements as part of a series of reports.

Quiet Spacecraft Cabin Ventilation Fan: Acoustic Measurements Results

A spacecraft cabin ventilation fan suitable for aerodynamic and acoustic ground tests was designed and two copies of the fan assembly were fabricated - designated as Quiet Space Fan. Both fans were tested for aerodynamic performance and acoustic levels in the NASA Glenn Research Center Acoustical Testing Laboratory. A new test rig for small axial flow fans was designed to accommodate the instrumentation and back-pressure adjustments. Measurements acquired were - static pressures for measuring performance, a 72-channel in-duct microphone array, external microphone measurements for acoustics, and inter-stage hot wire measurements of the fan wake. This report documents the acoustic measurements as part of a series of reports.

Quiet spacecraft cabin ventilation fan: aerodynamic measurements results

A metal spacecraft cabin ventilation fan suitable for aerodynamic and acoustic ground tests was designed and two copies of the fan assembly were fabricated. Both fans were tested for aerodynamic performance and acoustic levels in the NASA Glenn Research Center Acoustical Testing Laboratory. A new test rig for small axial flow fans was designed to accommodate the instrumentation and back-pressure adjustments. Measurements acquired were from: static pressures for measuring performance, a 72-channel in-duct microphone array, external microphone measurements for acoustics, and inter-stage hot wire measurements of the fan wake. This report documents the aerodynamic measurements as part of a series of reports.

Light at the end of the tunnel of Corti

Light at the end of the tunnel of Corti

MYRiAD: a multi-array room acoustic database

In the development of acoustic signal processing algorithms, their evaluation in various acoustic environments is of utmost importance. In order to advance evaluation in realistic and reproducible scenarios, several high-quality acoustic databases have been developed over the years. In this paper, we present another complementary database of acoustic recordings, referred to as the Multi-arraY Room Acoustic Database (MYRiAD). The MYRiAD database is unique in its diversity of microphone configurations suiting a wide range of enhancement and reproduction applications (such as assistive hearing, teleconferencing, or sound zoning), the acoustics of the two recording spaces, and the variety of contained signals including 1214 room impulse responses (RIRs), reproduced speech, music, and stationary noise, as well as recordings of live cocktail parties held in both rooms. The microphone configurations comprise a dummy head (DH) with in-ear omnidirectional microphones, two behind-the-ear (BTE) pieces equipped with 2 omnidirectional microphones each, 5 external omnidirectional microphones (XMs), and two concentric circular microphone arrays (CMAs) consisting of 12 omnidirectional microphones in total. The two recording spaces, namely the SONORA Audio Laboratory (SAL) and the Alamire Interactive Laboratory (AIL), have reverberation times of 2.1 s and 0.5 s, respectively. Audio signals were reproduced using 10 movable loudspeakers in the SAL and a built-in array of 24 loudspeakers in the AIL. MATLAB and Python scripts are included for accessing the signals as well as microphone and loudspeaker coordinates. The database is publicly available (https://zenodo.org/record/7389996).

Source separation using bandlimited external microphones and a microphone array

Modern listening devices are equipped with air-conducted microphones and contact microphones. External microphones, like those on a listening device, have been used to estimate relative transfer functions (RTFs) at microphone arrays. With numerous active sound sources, the air-conducted microphones perform poorly while the contact microphones are robust to external noise. A drawback of contact microphones is that they are bandlimited. Past work has shown that the contact microphone and microphone array can be combined to estimate RTFs in the low frequencies. To overcome the limitations of the contact microphone, we propose a method that leverages the full-band signal at the microphone array to provide beamforming gains at higher frequencies. We demonstrate this method by separating three human talkers in a noisy environment.

Design and testing of ultraminiature microelectromechanical systems middle ear accelerometers

Moderate to severe hearing loss is a debilitating condition that affects over 5% of the world’s population. Hearing aids and cochlear implants positively impact the lives of those who suffer from sensorineural hearing loss. However, both display numerous limitations that affect their adoption and use rates, notably including those associated with the external elements of these devices (e.g., microphone and signal processor). These external components impact device safety, appearance, acoustic performance, and ease-of-use. A totally implantable auditory prosthesis would help to address these issues by eliminating external components. A major barrier to progress toward this goal is the lack of a completely implantable acoustic sensor capable of matching or exceeding the performance of commercial external microphones. Our previous studies have indicated that piezoelectric microelectromechanical systems (MEMS) accelerometers have the potential to function as implantable sensors within the middle ear meeting a 20-phon noise floor over a 100–8 kHz range. In this paper, we describe a process to design and fabricate dual and tri-resonance devices that are comprised of piezoelectric cantilever bimorph beams tip-loaded by a proof mass, can meet or exceed the 20-phon noise floor, and can produce a measurable voltage output when deflected by sound-induced ossicular vibrations.

Hard of hearing: the effect of distance and experimental noise on mountain chickadee song transmission

ABSTRACT Urban noise can disrupt avian communication networks, resulting in reduced communication among individuals. Mountain chickadees alter their vocalisations in areas of high ambient noise; however, it is unknown how audible their signals are within the nest cavity, where the female remains during dawn signalling. To test the relative audibility of songs within the nest box of urban and rural chickadees, we conducted a playback experiment directed at empty nest boxes using an autonomous recording unit above the box with external microphones and an internal microphone inside the nest box. We placed a speaker 25-75 m from the nest box and played two playback files of mountain chickadee songs – one with added noise and one without. Songs had a higher signal-to-noise ratio (SNR) in rural habitats and in ‘Without Added Noise’ treatments, however, SNR decreased with increasing distance from the nest box. The lower frequency song notes had a lower SNR inside the nest in both treatment types. As expected, noise and distance resulted in decreased SNR of chickadee songs within the nest cavity. These findings suggest a possible constraint in urban birds requiring them to reduce their distance from the nest to ensure audibility to the female while in noise.

Active Sound Power Attenuation with a Ring of Harmonic Acoustic Pneumatic Sources fOr Destructive Interference (RHAPSODI) and near field in-duct microphones

Much research has been conducted to investigate active noise control of turbofans with loudspeakers as noise cancellation sources. However, the required power consumption, fragility, and weight and volume penalty make them unsuitable for engine nacelle applications. An alternative source technology, developed at Sherbrooke, is a harmonic acoustic pneumatic source (HAPS). They are mounted on a ring to perform multimodal active noise control in duct by destructive interference of primary noise (RHAPSODI). A dedicated MIMO harmonic control strategy based on complex envelopes is required to control the RHAPSODI with in-duct microphones located at a very close distance from it or with external in-duct microphones located 1 meter away from the duct mouth. During a training phase, active radiated power minimization is performed with the external microphones for different modal components of the primary harmonic noise. The optimal HAPS control and the optimal signals from the in-duct microphones are then used to tune the specific MIMO controller with a field compensation matrix close to the in-duct microphone signals. A typical result shows that RHAPSODI using 5 in-duct microphones and 5 HAPS can provide high attenuation of radiated sound power (22 dB-SPL, 1 kHz, primary sound power 130 dB).