Acoustic Calibration Research Articles

Cross-comparison of the optical and acoustical calibration methods for microphones based on microelectromechanical system technologies

Calibration methods and associated international standards in airborne acoustics have enabled national metrology institutes to establish and maintain a fully defined traceability chain for designated laboratories and end users of microphones. However, such microphones need to be reciprocal, of condenser type and of specific dimensions; this, in effect, does not allow for the calibration of alternative existing sensor technologies and creates a further obstacle for the calibration of emerging technologies. An example relates to microphones based on microelectromechanical systems which are an integral part of a wide range of electronic devices; yet, there is no established calibration traceability chain other than methods employed by manufacturers. From a metrological perspective, new calibration methods that can accommodate microphones regardless of their size, reciprocal nature and utilised technology must be developed and subsequently standardised and adopted. This paper discusses the optical calibration method based on free field photon correlation and the acoustical calibration methods based on pressure comparison and free field substitution. These approaches can provide traceability to the international measurement standard system for novel types of microphones, and the measurement results showed themselves to be consistent. Based on this study, the possibility of expanding the new standard system was investigated.

All-optical infrasound sensor based on a Fabry-Perot interferometer

Recent demands for infrasound measurement, whether for detecting violent atmospheric events or evaluating the environmental impact of wind farms, require new acoustic calibration standards in the frequency range below 2Hz. Expanding the frequency bandwidth of microphones remains a limited strategy since they are designed to filter out continuous components. An alternative method for measuring infrasound is proposed, which relies on a Fabry-Perot interferometer. This technique has been studied extensively for static pressure measurements with success. Therefore, adapting a Fabry-Perot refractometer to perform acoustic measurements is not only a technical challenge but also an opportunity to bridge the gap between static pressures and acoustic metrology. As acoustic movement involves both small pressure and temperature variations, it is important to account for their coupled effects in interferometer measurement results. Since the temperature variation field in the measurement system cannot be characterised experimentally, an analytical model has been developed. The chosen theoretical and technical solutions are validated by the good agreement between experimental results obtained with the refractometer carried out and other calibrated sensors in the frequency range from 40mHz to 1.5Hz. These results also highlight the improvements required to bring the device up to the level of an infrasound reference instrument.

Acoustical measurements enabled by low cost electronics and digital oscilloscopes

The advent of low-cost impedance analyzers and digital oscilloscopes have enabled the realization of cost-effective measurement systems for research, development, calibrations, and classroom/laboratory demonstrations. Traditionally, we have relied on HP/Agilent 4194 impedance anyalzers for laboratory use, but these units are heavy and expensive, originally costing about $30,000. Over the years, we have acquired and repaired many used units from ebay but recently found an alternative. Digilent offers a PC-based impedance measurement ($30) as add on to the Discovery logic Analyzer and Waveforms software, costing less than $300 that is lightweight and ideal for field or classroom use. Digital PC-based oscilloscopes and data acquisitions systems (e.g., TiePie, Cleverscope, Digilent) have also enabled the development of comprehensive low-cost acoustic calibration systems. We have developed such a system based on the TiePie Digital Oscilloscope (DIFF 1000MS/s), PC based signal generation and acquisition systems, a power amplifier, a preamplifier, and a stepper motor. The transmit signal is from a TiePie HS5-540XM 5 (500 MHz, 1-channel generator, 2-channel acquisition). The calibration and data display are controlled throught a MATLAB (GUI). Measurements of Transmit Pressure Response per Volt (TR/V or TVR), Free Field Voltage Sensitivity (FFVS), and Beam Pattern measurements and dependence on environmental pressure and temperature will be presented.

Research on Sonar Motion Compensation Method Based on Acoustic Calibration System

The influence of sonar motion error restricts the improvement of sonar imaging resolution. High-precision sonar motion compensation is an important guarantee for high-quality imaging. In this paper, a sonar motion compensation method based on acoustic calibration system is proposed, and the imaging results are compared with those based on the traditional combined inertial guidance measurement method. Experimental results show that the sonar motion compensation method based on acoustic calibration system plays a crucial role in imaging, which proves that acoustic calibration method is an effective means to improve the resolution of sonar imaging.

Evaluating the Performance of a Dual-Frequency Multibeam Echosounder for Small Target Detection

With rising interest in marine renewable energy (MRE) associated with offshore wind, waves, and tidal flows, the effects of device placement on changes in animal behaviour require proper assessment to minimise environmental impacts and inform decision making. High-frequency multibeam echosounders, or imaging sonars, can be used to observe and record the underwater movement and behaviour of animals at a fine scale (tens of metres). However, robust target detection and tracking of closely spaced animals are required for assessing animal–device and predator–prey interactions. Dual-frequency multibeam echosounders combine longer detection ranges (low frequency) with greater detail (high frequency) while maintaining a wide field of view and a full water column range compared to acoustic or optical cameras. This study evaluates the performance of the Tritech Gemini 1200ik imaging sonar at 720 kHz (low frequency) and 1200 kHz (high frequency) for small target detection with increasing range and the ability of the two frequency modes to discriminate between two closely spaced targets using a 38.1 mm tungsten carbide acoustic calibration sphere under controlled conditions. The quality of target detection decreases for both modes with increasing range, with a 25 m limit of detection at high frequency and a low-frequency mode able to detect the target up to 30 m under test conditions in shallow water. We quantified the enhanced performance of the high-frequency mode in discriminating targets at short ranges and improved target detection and discrimination at high ranges in the low-frequency mode.

Nonembedded measurement method based on amplitude correction for unsteady surface pressure estimation in a high-subsonic compressor cascade

Unsteady surface pressure (USP) is a crucial physical quantity for studying blade loads and boundary layer flow. However, the unique characteristics of high-load compressor cascades, including thin walls, narrow passages, and significant geometric deflection angles, pose considerable challenges for USP measurements. The primary innovation of this study lies in proposing a nonembedded measurement method based on amplitude correction for USP measurement, which can provide frequency and amplitude information of dynamic pressure on measured surface. Unlike existing methods that rely on theoretical models for amplitude correction, the proposed method establishes amplitude correction transfer models using Gaussian process regression (GPR) based on pre-calibration data. This innovation overcomes the constraints faced by theoretical models when dealing with high-speed complex geometries, such as those found in compressor blades, which are limited by geometric and Reynolds number considerations. The principle of this method is to perform indirect measurement by leading the airflow out of the measured surface through an air tube and correcting the amplitudes through transfer models. An acoustic calibration system was developed for amplitude calibration and measurement verification. The results demonstrate that the developed method accurately provides the dynamic pressure frequencies in the range of 1–10 kHz with a tube length of ≤ 55 mm and from 1 to 7 kHz with the tube length of 80 mm. Verification results proof that the GPR statistical model can reasonably estimate amplitude attenuation. Ultimately, the developed method was successfully applied to unsteady pressure measurement in a high-subsonic compressor cascade and showed highly encouraging results.

Signal processing and acoustic calibration method of millimeter-wave vibration sensor

Millimeter-wave sensors can be utilized as non-contact vibration sensors. Applications of millimeter-wave vibration sensors are the vital sensing of humans (heartbeat, respiration, body motion), factory machines, and vibration sensing of social infrastructures, such as buildings and bridges. Millimeter-wave vibration sensors can simultaneously detect the position and the waveforms of the vibration displacements of vibration objects. The primary signal processing of millimeter-wave sensors is two-dimensional fast Fourier transform (2D-FFT), detecting the arrival direction (DOA) and processing the micro-Doppler signals. The detectable areas of the millimeter-wave vibration sensors are defined using the parameters related to these three signal-processing blocks. Measured vibration waveforms by millimeter-wave vibration sensors include all components of the vibration displacements in the defined detectable area. Therefore, the waveform of the vibration displacement is influenced by the definition of the detectable area and the vibration form of the vibrating object. The measured values of millimeter-wave vibration sensors must be calibrated with attention to these influences. The vibration waveforms of vibrating objects are estimated by acoustic measuring methods, such as the laser Doppler vibrometer and the parallel-phase shifting interferometry. This paper describes calibration methods of millimeter-wave vibration sensors employing these two measuring methods.

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.

AUV planning and calibration method considering concealment in uncertain environments

IntroductionAutonomous underwater vehicles (AUVs) are required to thoroughly scan designated areas during underwater missions. They typically follow a zig-zag trajectory to achieve full coverage. However, effective coverage can be challenging in complex environments due to the accumulation and drift of navigation errors. Possible solutions include surfacing for satellite positioning or underwater acoustic positioning using transponders on other vehicles. Nevertheless, surfacing or active acoustics can compromise stealth during reconnaissance missions in hostile areas by revealing the vehicle’s location.MethodsWe propose calibration and planning strategies based on error models and acoustic positioning to address this challenge. Acoustic markers are deployed via surface ships to minimize navigation errors while maintaining stealth. And a new path planning method using a traceless Kalman filter and acoustic localization is proposed to achieve full-area coverage of AUVs. By analyzing the statistics of accumulated sensor errors, we optimize the positions of acoustic markers to communicate with AUVs and achieve better coverage. AUV trajectory concealment is achieved during detection by randomizing the USV navigation trajectory and irregularizing the locations of acoustic marker.ResultsThe proposed method enables the cumulative determination of the absolute position of a target with low localization error in a side-scan sonar-based search task. Simulations based on large-scale maps demonstrate the effectiveness and robustness of the proposed algorithm.DiscussionSolving the problem of accumulating underwater localization errors based on inertial navigation by error modeling and acoustic calibration is a typical way. In this paper, we have implemented a method to solve the localization error in a search scenario where stealth is considered.

Acoustic Characterization and Quality Assessment of Cremona’s Ponchielli Theater

The Ponchielli theater of Cremona was built in 1808 after a fire destroyed the old wooden structure. The interior, the architecture and the shape of the plan layout are reminiscent of the Teatro alla Scala, Milan, a masterpiece by the architect Piermarini, albeit on a smaller scale. The four orders of balconies crowned by the top gallery are typical features of a 19th Century Italian Opera theater. Acoustic measurements have been undertaken across the stalls and in some selected boxes according to ISO 3382. The main acoustic parameters resulting from the measurements have been used for the acoustic calibration of a 3D model representing the Ponchielli theater. The calibration has been used to compare different scenarios involving the acoustic response of the main hall at 50% and 100% occupancy. The outcomes indicate that no significant change can be detected when the seats are provided with robust upholstery, which can be considered a positive result, especially for the actors who are not forced to change their effort between rehearsal and live performance. In order to contextualize the measured values in relation to the optimal ones, a comparison with other Italian Opera theaters provided with similar architectural characteristics has been carried out. Overall, the findings indicate that the acoustics of the Ponchielli theater are suitable for both music and speech in line with the other selected theaters, as these places were mainly created for multifunctional purposes in the 19th Century.

Measurement of electroacoustic transducer sensitivity in extreme hydrostatic pressure environments

The measurement and acoustic calibration of electroacoustic transducers for underwater sound under extreme pressures (to 10,000 psi / 7km depth) and variety range of temperatures is a great challenge. Specialized facilities consisting of large pressure vessels with pressure and temperature control do exist at Navy faciliites (www.navsea.navy.mil + USRD) but operate to moderate pressures, have limited availability, are expensive and limited access. An alternative or supplement is to measure the change in the electro-mechanical impedance of the of a transducer and use equivalent electrical cirucuit analysis to determine the resulting change in all electrical, electromechanical, and mechanical properties. Having the pressure and temperature depedence of all the consitutent parameters allows an accurate pediction of the transduer performance sensitivity and frequency response (such as TVR Transmit Pressure per Volt, and receive voltage per pressure sensitivity. We measured transducer performance of several devices in the laboratory pressure vessels up to 10 000psi and report on findings.

Practical calibration method of airborne ultrasound measurement system by using acoustic calibrators

Airborne ultrasonic apparatus, such as haptic devices and parametric speakers, have been actively developed and are becoming increasingly popular. In order to evaluate the performance of these apparatuses and to assess their safety against exposure to airborne ultrasound, quantitative sound pressure measurement of the emitted airborne ultrasound is required. Currently, various instruments are used to measure airborne ultrasound. However, since there is no instrument like a sound level meter that integrates the measurement and the display of the measured value, we need to set up a measurement system and then calibrate the system. For the feasibility of calibration, a system comprising a measurement microphone as specified in IEC 61094-4 and general measuring instruments is more realistic. There are a few possible calibration methods for this system. Considering the calibration effort and the required accuracy in actual measurement, it is practical to calibrate one specific frequency by an acoustic calibrator and the other frequencies by adopting the relative sensitivity curve of the microphone given by a manufacturer or the specification of the instruments. The paper discusses the uncertainty when the measurement system is calibrated as described above.

AFRIMETS.AUV.A-S2 final report, calibration of a multi-function acoustic calibrator

Main textResults of Regional Metrology Organisation supplementary comparison AFRIMETS.AUV.A-S2 concerning the calibration of a Brüel & Kjær 4226 multi-frequency sound calibrator are reported here. Sound pressure level results at frequencies from 31.5 Hz to 16 kHz and nominal sound level settings of 94 dB and 114 dB, were evaluated for consistency, the calculated comparison reference values and Degrees of Equivalence are reported here. The comparison's purpose was to prove technical capabilities supporting the submissions of calibration measurement capabilities in the BIPM key comparison database. The light shines quite far, the new calibration measurement capabilities that may result from this work underpin some important fundamental acoustic calibration services, e.g., sound calibrators, sound level meters and personal sound exposure meters. These instruments are intrinsic to the effective monitoring and implementation worldwide of human hearing conservation and hearing loss assessment programs, all of which impacts quality of life. According to the World Health Organization, nearly 1.5 billion people experience some decline in their hearing capacity during their lives [1].To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCAUV, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Assessing the impacts of anthropogenic sounds on early stages of benthic invertebrates: The “Larvosonic system”

AbstractNoise produced by human activities has increased in the oceans over the last decades. Whereas most studies have focused on the impact of anthropogenic noise on marine mammals and fishes, those focusing on marine invertebrates are rarer and more recent, especially when considering peri‐metamorphic benthic stages, highly sensitive to anthropogenic perturbations. A careful review of the literature reveals a simplistic characterization of the acoustics within the containers used to quantify larval and juvenile responses to noise, thus weakening the conclusions of such works. To address this problem, we developed the Larvosonic system, a laboratory tank equipped with acoustic assets to assess the impacts of noise on young stages of marine invertebrates. We first provide a careful analysis of the tank sound field using different sound types, and we assess the effects of expanded polystyrene units on the sounds emitted by a professional audio system in order to dampen reverberation and resonance. Then, we apply this acoustic calibration to the effects of both pile driving and drilling noises on postlarvae of the scallop bivalve Pecten maximus. Acoustic recordings highlight that diffuser and bass trap components constitute effective underwater sound absorbents, reducing the reflection of the whole frequency bandwidth. Scallop experiments reveal that both type and level of the tested noise influenced postlarval growth, with interactive effects between trophic environment and noise level/spectra. The Larvosonic system thus constitutes an efficient tool for bioacoustics research on bentho‐planktonic invertebrate species.

Au–Au Bonding-Associated Lapping and Polishing Technique for Sapphire-Based Fabry–Perot Acoustic Sensor Applied for Harsh Environment

This article presents a sapphire-based Fabry–Perot acoustic sensor with potential for application in harsh environment acoustic sensing. The key component of the sensor is a thin sapphire diaphragm with a diameter of 20 mm and thickness down to 10 proposed Au–Au bonding-associated lapping and polishing technique. Microfabrication characterizations have corroborated the availability of realizing wafer-class thin sapphire diaphragm fabrication by employing the Au–Au bonding-associated lapping and polishing technique, and the diaphragm can be then easily transferred and assembled as a sensor. The strategy for optimizing the stripping phenomenon during lapping is also proposed. Acoustic calibration experiment through a plane wave tube indicates the sensitivity of 13.58 mV/Pa at 10 kHz and the frequency response range of 100250 kHz. The temperature tolerance experiment through the muffle furnace shows that no structural damage or optical spectrum invalidity occurs even if the environmental temperature reaches 800°, which indicates a high working temperature of the sensor up to 80°. Major findings and future application directions of this article are concluded as: 1) realization of an innovative sapphire-based Fabry–Perot acoustic sensor that shows significant potential in applications of numerous key industrial domains, such as aerospace engineering, and 2) a novel approach for achieving wafer-class sapphire ultrathin diaphragm fabrication, which might offer innovative methods for the optimization of sapphire-based harsh environment sensors and give reference to the sapphire lapping process as demanded in the gallium nitride (GaN)-based light-emitting diodes (LED) industry.

Low cost acoustic transducer calibration system

An acoustic calibration system was developed primarily for underwater acoustic transducers, although applicable for a variety of acoustic applications. Historically, such systems have been large, highly customized, and very expensive. With the advent of compact cost-effective digital PC-based oscilloscopes and data acquisitions systems (e.g., devices from TiePie, Cleverscope, and Digilent), a development that began as a senior capstone-design project has recently been demonstrated. Our system is based on the TiePie Digital Oscilloscope, a PC based signal generation and acquisition systems, a power amplifier, optional preamplifier and stepper motor with controller for radiation patterns. More specifically, the receive sensor signals are acquired with a TiePie Handyscope HS6 DIFF (1000MS/s, USB 3.0 oscilloscope, with four differential analogue channels) and the transmit signal (signal generation, transmit voltage and current acquisition) utilizes a TiePie HS5-540XM 5 (500 MHz, 1-channel generator, 2-channel acquisition) measuring system. The calibration and data display is controlled with MATLAB and controlled through a graphical user interface (GUI). Examples of Transmit Pressure Response per Volt (TR/V or TVR), Free Field Voltage Sensitivity (FFVS), and Beam Pattern measurements will be provided. [Work supported by BTech Acoustics LLC.]

Kiel Probes for Stagnation Pressure Measurement in Rotating Detonation Combustors

Kiel probes have the potential to be a versatile tool for determining stagnation pressure gain in rotating detonation combustors (RDCs), accompanying the commonly used equivalent available pressure method. Although average pressure gain values determined with Kiel probes are comparable to those from thrust stand experiments, one can expect several sources of measurement error from the unsteady trans- and supersonic environment. This work investigates the response of a Kiel probe in highly unsteady flow, similar to what would be encountered in an RDC. The probe is subjected to an underexpanded starting jet behind an incident shock with Mach numbers of 1.6–2.7, emanating from a shock tube with a reservoir ratio of about 394. The incidence angle of the probe is varied between 0 and 90 deg, as is the probe’s axial location with respect to the tube’s exit plane. High-speed schlieren images reveal the Mach number of the moving shock wave and the structure of the detached bow shock at the Kiel head, which is similar to that of a bluff body. It is shown that the measured stagnation pressure signal is independent of inflow angle over a range of , and that signal attenuation is caused by gas processing through the bow shock and viscous losses in the probe’s capillary. The frequency response of the Kiel probe to sinusoidal, small-amplitude pressure fluctuations is determined in an acoustic calibration facility up to 5500 Hz, confirming linear behavior and that no unwanted resonance is present in the probe. A Berg–Tijdeman representation delivers amplitude ratio and phase lag of comparable magnitude. An assessment of representative boundary conditions reveals that the average stagnation pressure measurement error is of the order of 1%.

Multimodal Intelligent Acoustic Sensor-Assisted English Pronunciation Signal Acquisition and Phonetic Calibration

In this paper, a multimodal intelligent acoustic sensor is used for an in-depth study and analysis of English pronunciation signal acquisition and calibration analysis of English phonetic symbols based on the acquired sound signals. This paper proposes a bimodal fusion algorithm around the direction of feature extension and fusion of acoustic recognition features. After each unimodal classification error cost is minimized, the current fusion process is determined by adaptive weights to fix its one decision layer on the fusion. The adaptive weight approach in this algorithm improves the drawback of always identifying one mode as the optimal mode in fixed-weight fusion and further improves applicability and performance compared to unimodal recognition. The random network generation algorithm is used to generate a random network for sound source data acquisition; then, the algorithm is investigated using the decomposition containing fusion center algorithm to each node, and data preprocessing is implemented at each node; finally, the distributed consistency algorithm based on average weights is used for consistent averaging iterations to achieve a consistent speech enhancement effect at each node. The experimental results show that this distributed algorithm can effectively suppress the interference of noncoherent noise, and each node can obtain an enhanced signal close to the source signal-to-noise ratio. In this study, factors that may affect the readability of spoken texts are summarized, analyzed, defined, and extracted, and the difficulty of spoken items obtained from the divisional scoring model is used as the dependent variable, and the extracted influencing factors are used as independent variables for feature screening, model construction, and tuning, and the generated results are interpreted and analyzed. From this, it was found that phonological features have a strong influence on the readability of spoken texts, mainly in features such as phonemes, syllables, and stress. This study is summarized, and the shortcomings of location-based contextual mobile learning of spoken English in terms of student management, device deployment, and empirical evidence are pointed out, to provide references and lessons for the research on IT-supported language learning.

Gain and Phase Calibration of Uniform Rectangular Arrays Based on Convex Optimization and Neural Networks

A calibration method based on convex optimization (CVX) and neural networks is proposed for the large planar arrays of phased array three-dimensional imaging sonar systems. The method only needs an acoustic calibration source at an unknown position in the far field, and the direction of arrival (DOA) and gain and phase error are jointly estimated. The method uses a CVX algorithm to solve an optimization problem and initially estimates the DOA of the calibration source robustly. Subsequently, according to the estimation results, a neural network is used for fitting to obtain off-grid DOA estimation of the calibration source. Thereafter, spatial matched filtering is performed to obtain the gain and phase residual estimations. The root mean square error (RMSE) of the beam pattern calibrated by the method for uniform planar arrays can reach a value of 4.9542 × 10−5. The experimental results demonstrate the efficiency of the proposed method for gain and phase calibration.

DEchorate: a calibrated room impulse response dataset for echo-aware signal processing

This paper presents a new dataset of measured multichannel room impulse responses (RIRs) named dEchorate. It includes annotations of early echo timings and 3D positions of microphones, real sources, and image sources under different wall configurations in a cuboid room. These data provide a tool for benchmarking recent methods in echo-aware speech enhancement, room geometry estimation, RIR estimation, acoustic echo retrieval, microphone calibration, echo labeling, and reflector position estimation. The dataset is provided with software utilities to easily access, manipulate, and visualize the data as well as baseline methods for echo-related tasks.