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Statistical distribution and statistical upper limit (the value which 93.5 % of the batch of new equipment are expected to lie) of A-weighted sound power level for one office printer were experimentally estimated from 10 new samples picked up from market. The printer is capable of A4-size printing with electrophotographic engine which corresponds Annex C.16 Page printers in ECMA74 17th (2019). A-weighted sound power level for continuous printing mode was determined in accordance with noise test code for ITTE (Information Technology and Telecommunications Equipment such as printers and personal computers), ISO 7779:2018 and ECMA-74 Annex C. Sample standard distribution of production of overall A-weighted sound power level (determined from 100-10000 Hz one-third-octave band) is 0.25 dB, whereas individual one-third-octave band has larger distribution. The value obtained is better than reference distribution 1.32 dB set in ISO 9296:2017 which states estimation of statistical upper limit value of the batch of equipment for ITTE.

Pressure Acoustic Transfer Functions or Vectors (PATVs) relate the surface velocity of a structure to the sound pressure level at a field point in the surrounding fluid. These functions depend only on the structure geometry, properties of the fluid medium (sound speed and characteristic density), the excitation frequency and the location of the field point, but are independent of the surface velocity values themselves. Once the pressure acoustic transfer function is computed between a structure and a specified field point, we can compute pressure at this point for any boundary velocity distribution by simply multiplying the forcing function (surface velocity) with the acoustic transfer function. These PATVs are usually computed by application of the Reciprocity Principle, and their computation is well understood. In this work, we present a novel way to compute the Velocity Acoustic Transfer Vector (VATV) which is a relation between the surface velocity of the structure and fluid particle velocity at a field point. To our knowledge, the computation of the VATV is completely new and has not been published in earlier works. By combining the PATVs and VATVs at a number of field points surrounding the structure, we obtain the Quadratic Power Transfer Vector (QPTV) that allows us to compute the sound power radiated by a structure for ANY surface velocity distribution. This allows rapid computation of the sound power for an arbitrary surface velocity distributions and is useful in designing quiet structures by minimizing the sound power radiated.

Round-robin testing for two samples, Reference Sound Source in accordance with ISO 6926 and Office printer with electrophotographic engine, were executed by seven testing laboratories in Japan on 2020. All tests were executed with parallelepiped measurement surface in hemi anechoic chamber in accordance with testing standard for engineering-grade sound power determination, ISO 3744:2010. The results show that sample standard deviation for RSS is better than printer. Standard deviations for overall A-weighted sound power level for two samples are better than combined standard uncertainties calculated with reference example of standard deviations in ISO 3744 (1.5 dB for Reference Sound Source as standard deviation of operating/mounting condition is negligibly small, 1.6 dB for printer as stable operating/mounting condition 0.5 dB). This paper also indicates tips for those who would conduct round-robin testing to obtain valid results by obviating incorrect operations and malfunctions of printers or similar equipment from the experience of some round-robin tests.

As the first step to obtain a city urban area noise map of road traffic noise, sound power levels of vehicles on the roads should be accurately estimated over a wide area. In Japan, ASJ RTN-Model 2018 was proposed as the representative road traffic noise prediction model, and by using the model sound power level of a vehicle can be determined if the vehicle type, traveling speed, and driving mode are known. As such data on urban road network, the Ministry of Land, Infrastructure and Transport of Japan publishes the road traffic census including road traffic volume and travel speed of major roads in Japan. The data, however, is limited to major roads and there is no data on minor roads. In this study, to estimate noise condition and situation on arbitrary road, a method for estimating the traveling speed and the traffic volume of vehicles on the road from aerial photographs was examined. Road traffic noise levels along several roads in Tokyo were analyzed by the proposed method and the validity of the calculation results were verified by comparing with short-time measurement results obtained along the target roads.

Vibration-based sound power (VBSP) methods based on elemental radiators and measurements from a scanning vibrometer have been shown to be accurate for flat plates and cylinders. In this paper, the VBSP method is extended to account for simple curved structures, with a constant radius of curvature. Data are also presented that suggest the VBSP method is more accurate than the ISO 3741 standard for measuring sound power when significant background noise is present. Experimental results from ISO 3741 and the VBSP methods are compared for three simple curved plate structures with different radii of curvature. The results show good agreement for all three structures over a wide frequency range. The experimental results also indicate that the VBSP method is more accurate in the low frequency range where the curved plates radiated relatively little and significant background noise was present.

Active structural acoustic control is an active control method that controls a vibrating structure in a manner that reduces the sound power radiated from the structure. Such methods focus on attenuating some metric that results in attenuated sound power, while not necessarily minimizing the structural vibration. The work reported here outlines the weighted sum of spatial gradients (WSSG) control metric as a method to attenuate structural radiation. The WSSG method utilizes a compact error sensor that is able to measure the acceleration and the acceleration gradients at the sensor location. These vibration signals are combined into the WSSG metric in a manner that is closely related to the radiated sound power, such that minimizing the WSSG also results in a minimization of the sound power. The connection between WSSG and acoustic radiation modes will be highlighted. Computational and experimental results for both flat plates and cylindrical shells will be presented, indicating that the WSSG method can achieve near optimal attenuation of the radiated sound power with a minimum number of sensors.

The uncertainty of determining the sound power of HVAC equipment using the AHRI Standard 230 sound intensity measurement method is presented. Measurements of six different reference sound sources (RSS) at four different laboratories, by nineteen different individuals with four different instrumentation systems are presented. From 2004 through 2020, these measurements were performed as part of a training program at Johnson Controls HVAC test laboratories to qualify technicians and engineers on the use of sound intensity instrumentation. The results illustrate the reproducibility of sound intensity measurements using the scanning method of AHRI Standard 230.

To support purchasing low noise products, sound power and sound energy measurements of sufficient quality need to be routinely made by consumers on a global scale. Sound power measurements using ISO 3744, 3745, and 3746 are conducted in a free field using an acoustic far-field approximation of the intensity integrated over an enveloping measurement surface. Sound power and sound energy measurements generally use a hemispherical, parallelepiped, or cylindrical measurement surface. Those measurement surfaces have limitations and assume that the measurement points lie on the measurement surface often in preferred positions. An alternative approach is to choose microphone positions that optimally satisfy the assumptions of the measurement. The measurement surface should then be fit to the chosen microphone positions. Regression methodologies are available for fitting ellipsoids. The number of microphone positions can be as few as three to fit an ellipsoid. An ellipsoidal measurement surfaces can abut zero, one, two, or three orthogonal reflecting planes. Correction equations for the microphone locations and the angle errors for the microphone orientation and wave propagation direction are shown. This paper will present simulations of sound power, sound energy, and corrections for environmental reflections for ISO 3745 and other measurement surfaces.

This study considers the acoustic emission from a DJi Phantom 4 commercial drone using different rotor blades. Measurements were taken from a hovering drone with four commercial product blade configurations. Measurements were taken in accordance with (BS) EN ISO 3745: 2009 'Acoustics - Determination of sound power levels and sound energy levels of noise sources using sound pressure - Precision methods for anechoic rooms and hemi-anechoic rooms'. The aim of the project was to consider the sound characteristics emitted, specifically tonality and to determine the distance a drone could be heard from, with the different blade configurations, in a rural setting. By considering the different blade configurations within a rural setting, the role drones have within society is considered.

The utilisation of biodiesel nowadays has become familiar with rapid production types of biodiesel in order to replace the dependency on the fossil fuel parallel to the implementation of green technology that emphasises the products to be more environmental-friendly. Nevertheless, the emerges of various kinds of biodiesel cannot be simply used, despite using the biodiesel does not need any major modification on the engine; it still needs a few analyses that must be done to determine whether it will give advantages or disadvantages. Therefore, this research was carried out to investigate the effect of using palm oil methyl ester (POME) biodiesel on the engine in terms of noise emission. The sound intensity mapping method was used to indicate the effectiveness of the biodiesel by identifying the noise radiation. Along with the mapping, the sound power level (SPL) is also being obtained to provide a clear comparison between the parameters. Generally, switching up the engine speed and load increased the sound power level. Based on the results obtained related to the SPL, the intensity mapping tends to show a higher colour-coded in the noise source image for the higher engine speed and load setup. It was found that the engine speed and load give a significant contribution to noise emission produced by the engine, and it can be inferred that this method can be utilised to accomplish the noise emission analysis.

In this paper, we propose a novel porous metamaterial structure with an improved acoustic energy absorption performance at high-temperature and in the low-frequency range. In the proposed novel porous metamaterial structure, a porous material matrix containing periodically perforated cylindrical holes arranged in a triangular lattice pattern is applied, and additional interlayers of another porous material are introduced around these perforations. The theoretical model is established by adopting the double porosity theory for the interlayer and the cylindrical hole which form an equivalent inclusion and then applying the homogenization method to the porous metamaterial structure formed by the equivalent inclusion and the porous matrix. The temperature-dependent air and material parameters are considered in the extended theoretical model, which is validated by the finite element results obtained by COMSOL Multiphysics. The acoustic or sound energy absorption performance can be improved remarkably at very low frequencies and high temperature. Furthermore, the underlying acoustic energy absorption mechanism inside the unit-cell is investigated by analyzing the distribution of the time-averaged acoustic power dissipation density and the energy dissipation ratio of each constituent porous material. The results reveal that regardless of the temperature, the acoustic energy is mostly dissipated in the porous material with a lower airflow resistivity, while the acoustic energy dissipated in the porous material with a higher airflow resistivity also becomes considerable in the high-frequency range. The novel porous metamaterial structure proposed in this paper can be efficiently utilized to improve the acoustic energy absorption performance at high temperature.

This work is devoted to the description of a new design solution for the gas distribution mechanism of a reciprocating compressor. The study of the factors that have a significant effect on the vibration and noise performance of hermetic refrigerant compressors allows the authors to conclude that the world leaders in the cost and sales of compressors are manufacturers whose products have a sound power level in the range of 32-36 dBA. The authors propose a new design solution for a unified valve plate for use in a parametric range of hermetic piston refrigerant compressors of the SKO series. The proposed valve train contains a 1.015 mm thick composite valve plate containing five 0.203-mm Sandvik 20-C valve steel plates that are bonded with anaerobic adhesives. Laboratory studies revealed the advantages of S-KO compressors in terms of the average sound power level at 4.8-5.54 dBA; supply coefficient (refrigeration coefficient) decreased by 27.4 ÷ 14.4%. Such results were achieved due to the use of anaerobic adhesives, which made it possible, instead of a machined valve plate, to use a composite 1.015 mm thick and provide a stronger contact between the surfaces of the plates.

This work proposes a novel two-dimensional (2D) graded core with anti-tetrachiral cells and evaluates the numerical vibroacoustic response of sandwich panels with these particular cores. First, a homogenization scheme is utilized to model the sandwich structure, followed by a modal analysis of the homogenized model in the frequency range of 0–200 Hz. The results have been compared with those obtained from an exact and full-scale finite element model of the sandwich structure. A general good agreement has been observed for the first six natural frequencies. Next, the radiated sound power level in the frequency band of 0–200 Hz is calculated and minimized for different geometry parameters of the sandwich structure. A hybrid design optimization approach using method of moving asymptotes and genetic algorithm is used. The optimized 2D gradient configurations show a significant 78% reduction of the normalized radiated sound power level and a 15% increase of the fundamental frequency, compared to the baseline sandwich panel configurations.

The characteristics of an acoustooptic (AO) Bragg cell of two-color radiation as a differential spatial-frequency filter, in which the first diffraction order is the working one, have been investigated. It is shown that in a general case, it is impossible to provide two-dimensional image differentiation simultaneously at two wavelengths. A regime has been found that allows one to change from one wavelength to another with preservation of the two-dimensional differentiation operation by adjusting the sound power. This variant has been confirmed experimentally by the formation of a two-dimensional contour using two-color radiation of an Ar laser at wavelengths of 0.488 × 10–4 and 0.514 × 10–4 cm, as well as a TeO2 AO cell that operates at a sound frequency of 51 MHz.

This study investigates source-related noise characteristics of the Falcon 9, a modern launch vehicle with a high operational tempo. Empirical prediction of the noise characteristics of launched rockets has long been a topic of study; however, there are relatively few comparisons with high-fidelity, far-field data, and historical inconsistencies persist. Various quantities are considered: overall directivity, overall sound power, maximum overall sound pressure level (OASPL), and peak frequency. The noise directivity of the Falcon 9 vehicle is shown to be between two disparate ranges given in the historical literature, but the observed peak directivity angle is well represented using convective Mach number concepts. A comparison between mechanical and acoustic power yields a radiation efficiency is consistent with the literature. Two independent methods of predicting maximum OASPL produce results accurate within 2 dB, even at distances of several kilometers. Various scaling parameters are calculated for observed spectral peak frequency and connect these measurements with prior observations. Finally, the impact of terrain shielding on levels and spectra is assessed. These determined source characteristics of the Falcon 9 vehicle provide a connection to prior launch vehicle acoustics studies, which helps identify useful models and methods for understanding rocket noise.

In order to determine the effect of the divergent nozzle length on the single-hose nozzle geometry, the computational couple simulation approach was employed. Furthermore, a model was successfully provided for the two-way exchange of mass, momentum, and energy between two phases. The energy that was exchanged between two involved phases, the solid dry ice particle and a working medium of compressible air-fluid, was also obtained. The model was then coupled with the acoustic programming code solved using the Mump solver. The result revealed that the most extended divergent length showed the highest flow velocity across the nozzle cavity and induced the lowest turbulence flow. Thus, the acoustic sound pressure level was reduced. The shortest divergent nozzle length, equal to 200 mm, produced the highest sound pressure level equal to 85 dBA within the frequency range of 1000 to 1200 Hz. It also produced an average maximum of sound power level, which is 100 dB, across all frequency ranges. Therefore, this study is highly essential since the characteristics of the gas-particle flow within a nozzle cavity provide a deeper understanding of the multiphase flow in turbine and jet engine flow analysis.

In the present study, a novel hybrid method was considered to identify and measure inertial cavitation activity using acoustic and optical emissions from violent bubble collapses. A photomultiplier (PMT) tube and a calibrated cylindrical needle hydrophone were used to simultaneously detect sonochemical luminescence (SCL) signals and acoustic emissions, respectively, during sonication. A cylindrical focusing ultrasound transducer operating at 398.4 kHz was employed to produce a dense cavitation bubble cloud at the focus. The results clearly showed that a similar trend between the PMT output (i.e., the SCL results) and the broad band acoustic emissions started to appear at the frequencies considered above the fourth harmonic of the sonication frequency. The experimental observation suggests that the occurrence of inertial cavitation can be monitored using the high pass spectral acoustic power and the cut-off frequency can be effectively chosen with the aid of sonochemical luminescence measurement. The hybrid method is expected to be useful for cavitation dosimetry in various medical and industrial applications.

Sound radiation from thin metal plates has consistently been recognized as a severe noise problem. One of the most popular approaches to suppressing this noise is applying viscoelastic layers, also called free layer damping (FLD), on the plate surface, which can damp the structural motion and minimize the radiated sound. The thickness of the FLD is an important parameter. It needs to be optimized for the target acoustic limits through numerical simulations, as the total mass and the costs may rise unnecessarily. This paper investigates the sound radiation from thin metals of particular sizes with different thickness values of FLD. A unique test setup was established to measure vibration and sound for three different sized plates, with each one having three different FLD thicknesses, namely, 0.5 mm, 0.75 mm, and 1 mm. In parallel, vibro-acoustic analyses were performed for the same configurations using the finite element method. The damping of the FLD was defined using the Rayleigh damping model, of which coefficients were obtained through a prediction formula developed earlier by the authors. After validating the model with the test, the effect of FLD on the extended acoustic parameters (radiated sound power, directivity) was also analyzed.

According to studies by Airbus, one of the biggest concerns among the public regarding drones is the noise they produce. ICAO have also stated that when drones are flown “low and in great numbers” they will cause a significant level of noise. To date there is literature around the public’s perception of drone usage and noise, however there is currently no recommended software package for modelling drone noise. There has also been little work done into the level of noise that is likely to be emitted by drones used in the commercial market for tasks such as parcel delivery. This research aimed to investigate the noise emitted by drones and determine suitable operating conditions and flight paths to mitigate this noise. The research also aimed to investigate the suitability of the software package ‘iNoise’ for modelling noise emission by drones. The results showed noise emission can be mitigated by maintaining high altitudes and high speeds, as well as vertical take offs and landings. Although many of the noise levels recorded in this research for different flight conditions and flow numbers were lower than the maximum recommended LDEN for road traffic noise, they did approach this value at low speeds. As the sound power level used in this project came from a small quadcopter, it is reasonable to assume larger, commercial drones will have a higher sound power level, thus increasing the need for noise mitigation measures. The research also demonstrated the suitability of iNoise for modelling noise emissions caused by drone activity.

Aiming at the reduction of low-frequency noise for large equipment, a damping optimization method based on the Operational Mode Analysis (OMA) is proposed. Due to the stability of the mode frequencies and shapes, damping application could make efficient noise reduction without bringing new problems compared with structural optimizations, which makes it one of the most important means for finalized products. Taking the engine compartment of an excavator as the study object, a damping optimization method based on the OMA test is proposed in this article, which makes a more efficient optimization for large equipment by its feasible modal test. Through simulation and experimental verification, the method is effective. The test results show that based on the OMA damping application method, the low-frequency sound power level has been significantly reduced, and after the damping application, the sound radiation power level defined by the national standard has also been reduced.

Abstract This article investigates the radiated sound power from idealized propeller noise sources, characterized by elemental monopole and dipole acoustic sources near the sea surface. The free surface of the sea is modeled as a pressure-release surface. The ratio of sound power of the near surface sources to the sound power from the same sources in an unbounded fluid is presented as a function of source immersion relative to sound wavelength. We herein show that the sound power radiated by submerged monopole and horizontal dipole sources is greatly reduced by the effect of the free surface at typical blade passing frequencies. By contrast, the sound power from a submerged vertical dipole is doubled. A transition frequency for the submerged monopole and horizontal dipole is identified. Above this transition frequency, the radiated power is not significantly influenced by the sea surface. Directivity patterns for the acoustic sources are also presented. Introduction The principal sources contributing to underwater radiated noise (URN) over a wide frequency range are propellers and onboard machinery (Urick 1983; Ross 1987; Collier 1997; Carlton 2007). Propeller sources are highly complex, but simplification is possible at low frequencies where the wavelength of underwater sound is much larger than propeller dimensions. The propeller may then be regarded as a set of fluctuating forces at the propeller hub and a stationary monopole source that represents the growth and collapse of a cavitation region as each blade passes through the region of wake deficit. This type of model was used by Kinns and Bloor (2004) to examine the net fluctuating forces on a cruise ship hull due to defined propeller sources. The nature of the monopole source was considered by Gray and Greeley (1980), who focused on singlescrew merchant ships where cavitation is dominant at operational speeds. Nonuniformity in the wake, as well as static pressure that falls toward the sea surface, causes this monopole source to be located near top dead center, closer to the surface than the propeller hub. It introduces cyclic components at multiples of propeller blade passing frequency (bpf) as well as broadband noise over a wide frequency range. These components create a pressure field that acts on nearby hull surfaces, but the URN is controlled by the presence of the pressure release surface that corresponds to the free surface of the sea. The aim of this article was to investigate how idealized propeller noise sources are influenced by the surface of the sea.

The cascade’s response function can be used to effectively deal with the unsteady response of the interaction between the harmonic turbulence and the cascades. Based on this function, this paper presents the formulas for the stator broadband and tonal noises, whose inflow models are different from each other. The broadband noise comes from the impact of the random turbulence wave in the rotor wake on the stator, while the tonal noise comes from the interaction between the periodic rotor wake and the stator. According to the formulas for predicating the two kinds of noise, their inflow models are different from each other. Comparing with the test models of subsonic fan, the prediction models of the broadband and tonal noise prove to be correct. Meanwhile, the influence of the blade number on stator tonal and broadband noise is carried out through the prediction models, and the results are summarized that (1) the greater the number of blades, the higher the broadband sound power level of the stator in the high frequency. (2) An increase in the number of blades can “cut off” the tonal noise of the stator at BPF. So, reasonable arrangement of the number of stator and rotor blades is significant to the passive suppression of stator noise.

To capture sound emissions of industrial machines (e.g., heat pumps) that are resolved in terms of frequency, time and space, an acoustic dome geometry with up to 64 microphones is used. Exact coordinates of all microphones are needed to ensure reproducibility of measurements as foundation for other algorithms (e.g., sound power level analysis) and for visualization purposes (plots and augmented reality applications). As the coordinates are difficult and imprecise to produce by hand, an acoustic solution independent of hardware and software using multilateration and Time Difference of Arrival is being developed to automatically and efficiently determine their position. The calculation procedure starts with playing predetermined audio samples (based on a sequence of non-repeatable numbers) on speakers with known coordinates and recording the microphone data. By cross-correlating the sent data with the recorded data, it is possible to extract the signal travel times. These propagation times, the precisely known coordinates of the speakers and the temperature-dependent speed of sound are used as input for the multilateration algorithm, which returns the coordinates of the microphones. Within the accuracy required for the application, the system works for measurements in line of sight. Performance degrades in settings with too many multipath effects (reflection and diffraction), which may cause unrecoverable loss of information. Several validation measurements and simulations were conducted. Various error sources with possible fixes are identified and discussed.

Transcranial high-intensity focused ultrasound is used in clinics for treating essential tremor (ET) and proposed for many other brain disorders. This promising treatment modality requires high energy resulting eventually in undesired cavitation and potential side effects. The goals of the present work were: 1) to evaluate the potential increase of the cavitation threshold using pseudorandom gated sonications and 2) to assess the heating capabilities with such sonications. The experiments were performed with the transcranial magnetic resonance (MR)-compatible ExAblate Neuro system (InSightec, Haifa, Israel) operating at a frequency of 670 kHz, either in continuous wave (CW) or with pseudorandom gated sonications of 50% duty cycle. Cavitation activity with the two types of sonications was compared using chemical dosimetry of hydroxyl radical production at the focus of the transducer, after propagation in water or through a human skull. Heating trials were performed in a hydrogel tissue-mimicking material embedded in a human skull to mimic a clinical situation. The temperature was measured by MR-thermometry when focusing at the geometrical focus and steering off focus up to 15 mm. Compared with CW sonications, the use of gated sonication did not affect the efficiency (60%) nor the steering abilities of the transducer. After propagation through a human skull, gated sonication required a higher pressure level (10 MPa) to initiate cavitation as compared with CW (5.8 MPa). Moreover, at equivalent acoustic power above the cavitation threshold, the level of cavitation activity initiated with gated sonications was much lower with gated sonication than with continuous sonications, almost half after propagation through water and one-third after propagation through a skull. This lowered cavitation activity may be attributed to a breaking of the dynamic of the bubbles moving from monochromatic to more broadband sonications and to the removal of residual cavitation nuclei between pulses with gated sonications. The heating capability was not affected by the gated sonications, and similar temperature increases were reached at focus with both types of sonications when sonicating at equivalent acoustic power, both in water or after propagation through a human skull (+15 °C at 325 W for 10 s). These data, acquired with a clinical system, suggest that gated sonication could be an alternative to continuous sonications when cavitation onset is an issue.

Stirling / pulse tube hybrid refrigerator (SPR) has attractive prospects due to its high reliability, high efficiency and compactness around 30 K. As the typical characteristics of the SPR, the inter-stage cooling capacity allocation characteristics allows the refrigerator to shift cooling capacity of both stages by adjusting the movement of the displacer, which enables the SPR to meet the demand of time-varying heat loads at different cooling temperatures and makes it a competitive choice in complicated space applications. In this paper, a SPR designed by our lab is adopted to study the typical characteristics. A one-dimensional thermoacoustics-based numerical model is adopted to optimize the structure parameters and the operating parameters. The cooling capacities, relative Carnot efficiencies at different displacer phases are given. The axial distributions of gas temperature and wall temperature in SPR are drawn. In addition, axial distributions of pressure amplitude, phase difference between volume flow and pressure wave and acoustic power are presented and compared. Experimental results operating at different mean pressures and frequencies are given. Compared the experimental results with the corresponding simulation results, a good consistency is revealed. The experimental results show that the SPR can obtain cooling capacities of 8.8 W at 80 K plus 0.81 W at 30 K with an input electric power of 245 W, which indicates an overall relative Carnot efficiency of 12.85%.

While studies of urban acoustics are typically restricted to the audio range, anthropogenic activity also generates infrasound (

The aerodynamic noise emitted by a subsonic flow of dry air through an orifice plate is estimated in terms of internal sound power level and external sound pressure level (SPL) by application of the methodology described in the international standard IEC 60534-8-3. A shortcoming of the standard in defining the efficiency of the transformation of the mechanical energy of the flow into acoustic energy is discussed. Experimental evidence of the matter is also described. An alternative model employing the resolution of Reynolds Averaged Navier-Stokes equations (RANS) by means of Computational Fluid Dynamics (CFD) techniques for the calculation of the acoustic power generated by the turbulent flow through the orifice plate is applied so as to overcome the issue.

Based on judging the different stages of cavitation through high-speed photography experiments, this paper presents a strategy for analyzing the variation in noise under different cavitation stages using the BEM method and Proudman theory. A multi-field synchronous test bench for marine pump hydraulic performance, flow noise, cavitation performance and cavity distribution is built. The critical cavitation numbers in different cavitation stages were determined by combining the cavitation performance curve and the morphology of the cavitation in high-speed photography. The research shows that with the development of cavitation, the rotor–stator interaction-induced noise is no longer the main noise source. The bubble will gradually block the flow passage and play a role in absorbing sound to reduce the area of the high sound power region. The sound pressure level of the blade passing frequency and its harmonic frequency gradually decreases. Under the action of the fan sound source, the drop in the 2BPF is the most obvious, and the maximum drop is 10%. The sound pressure level at the shaft frequency and the broadband total sound pressure level above 1000 Hz gradually increase, reach the maximum value under the developed cavitation stage. Cavitation-induced noise is broadband noise and its energy is concentrated in high frequencies.

The harmful factors in the woodworking industry include the increased noise level in the workplace. This is especially true when working with multi-spindle drilling woodworking machines. The main sources of noise include the constant speed of drills, the geometric shape of the motor and the body of the cutting units, as well as the pneumatic feed mechanism of the cutting units or workpieces. The article presents a theoretical justification of noise sources, which allowed us to obtain the equation of sound power of noise sources in general form. The acoustic calculation of the main noise sources was performed using the obtained formulas. The obtained acoustic models of the main noise sources showed that the practical calculation of sound pressure levels or sound power is actually reduced to determining the vibration rates on the natural vibration forms of the sources.

The influence of acoustic radiation is considered in the prediction of noise attenuation effect of sound barrier, which provides a theoretical reference for further improving the insertion loss of sound barrier. Based on the theory of thin plate vibration, the vibration mode and natural frequencies of sound barrier under arbitrary boundary conditions are established by using two-dimensional beam function method, and the forced vibration response of the sound barrier is calculated based on the modal superposition method. MATLAB software (MathWorks Company, Natick, Massachusetts, USA) is used to calculate the natural frequencies and the radiated sound power level of the sound barrier, which indicated that the sound radiation caused by external excitation would significantly increase the sound pressure level at the received point, which should be considered as one of the influencing factors in the prediction of noise attenuation effect. The influence of diverse structural parameters on the radiated acoustic power is compared, providing an excellent reference for the design of sound barrier with low noise.

In musical instruments, the geometric design and material features of the instrument are the most important factors that determine the sound characteristics of the instrument. Traditional replication and experiment-based handcrafting methods are predominant in the production of Turkish Folk Music wind instruments. The instrument manufacturing and standardization approaches, which include the relevant rules of physics and engineering practices, are limited purely to prototype studies for scientific research purposes. It is almost impossible to find studies on Turkish Folk Music wind instrument design and production involving computer aided design and engineering applications. In this study, an example Turkish woodwind instrument, the Turkish Treble Recorder (dilli kaval) is considered, and the air flow behaviour and acoustic (sound) power magnitudes that occur at different air flow rates are simulated in a computer environment using a Computational Fluid Dynamics (CFD) simulation technique. In the study, numerical and visual outputs related to air behaviour at different air flow rates that may be used in the instrument manufacturing phases were obtained. Acoustic power level was also measured experimentally. Simulation outputs (the acoustic power level) were compared to experimental results in order to validate the simulation results. The comparison revealed that the highest relative difference was calculated as 13.32(%). This value indicated that the simulation results were reasonably consistent with the results of the experimental measurement. Additionally, this study was constructed as a case study that may provide reference for future research studies in this field.

An optimal filter design method for a virtual mechanical impedance (VMI) control system is presented in this report. Existing passive methods for reducing machinery noise have limited applications because of weight reduction, cooling, and appearance problems. The VMI control method, which does not require a sensor and can be implemented using a small number of actuators, is an active approach that can be used to replace passive methods when mechanical tuning is difficult. However, VMI control methods can only reduce single-tone noise. In this regard, we improved the VMI control system to reduce the radiated sound power of the enclosure panel at multiple frequencies. To achieve this, we propose an optimal filter design method for a multichannel feedback controller. Unlike conventional VMI control, the presented technique is capable of multifrequency control and considers the radiation efficiency, damping, and estimates the errors of the structural-acoustic system. The controller designed using the proposed method satisfies the required robustness and minimum steady-state error in the target frequency band. Thus, this filter design method facilitates the quantitative determination of several criteria that are needed to evaluate system parameter changes such as radiation efficiency, damping, and estimation error, which are overlooked in a standard active structural acoustic controller. The results obtained using a finite element-based model and experimental investigations show that the radiated sound power of the enclosure panel is reduced at multiple target frequencies after the implementation of control.

During the COVID-19 outbreak, the auscultation of heart and lung sounds has played an important role in the comprehensive diagnosis and real-time monitoring of confirmed cases. With clinicians wearing protective clothing in isolation wards, a potato chip tube stethoscope, which is a secure and flexible substitute for a conventional stethoscope, has been used by Chinese medical workers in the first-line treatment of COVID-19. In this study, an optimal design for this simple cylindrical stethoscope is proposed based on the fundamental theory of acoustic waveguides. Analyses of the cutoff frequency, sound power transmission coefficient, and sound wave propagation in the uniform lossless tube provide theoretical guidance for selecting the geometric parameters for this simple cylindrical stethoscope. A basic investigation into the auscultatory performances of the original tube and the optimal tube with proposed dimensions was conducted both in a semi-anechoic chamber and in a quiet laboratory. Both experimental results and front-line doctors' clinical feedback endorse the proposed theoretical optimization.

This paper presents a method for decreasing sound radiation from vibrating plates. The method uses Functionally Graded Materials (FGM) for building the plates instead of isotropic material. The graded pattern of material composition is characterized within the in-plane directions based on a two-dimensional trigonometric law. In the proposed method, the finite element method (FEM) is utilized for estimating the dynamic response of the plates. Then, the Lumped Parameter Model (LPM) is used for calculating sound radiation power. A genetic algorithm is applied as an optimization tool for determining the best distribution of the FGM. The efficacy of the proposed method is demonstrated by three design problems; minimizing the radiated sound from vibrating FGM plate at a particular excitation frequency, over a frequency band, and at a particular natural frequency. The design problems show that a considerable decrease of sound power can be accomplished with the optimal design of FGM plates in comparison with the isotropic plates.

This article presents the modelling of vibroacoustic characteristics, vibration rates of transport vehicle bodies during abrasive processing of welds. Welding is one of the most comprehensive technologies for joining metal structures. However, one of the mandatory steps after welding is the mechanical processing of welded joints. To control the vibroacoustic characteristics, reduce the noise and vibration, energy balance equations are obtained for the conditions of the abrasive treatment of welds in the body of an electric locomotive. The energy flows and sound power emitted by each element of the body structures are determined during the abrasive treatment of welds. Theoretical and experimental assessment of noise and vibration levels during the abrasive processing of welded joints of plate structures is carried out. It is shown that in the frequency range from 0.25 kHz and higher, the sound power exceeds the maximum permissible values.

Research has shown that using acoustic radiation modes combined with surface velocity measurements provide an accurate method of measuring the radiated sound power from vibrating plates. This paper investigates the extension of this method to acoustically radiating cylindrical structures. The mathematical formulations of the radiation resistance matrix and the accompanying acoustic radiation modes of a baffled cylinder are developed. Computational sound power calculations using the vibration-based radiation mode (VBRM) method and the boundary element method are then compared and shown to have good agreement. Experimental surface velocity measurements of a cylinder are taken using a scanning laser Doppler vibrometer and the VBRM method is used to calculate sound power. The results are compared to sound power measurements taken using ISO 3741.

The study focusses on two major aspects: measurement methodology and uncertainty in the realization and dissemination of unit watt in airborne sound and consideration in legal sound regulations for various noise sources. Although sound power level is the fundamental unit invariant of distance from the source, yet there is no direct method for its measurement. An National Metrology Institute (NMI) perspective for the realization, dissemination and application of acoustical quantities: sound pressure and sound power level for strengthening the measurement traceability chain in India and formulation of legal noise limits and regulations of various noise sources is described. The low frequency limitations may yield different results using different methods, which thus necessitates the use of a harmonized approach in realizing the sound power parameter for improving the traceability for the unit watt in airborne sound. The use of sound power level and sound pressure level for noise labeling of appliances and other noise sources in India is recommended.