Noise Control Design Research Articles

Expectations of Mothers with Infants in The Neonatal Intensive Care Unit for Healing Care Processes: A Qualitative Study

Purpose: The study aimed to describe the expectations of mothers whose infants were hospitalized in the neonatal intensive care unit regarding the healing care environment. Material and Methods: This is a descriptive qualitative study. The study was conducted with mothers whose infants were hospitalized in the neonatal intensive care unit of a private hospital. Data were collected between October and November 2022 by using a purposive sampling method. Semi-structured interviews were conducted with 11 mothers. Data were collected with semi-structured interviews. All interviews were recorded via an audio recorder and transcribed verbatim. The inductive thematic analysis method was used to analyze the data. Results: Three main categories and seven sub-themes emerged from the analysis: “humanistic healing care behaviors, healing physical environment and supports”. Watson's Theory of Human Caring was based on the themes related to mothers' expectations from healing care processes. Conclusion: It has been determined that mothers need humanistic healing behaviors within the healing care processes. At the same time, it has been reported that the design of neonatal intensive care units and noise control are important for the healing environment. It is thought that it will contribute to the institutions in providing a healing care environment.

Measuring the radiation of sound sources with the radiation mode method: Towards realistic problems.

The measurement of the pressure field radiated by a sound source has many applications in the fields of noise control and loudspeaker system design. In this paper, the radiation mode method is used to measure the field radiated by a complex acoustic source whose surface impedance is arbitrary and does not correspond to the Neumann boundary condition used for the calculation of radiation modes. The most effective radiation modes are used as test functions to calculate a pressure expansion around the source under test, an expansion that matches the measured pressure at a limited number of points close to the source. This expansion is then used to calculate the radiated pressure at a greater distance at unmeasured locations. In a first step, numerical simulations are performed to evaluate the method's most influential parameters. Then, measurements are performed in a semi-anechoic room on two real sources of increasing complexity. Obtained results show that the radiation mode method allows an accurate evaluation of the pressure field radiated by the test object over a fairly wide frequency band (between 100 Hz and 2 kHz) even for complex sources.

Identifying noise control strategies for variable air volume (VAV) boxes in acute care hospital design

Variable air volume boxes are frequently used within new acute care hospital design of heating, ventilation and air conditioning systems in Canada. Spatial and room-use noise limits as defined within the project requirements [PM1] are often necessarily onerous to provide acoustical conditions that promote well-being and patient recovery, with appropriate noise control design crucial to the success of meeting the project requirements. Additionally, the desire for fiber-free linings to ductwork exacerbates the noise control limitations. This paper will review the available noise control strategies, the acoustic performance of fiber-free variable air volume box types with and without an attenuator and identify cost-benefits to the Design-Builder. This study will demonstrate how the implementation of a variety of variable air volume box models, sizes, operating conditions, pressure drops are affecting the noise performance. This study will summarize the appropriate variable air volume box types and design conditions that meet the project noise limits used in Canadian healthcare standards such as CSA Z8000, LEED and other provincial technical guidelines.

Considerations for noise control design in retrofit Combined Heat and Power Plants for Healthcare Facilities

Combined Heat and Power (CHP) plants have gained popularity in industrial and institutional applications due to their ability to recapture and repurpose wasted heat energy from the power generation process, resulting in significant energy savings and carbon emission reductions. However, noise control considerations have become increasingly critical in retrofit CHP systems, particularly in healthcare facilities. Often, strict noise performance requirements must be met due to the proximity of residential communities and to ensure a comfortable healing environment for patients.This technical paper explores critical noise control considerations for retrofit CHP systems in healthcare facilities, focusing on a case study from Hamilton Health Sciences, a healthcare network in Ontario, Canada. The paper examines the design challenges of upgrading the existing CHP plants across three separate hospitals when addressing stringent sound performance, system ventilation, air tempering, and structural capacity limitations within a limited space. The paper also discusses the unique sound attenuation design solutions implemented to address these challenges.The case study demonstrates the successful implementation of combining noise control design, ventilation design, and structural design into one integrated solution, specifically to overcome common design challenges in retrofit CHP systems.

Case study of HVAC noise in a conference room under varying operating conditions

Conference rooms are acoustically sensitive environments due to the need for high speech intelligibility both in-person and over teleconferencing systems. Room noise from building systems is a key contributing factor to speech intelligibility. Mechanical design, and in turn noise control design, focuses on peak heating and cooling demand; however, operating conditions vary based on the demand at any given time. This case study presents sound pressure level measurements from a conference room on the top floor of an office building, which was below a mechanical penthouse. The measurements were guided by ANSI/ASA S12.2, "Criteria for Evaluating Room Noise." Commissioning and developer agents varied the operating conditions of the entire building heating and cooling system to identify the primary contributors to room noise levels in the conference room, which varied as much as 13 dBA over background. Particular attention is given to the correlation between room noise levels and airflow from the air terminal unit serving the space. Comparisons between measured noise levels and noise modeling predictions are also provided.

Ultrabroadband sound control with deep-subwavelength plasmacoustic metalayers

Controlling audible sound requires inherently broadband and subwavelength acoustic solutions, which are to date, crucially missing. This includes current noise absorption methods, such as porous materials or acoustic resonators, which are typically inefficient below 1 kHz, or fundamentally narrowband. Here, we solve this vexing issue by introducing the concept of plasmacoustic metalayers. We demonstrate that the dynamics of small layers of air plasma can be controlled to interact with sound in an ultrabroadband way and over deep-subwavelength distances. Exploiting the unique physics of plasmacoustic metalayers, we experimentally demonstrate perfect sound absorption and tunable acoustic reflection over two frequency decades, from several Hz to the kHz range, with transparent plasma layers of thicknesses down to λ/1000. Such bandwidth and compactness are required in a variety of applications, including noise control, audio-engineering, room acoustics, imaging and metamaterial design.

Acoustic behaviour of CLT structures: influence of decoupling bearing stripes, floor assembly and connectors under storey-like loads

Timber buildings do not have a high acoustic performance regarding vibration transmission through the structure. Sophisticated acoustic design methods are usually not applied and noise control design for wooden buildings is often merely based on the experience of engineers. To find out the peculiarity of timber transmission, an acoustic lab test with CLT was set up. Several measurement configurations were built and airborne sound measurements according to EN ISO 16283-1 and impact sound measurements according to EN ISO 16283-2 were carried out. The test results were set in relation to reference measurements on the bare CLT slab and on a floor assembly, with and without decoupling bearing stripes and with and without connectors. In addition to the standard sound measurements, the sound transmissions through the ceiling element and through the flank components (walls) were also measured with accelerometers. The results showed in an experimental evaluation method a reduction in sound transmission and standard impact sound level. All tests were carried out with the same load of 17 kN/m on the decoupling bearing stripes and the ceiling element. The load was applied by means of threaded rods and secured by strain gauges. The influence of decoupling bearings stripes, types of fastening systems and floor structures on sound transmission through the flanking components on a real scale mock-up could therefore be investigated.

Numerical simulation of structure-borne noise in a T-shaped tee considering fluid–structure interaction

In order to research the structure-borne noise characteristics of a T-shaped tee considering fluid–structure interaction (FSI), large eddy simulation and the acoustic finite element method were used to simulate the flow field and structure-borne noise related to T-shaped tees under different inlet and outlet combinations. The results show that the frequency domain sound pressure level (SPL) distribution under various inlet flow velocities is stable, the structure-borne noise of the T-shaped tee is a high-frequency noise, and the SPL curves provide a peak distribution. Meanwhile, the distribution characteristics of the structure-borne noise in the frequency domain follow similar trends under different inlet flow velocities. Additionally, the structure-borne noise does not produce the mechanical resonance of the system. When the inlet velocity increases from 1 to 3 m/s, the total sound pressure level (TSPL) increases from 83.71 to 98.18 dB, a relative increase of 17.3%. In addition, the frequency domain distributions of the SPL under various inlet and outlet combinations are basically similar. The TSPL of four inlet and outlet combinations for the structure-borne noise are III, IV, II, and I in descending order. When the inlet flow velocity is 1, 2, and 3 m/s, in the case of combination I, the TSPL of the structure-borne noise decreases by 6.28, 5.59, and 6.39 dB, in contrast to the case of combination III, respectively. This study provides the guidance for the noise control and structural optimization design of a T-shaped tee considering the FSI.

A directional active noise control algorithm based on all-pass/minimum phase decomposition

In this paper, we propose the design of a directional active noise control (ANC) system, which can suppress the noise coming from one specific direction without affecting the noise coming from other directions. The proposed directional ANC system integrates the sound extraction feature of a beamforming system with the active noise canceling feature of an ANC system. Instead of using the signals collected by the reference microphones as the reference signals directly, the directional ANC system uses the signal filtered by carefully designed minimum phase beamforming filters as the new reference signal, in which the noise signal coming from the look-direction of the beamformer is enhanced and at the same time noise signals coming from other directions are suppressed. Usually, the filtered signal of a beamforming system cannot be used as the reference signal of an ANC system because the delays introduced by the beamforming process degrade the performance of the ANC system. To resolve the problem, a spectral factorization technique is introduced and used to extract the minimum phase component of the beamforming filters which decreases the required delays of the beamforming system.

Band Gaps and Vibration Attenuation Characteristics Analysis in Homogeneous Beam Coupled With Periodic Oscillators Based on the Method of Reverberation-Ray Matrix

A periodic beam-oscillators coupling system is proposed as a physical model in this paper for analyzing the dynamic characteristics of periodic support beams and low-frequency flexural wave vibration of slender stiffened plate structures. The dispersion relation of flexural wave in the infinite long homogeneous beam coupled with periodic oscillators is calculated using the method of reverberation-ray matrix combined with the Bloch theorem. The accuracy and effectiveness of the method of reverberation-ray matrix in analyzing the band gaps and vibration characteristics of the homogeneous beam coupled with periodic oscillators are verified by the numerical results of the finite long homogeneous beam coupled with periodic oscillators. Both the analytical and numerical results show the existences of flexural wave band gaps in the homogeneous beam coupled with periodic oscillators, in which the propagation of the flexural waves is prohibited and flexural wave vibration is significantly suppressed. Furthermore, the effects of structural and material parameters on the flexural wave band gaps characteristics are respectively investigated. The flexural wave band gaps can be adjusted and optimized manually by adjusting structural and material parameters, which can be applied to vibration and noise control design of periodic support beams and slender stiffened plate structures.

Constrained optimal filter design for multi-channel active noise control via convex optimization.

In many practical multi-channel active noise control (ANC) applications, various constraints need to be satisfied, such as stability, enhancement, etc. One way to enforce these constraints is to add a regularization term to the Wiener filter formulation, which, by tuning only a single parameter, can over satisfy many constraints and degrade the ANC performance. Another approach for non-adaptive ANC filter design that can produce better ANC performance is to directly solve the constrained optimization problem formulated based on the H2/H∞ control framework. However, such a formulation does not result in a convex optimization problem and its practicality can be limited by the significant computation time required in the solving process. In the presented work, the H2/H∞ formulation is convexified and a global minimum is guaranteed. It is then further reformulated into a cone programming problem which can be solved using specialized algorithms. Results show that the proposed method can produce better noise control performance than the regularization method. Compared with the traditional H2/H∞ formulation, the proposed method is more reliable and the computation time can be reduced by several orders, which, practically, provides a potential to extend its application to adaptive control.

Acoustical Conformance with FGI for Tenant Improvements in Outpatient, Medical Office or Clinic Facility Sound Isolation/Privacy Design

Acoustical privacy and noise control design and implementation guidance is needed, regarding Facility Guidelines Institute (FGI) criteria for outpatient medical facilty tenant improvements (TI). TI in existing commercial buildings or medical office buildings may not have capital budgets or expected facility/lease life that hospitals enjoy. Full conformance to FGI criteria and guidelines may be limited; by economic feasibility and by constructability. Design professionals can use "good practice" space planning, demising assembly selection, and electronic sound masking to achieve appropriate acoustical privacy within reasonable capital expense budgets. Consider FGI criteria for demising partition, ceiling, door and window selections plus infrastructure equipment and material selections that can provide cost-effective lightweight, common construction standards. The objectives are to protect the privacy of patient information and provide quiet spaces, free of transient disturbance for clear speech communications. Continuous ambient sound increases speech privacy including speech transmitted from enclosed quiet spaces. Criteria for acoustics, speech privacy,continuous noise and masking exists in FGI. Temporal level changes (on/off, transients) and tonality (spectrum smoothness or balance) should be considered in basis-of-design (BoD). This paper will present design guidelines for selecting demising assemblies and supplemental sound masking for outpatient clinical spaces in commercial or medical office buildings.

Priorities for occupational noise in Britain

Regulation of occupational exposure to noise in Britain for 50 years has reduced risk. However, statistics from around the globe (and in Britain alone) suggest that the range in harm is between around zero and more than 1 in 4 workers exposed to high noise. The uncertainty in statistics and the potential high incidence and prevalence of harm justifies investigation. In Britain, we will investigate the current risk of occupational hearing loss and the effectiveness of current noise control measures. We propose to gather data during inspections of industries that are known to have high levels of workplace noise. Finding high incidence of hearing damage will indicate a failure of immediate management of risk and likely result in enforcement action. We propose to review employers' control of noise propagation in the workplace through use and maintenance of noise controls supplied with machines and supplemented with acoustic barriers and noise havens. We propose to review suppliers design and build of noise control into their products and their reported noise emissions for noisiest typical use. We are looking to benefit from the experience of our global counterparts before finalising our plans.

A Hybrid and Efficient Low-noise assessment Platform for Urban aerial mobility (HELPU)

Urban aerial mobility (UAM) is a promising approach to improve the traffic situation in gigantic cities, which, however, may encounter significant noise pollution issues. An integrated research platform, which is being established at HKUST, to include noise generation, long-distance propagation, and perception at the observers is timely to assess the environmental impact of UAM noise and to develop low-noise designs and flight planning. A high-quality test rig in the anechoic aerodynamic facility at HKUST is employed to measure the propeller aeroacoustics and aerodynamics, and to enable the innovative noise control device and design studies. The measurements and high-fidelity simulations using an in-house computational aeroacoustics solver can lead to comprehensive databases to facilitate and validate the development of physics-oriented noise prediction models. Also, high-efficient implementation of the boundary element method is conducted to account for the noise scattering due to the fuselage and then to evaluate the impact of UAM layout on the directivity patterns, which will then be efficiently projected to the far-field observers using the advanced Gaussian beam tracing with the effects due to moving source, atmospheric attenuation, and refraction, complex boundary absorption and reflection incorporated. Low-noise flight planning is then be made accordingly.

Optimal parametric design of delayless subband active noise control system based on genetic algorithm optimization

Active noise control systems are generally application-specific, and an appropriate algorithm with an optimal configuration is desirable in the first stage of active noise control system design and deployment. This study presents a design of the subband active noise control system with optimal parameters for a practical broadband active noise control. Although the delayless subband active noise control has gained wide attention for broadband noise cancellation, an optimal design remains a challenge because of the complex interplay between multiple factors such as spectral leakage, delay and weight stacking distortion subject to a number of configurable parameters, and weight stacking method. The configurable parameters can hardly be optimized independently because the active noise control performance depends on the combined configuration. A simple near black box active noise control algorithm optimization model is thus established by incorporating the genetic algorithm optimization into the parametric design of the delayless subband algorithm. The automated process does not require an understanding of the performance characteristics for different parameters. The significance of applying the automated genetic algorithm optimization to the complex multiparameter nonlinear active noise control design is revealed by numerical simulations, particularly for the multichannel low-frequency broadband active noise control system configured with the delayless subband algorithms. This provides a way for the optimal parametric design of subband active noise control before being used in a practical complex scenario.

Noise source identification in indoor substation using a sparse equivalent source method

Noise source identification is a key step in the noise control design of the transformer. The sound propagation is influenced by the reverberation effect in the indoor substation, which leads that the traditional method cannot give correct results in such environment. To supress the reverberation effect, a sparse equivalent source method is proposed to realize the noise source identification in indoor substation. This method first establishes the indoor sound transfer function model between the equivalent source surface and the acquisition surface by using wave simulation. Based on the wave simulation and combined with the sound pressure sampling data, the distributed equivalent source is recovered on the equivalent source surface by sparse recovery algorithm, and finally the sound pressure reconstruction on the reconstruction surface is realized. The numerical verification demonstrates that this method is capable of extracting the real noise information in the reverberation sound and giving the real noise source distribution result. This method can be used as an effective method in the noise source identification in the indoor substation.

Factors influencing low-frequency noise reduction in typical Chinese dwelling layouts

Existing approaches to reducing the low-frequency noise exposure of dwellings are not always sufficient. This study investigated the significance of dwelling layout design for low-frequency noise control. The sound distribution in six typical Chinese dwelling layouts was analysed using in-situ measurements under steady-state noise of various low frequencies. The results showed that among two-bedroom dwelling layouts, the overall average noise reduction varied considerably (6 dB). The noise reduction for room levels (number of rooms sound crosses) 1–2 and 2–3 varies by 5 and 3 dB, respectively, and the noise reduction at door openings varies by 5 dB. A model to approximate the low-frequency noise reduction of a layout was developed using the polyline distance from the noise source and the number of walls the polyline has to cross, which were clearly shown to influence low-frequency noise reduction and seem to be the strongest investigated factors.

Controller design for active noise control of compressor by using the time window POCS technique

To design an active noise controller, the transfer function between the reference signal and the error signal should be measured and defined. When the noise source operates at specific frequencies, the transfer function can only be measured at the operating frequency and its harmonics. This transfer function has reliable values only at the operating frequency and its harmonic frequencies. The frequency domain controller is implemented as an FIR filter, and the coefficients are calculated using the inverse Fourier transform. At this time, the second half part of the coefficient values of the FIR filter is high due to the insufficient frequency resolution and the unreliable transfer function. As a result, the magnitude and phase response of the filter do not follow the design values. To overcome this problem in filter design, the time window projection onto convex sets (POCS) technique is proposed. POCS technique is utilized repeatedly to make the response of the filter to converge by setting the second half part of the filter to 0, and to reassign the response in the control frequency band. The response of the converged filter was verified by comparing it with that of a time-shifting filter and Wiener filter. As a result, the FIR filter designed using POCS showed high performance, regardless of the magnitude of the disturbance and the reference signal.

Experimental Study on the Vibration Characteristics of Oil Tank Model of Oil-Immersed Transformer

The problem of vibration and noise of transformers in urban substations is more and more concerning to society. With a 110kV transformer substation as the research object, the oil tank model of the oil-immersed transformer is designed according to the principle of similitude. Through the modal test of the oil tank model, the vibration characteristics of a 110kV oil-immersed transformer model are obtained, which will help avoid the resonance frequency in the structure design of transformer oil tanks and provide measured data for the vibration and noise control design of transformers. Finally, the finite element model of transformer oil tanks is established, and the vibration characteristics of the oil tank are simulated, and consistent analysis results are obtained.

Sound radiation from plates with elastic boundary conditions embedded in an infinite perforated rigid baffle

Sound radiation from plates with elastic boundary conditions embedded in an infinite perforated rigid baffle (PRB) is analyzed in this paper. Based on the wavenumber domain approach and the solution for transverse vibration of plates with general elastic boundary conditions, the sound power and the radiation efficiency of the plates embedded in the PRB (named ‘PRB-ed plate’ in the following) are derived theoretically. By comparing with the results of sound radiation from baffled and unbaffled plates, it can be found that the PRB-ed plates behave like the dipole source radiation in the fundamental mode region as the perforation in PRB introduces communication of the sound field, while not sufficient to reach the lowest radiation efficiency as unbaffled cases. The parametric analysis of boundary conditions shows that the PRB-ed fully free plate has the lowest radiation efficiency below the critical frequency. For the cases of plates with constraints, the greater the constraints are, the lower the radiation efficiency is in the fundamental mode region, and this order will become totally opposite in the short-circuiting region. Further, the effects of PRB parameters on sound radiation from PRB-ed plates are compared. With the decrease of the PRB thickness and the hole diameter, or the increase of the PRB perforation ratio, the sound power radiated from PRB-ed plates is decreased below the critical frequency. This research could possibly provide ideas on the design of noise control for plate-like structures.