Noise Control Treatments Research Articles

HVAC noise control using natural materials to improve vehicle interior sound quality

Heating, Ventilation and Air Conditioning (HVAC) unit is a major noise source in a vehicle’s interior space. Reducing this noise will improve the sound quality of the vehicle’s interior space and enhance passengers’ experience. However, current noise control techniques are high-cost and hazardous to environment. Therefore, this paper studies the first ever usage of low-cost, biodegradable natural materials for vehicle’s HVAC noise control. Jute felt and waste cotton were found to have higher sound absorption coefficients than other common sound absorbing natural materials, and were chosen as sound absorbers for noise control treatment of a prototype HVAC unit. Noise sources in the unit were identified and ranked, and the treatment was applied to these. The treatment significantly reduced the noise level (by 4 dBA) and loudness level (by 7 sones) due to the unit at the reference passenger’s ear location, with negligible cost and weight. Sound quality evaluation by 24 participants showed that the treatment significantly reduced the annoyance of the vehicle interior soundscape comprising the HVAC noise. Thus, jute felt and waste cotton are low-cost, light-weight, biodegradable and recyclable natural materials with high potential for HVAC noise control.

A hybrid patch transfer-Green functions method to solve transmission loss problems of flat single and double walls with attached sound packages

This paper presents and studies the performance of a sub-structuring method that employs a patch transfer approach (PTF) to couple the standard finite element schemes of the structures and cavities with an analytical model of the sound package. First, the approach is presented followed by a convergence study to define a patch mesh criterion. Then, the accuracy of the proposed methodology is assessed for single and double wall transmission problems with two different attached noise control treatments. The obtained results are systematically compared to three models, namely full finite element/boundary element strategies (FEM/BEM), and to two sub-structuring approaches based on the modeling of the sound package by (i) a locally reacting model and (ii) FEM. It is observed that the proposed method predict accurately and efficiently the dynamic behavior of flat trimmed vibroacoustic systems.

The Effect of Damping Treatment for Noise Control on Offshore Platforms Using Statistical Energy Analysis

The Effect of Damping Treatment for Noise Control on Offshore Platforms Using Statistical Energy Analysis

Efficient prediction of the transmission loss of curved systems with attached noise control treatment

This paper discusses the modeling of the transmission loss of curved panels with attached sound absorbing materials (foam or fiber). Two approaches are compared. The first is a classical coupled FEM/BEM (Finite element/Boundary element) approach wherein the panel and its cavity are modeled using the FEM and the blocked pressure on the excitation side and radiation from the transmission hole are modeled using the BEM. The second is an approximate approach using a Patch Transfer Function (PTF) method to describe the coupling between the panel, the sound package, the cavity and the transmission hole. To compute the PTF relations, the panel and the cavity are described by FEM while the effect of the sound package is described by a Green’s function methodology using the Transfer Matrix Method (TMM) to speed up the process. It is shown that this latter approach is quick and accurate enough to estimate the TL of the system. Moreover, it allows for a quick comparison of the performance of various sound packages f...

Feedforward control of sound transmission using an active acoustic metamaterial

Metamaterials have received significant interest in recent years due to their potential ability to exhibit behaviour not found in naturally occurring materials. This includes the generation of band gaps, which are frequency regions with high levels of wave attenuation. In the context of acoustics, these band gaps can be tuned to occur at low frequencies where the acoustic wavelength is large compared to the material, and where the performance of traditional passive noise control treatments is limited. Therefore, such acoustic metamaterials have been shown to offer a significant performance advantage compared to traditional passive control treatments, however, due to their resonant behaviour, the band gaps tend to occur over a relatively narrow frequency range. A similar long wavelength performance advantage can be achieved using active noise control, but the systems in this case do not rely on resonant behaviour. This paper demonstrates how the performance of an acoustic metamaterial, consisting of an array of Helmholtz resonators, can be significantly enhanced by the integration of an active control mechanism that is facilitated by embedding loudspeakers into the resonators. Crucially, it is then also shown how the active acoustic metamaterial significantly outperforms an equivalent traditional active noise control system. In both cases a broadband feedforward control strategy is employed to minimise the transmitted pressure in a one-dimensional acoustic control problem and a new method of weighting the control effort over a targeted frequency range is described.

Engineering out the noise

The US Navy, through an Office of Naval Research (ONR) lead effort on Noise Induced Hearing Loss (NIHL), is investigating methods and techniques to mitigate hearing loss for the crews and warfighters. Hearing protection is a viable and increasingly popular method of reducing hearing exposure for many ship crew members; however, it has limitations on comfort and low frequency effectiveness. Furthermore, Personal Hearing Protection (PHP) is often used improperly. Proper vessel planning, programmatic changes and advances in noise control engineering can also have significant impacts by inherently reducing noise exposure through ship design and use of noise control treatments. These impacts go beyond hearing loss mitigation since they can improve quality of life onboard vessels and provide enhanced warfighter performance. Such approaches also can be made to work in the lower frequency range where hearing protection is not as effective. This paper describes non-hearing protection methods being implemented to mitigate and control noise within the US Navy and US Marine Corps. These approaches reflect the latest changes to Mil-Std 1474E, Appendix F.

Study on the Acoustical Properties of Natural Jute Material by Theoretical and Experimental Methods for Building Acoustics Applications

Noise control treatment is essential to maintain a quiet and comfortable environment in buildings. In order to control noise, sound absorbing materials play a significant role. Nowadays, natural materials have gained importance in noise control field. In this study, acoustical characterization of a natural material jute is performed using experimental and numerical techniques. Normal incidence sound absorption coefficient and sound transmission loss of building materials using jute are predicted using the transfer matrix method. The theoretical and numerical predictions show a good match with the experimental data in the mid and high-frequency range of interest.

Computational investigation of microperforated materials: End corrections, thermal effects, and fluid-structure interaction

The concept of microperforated noise control treatments was introduced by Maa 1975; in that theory, the transfer impedance of the microperforated layer was calculated based on oscillatory viscous flow within a small cylinder combined with resistive and reactive end corrections. Recently, new manufacturing procedures have dramatically lowered the cost of these materials, and as a result, there has been renewed interest in studying their properties. Since 1975, Maa’s original theory has been widely used. However, in principle, that theory can only be used to describe cylindrical perforation, while in practice, perforations are rarely cylindrical. In addition, there have been questions about the dependence of end corrections on frequency, and on the effect of coupling between the motion of the fluid in the perforations and the solid sheet in which they are formed. Additionally, in his original paper, Maa drew a distinction between the dissipative properties of thermally conducting and adiabatic materials. Th...

Efficient modeling of flat and homogeneous acoustic treatments for vibroacoustic finite element analysis. Direct field formulations

This paper is concerned with the development of a simplified model for noise control treatments to speed up finite element analysis in vibroacoustic applications. The methodology relies on the assumption that the acoustic treatment is flat and homogeneous. Moreover, its finite lateral extent is neglected. This hypothesis is justified by short wavelength and large dissipation, which suggest that the reflected field emanating from the acoustic treatment lateral boundaries does not substantially affect its dynamic response. Under these circumstances, the response of the noise control treatment can be formally obtained by means of convolution integrals involving simple analytical kernels (i.e. Green functions). Such fundamental solutions can be computed efficiently by the transfer matrix method. However, some arbitrariness arises in the formulation of the mathematical model, resulting in different baffling conditions at the two ends of the treatment to be considered. Thus, the paper investigates the possibility of different formulations (i.e. baffling conditions) within the same hybrid finite element-transfer matrix framework, seeking for the best strategy in terms of tradeoff between efficiency and accuracy. Numerical examples are provided to show strengths and limitations of the proposed methodology.

Active noise control of a diesel generator in a luxury yacht

Active noise control has been applied to a variety of systems in order to improve performance without the increases in size and weight that would otherwise be required by traditional passive noise control treatments. This paper investigates the application of an active noise control system to the control of generator noise in the master cabin of a luxury yacht. A multichannel, multi-tonal active noise control system employing loudspeakers and microphones in the master cabin of the yacht is investigated. It is shown that, due to the high number of engine orders produced by the generator, in order to achieve significantly perceptible levels of noise attenuation it is necessary to control at least 7 individual orders. A controller is investigated which targets 19 engine orders and it is shown to achieve in excess of 5dB broadband attenuation, whilst achieving up to 23dB attenuation in individual orders. This corresponds to a 23% reduction in the Zwicker loudness.

The Effect of Damping Treatment for Noise Control on Offshore Platforms Using Statistical Energy Analysis

The Effect of Damping Treatment for Noise Control on Offshore Platforms Using Statistical Energy Analysis

A review of academic research and data related to laboratory testing for sound transmission loss

The building noise control design and manufacturing industry currently relies heavily on laboratory-tested sound transmission loss data for the design and implementation of noise control treatments in buildings. Although most sound transmission loss laboratories achieve acceptable measurement repeatability, the reproducibility of this test data has recently fallen under scrutiny and is currently unknown for common building noise control partition designs. Key academic articles will be discussed that provide a fundamental understanding of how laboratory sound transmission loss measurement procedures and laboratory facilities may affect reproducibility. A review of comparative sound transmission loss data for various laboratories will also be provided in an effort to clearly illustrate why sound transmission loss testing reproducibility has come under scrutiny. It is essential that organizations for standards and design professionals become more aware of these realities.

Theoretical Modelling and Effectiveness Study of Slotted Stand-Off Layer Damping Treatment for Rail Vibration and Noise Control

A promising means of reducing railway noise is to increase the damping of the rail, which decreases the vibration of the rail to reduce noise. To achieve this goal, a slotted stand-off layer damping treatment has been developed, and a compound track model with this treatment is developed for investigating the effectiveness of this treatment in terms of the vibration reduction. Through the dynamic analysis of the track undergoing the slotted stand-off layer damping treatment, some guidelines are proposed on the selection of materials and structure parameters for this treatment. In addition, the prototype of the optimal slotted stand-off layer damping treatment has been built and tested in the laboratory. It is found that the slotted stand-off damping treatment shows significant effects in decreasing the amplitude of the accelerance of the rail and a significant reduction of sound emission reflected as the radiation sound pressure level decreases by 8.2 and 9.4 dB at vertical excitation and lateral excitation, respectively, in the frequency range of 0–4000 Hz.

Noise induced hearing loss mitigation via planning and engineering

The US Navy, through an ONR lead effort, is investigating methods and techniques to mitigate hearing loss for the crews and warfighters. Hearing protection is a viable and increasingly popular method of reducing hearing exposure for many ship crew members; however, it has limitations on comfort and low frequency effectiveness, and is often used improperly. Proper naval vessel planning, programmatic changes, and advances in noise control engineering can also have significant impacts by inherently reducing noise exposure through ship design along with the use of passive noise control treatments. These impacts go beyond hearing loss mitigation since they can improve quality of life onboard vessels and provide enhanced warfighter performance. Such approaches also can be made to work in the lower frequency range where hearing protection is not as effective. This paper describes the programmatic and noise control methods being pursued to mitigate and control noise within the US Navy and US Marine Corps. Methodologies to assess the cost impact are also discussed.

Acoustic and vibration response of a structure with added noise control treatment under various excitations.

The evaluation of the acoustic performance of noise control treatments is of great importance in many engineering applications, e.g., aircraft, automotive, and building acoustics applications. Numerical methods such as finite- and boundary elements allow for the study of complex structures with added noise control treatment. However, these methods are computationally expensive when used for complex structures. At an early stage of the acoustic trim design process, many industries look for simple and easy to use tools that provide sufficient physical insight that can help to formulate design criteria. The paper presents a simple and tractable approach for the acoustic design of noise control treatments. It presents and compares two transfer matrix-based methods to investigate the vibroacoustic behavior of noise control treatments. The first is based on a modal approach, while the second is based on wave-number space decomposition. In addition to the classical rain-on-the-roof and diffuse acoustic field excitations, the paper also addresses turbulent boundary layer and point source (monopole) excitations. Various examples are presented and compared to a finite element calculation to validate the methodology and to confirm its relevance along with its limitations.

Green performance criteria for sustainable ports in Asia

PurposeThe purpose of this paper is to measure a port's green performance. The literature is reviewed and a survey is carried out to identify major green port performance indicators and to evaluate three major ports' overall green performance in Asia. Indicators located in the critical quadrants with a high degree of importance and low degree of performance are identified and resources are suggested that can be employed to improve the ports' overall sustainability performance effectively.Design/methodology/approachPort performance indicators are reviewed to select the green‐related ones by a session of brain storming with academicians from China, Hong Kong, and Taiwan in the shipping discipline. Selected indicators are used to design an analytic hierarchy process (AHP) questionnaire. The weight and degree of performance of each of the 17 green indicators among three major container ports are calculated by the data obtained from the AHP round survey respondents.FindingsAvoiding pollutants during cargo handling and port maintenance, noise control, and sewage treatment were perceived to be the three critical indicators by respondents in two of the three ports investigated. Among the three investigated ports, Shanghai port had the highest number of critical indicators to be improved. Air pollutants avoidance, encouraging the use of low‐sulphur fuel, and using electrically powered equipment were three of the five critical indicators found in Shanghai port, but not in the other two investigated ports in this study.Originality/valueThe theoretical implications of this research are the development of a conceptual framework to measure the degree of importance of a set of green port performance indicators, and to provide a decision support system to help port authorities to evaluate their performance regarding the 17 green port performance indicators compared with that of other ports.

On a simple technique to measure the airborne noise in a car interior using substitution source

From various methods of measuring noise in a motor vehicle, a technique to separate the airborne and structure-borne noise is of interest as an important measure to improve the noise control treatment. This paper proposes a simple technique to measure the contribution of the airborne noise in a vehicle cabin using substitution source method. A cone loudspeaker was used as the substitution source and the airborne transfer function was measured. The technique has successfully separated the airborne transmission with the intersection frequency at roughly 400 Hz with the structure-borne noise. It is found that this is independent of the engine speed.

Transmission loss of curved sandwich-composite panels with attached noise control materials

This paper discusses the modeling of the transmission loss of curved sandwich-composite panels with attached noise control treatments using both analytical and numerical methods. Special attention is devoted to the modeling using the Transfer Matrix Method (TMM) and Statistical Energy Analysis (SEA) of these structures in various mounting conditions (single wall and double wall) under diffuse acoustic field excitation with a systematic comparison with an efficient FEM/VBEM formulation of the problem. Classically, in SEA models the sound package is unwrapped and the TMM is used to calculate its effects in terms of added damping, absorption, and insertion loss. Examples are presented to examine the validity of this practice and demonstrate its range of applicability and usefulness.

Measurement and control of aircraft landing gear broadband noise

Noise generated by aircraft landing gear is a major contributor to the overall airframe noise during landing approach of a commercial aircraft. Fairings covering geometrically complex areas of the gears have proved to be very effective in noise reduction, but in tests on an A340 main landing gear the overall benefits of the fairings were offset by an increase in low-frequency noise. In this study the measurement and control of broadband noise throughout the frequency range have been investigated using a 1/4 scale A340 main landing gear model that has been tested using a range of different measurement methods and wind facilities. Experiments were firstly conducted in a conventional closed-section wind tunnel using two phased microphone arrays mounted on the ceiling and sidewall of the tunnel respectively, and noise control strategies with modified fairings were developed. Noise tests were then performed in an open-jet aeroacoustic facility using far-field microphones to verify the wind-tunnel test results. Comparison between the two tests showed that the relatively smaller noise-reduction potential of the fairings measured in wind tunnel was due to the higher flow blockage of the tunnel. Nevertheless, the experiments indicated that the phased microphone arrays could be applied to measure the noise reductions achieved by noise control treatments with reasonable accuracy, especially in mid- and high-frequency range. The aeroacoustic facility test results were finally projected to full scale and compared to the full-scale model wind-tunnel test. Both results were shown to agree over a wide frequency range, indicating the validity of the tests on the 1/4 scale model.

A review of noise control methods for composite structures.

Composite materials and structures offer great promise to all air vehicles and are being increasingly considered for lightweight advanced applications. However, composite structures are efficient radiators of noise mainly due to excitation and propagation of supersonic bending and/or shear waves in the structures. Composite skin-stringer structures mostly support supersonic flexural or bending waves propagating in the laminated structure whereas noise radiation by sandwich structures is dominated by supersonic shear waves in the core. The vibro-acoustic behavior of sandwich composites has been studied by several investigators. Wave number diagrams have been useful in identifying supersonic flexural and shear waves in composite structures. It has been shown that the radiating wave number components increase with increasing plate stiffness, causing increased sound radiation. Although design criteria for sandwich composites in terms of sub-sonic core wave speeds have been evolved, skin-stringer composite structures must use added noise control treatments. Noise control of composite structures, thus, still presents a significant technical challenge as the main advantages afforded by these structures, such as low weight and high strength, must not be compromised by added treatments. This paper presents a review of recent advances in the noise control techniques for composite structures.