Sound Reduction Performance Research Articles

Impact sound insulation performance of floor coverings in a heavyweight reference floor with a floating floor

This study investigates the impact sound reduction performance of floor coverings used on the heavyweight standard floor of a floating floor structure in comparison with bare slab testbeds through on-site experiments. The laboratory performance evaluation of floor coverings designates only a bare slab between 100 mm and 160 mm as the heavyweight reference floor according to Annex C in ISO 10140-5. However, the recent expansion of over-floor heating systems has led to an increased need for understanding the impact sound reduction performance of floor coverings on floating floors, to enhance occupants' thermal comfort. In this study, it was measured the heavyweight and lightweight floor impact sound reduction levels of various floor covering test specimens in testbeds with different thicknesses of bare slabs and actual apartment houses with floating floors applied. The reduction rate for each frequency band was determined before and after installing floor coverings including single number quantity in accordance with ISO 717-2. Additionally, the impact of heavyweight reference floor conditions on quantifying the sound performance of floor coverings was discussed.

Meta-barriers for ventilated sound reduction via transformation acoustics

Resolving the trade-off problem between wave obstructing and flow transport is an intriguing but challenging task that may find potential applications in many noise control scenarios. Herein, we present a meta-barrier for achieving broadband sound reduction yet keeping efficient ventilation based on transformation acoustics. The proposed meta-barrier consists of an internal core and a coating made of double-negative acoustic metamaterial with high damping dissipation. Unlike conventional barriers, the meta-barrier has a magnified scattering cross-section far beyond its actual size, allowing it to provide the coherent interference effect in addition to the enhanced blocking effect. The coherent interference effect can directly reduce the sound radiation efficiency of sound waves radiating from an aperture. Moreover, the inherent material loss in the coating has a positive effect on the sound reduction performance of the meta-barrier over a wide frequency range. The robust sound reduction performance of the meta-barrier is demonstrated numerically for the cases of large placed distances and wide-range incident angles. Experiments were conducted to confirm the effectiveness of a meta-barrier sample constructed of a plate-type double-negative acoustic metamaterial with multiple constituent layers for sound reduction and ventilation. The fabricated meta-barrier sample, with the wind-speed ratio of 75 %, can achieve superior sound attenuation in the frequency range of 500–1000 Hz. This work may inspire the design and development of passive acoustic devices to suppress low-frequency airborne noise while supporting large-area ventilation.

Impact Sound Reduction Performances of Additional Floor Mats for the Retrofitting of an Existing Apartment Building in Accordance with Test-Bed Conditions

Floor mats are commonly used to improve the impact sound performance of existing homes, but actual impact sound reductions do not consistently appear, as they depend on the test-bed conditions used to determine impact sound performance. Therefore, this study evaluated the effects of the environmental conditions of the test bed on the impact sound reduction performances of different floor mats. The Korean industrial standard KS F 2865 specifies the measurement method in the test room and sets the thickness range of the available target floor structure to bare slabs with thicknesses ranging from 120 mm to 210 mm. The evaluation method is ∆L, which is the difference in standardized impact sound levels before and after the installation of the floor finishing material. In this study, a total of eight types of floor mats were tested in four different test beds according to KS F 2865. The impact sources used were tapping, bang machines, and a rubber ball, and we used these sources to consider both light-weight and heavy-weight impact sounds. The results were derived as the impact sound reduction performance for each frequency band and a single-number quantity. The results showed that light impact sound had a similar minimum reduction characteristic of at least 38 dB, regardless of the floor structure on which the mat was installed. However, the heavy-weight impact sound showed different tendencies depending on the floor mat and the characteristics of the floor structure of the test bed when a bang machine and a rubber ball were used. In particular, the reduction achieved by the bang machine showed less than half the tendency of the reduction by the rubber ball, and the tendency of the heavy-weight impact sound was shown to be reducible depending on how the floor mat was maintained, but the reductions differed depending on the test bed. The reductions were larger in the box-type test room than in the real-life-type test room, and among the box-type test rooms, the one with a thicker bare slab showed a relatively larger reduction. In addition, the reliability of the measurement results was evaluated through a correlation analysis between the single-number quantities depending on the thicknesses of the bare slabs of the test beds.

Aeroacoustic simulation of bluff bodies with protrusions at moderate Reynolds number

This paper presents an evaluation of passive control methods that employ surface protrusions to mitigate the aerodynamic sound generated from a cylinder wake flow. Building on previous designs optimized for low Reynolds numbers (Re = 150) through adjoint-based aeroacoustic shape optimization, this study investigated the performance under a moderate Reynolds number (Re = 67 000) condition typical of mechanical engineering applications using aeroacoustic simulations based on the lattice Boltzmann method. Three configurations of surface protrusions were tested, all of which were found to significantly reduce the mean drag by at least 45% compared with that of an unmodified circular cylinder. Designs featuring rear protrusions outperformed the conventional splitter plate in terms of the sound reduction performance, with symmetrical protrusions on both the front and rear surfaces achieving a tonal sound reduction of 13 dB. However, a specific protrusion design increased the low-frequency sound owing to the intensified large-scale flow separation. These findings highlight the effectiveness of rear protrusions in suppressing wake oscillations and dipole sound generation in the subcritical Reynolds number range. Moreover, the study revealed the need to tailor the front protrusion shape to the Reynolds number for performance optimization.

Sound radiation control of an unbaffled long enclosure using wavy micro-perforated panel absorbers

The sound radiation control of an unbaffled long enclosure using wavy micro-perforated panel absorbers (WMPPAs) was numerically and experimentally investigated. First, a hybrid model based on the finite element method (FEM) and the Wiener-Hopf (W-H) technique was established to calculate the sound pressure level (SPL) radiated from an unbaffled long enclosure lined with MPPAs. Then, the hybrid model was validated, and the sound suppression performance of a single WMPPA was evaluated. The results demonstrate that the WMPPA exhibits better sound absorption properties than the flat and corrugated micro-perforated panel absorber (FMPPA and CMPPA), especially in the middle- to high-frequency range. To further enhance the sound attenuation performance, an array of WMPPAs was subsequently proposed to absorb higher-order acoustic modes inside the long enclosure so that broadband-radiated noise could be suppressed. The comparison results demonstrate that the WMPPAs can reduce the radiated SPL within a wide frequency range which is favourable for the suppression of environmental noise. In addition, the WMPPA array shifts the sound reduction curve towards a low-frequency range by approximately 500 Hz compared with that of a single WMPPA, which is promising for the reduction of broadband noise. After that, a mechanistic study was conducted to explain the sound reduction performance of WMPPAs from the perspective of modal contributions. In addition, the diffraction effect of sound waves at the sharp edge of a long enclosure was illustrated. Besides, the contribution of the wavy structure's scattering effect to the sound reduction performance of WMPPAs was analysed. Finally, the sound absorption abilities of the WMPPAs were examined using a quasi-two-dimensional (quasi-2D) experiment. The results show that the WMPPAs exhibit good sound reduction performance in the middle- to high-frequency range, which verifies the feasibility of applying WMPPAs to suppress the broadband noise radiated from long enclosures.

Floor impact sound reduction and impact absorption performance of floor mat

In Korea, the post evaluation system of floor impact sound performance was implemented in August 2022. Therefore, it is necessary to check the floor impact sound performance after the completion of the apartment. If a floor impact sound performance does not meet the regulation limit, compensationm and follow-up renovations are required. In this study, in order to develop a floor mat that can reduce heavy weight floor impact sound, the floor impact sound reduction performance and impact absorption performance of each condition of the sample were confirmed. Floor impact sound reduction performance was measured using the test methods of KS F 2865 and ISO 10140-3, and impact absorption performance was measured according to the test method of JIS A 6519. As a result of the measurement, the performance of reducing floor impact sound showed a clear difference in performance according to thickness rather than material type. Impact absorption performance was found to be affected by surface hardness and material thickness. In conclusion, it is considered that the selection, thickness, and surface hardness of materials are important design factors when developing floor mats.

A study on the evaluation of impact sound reduction performance of floor mats for reducing floor impact sound in apartment buildings

This is a study on the performance evaluation of floor mats used to reduce floor impact sound in apartment houses in South of Korea. A total of 8 types of floor mats and 5 or more test rooms with different floor structures were used to measure and evaluate impact sound reduction performance. The impact source is a Bang machine (heavy-weight impact sound 1), a rubber ball (drop of height 100 cmHeavy-weight impact sound 2) tapping machine (light-weight impact sound), and a rubber ball drop height of 40cm that simulates the actual impact force. As a result of the test, the impact sound reduction performance for the light-weight impact sound was evaluated as excellent. It was evaluated at the level of ambient background noise. Also, the reduction performance of the bang machine was somewhat different depending on the floor structure. In addition, there are cases where it is rather amplified in the low frequency band (63 Hz). In the case of rubber ball (drop of height 100 cm), the reduction performance was different depending on the floor structure. However, the impact sound reduction performance was evaluated to be sufficiently reduced. The impact noise reduction performance at the rubber ball drop height of 40 cm was found to be slightly higher than that at the drop height of 100 cm.

Analysis of coupling effect between chambers of reactive muffler

The efficient optimisation of the sound reduction performance of multi-chamber reactive mufflers has always been a challenging problem, not only because of the presence of multiple muffler units but also because of the complicated interactions between the chambers. Previous studies have shown that the interactions between chambers can significantly affect the performance of mufflers. To better understand the coupling mechanism between the chambers and thus provide guidance for the optimisation design of reactive mufflers, first, the sound propagation characteristics in (1) a muffler with two expansion chambers and (2) a muffler with a resonant chamber and an expansion chamber were solved using a two-dimensional (2D) axisymmetric analytical method, combined with a new analytical model of transmission loss (TL), by considering multiple acoustic modes in the mufflers. The influences of key structural parameters on the chamber-coupling effect of the mufflers were investigated. The results reveal that the noise reduction performance of the first chamber deteriorated while that of the second chamber was improved by the coupling effect. To further understand the coupling effect, the coupling mechanism was analysed using acoustic impedance transfer theory. Impedance-tube measurements were carried out to validate the proposed analytical model and inter-chamber coupling effect. Based on the results, the optimisation of a reactive muffler for a bulldozer was carried out. The results obtained by numerical analyses and experiment reveal that the noise attenuation characteristics of the optimised muffler are obviously better than those of the original muffler, and the average insertion loss (IL) increased by 8 dB.

Study on Noise Reduction Effect of Helmholtz Resonator Using Lattice Boltzmann Method

It is necessary to reduce the aerodynamic sound generated by fans since they are often used for air-conditioner, which are placed in human living areas, such as homes and offices. To reduce the aerodynamic sound, we focused on the Helmholtz resonator (HR). Toward developing HR that can be installed into air-conditioners and reduce aerodynamic sound, the present study investigated a numerical analysis method and the effect of cavity shapes on the sound reduction performance of HR using a simple computational model. As a numerical analysis method, we used the lattice Boltzmann method (LBM), which can simultaneously simulate aerodynamically sound generation in fans and the acoustic resonance in resonators. First, the capability of the LBM to simulate acoustic resonance was validated. As a result, it was shown that the calculation results were consistent with the theoretical equation. Furthermore, the present study revealed the relationship between the depth of the resonator cavity and the sound reduction effect.

A Fano-based acoustic metamaterial for ultra-broadband sound barriers

Ultra-broadband sound reduction schemes covering living and working noise spectra are of high scientific and industrial significance. Here, we report, both theoretically and experimentally, on an ultra-broadband acoustic barrier assembled from space-coiling metamaterials (SCMs) supporting two Fano resonances. Moreover, acoustic hyper-damping is introduced by integrating additional thin viscous foam layers in the SCMs for optimizing the sound reduction performance. A simplified model is developed to study sound transmission behaviour of the SCMs under a normal incidence, which sets forth the basis to understand the working mechanism. An acoustic barrier with 220 mm thickness is then manufactured and tested to exhibit ultra-broadband transmission loss overall above 10 dB across the range 0.44–3.85 kHz, covering completely nine third-octave bands. In addition, unconventional broadband absorption in the dampened barrier (65%) is experimentally observed as well. We believe this work paves the way for realizing effective broadband sound insulation, absorption and sound wave controlling devices with efficient ventilation.

Research and Application of Noise Barriers in Highway Construction

In recent years, with the rapid development of highways, traffic noise has become a risk source in the environment, and noise control has attracted wide attention. As an economical and effective method, highway noise barriers were the best way to reduce traffic noise and protect residents’ acoustic environment. At the same time, considering the various surroundings in selecting suitable materials (sound-reflective or sound-absorbing materials), types (such as concrete, organic glass, foam metal and photovoltaic noise barriers) and structures (such as vertical, T-shaped, Y-shaped, and inverted L-shaped) could greatly improve the sound reduction performance of barriers. This paper summarizes the current development of noise barriers from perspectives of the material, type and structure to introduce a variety of noise barriers and provides a reference for relevant research. With these analyses, it is possible to design more cost-effective and appropriate noise barriers for particular areas.

Thermoplastic polyurethane/laponite nanocomposite for reducing impact sound in a floating floor

An effective way to reduce impact sound in buildings is to install a floating floor consisting of a floating slab separated from the structural slab by a continuous viscoelastic layer. Although a considerable amount of work has been reported on nanomaterials in the past decades, the impact sound reduction performance of polymer/clay nanocomposites has not been specifically addressed in the literature. In this paper, we report the synthesis and characterization of a nanocomposite made of thermoplastic polyurethane (TPU) with laponite clay filler and its potential use for reducing impact sound in floating floor technology. Samples were prepared with laponite content ranged between 0.5 and 10 wt% for each nanocomposite synthesized using a solvent solution mixing process. The characterization of the nanocomposites confirmed that the clay content in the TPU matrix has significant impact on the viscoelastic properties. In particular, the incorporation of 5–10 wt% laponite clay in the TPU matrix increased mechanical damping and reduced dynamic stiffness as compared to the pristine TPU. The experimental results were compared with a constitutive model that extends the Cremer-Vér model. The results predicted a considerable improvement of the impact sound insulation at the resonance frequency when the nanocomposite is used as a continuous viscoelastic layer supporting the floating slab. These results were attained without significantly increasing the total weight of the floating layer.

Thermal and acoustic performance of an integrated automotive thermoelectric generation system

In recent years, the use of thermoelectric generators (TEGs) to recover secondary energy from exhaust heat has increased speedily with applications ranging from microwatts to kilowatts. In terms of automotive exhaust system, there are compatibility problems among automotive TEG, catalytic converter and muffler. An integrated automotive thermoelectric generator (IATEG) which contains automotive TEG, catalytic converter and muffler that converts engine exhaust waste heat into electricity is constructed and simulated. Through comparison of steel, aluminum and copper heat exchangers, it is found that both the average interface temperature and the maximum output power increase are highly dependent on the thermal conductivity of the heat exchanger material. An engine bench test and an acoustic bench test are developed to analyze the performance of the IATEG system characteristics, which are undertaken to assess the feasibility of automotive applications. The numerical simulations and experiment results indicate that the IATEG has better sound reduction performance in high frequency noise and higher temperature distribution which can generate a high power while the power output of the TEG can reach 515 W. Through these experiments, thermal, electrical and acoustic performance of the system is characterized. The results establish the fundamental development of IATEG system that enhances the TEG efficiency for vehicles.

Sound transmission in two-dimensional periodic poroelastic structures

To obtain excellent sound reduction performance, in this paper we introduce a novel periodic poroelastic composite structure, which combines poroelastic material and periodic structure and aims at using the remarkable acoustic performance of these two. This periodic composite structure comprises three parts, i.e. the poroelastic domain, the elastic domain (thin plate), and the periodic resonators, which can be simple single-degree-of-freedom resonators (SRs) or composite two-degree-of-freedom resonators (CRs). A theoretical model is established by using Biot theory for the poroelastic domain, and by using the effective medium method for the resonator-plate coupling system, which is considered as an isotropic plate with an equivalent dynamic density. This method is validated with degenerated model in the literature; the results obtained by this method are in excellent consistence with the results in the literature. Parameter analyses are performed to test the influences of poroelastic addition and periodic resonator on the sound transmission loss (STL) of this periodic composite structure under two kinds of boundary conditions. The poroelastic addition is found to increase the STL while the influences of resonators are complicated. The STL increases notably in the frequency range bounded by the characteristic frequencies of these resonators, however, a decrease just follows when it exceeds these frequencies, which can be observed in both SR case and CR case under the two boundary conditions. In the meantime, when multiple SR is placed in a periodic lattice, it is found that different resonators with ascending mass and characteristic frequencies have superior STL to those with ascending characteristic frequencies but have equal mass. The case with CR, which is more complicated as expected, shows less STL decrease than the case with SR, but wider frequency range where the STL increases than a poroelastic composite structure without resonators. This results from the fact that the frequency band of vibration suppression in the CR case is wider than in the SR case. As a result, to achieve the desired STL performance in a frequency range, the proposed composite structure using SR with tuned characteristic frequencies is enough; however, if a wider frequency band is expected even if there is a slight STL tradeoff, the CR case is a better option. Though the method proposed is only valid in the low-to-medium frequency range, the results obtained can benefit theoretical development of low-to-medium sound modulation applications, they are also valuable and illuminating for investigating the broadband sound modulation.

Numerical investigation on the performances of automotive thermoelectric generator employing metal foam

The automotive thermoelectric generator (TEG) can recover the thermal energy of automotive exhaust and convert it into electric energy. The metal foam can provide a high heat transfer performance as well as sound absorption function, when it is applied in heat exchanger in TEG. The heat exchanger whose wall is attached with metal foam is modeled, and the temperature distribution and acoustic performance are calculated. The numerical simulations indicate that the TEG with metal foam has better sound reduction performance in high frequency noise and higher temperature distribution which can generate a high power while the power output of the TEG can reach 323.424W. Then three parameters of the metal foam, including porosity, thickness of the foam that attached to the eight surfaces and the octagonal foam attached to the outlet are calculated to invest their impacts. The results reveal that temperature distribution and output power gradual peak and decline as the porosity decreases, which will also lead to a deteriorative acoustic performance. The increase of metal foam thickness will contribute to enhance the thermal performance of the TEG, and better sound reduction can be obtained.

Active sound radiation control with secondary sources at the edge of the opening

Planar virtual sound barriers with secondary sources over the entire opening have been demonstrated an effective way to achieve global control of sound transmission through the opening, but loudspeakers in the middle of the opening affect ventilation, lighting and normal access through it. To avoid the problem, this technical note proposes to implement secondary sources at the edge of a cavity opening and investigates the active sound reduction performance of the system numerically and experimentally. Unlike secondary sources over the entire opening which can achieve sound reduction at any frequency as long as there are sufficient of them, there exists an upper bound of effective frequency for global control when secondary sources are at the edge of the opening; however, local control is always achievable. Preliminary experiments were conducted on an open wooden box and a semi-closed meeting room to support the conclusions.

Evaluation of the long-term sound reduction performance of resilient materials in floating floor systems

Building multi-dwelling units is one of the practical engineering solutions to housing shortage in urban areas with high population density. However, noise from upstairs is a major issue. The use of resilient materials in floating floor structures is recognized as an effective method to reduce such noise. In general, soft materials are considered as better resilient materials due to their superior performance in impact sound reduction. However, it is often overlooked that the sound reduction performance of soft resilient materials is susceptible to being degraded over time when subjected to a long-term load. In this study, the long-term performance of eight resilient materials is evaluated by monitoring their dynamic stiffness for 270 days under the two sustained load conditions: 250N and 500N. According to the experimental study, the dynamic stiffness increases consistently with loading time for all resilient materials. This leads to a decrease in the sound reduction performance. More rapid reduction in the dynamic stiffness and hence in the sound reduction performance is observed when a larger sustained load is applied. A greater decrease in the sound reduction performance is found in soft resilient materials.

Changes in Floor Impact Sound Insulation Performance with Time

Floating floor structures installed with resilient materials are commonly used to reduce sound from floor impacts. Resilient materials minimize the transmission of vibrations by absorbing shock vibrations occurring on the upper part. The floor impact sound reduction performance of resilient materials is related to the dynamic stiffness, which is a physical characteristic of materials. However, the dynamic stiffness varies according to the increase in the loading time of the load that is installed on the upper part of resilient materials. The dynamic stiffness values increase with an increase in the loading time; an increased dynamic stiffness value decreases the vibration reduction effect. The present study focuses on a floor structure installed with resilient materials, and identifies the degree of reduction in floor impact sound insulation performance with the elapse of time. The insulation of sound from lightweight impact sound decreased with the elapse of time, whereas the heavyweight impact sound did not show significant changes.

건식이중바닥구조의 중량충격음에 대한 실험적 평가 - 지지구조 및 천장구조 구성에 따른 영향 -

The 1st assessment(performance test) was applied to assure the floor impact sound performance for developing the dry double-floor with the change of rubber hardness of the upper panel's support and the ceiling structure of the sub-floor. Depends on the change of the rubber hardness in sub-structure, the heavy-weight sound impact value is improved up to 3 dB, and the light-weight sound impact value is moved up to 21 dB, comparing with the bare-slab. Also, the improved value for the floor impact sound conjugating with the sub-floor's ceiling was 5 dB. Based on this result, the 2nd assessment(performance test) was made the state that the rubber hardness of the sub-floor support was ranged between 50 and 70 for considering the stability of walking patients. In addition to this process, the assessment was carried out with a variety of ceiling structure applied to the dry double-floor structure with the air flow system on the sub-floor's ceiling. The result for the 2nd assessment proved that TYPEII-3 had the better sound reduction performance in the heavy-weight impact sound test than other types, and also for the light-weight impact sound TYPEII-3 had the 29 dB sound reduction performance overall. Henceforth, based on the result the research for the sound reduction performance from the floor impact sound shall be ongoing process as well as the development of a double-dry floor and a sound reduction ceiling to suitable on the field.

Design and Acoustic Performance of a Drum Practice Music Studio

Minimising the impact of music practice and “Garage Band” performances upon neighbours in a residential area is challenging in terms of noise emissions from musical instruments, but particularly so when drums and percussion instruments are involved. Normal residential building façades and roofing designs offer limited low frequency noise attenuation and domestic building construction methods can severely compromise the performance of seemingly adequate partition construction details. This paper presents the results of design, construction and testing activities for a private drum studio that was required to meet stringent boundary noise emission targets in order to comply with local council Development Application requirements. High transmission loss lightweight partition test data is provided for the as-built final installation, along with details of cavity absorption, panel damping and vibration isolation treatments that contributed to maximising façade sound reduction performance. A range of room internal absorption treatments, including low frequency “tube traps”, corner traps and diffusers were successfully employed to achieve compliance with BBC recommended reverberation times for small recording studios