Sound Noise Research Articles

The design of noise attenuation for gas turbine GTS 22 engine

Nowadays, awareness of global society to the green concept where life should be in harmony with nature has been increasing. One of the ideas in the green concept is to reduce excessive sound exposures or noise. Within this context, gas turbine GTS 22 engine is one of mechanical system that generates a very high sound pressure level. Hence, it is instructive to develop noise controls for the gas turbine in order to have acceptable sound pressure level. This research is focused on the design of muffler as noise control treatment after carefully analyzing the dominant noise spectrum of the gas turbine. In this paper, numerical approach is employed to design the muffler. The results are then validated by experimental ones. Moreover, noise reduction (NR) is used to assess the muffler performances. The design of muffler in this research contains all of combination treatment: area cross section expansion chamber, perforated system (micro perforated panel), porous material, partition chamber and concentric tube. The chosen final design of muffler is combination treatment design where NR 38.77 dB is present. This NR leads to sound pressure level of 80.82 dB or 68.95 dBA exist after the muffler applied on the exhaust of gas turbine. The deviation of experimental results compared to numerical ones is 7.14% in average. Moreover, the pressure drop (ΔP) of the muffler is only 0.4042% which is acceptable to keep the mechanical performance.

Synthesis and Evaluation of Polyurethane Foam Composites for Enhanced Sound Absorption at Low Frequency

Polyurethane foams are extensively used as sound absorbing materials in various automobile parts. However, the sound absorption capability of polyurethane foam ispoorin low frequency range. The advancement of technologies to develop newerpolymer composites, provide scope to develop composite polyurethane foam with better sound absorption coefficient in low frequency range. Composite foams are made with two different filler materials as crumb rubber and coconut fiber, in varying weight fraction of up to 2.0%. Density, Sound absorption coefficient, and Noise reduction, measurements were done on all polyurethane foams. The effect offiller additionsto polyurethane foams ondensity and sound absorption coefficient at low frequency are discussed.The 1.4 % crumb rubber polyurethane foam offers the best combination of low density, improved sound absorption coefficient value and noise absorption at low frequency.

The effects of spatial separations between water sound and traffic noise sources on soundscape assessment

Many studies have investigated the effects of water sound on soundscape with an assumption that target noise coincides with the masker (co-location), while no attention has been paid to spatial separations between target noise and water sound sources. This study aims to explore the effects of spatial separations between target noise and water sound on perceived loudness of target noise (PLN) and overall soundscape quality (OSQ) through laboratory experiments. Traffic noise (target) and a water sound (masker) were recorded as acoustic stimuli and a spherical panoramic video recording of a water fountain was also used as visual stimuli. The audio-visual stimuli were reproduced through a virtual reality head-mounted display and a multichannel ambisonic loudspeaker setup. The traffic noise and water sound were played simultaneously at various azimuthal separations and were combined with a panoramic recording of a water fountain as visual stimulus. Participants assessed the audio-visual stimuli in terms of PLN and OSQ. The effect of the spatial separation between the traffic noise and water sound was significant in both PLN and OSQ. Specifically, the PLN increase at 135° separation was equivalent to an estimated target noise level increment of ~1–2 dB. Similarly, the OSQ decrease at 135° and 180° separation was equivalent to an estimated target noise level increase of ~2–5 dB. Since the typical field of view of users in space is less than 135°, the results suggest that placing water features within a user's field of view could achieve better soundscape.

Tertiary Waves Measured during 2017 Pohang Earthquake Using an Underwater Glider

An underwater glider equipped with a hydrophone observed the acoustic sounds of an earthquake that occurred on 15 November 2017 05:29:32 (UTC) in the Pohang area. The underwater glider observed the earthquake sounds after 19 s (05:29:51) at approximately 140 km from the Pohang epicenter. In order to distinguish the earthquake sound from the glider’s operation noise, the noise sources and Sound Pressure Level (SPL) of the underwater glider were analyzed and measured at laboratory tank and sea. The earthquake acoustic signal was distinguished from glider’s self-noises of fin, pumped Conductivity-Temperature-Depth profiler (CTD) and altimeter which exist over 100 Hz. The dominant frequencies of the earthquake acoustic signals due to the earthquake were 10 Hz. Frequencies at which the spectra had dropped 60 dB were 50 Hz. By analysis of time correlation with seismic waves detected by five seismic land stations and the earthquake acoustic signal, it is clearly shown that the seismic waves converted to Tertiary waves and then detected by the underwater glider. The results allow constraining the acoustic sound level of the earthquake and suggest that the glider provides an effective platform for enhancing the earth seismic observation systems and monitoring natural and anthropogenic ocean sounds.

Auditory Localization and Spatial Release From Masking in Children With Suspected Auditory Processing Disorder.

We sought to investigate whether children referred to our audiology clinic with a complaint of listening difficulty, that is, suspected of auditory processing disorder (APD), have difficulties localizing sounds in noise and whether they have reduced benefit from spatial release from masking. Forty-seven typically hearing children in the age range of 7 to 17 years took part in the study. Twenty-one typically developing (TD) children served as controls, and the other 26 children, referred to our audiology clinic with listening problems, were the study group: suspected APD (sAPD). The ability to localize a speech target (the word "baseball") was measured in quiet, broadband noise, and speech-babble in a hemi-anechoic chamber. Participants stood at the center of a loudspeaker array that delivered the target in a diffused noise-field created by presenting independent noise from four loudspeakers spaced 90° apart starting at 45°. In the noise conditions, the signal-to-noise ratio was varied between -12 and 0 dB in 6-dB steps by keeping the noise level constant at 66 dB SPL and varying the target level. Localization ability was indexed by two metrics, one assessing variability in lateral plane [lateral scatter (Lscat)] and the other accuracy in the front/back dimension [front/back percent correct (FBpc)]. Spatial release from masking (SRM) was measured using a modified version of the Hearing in Noise Test (HINT). In this HINT paradigm, speech targets were always presented from the loudspeaker at 0°, and a single noise source was presented either at 0°, 90°, or 270° at 65 dB A. The SRM was calculated as the difference between the 50% correct HINT speech reception threshold obtained when both speech and noise were collocated at 0° and when the noise was presented at either 90° or 270°. As expected, in both groups, localization in noise improved as a function of signal-to-noise ratio. Broadband noise caused significantly larger disruption in FBpc than in Lscat when compared with speech babble. There were, however, no group effects or group interactions, suggesting that the children in the sAPD group did not differ significantly from TD children in either localization metric (Lscat and FBpc). While a significant SRM was observed in both groups, there were no group effects or group interactions. Collectively, the data suggest that children in the sAPD group did not differ significantly from the TD group for either binaural measure investigated in the study. As is evident from a few poor performers, some children with listening difficulties may have difficulty in localizing sounds and may not benefit from spatial separation of speech and noise. However, the heterogeneity in APD and the variability in our data do not support the notion that localization is a global APD problem. Future studies that employ a case study design might provide more insights.

Electrostatically tunable small-amplitude free vibrations of pressurized electro-active spherical balloons

Designing tunable resonators is of practical importance in active/adaptive sound generation, noise control, vibration isolation and damping. In this paper, we propose to exploit the biasing fields (induced by internal pressure and radial electric voltage) to tune the three-dimensional and small-amplitude free vibration of a thick-walled soft electro-active (SEA) spherical balloon. The incompressible isotropic SEA balloon is characterized by both neo-Hookean and Gent ideal dielectric models. The equations governing small-amplitude vibrations under inhomogeneous biasing fields can be linearized and solved in spherical coordinates using the state–space formalism, which establishes two separate transfer relations correlating the state vectors at the inner surface with those at the outer surface of the SEA balloon. By imposing the mechanical and electric boundary conditions, two separate analytical frequency equations are derived, which characterize two independent classes of vibration for torsional and spheroidal modes, respectively. Numerical examples are finally conducted to validate the theoretical derivation as well as to investigate the effects of both radial electric voltage and internal pressure on the resonant frequency of the SEA balloon. The reported analytical solution is truly and fully three-dimensional, covering from the purely radial breathing mode to torsional mode to any general spheroidal mode, and hence provides a more accurate prediction of the vibration characteristics of tunable resonant devices that incorporate the SEA spherical balloon as the tuning element.

Asynchronous Localization of Underwater Target Using Consensus-Based Unscented Kalman Filtering

Most applications of underwater acoustic sensor networks (UASNs) rely on accurate location information of targets. However, the asynchronous clock, stratification effect, and strong-noise characteristics of underwater environment make target localization more challenging as compared with terrestrial sensor networks. This paper focuses on an asynchronous localization issue for underwater targets, subjected to the isogradient sound speed and noise measurements. A network architecture including surface buoys, sensors, and the target is first designed, where the clocks on sensors and the target are not required to be synchronized. To eliminate the effect of asynchronous clocks, we establish the relationship between the propagation delay and the position. Particularly, the ray tracing approach is adopted to model the stratification effect. Then, a localization optimization problem is formulated to minimize the sum of all measurement errors. To solve the localization optimization problem, a consensus-based unscented Kalman filtering (UKF) localization algorithm is proposed, where the convergence conditions and Cramér-Rao lower bounds are also given. Finally, simulation results reveal that the proposed localization approach can reduce the localization time by comparing with the exhaustive search method. Meanwhile, the consensus-based UKF localization algorithm can improve localization accuracy as compared with other works.

Direction Finding of a Noise Sound Source

A new direction-finding algorithm has been proposed based on the interferometric localization of a noise sound source. It implies the use of a single vector-scalar receiver, which makes it possible to determine unambiguously the direction. The results of a numerical experiment are presented.

Full space destructive interference by acoustic-null medium

Traditional destructive interference between two out-phase acoustic sources only occurs at certain spatial areas. We propose a method to achieve acoustic destructive interference in the whole space by setting two out-phase acoustic sources inside the acoustic-null medium (ANM). ANM is a highly anisotropic medium designed by transformation acoustics, whose function is to greatly compress its inner points along the main axis. We design an implementation model of ANM by filling hydrogen in brass slabs, which shows good full space destructive interference effect by numerical simulations. The proposed method will provide a new way to achieve sound suppression and noise reduction.

Mandarin Electrolaryngeal Speech Recognition Based on WaveNet-CTC.

Purpose The application of Chinese Mandarin electrolaryngeal (EL) speech for laryngectomees has been limited by its drawbacks such as single fundamental frequency, mechanical sound, and large radiation noise. To improve the intelligibility of Chinese Mandarin EL speech, a new perspective using the automatic speech recognition (ASR) system was proposed, which can convert EL speech into healthy speech, if combined with text-to-speech. Method An ASR system was designed to recognize EL speech based on a deep learning model WaveNet and the connectionist temporal classification (WaveNet-CTC). This system mainly consists of 3 parts: the acoustic model, the language model, and the decoding model. The acoustic features are extracted during speech preprocessing, and 3,230 utterances of EL speech mixed with 10,000 utterances of healthy speech are used to train the ASR system. Comparative experiment was designed to evaluate the performance of the proposed method. Results The results show that the proposed ASR system has higher stability and generalizability compared with the traditional methods, manifesting superiority in terms of Chinese characters, Chinese words, short sentences, and long sentences. Phoneme confusion occurs more easily in the stop and affricate of EL speech than the healthy speech. However, the highest accuracy of the ASR could reach 83.24% when 3,230 utterances of EL speech were used to train the ASR system. Conclusions This study indicates that EL speech could be recognized effectively by the ASR based on WaveNet-CTC. This proposed method has a higher generalization performance and better stability than the traditional methods. A higher accuracy of the ASR system based on WaveNet-CTC can be obtained, which means that EL speech can be converted into healthy speech. Supplemental Material https://doi.org/10.23641/asha.8250830.

Excessive sound noise risk assessment in textile mills of an Ethiopian-Kombolcha textile industry share company

In countries like Ethiopia, the textile industries are facing a big problem of sound noise pollution. In these countries, the industrial hearing conservation program is not yet clearly developed. Thus, characterizing excessive noise pollutions in textile industries have been the aim of this research project and Kombolcha Textile Mill (KTM) is chosen as the case study. The study is concerned with the noise exposure and its characteristics at the different section of the Textile Mill. Before the actual excessive noise level measurements were collected in the Textile Mill, main areas where measurements were done had to be identified. This was done by prior physical observation and A-Weighted time-averaged sound pressure levels (L_Aeq) survey. More than one hundred walkthrough measurement points were done inside the textile mill. These data were analyzed using MATLAB software packages. Based on our analysis, the spinning and the weaving sections of the mills with its unit processes were identified as potential noise pollution in the factory. On these sections, the measurements were done for 4 – 5 h/d. The instrument used for measurements was a precision integrated portable professional sound level meter. The findings revealed that the KTM employees are working in hazardous environments of above 90 dB, which is the recommended safe limit of noise in the working environment for 8 h used in international standard. As a result an engineering and administration programs which includes different methods of how to control the problem has been recommended for conserving hearing at the KTM.

Development of Kenaf Nonwoven as Automotive Noise Absorption

Getting rid of unwanted noise in car compartment is necessary and really significant measure for automotive makers. This research was directed to produce nonwoven material from Kenaf fiber using the needle-punching machine and the ability of the produced material to absorb sound will be tested. The performance in sound absorption of the sample was analyzed by the sound absorption coefficient (SAC) and noise reduction coefficient (NRC) using the impedance tube test referring to ASTM E1050-98. The sound absorption frequencies were evaluated utilizing the two-microphone transfer function technique in the impedance tube that has a 100 mm diameter for low frequency and 28 mm for high frequency, 0 Hz to 4000 Hz respectively. The physical examination also was executed according to ASTM D1772 to determine the density and the thickness of each sample. The parameter verified in this research is the number of layers to form the samples and it also were compared with the commercial products. As the outcome of this research, the sound absorption coefficient (SAC) showed that the sound reduction coefficient value was increased as the number of layers of the sample increase. In summation, the result also proved that the denser the samples, the higher the absorption coefficient value. On the other hand, for the noise reduction coefficient (NRC), overall result showed slight differences between each sample. The result is due to the rating is an average, two materials with the same rating might not perform the same. Referring to the previous research, the sample with higher areal density is dependable for higher sound reduction and there is a negative relationship between area density and bulk density of needle-punched nonwoven and sound reduction. With the rise in the number of density of nonwoven fabric, the sound reduction through the fabric increases at first but after the maximum it remains almost unaffected.

Association of incisal overlaps with /s/ sound and mandibular speech movement characteristics

Modern anterior restorations are intended to achieve esthetic and functional reconstruction and coordination. The positioning of the anterior teeth can affect pronunciation, but the effect of anatomic factors on pronunciation after anterior restoration has not been critically tested. The purpose of this study was to provide possible references for the design of the anterior overlaps in future anterior restorations. Thirty-nine subjects with normal occlusion (NO) participated. They completed questionnaires, were examined clinically, and were recorded pronouncing the /s/ sound. Links between overlaps with spectral features of the /s/ sound and mandibular movements during speech were investigated. When NO subjects pronounced the /s/ sound, the average fricative length was 202.54±44.57ms; the average noise peak was 4052.89±445.80Hz, which was in the high-frequency region; the center of gravity was 2452.85±623.50Hz; and the mean intensity was 40.61±4.99dB. The mandibular speech movements showed a slightly long and narrow backward and downward oblique path. Overbite positively correlated with the /s/ sound's noise peak frequency and negatively correlated with the maximum closing speed. Overjet negatively correlated with the maximum distance in the sagittal plane. This is the first attempt to correlate the spectral features of the /s/ sound and speaking movements with incisal overlaps. The results suggest that significant associations exist and that these associations can offer some references for esthetic anterior restoration.

Joint parameter identification, vibration and noise analysis of gearbox

A certain type of gearbox is investigated for the problem that the stiffness and damping of bearings are difficult to be accurately determined and then affect the analysis of vibration and noise of gearbox. Firstly, a coupled dynamic lumped parameter model of three-stage helical gear system with consideration of bearing stiffness, bearing damping, and transmission error is established. The modal parameters of gear system are obtained by using the experimental modal analysis method with single-input and multiple-output. The equation for joint parameter identification of gearbox is established which is based on the experimental modal analysis theory and the dynamic lumped parameter model, and subsequently the parameters of the joint are obtained by the least square method. Then, a gear-shaft-bearing- housing coupled dynamic finite element model is developed on the basis of the identified parameters, and after that the dynamic response results of gearbox are solved by using the modal superposition method and compared with the vibration test results. Finally, an acoustic boundary element model of gearbox is established by taking the dynamic response results as the acoustic boundary condition, and the surface sound pressure and radiation noise of gearbox are solved by the boundary element method (BEM), and then the results are compared with the noise test. The results show that the simulation laws and test laws are in good agreement, and thus the method of joint parameter identification, vibration and noise analysis of gearbox is feasible.

Structural–Acoustic Modeling and Analysis for a Flexible Partition Panel in Three-Dimensional Acoustic Cavity

Structural–acoustic coupling problem can be commonly seen in sound field analysis and noise reduction areas. It is of great significance for the further research of the structural–acoustic coupling between flexible panel and enclosure cavity. For the purpose of this paper, a three-dimensional acoustic cavity with flexible partition is modeled. The field functions of structural–acoustic coupling solution domain are described by employing improved Fourier series method. Various different boundary conditions of the panel partition are presented by means of continuous distribution of restrained springs along each edge of the panel partition. The general formula considering the structural–acoustic coupling between the panel and the cavities is obtained by the Rayleigh–Ritz method based on the energy principle. A series of numerical examples are given to demonstrate the performance of the present method by comparison with FEM, as well as experimental works. Meanwhile, the results are provided to examine the effect of the translational and rotational stiffness of structural boundaries on the structural–acoustic coupling characteristics of the model. The effectiveness of the present model is validated by a good agreement obtained in the comparison works. This study also shows that how the structural boundary condition affects the coupling system in detail. These results provide a theoretical basis for structural–acoustic coupling analysis and low-noise design of enclosures with panel partition.

Wood ash as a supplementary cementing material in foams for thermal and acoustic insulation

Abstract This study characterizes a Portland cement based cellular system prepared with a preformed foam. Wood ash, locally sourced from pulp and paper mills, was first characterized and later, blended at up to 20% of the binder. The resulting mixtures were cast at three densities between 1000 and 1400 kg/m3 and examined for mechanical, thermal and acoustic properties. A phase analysis was performed using X-ray diffraction to identify the components of the wood ash and again, in the hydrated system. The thermal constants were measured using the Transient Plane Heat Source (TPS) technique per ISO 22007-2. Sound absorption and noise reduction coefficients were evaluated using the impedance tube method per ASTM C384-04. The results show that although blending wood ash led to lower compressive strength and elastic modulus, the drop in strength was within 20%. While not as effective in reducing noise, the wood ash led to 20% lower thermal conductivity. These findings offer wood ash as a viable, replenishable and sustainable substitute for Portland cement in insulating foams.

Impact of road traffic noise on functional connectivity of human brain networks

With the rapid economic development, the rapid increase in motor vehicle holdings, a sharp increase in urban road traffic, road traffic noise exposure is becoming increasingly serious. This paper focuses on the impact of traffic noise exposure on the human brain. We collected road traffic noise sounds of different sound pressure levels (SPLs), and recorded the electroencephalograph (EEG) when subjects exposed under different SPLs’ road noise. Using the graphic theoretical-based EEG method, the effects of road traffic noise with different SPLs on the functional connectivity of human brain networks were studied. Using time-frequency analysis, the beta2 bands was found to be most sensitive frequency band to different SPLs road noise. The brain network characteristic parameters of different SPLs noises were calculated. It is found that in these two frequency bands, the higher the noise SPL, the lower the clustering coefficient and the higher the characteristic path length. In summary, the paper points out the specific effects of road noise with different SPLs on the human brains. It is found that the higher the SPL of noise, the greater the damage to the functional connectivity of the human brain. That means, noise exposure can affect the rate at which the brain processes, analyses, and transmits information. The research results can provide a basis for road noise evaluation and prevention.

Harmonicity aids detection of speech and other sounds in noise

Acoustic grouping cues, such as the tendency of frequencies to be harmonic, are used to segregate multiple sounds, as when listening to one of several concurrent speakers. However, we often must listen to sound sources in noise. Here we investigate the role of traditional acoustic grouping cues in detecting sound sources in noise. We measured detection thresholds for several types of sounds embedded in noise: speech, musical instruments, and synthetic complex tones. In each case the sounds were resynthesized with harmonic and inharmonic carrier frequencies to test the importance of harmonic frequency structure for hearing in noise. We found that harmonic signals were consistently easier to detect in noise than otherwise similar inharmonic signals. This harmonic advantage persisted even when the phases of harmonic components were randomized, such that the advantage is unlikely to reflect differences in the depth of modulation (from beating). Near threshold, harmonic signals were readily audible in conditions where inharmonic signals could not be heard. These results suggest that harmonicity is critical for detecting real-world signals in noise, demonstrating its relevance to another important aspect of auditory scene analysis.

Ultra-open acoustic metamaterial silencer

Recently, with advances in acoustic metamaterial science, the possibility of sound attenuation using subwavelength structures, while maintaining permeability to air, has been demonstrated. However, the ongoing challenge addressed herein is the fact that among such air-permeable structures to date, the open areas represents only small fraction of the overall area of the material. In the presented work, in order to address this challenge, we firstly demonstrate that a transversely-placed bilayer medium with large degrees of contrast in the layers' acoustic properties exhibits an asymmetric transmission, similar to the Fano-like interference phenomenon. Next, we utilize this design methodology and propose a deep-subwavelength acoustic metasurface unit cell comprising nearly 60% open area for air passage, while serving as a high-performance selective sound silencer. Finally, the proposed unit cell performance is validated experimentally, demonstrating a reduction in the transmitted acoustic energy of up to 94%. This ultra-open metamaterial (UOM) design, leveraging a Fano-like interference, enables high-performance sound silencing in a design featuring a large degree of open area, which may find utility in applications in which highly efficient, air-permeable sound silencers are required, such as smart sound barriers, fan or engine noise reduction, among others.

Restaurants part 3: The acoustics of dining spaces

Restaurants are spaces where people gather to eat, talk, share, and spend time. They are also facilities where food is prepared and served to others. Restaurants have garnered much attention over the last several years as having high sound levels with some customers having difficulty in communication among patrons and staff. However, spaces such as cafeterias, dining rooms in country clubs, retirement centers, and hospitals serve similar functions as restaurants and suffer from similar acoustic issues. Acoustic measurements of alpha bar, reverberation time, reflected sound energy, noise reduction, and STI were made in various types of dining spaces that have required acoustic treatment. Data from these types of spaces have been added to the data previously collected at restaurants, to provide general information about the acoustics of dining spaces. The results show that dining spaces can be broken into similar treatment categories, regardless of the specific type of space. The sample of rooms was also analyzed by architectural and interior design style to identify design trends that affect the acoustical metrics in dining spaces.