Search Results (12)

Car cabin noise generated by heating, ventilation, and air-conditioning (HVAC) systems significantly impacts passengers’ acoustic comfort. In fact, with the reduction in engine noise due to the passage from internal combustion to electric or hybrid-electric engines, interior background noise has dramatically reduced, especially at 25% and 50% HVAC airflow rates. While previous research has focused on the effect of HVAC noise in car cabins, this paper investigates the possibility of using car infotainment-system audio cues to moderate onboard sound quality perception. A laboratory experiment combining the factors of infotainment-system audio (ISA) cues, signal-to-noise ratios (SNRs), and airflow rates (AFRs) at different levels was performed in two university laboratories in Italy and Japan involving groups of local individuals. The results indicate that introducing ISA cues in car cabins fosters improvements in the perceived aesthetic dimension of sound quality, making it more functioning, natural, and pleasant. For the Italian group, adding ISA cues also moderated the loudness dimension by reducing noise perception. The moderating effects of ISA cues differed between the Italian and Japanese groups, depending on the AFR. All these effects were more evident at the SNR level of −4 dB when the ISA cues competed with existing background noise. Full article

This paper endeavors to tackle the issue of horizontal vibrations encountered in high-speed and ultra-high-speed elevator cabins during operation. Given the limitations of traditional passive-control guide shoes in effectively mitigating these vibrations and the complexity and cost associated with active control systems, a novel approach involving passive-control rolling guide shoes (PCRGS) integrated with hydraulic damping is explored. The PCRGS incorporates a hydraulic actuator and hydraulic damping, which can be modeled by a mechanical and hydraulic co-simulation model using AMESim2020 software. The simulation reveals a substantial reduction in cabin vibrations equipped with PCRGS. Specifically, under pulse excitation, the reduction ranges from 26.2% to 27.5%; under white noise excitation, it varies between 14.3% and 17.1%; and under sine wave excitation, the reduction spans 21.2% to 24.1%. Notably, the system meets the stringent ‘Excellent’ (<=0.07 m/s²) performance criteria under sine wave excitation at lower frequencies, signifying its high effectiveness. These findings not only underscore the potential of hydraulic passive-control guide shoes in mitigating elevator vibrations but also provide invaluable guidance for their further development and refinement. Full article

Vibrations generated by the main rotor-gearbox assembly in a helicopter are the principal cause of damage to cockpit instruments and crew discomfort in terms of cabin noise. The principal path of vibration transmission to the fuselage is through the gearbox’s rigid support struts. This article is Part 2 of a two-part paper presenting an innovative solution involving the replacement of rigid struts with low-weight, high-performance active dampers for vibration control developed by Elettronica Aster S.p.A. Part 1 provided a comprehensive overview of the system layout obtained through a model-based design process and presented a thorough description of the adopted nonlinear mathematical model. Part 2 focuses on the physical realization of the damper and its dedicated experimental test bench. The mathematical model parameter fitting procedure is presented in detail, as it has been used to help in the definition and optimization of the control schemes and the verification of the expected performance. The experimental results obtained in Part 2 not only demonstrate the compliance of the active damper prototype with the acceptance tests outlined in the ATP but also provide compelling evidence reinforcing the promise of the presented solution for effective vibration reduction. Full article

The high level of noise in helicopter cabins considerably compromises the comfort and safety of the pilot and passengers. To verify the feasibility and effectiveness of microperforated panel composite sound absorption structures for noise suppression in helicopter cabins, simulation and experimental studies were conducted on a model of a light helicopter cabin. First, three microperforated composite sound absorption structures for the helicopter cabin wall panel were designed. Then, a finite element model of the main gear/body acoustic vibration coupling was established to obtain the target frequencies of the microperforated composite sound absorption structures; the acoustic effect was verified via simulation. Finally, a model helicopter cabin equipped with the three microperforated composite sound absorption structures was built, and a cabin noise test was performed. The test results showed that the combined microperforated panel acoustic structure and microperforated panel–porous material composite structure realized an overall cabin sound pressure level attenuation of 8–10 dB, on average, in a wide frequency range of 500–2000 Hz, with an amplitude of more than 20 dB. The microperforated panel–acoustic supermaterial composite structure achieved low-frequency sound absorption in the frequency range of 300–450 Hz. The sound absorption effect reached 50%, and it also exhibited good noise reduction effects in the middle- and high-frequency bands. Full article

It is a well-established practice to build a robust system for sound event detection by training supervised deep learning models on large datasets, but audio data collection and labeling are often challenging and require large amounts of effort. This paper proposes a workflow based on few-shot metric learning for emergency siren detection performed in steps: prototypical networks are trained on publicly available sources or synthetic data in multiple combinations, and at inference time, the best knowledge learned in associating a sound with its class representation is transferred to identify ambulance sirens, given only a few instances for the prototype computation. Performance is evaluated on siren recordings acquired by sensors inside and outside the cabin of an equipped car, investigating the contribution of filtering techniques for background noise reduction. The results show the effectiveness of the proposed approach, achieving AUPRC scores equal to 0.86 and 0.91 in unfiltered and filtered conditions, respectively, outperforming a convolutional baseline model with and without fine-tuning for domain adaptation. Extensive experiments conducted on several recording sensor placements prove that few-shot learning is a reliable technique even in real-world scenarios and gives valuable insights for developing an in-car emergency vehicle detection system. Full article

This study considered implementing an active road noise control (ARNC) system using an electronic sound generator (ESG) as a secondary actuator to suppress road noise in a car cabin. The ESG was installed to the cowl panel of a test car to generate structure-borne anti-noise by vibrating the panel. A robust multiple-reference single-input single-output (MR-SISO) ARNC algorithm based on the FxLMS was designed. Four 3-axis accelerometers and a microphone were adopted to acquire the reference signals and the error signal for the control algorithm. The radiated sound pressure from the ESG–cowl pair was high enough to suppress the road noise at a car speed of 60 kph. The optimized least number of reference signals and their locations were determined after computer simulation from the measured primary path data. Real-time control experiments showed an A-weighted sound pressure level reduction of 6.0 dB in the average of three dominant road booming noises in 100–250 Hz with the four optimized reference signals at 60 kph. More reference signals gave a further reduction such as 8.3 dB with 12 reference signals. Thus, this study suggests that the ESG coupled with the cowl panel can be an affordable alternative as a secondary actuator in an ARNC system to suppress road noise in a car. Full article

This paper presents an inside-cabin acoustic evaluation of the IAR PUMA 330 helicopter, manufactured by IAR S.A. Brasov. In this study, based on the acoustic assessment inside the helicopter, areas with high noise levels are identified. In this regard, several tests were carried out in accordance with the ISO 5129 standard. In the first stage of the assessment, a measurement campaign was performed to identify the acoustic leaks from the outside noise sources propagating inside the cabin (in the door area) and the acoustic attenuation of the helicopter structure. These tests were performed on the factory runway, with the helicopter in parked position (ground tests). During the ground tests, the helicopter engines were turned off. The tests consisted of placing two loudspeakers directed towards the helicopter door and generating pink noise. Inside the helicopter, the entire door frame opening was scanned with an intensity probe to identify acoustic leaks areas. The second assessment stage was to determine the areas of the cabin with the highest levels of noise. Within the measurement campaign, 16 microphones were placed inside the cabin, at the level of the passengers’ heads, arranged in seven zones. The tests were carried out with the helicopter engines started, staying at fixed point above the ground (hovering), and then a flight test, in which all the maneuvers necessary for the use of the helicopter were performed (in-flight tests). Based on the measurement results, it was possible to highlight the noise spectral components in each of the seven areas. The noise assessment revealed high noise levels inside the cabin, having as main noise sources the transmission gear and the door area, leading to the need for reducing the noise exposure for passengers and crew, thus the need to reduce noise levels inside the helicopter. Full article

This paper proposed a local active control method for the reduction of road noise inside a vehicle cabin. A multichannel simplified hybrid active noise control (sHANC) system was first developed and applied to the rear left seat of a large sport utility vehicle (SUV). The attenuation capability of the sHANC system was investigated through simulations, using reference signals provided by accelerometers on the suspensions and bodywork of the vehicle and microphones on the floor of cabin, respectively. It was shown that compared to the traditional feedforward system, the sHANC system using either vibrational or acoustical reference signals can produce a significant suppression of the narrowband peak noise between 75 and 80 Hz, but the system lost the control capability in a range of 100–500 Hz when the acoustic signals were used as references. To reduce the practical implementation costs while maintaining excellent reduction performance, a modified simplified hybrid ANC (msHANC) system was further proposed, in which combined vibrational and acoustical signals were used as reference signals. The off-line analyses showed that four reference accelerometers can be substituted by ten microphones without compromising attenuation performance, with 3.7 dBA overall noise reduction being achieved. The effect of delays on the reduction performance of msHANC system was also investigated. The result showed that the msHANC system was more sensitive to the delays compared to the sHANC system if using only vibrational reference signals. Full article

This work deals with the reduction of aircraft interior noise using active sidewall panels (linings). Research work done in the past showed that considerable reductions of the sound pressure level (SPL) in the cabin are possible using structural actuators mounted on the lining and error microphones distributed in front of the linings. However, microphones are undesirable for error sensing because they are not suitable for the realisation of an integrated and autonomous active lining (smart lining module). Therefore, the goal of the present work is the replacement of the microphones by structural sensors. Using the structural sensors as remote sensors in combination with an acoustic filter, virtual microphones can be defined. The present study relies on experimental data of a double-walled fuselage system which is mounted in a sound transmission loss facility. Simulation results based on measured time data and identified frequency response functions are provided. Different configurations of virtual microphones are investigated regarding the SPL reduction and the induced vibration of the lining panel. Full article

This Special Issue highlights the latest enhancements in the abatement of noise and vibrations of aerospace and automotive systems. The reduction of acoustic emissions and the improvement of cabin interior comfort are on the path of all major transportation industries, having a direct impact on customer satisfaction and, consequently, the commercial success of new products. Topics covered in this Special Issue deal with computational, instrumentation and data analysis of noise and vibrations of fixed wing aircrafts, satellites, spacecrafts, automotives and trains, ranging from aerodynamically generated noise to engine noise, sound absorption, cabin acoustic treatments, duct acoustics and vibroacoustic properties of materials. The focus of this Special Issue is also related to industrial aspects, e.g.,: numerical and experimental studies have been performed for an existing and commercialized engine to enable design improvements aimed at reducing noise and vibrations; moreover, an optimization is provided for the design of low vibroacoustic volute centrifugal compressors and fans whose fluids should be strictly kept in the system without any leakage. Existing procedures and algorithms useful to reach the abovementioned objectives in the most efficient way are illustrated in the collected papers. Full article

Propeller synchrophasing control is an active noise control method which can effectively reduce the noise in the cabin of a turboprop aircraft. The propeller signature model identified by the measured acoustic noise data is easily affected by flight speed, altitude, and the existence of the fuselage. Meanwhile, the noise excited by the propellers is nonstationary signal, which often fluctuates greatly, thus affecting the accuracy of the identification of the model. In this paper, a synchrophasing control experimental platform with a cylindrical scaled fuselage on ground is firstly established to validate the actual noise reduction in the cabin. Then, a minimum fluctuation data selection method based on wavelet filtering and three-parameter sinusoidal fitting is proposed to improve the identification accuracy of the propeller signature model. This method extracts the high-precision propeller blade passing frequency signal from the noise signal by using a wavelet filtering algorithm and selects the minimum fluctuation data segment by using a three-parameter sinusoidal fitting algorithm. The experimental results firstly show the significant noise attenuation achieved in the cabin using propeller synchrophasing control. Secondly, the propeller signature model improved by the minimum fluctuation data selection method has higher accuracy than that identified by the traditional method. Full article

Natural fibres have been extensively studied due to their potential in a wide range of applications. This study aims to demonstrate the viability of composite earmuffs for low-frequency noise reduction in continuous and transient noise environments. Pink noise and aircraft take-off exterior noise were considered for the former and the latter, respectively. The assembly components of the composite earmuffs were kept identical to a commercial earmuff, which served as a reference for results comparison. Based on the profile of the ear cups from the commercial earmuff, composite ear cups were fabricated from coir fibre and coir/carbon fibre fabrics reinforced with polypropylene. In contrast to the commercial earmuff, the composite earmuffs showed improvements in insertion loss at specific frequencies in the respective noise environments. In pink noise, up to 12 dB improvement in insertion loss was achieved. In aircraft take-off exterior noise, up to 8.6 dB improvement in insertion loss was achieved at 160–544 Hz particularly by the coir fibre-reinforced polypropylene earmuff. Consequently, the proposed earmuffs may find applications in areas where noise exposure is predominantly low-frequency—in some vehicle cabins, at airports, and at construction sites, for example. Full article