Cabin Noise Levels Research Articles

Sound-absorbing structures to reduce cabin and community noise of aircraft (Review)

The analysis of sound-absorbing structures is carried out taking into account their modern classification. The considered sound-absorbing structures can be used to reduce aircraft cabin and community noise levels. Depending on the spectrum of the main noise sources, the required type of sound-absorbing structure is selected, which is then adjusted to the problematic frequency range. Semiempirical and experimental methods are used to adjust sound-absorbing structures, and numerical methods are currently being actively developed.

Comparison of cabin noise of turboprop and turbofan aircrafts

Turboprop aircrafts are typically used for transporting cargos and for low-capacity short-haul air transport between regional cities. The new designs of turboprop aircrafts tend to focus on noise and comfort level of the aircrafts. Although turboprop aircrafts are known to have relatively higher cabin noise, there are limited reported studies in the open literature examining the actual cabin noise level in commercial flights. In this study, the cabin noise of the ATR 72-500 turboprop aircraft was examined and compared with that of the Bombardier CRJ 900 turbofan aircraft during actual commercial flights. Both are passenger planes which are designed to carry fewer than 100 passengers and are deemed to be a more compatible comparison. Both are single isle aircraft with two seats on each side of the isle. The Bombardier CRJ 900 is found to have a lower cabin noise in terms of both dBA and dBC for both taxing and cruising. As the average equivalent continuous sound pressure level (Leq) for cabin noise is found to be well below 85 dBA, there is no risk of exceeding the daily exposure to noise of 85 dBA for eight hours under the National Institute for Occupational Safety & Health (NIOSH) regulation. However, as many reported studies have shown that prolonged exposure to low frequency noise may lead to disorders, discomfort, sensitivity to and irritability from noise, annoyance, hearing loss, and cardiovascular diseases, there may be a need to carry out a more detailed study of the effect of low frequency noise on passengers.

Design, development and testing of digital MEMS pressure sensor array for full-scale vibroacoustic measurements

This manuscript addresses design, development, and application of micro-electro-mechanical systems (MEMS) based digital pressure sensor array for vibroacoustic measurements. These vibroacoustic measurements were conducted on a A320 type single aisle aircraft demonstrator subjected to broadband as well as tonal excitations. Cabin noise levels were measured with both condenser microphones as well as digital MEMS pressure sensor array. The measured cabin noise shows strong qualitative as well as quantitative agreement between both type of measurement devises for full scale cabin noise measurements inside an aircraft demonstrator. The observed strong agreement is valid for both single wall (fuselage with thermal insulation) and double wall (fuselage with thermal insulation and trim panel) cabin noise measurements. Such strong agreement within 1.0 dB tolerance is significantly motivating for further development of reliable but low-cost MEMS based measurement devises and corresponding efficient data post-processing algorithms for full scale vibroacoustic measurements in general. Additionally, it is also demonstrated that the large number of MEMS based digital pressure sensors can be used in areas where the physical space constraints are high. This demonstration shows strong potential to derive additional vibroacoustic indicator for the development and the testing of future noise control solutions in a non-traditional way.

Influence of public transport ergonomic features on passenger's functional state

The article means an analysis of the passenger transport services quality issue. Researches of public transport routes ergonomic features and their influence on a passenger functional condition are provided. The analysis of such indicators as cabin occupancy rate, noise level, vibration, and acceleration was carried out. Mathematical dependences of the passenger functional condition change considering vehicles ergonomic features were constructed. Threshold values of passenger compartment microclimate, providing the stress index normative values were determined. The most valuable result of the study is a comparative assessment of each type of public transport in terms of comfort and obtaining threshold values of noise, vibration, and acceleration which are acceptable for the normal passenger’s functional condition.

Substructuring verification of a rear fuselage mounted twin-engine aircraft

Dynamic substructuring allows for the reduction of large complex structures into substructures to increase computational efficiency and to isolate the local dynamic behaviors of concern. However, errors such as truncation, continuity and rigid body mode errors still limit the applicability of this method experimentally. Additionally, the feasibility of implementing substructuring techniques on finite element models of multi-component fuselage structures has yet to be shown in the literature. The objective of this paper is twofold: first to introduce a feasible substructuring methodology that mitigates the experimental and multi-component limitations with current methods; and secondly, to investigate the modal properties and applicability of substructuring analysis on a rear fuselage mounted twin-engine aircraft. This configuration is not well understood in the literature despite having been shown to have increased interior cabin noise and vibration levels. Experimental validation of the computational model was first performed. A substructuring analysis of the validated computational model produced natural frequencies of the local and global modes that agreed within 6.47% on average, and pseudo-orthogonality terms greater than 0.89 for all modes considered. This methodology proved to be useful for generating an accurate representation of local modes within a global structure for the aircraft configuration studied. This will allow for future work to more thoroughly investigate the local modes using innovative design methods with confidence that the local modes will correlate with the global modes.

DEVELOPMENT AND SOUND ABSORPTION TESTING OF A POROELASTIC KENAF/SISAL FIBRE COMPOSITE TRIM FOR LOWERING OF VEHICLE CABIN NOISE LEVELS

ABSTRACTThe automotive industry is under pressure to produce a product (vehicle) that is morerecyclable and environmentally-friendly with a high fuel efficiency. At the same time,customers are looking for a vehicle that will provide them with a comfortable ride andlow cabin noise levels. Therefore, the present work is concerned with thedevelopment and characterization of new poroelastic natural fibre-based soundabsorbers, which have not yet been contemplated. This newly developed material isto be recyclable and in addition, be an environmentally-friendly alternative tosynthetic absorbers which are currently used as internal trims in vehicles. Therefore,several sound absorber variants, based on the above, were developed and tested inorder to select an optimally performing product. These sound absorbers are made ofdifferent ratios of kenaf and sisal fibres, which are held together by AcrylonitrileButadiene Styrene (ABS) matrix. On evaluation of the results, it was found that theproposed sound absorbers have airflow resistivity and sound absorption coefficientvalues compatible to that of normal practice.

Thermal comfort, vibration, and noise in Chinese ship cabin environment in winter time

The temperature, vibration, and noise in air-conditioned Chinese vessel cabins in wintertime were investigated in this study. Field measurements were used to appraise the thermal sensation vote (TSV) of crew members and passengers in specific cabin environments. The survey data was summarized and analyzed to determine the neutral temperature, preferred temperature, thermal preference, and thermal acceptance rate. The determined neutral and preferred temperatures of 20.9 and 21.5 °C indicated that the ship occupants preferred a temperature higher than the neutral temperature in winter. The acceptable operative temperature range was determined to be 18.54–23.29 °C. Although most passengers preferred the neutral environment or a slightly warmer one, the acceptable air temperature was appropriately lower. A fitting analysis was conducted on the TSV and predicted mean vote (PMV) using different levels of subject activity. The thermal neutral temperature predicted by the PMV was higher than that predicted by the TSV; however, a modification of the PMV brought the former closer to the latter. The vibration vote indicated that most of the subjects considered the ship's vibration level to be acceptable. Although the noise level in the passenger cabins was higher than the recommendation, only 12% of the subjects considered it a little troublesome. Conversely, the noise evaluation in the dining room was not particularly impressive, with 6% of the subjects considering it very troublesome, and24% considering it a little troublesome.

Investigation and refinement of gearbox whine noise

Structure borne noises can be transmitted to interior cabin via physical connections by gearbox as well as other active components. Experimental Transfer Path Analysis (TPA) methods are utilized to investigate main paths of vibrations which are eventually perceived as noise components inside the cabin. In this study, contribution ranking of transmission paths from active system components through the physical connections into the interior cabin are investigated by Operational Path Analysis with Exogenous Inputs (OPAX) method. In addition, the sensitivity and rigidity characterization of the body through dominant paths according to OPAX were measured to reveal the reason for the whine noise to the inner cabin because of the operational forces generated in the dominant structure-borne paths. And also, operational modal analysis was carried out to examine the modes of the dominant path components. The modifications are applied on dominant transfer paths according to dominant paths characterization by operational deflection shape analyses. Thus, the root causes are investigated on vehicle level NVH tests while observing the variations in the interior cabin noise level.

A review of porous automotive sound absorbers, their environmental impact and the factors that influence sound absorption

The transport sector accounts for ~25% of worldwide carbon dioxide emissions, where cars and trucks account for the bulk of this. The need for lighter and more efficient vehicles is becoming ever more crucial in light of the current trend in the depletion of petroleum reserves and the increasing effects of global warming. The effect that noise has on vehicle occupants is a growing concern as studies reveal the harmful effects that noise has on the human body. Hence, the automotive industry is under immense pressure to produce automobiles that are more environmentally-friendly. By acquiring available knowledge on the properties of porous sound absorbing materials and understanding the factors that influence sound absorption, designers can reduce vehicle weight and increase passive sound absorption and hence, reduce carbon dioxide emissions and improve vehicle cabin noise levels.

A review of porous automotive sound absorbers, their environmental impact and the factors that influence sound absorption

The transport sector accounts for ~25% of worldwide carbon dioxide emissions, where cars and trucks account for the bulk of this. The need for lighter and more efficient vehicles is becoming ever more crucial in light of the current trend in the depletion of petroleum reserves and the increasing effects of global warming. The effect that noise has on vehicle occupants is a growing concern as studies reveal the harmful effects that noise has on the human body. Hence, the automotive industry is under immense pressure to produce automobiles that are more environmentally-friendly. By acquiring available knowledge on the properties of porous sound absorbing materials and understanding the factors that influence sound absorption, designers can reduce vehicle weight and increase passive sound absorption and hence, reduce carbon dioxide emissions and improve vehicle cabin noise levels.

Active and passive techniques for a cost-effective noise reduction in the interior of aircraft cabins

Different noise reduction techniques that can be applied to the interior of aircraft cabin are investigated, to determine the most cost-effective means, without any aircraft external modifications, such as jet engine design change, or fuselage modifications, with no significant added weight. The goal of this research is to arrive at a cabin interior design that can be retrofitted to the existing aircraft interior to reduce overall cabin noise. Relaxation oscillations of the aircraft cabin model, considered as a system in forced vibrations with non-linear damping, and sub-harmonic resonances are considered. Negative and positive damping coefficients, and some techniques for noise cancelation by active means are discussed. From noise power-spectrum results for a typical aircraft cabin, amplitude versus audible frequency, one can determine the most energetic cabin vibration modes. Those modes require the highest damping. The proposed technique will utilize a regular matrix of the multiple sets of open Helmholtz resonators, with sound absorbing surfaces, that are imbedded in the cabin interior walls, just below the surface, and tuned to the highest noise level frequencies inside the cabin. The resonators dissipate the noise energy inside the aircraft at the most dominant frequencies, and hence reduce the overall cabin noise level.

Impact of Sound Insulation in a Combine Cabin

Purpose: Recently, environmental pollution and safety problems in agricultural production have become important issues. Initially, bio-production machines focused on high production efficiency rather than workers’ safety and comfort, but this trend slowly has changed as time went on. Methods: This study was carried out to identify sound efficiently and reliably for noise reduction by using a combine cabin model. Ethylene propylene diene monomer (M-class) rubber (EPDM) was applied to improve noise reduction performance from parts connected directly to the front, rear, left side, and bottom side of the cabin. Results: As a result, an average noise reduction of 1.85 dB was achieved in the normal hearing range between 500 Hz to 2 kHz. Conclusions: Reducing the cabin noise levels can reduce a worker's fatigue, improve working environment, and contribute to future low-noise and high-quality cabin environment.

Aeroacoustic Analysis of a High-Speed Open Rotor

Owing to their inherent fuel efficiency, there is renewed interest in developing open rotor propulsion systems that are both efficient and quiet. The major contributor to the overall noise of an open rotor system is the propulsor noise, which is produced as a result of the interaction of the airstream with the counter-rotating blades. Prediction of the propulsor noise is, therefore, a necessary ingredient in any approach for designing low-noise open rotor systems that can meet community noise regulations and have acceptable cabin noise levels. To that end, there has been a resurgence of activities in the aeroacoustic modeling of open rotors in recent years. While direct numerical simulations are gaining traction, the bulk of existing prediction capability resides in hybrid approaches in which the aerodynamics of the open rotor system is computed via CFD and is used as input in some appropriate “linear” acoustic model for computing the open rotor noise. At NASA the focus has been on assessing the utility of hybrid approaches for accurately predicting the open rotor tone spectra with an emphasis on the understanding of the role of the various underlying mechanisms of noise generation and their relative importance at different operating conditions. Using high-fidelity aerodynamic simulations of a benchmark (non-proprietary) open rotor blade set, together with acoustic models based on a high-blade-count asymptotic approximation of the Ffowcs-Williams Hawkings equation, tone noise predictions for a number of configurations have been carried out. These aerodynamic and acoustic predictions have been compared with wind tunnel measurements of the benchmark open rotor blade set to establish the capabilities and the limitations of the hybrid approaches. The results suggest that while predicting the absolute spectral levels is difficult, the noise trends are reasonably well predicted by such hybrid approaches at a reasonable overall computational cost.

산악트램 객실 쾌적성 향상을 위한 저진동 랙앤피니언 추진장치 개발

급구배 등판을 위해 산악트램에서 적용하는 랙앤피니언 추진장치는 기어가 맞물리면서 발생하는 진동에 의해 객실 쾌적성을 저해하게 되어 관광객들의 불만이 되고 있다. 본 연구에서는 기존 랙앤피니언 추진 장치의 진동을 저감하기 위해 저진동 랙앤피니언 추진장치를 개발하고 시험체를 제작하여 차륜접촉 시험기를 통해 그 효과를 확인하였다. 기존 강체 랙앤피니언 추진장치에 비해 탄성 랙앤피니언 추진장치는 진동이 1/20 이하로 저감됨을 확인할 수 있었고, 탄성체의 교체를 편리하게 하기 위해 착탈 방식으로 설계하여 유지보수성도 향상시켰다. 탄성 랙앤피니언 추진장치를 산악트램에 적용하였을 시에 진동을 획기적으로 감소시켜 객실 쾌적성 향상에 크게 기여 할 수 있으리라 전망된다. Rack & pinion traction system on mountain tram for climbing steep gradient tracks makes worse the comfortability of cabin because of the vibration generated by gear contact. That is the main reason for complaint of tourists. In this study, to reduce the vibration level of the previous rack&pinion traction system, a low vibration rack&pinion traction system was developed and test models were made so that it could be verified by a wheel-rail contact testing machine. The vibration level induced by the low vibration rack&pinion traction system was 20 times less than that by the conventional rack&pinion traction system. This low vibration rack&pinion traction system can be maintained easily because simple replacement of resilient body is possible. If this resilient rack&pinion traction system is applied to a mountain tram, the vibration and noise level in cabins is reduced drastically so that the comfortability of tourists can be increased.

Mining Dump Truck Noise Sources and Mitigation Approaches

In order to reduce noise-induced hearing loss from work-related noise exposure, mine workers, union representatives, mine managers, equipment manufacturers must work in partnership to successfully construct and implement new and better noise controls. On new machines, cabin noise levels are not normally a problem. Insulation around engines and fans greatly reduces noise and sound-proofing of the cab can keep operator exposure well below 85 dB(A). In other words, over time, exposure to noise levels at or above 85 decibels can lead to permanent hearing loss. However, the benefits of soundproofing will be lost if windows and doors are not kept closed and low noise output air-conditioning units might be needed. This article is concerned with the main sources of noise in dump trucks used for mining application and also the noise reduction methodologies.

Altitude and airspeed effects on the optimum synchrophase angles for a four-engine propeller aircraft

Abstract Noise and vibration is a serious problem in all types of aircraft. Any techniques that lower cabin noise and vibration levels by even a few decibels with little or no weight or performance penalties are worth pursuing. Propeller synchrophasing is one such technique that has shown potential in aircraft with two or more propellers; however this technique is not being used to its full potential because the synchrophase angles are typically fixed. This paper provides a detailed examination of how the optimum synchrophase angles in a typical four-engine propeller aircraft vary with different altitudes and airspeeds, and how this information could lead to the design of new adaptive propeller synchrophasing systems and potentially yield improvements to other active noise control measures in propeller aircraft.

Noise control options for aircraft floors

Aircraft manufactures seek light weight, cost effective technologies to reduce cabin noise levels. Customers and regulatory bodies are demanding lower noise levels in the cabin. Composite light weight structures, used to increase fuel efficiently, often increase input acceleration levels due to their relatively high stiffness and low damping. Therefore, noise control solutions must provide additional attenuation to meet the challenges of fuel efficiency and lower cabin noise levels. Aircraft floors are large radiating bodies that must be addressed. This paper explores noise control options for aircraft floors. Various isolation and damping methods are investigated. Analytical estimates are compared to empirical measurements for a sample aircraft floor.

Civil aircraft cabin noise resource acoustic characteristic and transmission path analysis

Typically, there are mainly 4 different noise resources critical to cabin +F1184noise: auxiliary power unit (APU) noise, environment control system (ECS) noise, engine noise and turbulent boundary layer (TBL) noise. Because of the different acoustic characteristic and transmission path for each resource, their impacts to cabin noise level are not the similar. A vibration and noise test under ground and flight status of an in-service civil aircraft was conducted. Based on the test results, comparing the data under different test status, the acoustic characteristic and transmission path are analyzed for the 4 noise resources in this paper, including distribution characteristic, spectrum characteristic and transmission path. APU noise mainly affects the rear fuselage, ECS noise transmits by ducts, engine noise and TBL noise transmit through side panel.

함정의 실내소음 허용기준 설정을 위한 청감평가 및 분석

The noise inside a naval vessel is very important in considering the need for hearing protection, improving the working environment and maintaining good communications for crews living on board a naval vessel. The indoor noise of a ship usually is specified by the A-weighted sound pressure level, but other evaluating parameters are required to reflect human senses more effectively. This paper uses additional noise indices related to room acoustics, such as NR(noise rating), NC(noise criterion), RC(room criterion), PSIL(preferred speech interference level) and loudness level to evaluate the noise inside cabins on a naval vessel. Using these psychological noise indices, allowable limit of noise level in cabins is suggested through psycho-acoustic evaluation for the noise in cabins.

Novel sandwich composite aircraft sidewall architectures.

An aircraft sidewall constructed of honeycomb sandwich composite materials could have a mass per unit area, which is 60% less than a comparable stiffened aluminum structure. With reduced weight, the sandwich composites have a high stiffness to mass ratio which yields high radiation efficiency with the result that the sandwich composite can have a transmission loss up to 10 dB less than its aluminum counterpart. A lightweight sandwich composite fuselage will then produce higher cabin noise levels and require additional treatment. The initial weight savings gained through the use of the composite material would be compromised by the need for the additional treatment. It may be possible to the reduce radiation efficiency of sandwich composites through novel features machined into the material’s core. To explore this possibility, several Nomex honeycomb, sandwich composite panels were designed constructed and tested. The performance of the composite panels in terms of both transmission loss and vibration response will be compared to that of a stiffened aluminum panel. It will be shown that it is possible to recover a good portion of the transmission loss reduction incurred with respect to the aluminum structure without sacrificing panel strength.