Thomas Padois

École de Technologie Supérieure · Mechanical Engineering

To protect workers, it is necessary to characterize the noise and vibration emissions value of nailers. Standardized characterization methods exist but require three trained human operators, which leads to a dispersion in the results and a difficult implementation. An automatic test stand (ATS) was developed to characterize those values without the...

Acoustic imaging can be performed using a spherical microphone array (SMA) and conventional beamforming (CBF) or spherical harmonic beamforming (SHB). At low frequencies, the mainlobe width depends on the SMA radius for CBF and on the order of the spherical harmonics expansion for SHB, which is related to the number of microphones. In this letter,...

Hydraulic pumps are considered to have a major contribution to the structure borne noise generated inside aircrafts. Methods such as Component-Based Transfer Path Analysis (CB-TPA) are promising tools for aircraft manufacturers to build internal processes for the specification, design and validation of the impact of vibrating systems on new aircraf...

Structure borne noise induced by vibrating systems is considered as a major contribution to the noise generated inside vehicles and can be assessed using Transfer Path Analysis (TPA) methods. Their theoretical formulation requires the mobility of either the vibrating system, the receiving structure or the assembly of the two components according to...

In a workplace, sound waves come from all directions. Spherical microphone arrays are therefore more suitable than planar microphone arrays to localize sources. If the microphones are flush-mounted on a solid sphere, the microphone array is considered rigid. Otherwise, the microphones can be mounted on a wireframe and the microphone array is said t...

Developing innovative noise policies that build on international best practices is difficult when policies around the world differ along many dimensions, ranging from different sources covered to different levels of governance involved. This is particularly critical in the context of road traffic, identified as one of the main culprits leading to n...

Structure borne noise is considered a major contribution to the noise generated inside aircrafts. In order to analyze it, engineering methods have been developed such as Transfer Path Analysis (TPA) and Source Characterisation (SC). These methods are based on active and passive properties of the source and the receiving structure being coupled or d...

Nowadays, acoustic cameras have become a standard tool for visualizing sound sources. The main post-processing techniques for generating acoustic images are associated with beamforming in the time or frequency domain. While many advanced techniques have been developed for the latter in order to achieve high resolution, such as deconvolution or inve...

Over the past few decades, various low frequency noise control technology concepts incorporating acoustic metamaterials have been proposed in the literature. The proposed technologies showed promising performance, with a significant noise attenuation rate per thickness unit and are considered as an improved solution when compared to conventional so...

Many workers are exposed daily to excessive noise levels. In order to reduce the noise exposure at the workstation, the main noise sources have to be detected. This task can be done with a microphone array and a source localization technique. Previous studies have shown promising results with time domain beamforming based on the generalized cross-c...

The generalized cross correlation (GCC) is a standard technique for estimating time delay between microphone signals. A prefiltering operation by a weighting function may be included to whiten the cross spectrum of the microphones signals. The expected result is a narrow cross correlation function and a more accurate estimation of the time delay. A...

Many workers in the construction industry can be exposed to high level of impulsive noise and vibration from the operation of nail guns. Since these tools use a single shock to hammer a nail, using RMS weighted acceleration, such as the a hw value (ISO 5049-1), might not be sufficient to assess health risks from such impulsive vibration exposure. T...

Multiple vibratory sources are integrated in the aircraft and rotorcraft. The vibrational power of these sources is injected to the receiving structure through their connection points resulting in annoying acoustic levels in the cabin. This noise, referred to as structure borne noise, could be mitigated if vibrating systems, receiving structures an...

Phased microphone arrays have become a well-established tool for performing aeroacoustic measurements in wind tunnels (both open-jet and closed-section), flying aircraft, and engine test beds. This paper provides a review of the most well-known and state-of-the-art acoustic imaging methods and recommendations on when to use them. Several exemplary...

The generalized cross correlation (GCC) is an efficient technique for performing acoustic imaging. However, it suffers from important limitations such as a large main lobe width for noise sources with low frequency content or a high amplitude of side lobes for noise sources with high frequencies. Prefiltering operation of the microphone signals by...

In the construction industry, many workers are exposed daily to harmful levels of impulsive noise from nail guns. Therefore, a better knowledge of the noise generated by these tools is required in order to propose noise reduction solutions. The objective of this work is to propose an approach for source identification using a microphone array toget...

Microphone arrays are an efficient tool for localizing acoustic sources. Time domain beamforming is one of the techniques which can be used to build a sound source map. This technique based on the cross-correlation of the microphone signals can be seen as a broadband beamforming method. The spatial likelihood functions are averaged with the arithme...

For several years, lack of comfort has been pointed out as a major reason of earplug poor efficiency as noise control solution. The great complexity of comfort makes it difficult to predict it in the earplugs design phase. It is rather considered in an empirical way by the manufacturers using trial-and-errors approaches based on subjective assessme...

This paper addresses source localization technique in time domain for broadband acoustic sources. The objective is to accurately and quickly detect the position and amplitude of noise sources in workplaces in order to propose adequate noise control options and prevent workers hearing loss or safety risk. First, the generalized cross correlation ass...

In extremely noisy environments, it is normally recommended to use a combination of earplug and earmuff, denoted here as a dual protection, to protect workers from the excessive noise. Unfortunately, it has been shown repeatedly that the attenuation values obtained with the dual protection are generally less than the sum of the individual earplug a...

Microphone array techniques are an efficient tool to detectacoustic source positions. The standard technique is the delay and sum beamforming. In the time domain, the generalized cross correlation of the microphone signals is used to compute the Spatial Likelihood Functions (SLF) of all microphone pairs and the noisesource map is provided by the ar...

Microphone array associated to signal processing technique such as beamforming is an efficient tool to localize acoustic sources. In an open wind-tunnel, the microphone array can be set below, above or on the side of the flow. The microphones are spatially distributed over a two-dimensional (2D) plane and the geometry may be regular, circular or a...

Snowmobile manufacturers invest important efforts to reduce the noise emission of their products. The noisesources of snowmobiles are multiple and closely spaced, leading to difficult source separation in practice. In this study, source imaging results for snowmobile pass-by noise are discussed. The experiments involve a 193-microphone Underbrink a...

Millions of workers are exposed to excessive noise levels each day. Acoustic solutions have to be developed to protect workers from hearing loss. The first step of an acoustic diagnosis is the source localization which can be performed with a microphone array. Spherical microphone arrays can be used to detect the acoustic source positions in a work...

Microphone array techniques are an efficient tool to detect acoustic source positions. The delay and sum beamforming is the standard method. In the time domain, the generalized cross-correlation can be used to compute the noise source map. This technique is based on the arithmetic mean of the spatial likelihood functions. In this study, the classic...

The acoustic signature of a controlled-diffusion airfoil immersed in a flow is experimentally characterized. Acoustic measurements have been carried out in an anechoic open-jet-wind-tunnel for low Reynolds numbers (from 5 × 104 to 4.3 × 105) and several angles of attack. As with the NACA0012, the acoustic spectrum is dominated by discrete tones. Th...

Le développement croissant des moyens de transport a engendré des nuisances sonores en zone urbaine et périurbaine. Pour pallier ce problème les industriels sont amenés à effectuer des études en vue de la réduction du bruit. La première étape de ce travail consiste à localiser les zones responsables de la production sonore. Le traitement d’antenne...

Microphone arrays and beamforming have become a standard method to localize aeroacoustic sources. Deconvolution techniques have been developed to improve spatial resolution of beamforming maps. The deconvolution approach for the mapping of acoustic sources (DAMAS) is a standard deconvolution technique, which has been enhanced via a sparsity approac...

This study presents the first set of experiments with the Controlled-Diffusion (CD) airfoil in the newly-built anechoic wind-tunnel at Université de Sherbrooke. Velocity measurements in the latter show very uniform mean flow and low turbulence level (0.4 %) up to 56 m/s in the 30 cm square nozzle exit section. Acoustic and velocity measurements hav...

Sound environment reproduction of various flight conditions in an aircraft mock-up is a valuable tool for the study, prediction, demonstration, and jury testing of interior aircraft sound quality. To provide a faithful reproduced sound environment, time, frequency, and spatial characteristics should be preserved as much as possible. Physical sound...

The aim of sound field reproduction is to physically reproduce a sound field in an extended area using loudspeaker arrays. Typically, the virtual scene is described by a composition of simple sources (spherical waves, plane waves) fed by monophonic signals from proximity microphones or a microphone array recording. It would be useful to combine the...

The EXEJET project is a large-scale jet noise collaborative program by Snecma, Onera and Airbus. In this framework, an exhaustive experimental database has been collected on a realistic dual-jet stream mounted around a central plug. The high-bypass ratio jet is operated at approach conditions in the CEPRA19 anechoic wind-tunnel. In the present pape...

This paper summarizes the techniques used during a microphone array test campaign performed at Pierre-Elliott-Trudeau Airport in Montréal, Québec (Canada) during the summer of 2012. Emphasis is put on the actual measurement campaign as only a limited amount of analysis has been performed at this stage. An aircraft position tracking tool is presente...

Engines being quieter due to high by-pass ratios, the airframe noise, produced for instance by landing gears or high-lift devices, has become a significant contributor to the total noise radiated by aircraft during approach and landing. As part of the investigations carried out to understand noise generation mechanisms, the beamforming techniques d...

The detection of aeroacoustic sources in closed or open wind-tunnels usually involves microphone arrays. In this case, the source are searched in a planar two-dimensional grid. Recently, the potential of beamforming with a three-dimensional grid has been studied but with a two-dimensional planar array. In this paper, we apply sound source localizat...

Engines being quieter due to high by-pass ratios, the airframe noise, produced for instance by landing gears or high-lift devices, has become a significant contributor to the total noise radiated by aircraft during approach and landing. As part of the investigations carried out to understand noise generation mechanisms, the beamforming techniques d...

In June 2012, fly-over measurements were performed on landing aircraft at P.-E. Trudeau Montréal airport. A custom-made measurement system developed by GAUS (Groupe d'Acoustique de l'Université de Sherbrooke) including a 95-microphone array with its related audio pre-amplifying and recording system have been used to acquire a comprehensive data set...

The beamforming technique has become a common method to localise aeroacoustic sources. However, in the case of anechoic wind tunnel experiments, some shear flow corrections have to be taken into account in order to estimate accurately the position and power of the source. This study deals with the efficiency of such corrections. Several correction...

Audio is also an active topic for acousticians in the aircraft manufacturing industry. Typical concerns are sound quality, noise annoyance or realism, in case of flight simulators. Accordingly, sound field reproduction of real flight conditions in aircraft mock-ups is a valuable tool for jury testing, listening test or marketing purposes. Recently,...

The possibility of using the time-reversal technique to localize acoustic sources in a wind-tunnel flow is investigated. While the technique is widespread, it has scarcely been used in aeroacoustics up to now. The proposed method consists of two steps: in a first experimental step, the acoustic pressure fluctuations are recorded over a linear array...

Phased-microphone arrays associated with beamforming have become a standard tech-nique to localize aeroacoustic sources. The limitations of beamforming have been overcome thanks to deconvolution technique (DAMAS or CLEAN-SC) or iterative process (L1-GIB). However, the computational cost of these methods can be large or assumptions on the source coh...

This paper concerns the direct measurement of wavenumber-frequency spectra beneath a two-dimensional Turbulent Boundary Layer. The main contribution of this work is the proposed setup that should help achieving a compromise between a small sensor diameter (to avoid spatial averaging) and small sensor spacing (to gain high spatial resolution). The e...

Beamforming (BF) is a powerful technique to localise sound sources in a wind-tunnel, but theflow effects on the acoustic propagation should be taken into account. An experiment is carried outin an anechoic wind-tunnel in order to validate the BF treatment associated to flow corrections.The results show that the BF technique can estimate very accura...

The time-reversal (TR) technique has been extensively developed over the two last decades, but very few applications have concerned the field of aeroacoustics. The possibility of using the TR technique in the context of wind-tunnel measurements is then investigated in this study, in order to localize a sound source in a flow. The chosen strategy is...

The present study aims at assessing the potentiality of the time-reversal (TR) technique to localize sound sources in flows, in the context of wind-tunnel measurements. The proposed method is a two-step procedure : the pressure fluctuations are recorded on a linear array of microphones located outside the flow; then the back-propagation of the acousti...