In this study a centrifugal fan is studied for noise characteristics and measurements in a semi- anechoic room. A semi-anechoic room is constructed inside Fluid Mechanics Laboratory of Mechanical Engineering Department has been qualified with respect to ISO 3745 standard. The fan characteristic is obtained as proposed in AMCA standards 210-75, by simply measuring the voltage and current of the motor during operation and calculating the power consumption of the assembly. Noise measurements are taken using two microphones attached to a multi-channel data acquisition and processing system in the semi anechoic room. Several different configurations of the vacuum cleaner with some parts removed or replaced systematically are considered during the noise measurements. Some of the results showed that the damping material placed inside the motor cover is proved to be very effective in noise reduction. Two different damping materials are examined for comparative evaluation.

In this study, a method to predict vehicle pass-by noise in a finite dimensioned, semi-anechoic chamber with chassis dynamometer has been developed. Vehicle noise has been modeled as the summation of the individual contributions regarding the principal noise components, namely, engine including air intake, front tire and rear tire noises. This method employs wave propagation, Doppler shift, and time delay in the estimation of the sound pressure due to each component at points of interest specified by relevant standards. An acoustical simulation model has been developed in MaTLAB environment. The model has been applied on two different vehicles. Finally, the predicted sound pressure values are found to be in good agreement with the corresponding values acquired in outdoor measurements addressed in ISO 362 for vehicle pass-by noise measurement standard.

This Master´s thesis deals with principles of determination of the sound power level. At the very beginning there is an explanation of important concepts. Afterwards there is an overview of standards that deal with the sound power level determination, including the ČSN EN ISO 9614-1 standard which is used for the experiment. Last but not least, there is described the experiment, consisting of several measurements of the same object, but every time with different configuration of measuring and sound reflective surfaces.

Master thesis examines a selected part of electromagnetic compatibility. In this work, there is theoretically discussed how electromagnetic interference appears and how is spread through free space environment. To eliminate ambient interference signals, the measurements have been performed in anechoic chamber where the undesirable interference signals were suppressed. In the thesis, there are also described parameters of EMI receivers and limits of electromagnetic interference. The description of calculations of the antenna height for finding maximum intensity of electric field strength for standard measurement distance has been made. For proposed transformed measurement distance, calculations of intensity electric field with addition of parameters measuring antenna and object under test were performed. Correction curves for conversion intensity electric field have been obtained as the result.

Les techniques de mesure de diagramme de rayonnement d’antenne actuelles partagent un paradigme commun qui stipule que l’information utile est exclusivement portée par le signal de test généré. Cela implique un effort mécanique fastidieux en faisant tourner l'antenne sous test ou en déplaçant le système de sondes afin de couvrir des angles de mesure différents jusqu'à ce qu'une caractérisation complète soit effectuée ; une limitation qui est généralement surmontée en utilisant des systèmes multisondes coûteux. En outre, toute réflexion provenant du site de mesure et des équipements de test est considérée comme parasite perturbant le signal de test et est ainsi minimisée.Dans cette thèse, un concept de mesure du diagramme de rayonnement d'antenne remettant en cause ce paradigme commun est présenté comme un moyen d'accélérer le processus de caractérisation en utilisant des systèmes économiques. Le paradigme proposé consiste en la génération d'un ensemble d'échos contrôlées, en utilisant des configurations impliquant des plaques réfléchissantes, qui contribueraient directement à la mesure en couvrant différents angles, et récupérer les informations portées par l'ensemble des signaux générés simultanément. Une diversité fréquentielle est introduite afin de générer un système d'équations équilibré où le vecteur inconnu contenant les valeurs du diagramme de rayonnement est récupéré en inversant un problème matriciel. Par conséquent, une attention considérable est accordée au conditionnement du modèle mathématique afin d'assurer la stabilité et la robustesse du systèmeTrois configurations de différents niveaux de complexité en termes d'échos contrôlés sont étudiées, en mettant l'accent sur la configuration la plus simple impliquant un seul écho contrôlé. Des modèles ont été mis au point, avec des contraintes de conception des configurations proposées en termes de dimensionnement et de bandes passante de fonctionnement, mettant en évidence la viabilité mathématique du concept. Les aspects pratiques ont également été évalués en étudiant la tolérance des modèles développés vis-à-vis des erreurs systématiques, ainsi qu’à l'impact de l’application d'un ensemble d’hypothèses simplificatrices. La faisabilité du concept ainsi que son utilité pour accélérer le processus de caractérisation par rapport aux techniques classiques ont été mises en évidence par des simulations numériques. Ce travail ouvre la porte à l'exploitation des échos, généralement considérés comme perturbateurs, dans un contexte de mesure d’antennes. / Current antenna radiation pattern measurement techniques share a common paradigm which states that useful information is exclusively carried by the generated test signal. This implies an excessive, time consuming, mechanical effort by rotating the antenna under test or displacing the probe system in order to cover different measurement angles until a complete scan is performed; a limitation that is typically overcome using costly multi-probe systems. Moreover, any reflection from the measurement site and test equipment is considered spurious as it perturbs the test signal and thus is minimized.In this thesis, an antenna radiation pattern measurement concept challenging this common paradigm is introduced as a mean of accelerating the characterization process using cost-efficient systems. The proposed paradigm consists in the generation of a set of controlled echoes, using set-ups involving highly-reflective plates, which would directly contribute to the measurement alongside the line-of-sight signal by covering different measurement angles, and retrieving the ARP information carried by the set of all generated signals concurrently. Frequency diversity is used in order to generate a balanced system of equations where the unknown ARP vector is retrieved by inverting a matrix problem. Consequently, a considerable attention is paid into the conditioning of the mathematical model in order to ensure the system stability and accuracy.Three configurations of different complexity levels in terms of controlled echoes are studied, with focus on the simplest configuration involving a single controlled echo. Models have been developed with design guidelines for the proposed configurations in terms of set-up dimensions and operating frequency bandwidth highlighting the mathematical viability of the concept. Practical issues were also assessed by studying the tolerance of developed models to systematic practical errors, as well as to the impact of an applied set of simplifying assumptions. The feasibility of the concept as well as its usefulness in accelerating the measurement process with respect to classical techniques were highlighted via numerical simulations. This thesis opens the door for exploiting echoes, generally regarded as a nuisance, in an antenna measurements context.

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The desire to gather acoustic data of a propeller in simulated hover without environmental effects is met with the challenge of recirculating flow in a closed anechoic chamber. Flow recirculation in an anechoic chamber is not ideal because the effects of it being ingested by the rotor cause unsteady loadings on the propeller. This unsteady loading causes vortex noise from the turbulence introduced by the recirculation of the flow. The aim is to study the acoustic signature of a propeller separate from external factors and engine noise. Two different propellers with three different screen combinations were tested in a closed anechoic chamber. The results of these tests showed that the screens are able to reduce the vortex and broadband noise levels, with the reduction being more pronounced when the dual screen was installed.

A high-resolution directivity measurement system at Brigham Young University has been renovated and upgraded. Acoustical treatments have been installed on the microphone array, professional-grade audio hardware and cabling have been utilized, and user-friendly MATLAB processing and plotting codes have been developed. The directivities of 16 played musical instruments and several loudspeakers have been measured by the system, processed, and plotted. Using loudspeakers as simulated musicians, a comprehensive analysis was completed to validate the system and understand its error bounds. A comparison and evaluation of repeated-capture to single-capture spherical systems was made to demonstrate the high level of detail provided by the 5 degree resolution system. Analysis is undertaken to determine how nonanechoic effects in anechoic chambers influence results. An overview of directivity measurement systems from the literature is provided as well as a dedicated discussion of the directivity measurement system at Brigham Young University.

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