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Design and Measurement of Parameters of Acoustic Diffusors
Burda, Jan ; Vrba, Kamil (referee) ; Schimmel, Jiří (advisor)
This work focuses on the issue of acoustic diffusers. The introductory chapter describes the necessary theory of the sound distribution through enclosed space. Acoustic fields are also described. A description of the different diffusion element types and theirs design methods follows. It focuses mainly on design, which uses pseudo-random mathematical sequences. The aim of the work is to produce several types of acoustic diffusors and to verify their diffusion properties by means of measurements. The work uses the AFMG Reflex to simulate the diffusion properties of the proposed elements. Further, the thesis contains a description of the diffusion properties measurement process by the boundary plane method and the process of evaluating the measured data using the Matlab program.
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Compensation of loudspeaker measurements using standard baffle
Štěpáník, Jiří ; Schimmel, Jiří (referee) ; Balík, Miroslav (advisor)
The frequency response of the loudspeaker is one of the key data that needs to be known, for example, when designing a speaker cabinet or speaker system. The frequency response should be achieved with the highest possible accuracy and with a minimum of distortion. How to achieve such characteristics is described in the standard ČSN EN 60268-5, which states as one of the ways the use of standard enclosures. Except for the standard baffle, these baffles have correction curves for the measured characteristics described in the standard. However, this does not mean that the standard baffle does not distort the measurement. The aim of this work is to analyze the distortion of measurements caused by this baffle and other elements and their compensation. The work contains a description of certain parts of the standard ČSN EN 60268-5 with focus on the standard baffle. Especially on its construction and methods of measuring the speakers mounted on it. Several test measurements were performed within the work. These measurements were performed in a anechoic chamber with speakers mounted on a modular standard baffle, which is a modification of the standard baffle which is also described in the work. The measurements performed include the measurement of frequency characteristics at different distances of the microphone from the speaker at different positions of the baffle in the anechoic chamber. The test measurements show that the modular standard baffle and anechoic chamber cause measurement distortion. In other measurements, the distortion by the anechoic chamber is minimized and the distortion caused by the base of the modular standard baffle is completely eliminated. The thesis then presents the theory of sound diffraction at the edges of a standard baffle and the theory of the extended Biot-Tolstoy-Medwin method of modeling these diffractions using numerical calculations. Based on this theory, software compensation of diffraction distortion was performed in Matlab. It is not entirely clear from the results of the compensation to what extent it can be considered successful. It can be speculated that it only works on certain frequencies. It is necessary to verify the functionality of this compensation method by another test measurement.
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Beamforming using microphone arrays
Bartoň, Zdeněk ; Schimmel, Jiří (referee) ; Míča, Ivan (advisor)
The aim of the master thesis is to sum up theoretical information about beamforming methods of microphone arrays and to verify their functionality. At the beginning of this work there are simulated different varietes of linear uniform and nonuniform microphone arrays and circular arrays. The results are verificated by a practical measurement in ideal conditions. Then I will focuse on implementation of the DAS(Delay And Sum), SAB(Sub Array Beamforming), CDB(Constant Directivity Beamforming), CDB-CA(CDB-Circular Arrays) beamformer including theoretical and practical verification of the functionality in ideal conditions. At the end of this thesis are all beamforming methods compared with each other at SNR(signal to Noise Ratio) and directivity parameters.
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Software Sound Level Meter
Menšík, Václav ; Sysel, Petr (referee) ; Schimmel, Jiří (advisor)
This thesis discusses noise measurement devices, design and implementation of a software sound pressure meter. Sound pressure meter requirements specified by the IEC 61672 standard and selected acoustic physical properties are discussed. Further, the JUCE framework is presented along with an of the graphical user interface and digital signal processing capabilities of the SoundMeter program.
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Audio amplifier controlled by the IP protocol
Dvořák, Petr ; Schimmel, Jiří (referee) ; Kouřil, Jiří (advisor)
The bachelor thesis is intent on projection and realization of a device whitch is capable of communicate with a remote client through the Ethernet making use of the protocol set TCP/IP. This communication will be used for the control of analog and digital outputs of the device, which is able to be attached to any amplifier of audio signals. One of used protocols is UDP. This protocol is closely described, because it is used for transfer of data controlling outputs. The whole device is controlled by microprocessor ATmega32, which operates the communication with the ethernet interface through the controller ENC28j60, the communication with the D/A converters MCP4922 and controlling of digital outputs and a display. The device has its own IP and MAC address for identification in the network. It is possible to edit both addresses in the menu of the device with the help of the module LCD, the display of 2x16 characters with fours buttons. The audio amplifier staffed by the voltage controlled by the computing amplifiers SSM2018T is connected to this device. The amplifier is proposed as six-channel with symmetric inputs through the connectors XLR and unsymmetric outputs through the connectors CINCH. The operating programme which is able to be run on PC with the operating system Windows is necessary for the remote control of the device in the network and all functions of the device are controlled by this programme. This programme enables to control the device after setting the IP address of the destination device and the communication establishment. The motherboard is proposed as a universal module which keeps at disposal up to 6 analog outputs with the range of the control voltage 0 – 5 V and up to 21 binary inputs/outputs.
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Objective Criteria for Room Acoustics Assessment
Zwins, Jiří ; Kurc, David (referee) ; Schimmel, Jiří (advisor)
The aim of this thesis is to define basic concepts of acoustics, a closer acquaintance with the defined objective criteria for evaluation of acoustic spaces and practical processing algorithms in Matlab. The central part is presented technique of calculating the reverberation time by integrating the measured room impulse response and its graphical output. The reverberation time is just one of objective assessment criteria acoustic spaces. The calculation algorithm is based on the principle of a closed space Dirac excitation pulse and the subsequent decline in energy determination of the reverberation time of the acoustic pressure. The analysis of the data samples were used specified areas in VUT Brno.
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Modeling Sound Field in Closed Space at Low Frequencies
Hořák, Pavel ; Kiska, Tomáš (referee) ; Schimmel, Jiří (advisor)
This diploma thesis deals with issues of low frequency acoustics and simulation. In this work the FTDT method of simulation is used. Measuring and simulation are focused on live-sound system and are evaluated using basic sound system optimisation techniques. Main output of this work is verification of basic low-frequency acoustics principles using simulation and measuring.
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Application for Measurement of Room Impulse Responses
Vrbík, Matouš ; Balík, Miroslav (referee) ; Schimmel, Jiří (advisor)
This paper studies problematics of room impulse response measuring. Signals appropriate for measuring are mentioned, with emphasis on stepped sine signal (sweep) and MLS signals. Measuring methods suitable for particular signals are introduced. Another parameter characterizing room qualities is reverberation time. Theoretical and practical methods for determination of this parameter are described. First part of this thesis offers solution in MATLAB environment. Functions for generating measuring signals and for subsequent processing of measured data were created. In second part of this thesis, methods were implemented in C++ language and standalone application, which uses ASIO technology, was created.
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Lossy Video Compression
Šiška, Michal ; Průša, Zdeněk (referee) ; Schimmel, Jiří (advisor)
This thesis deals with description of lossy video compression. Theoretical part of the work describes the fundamentals of the video compression and standarts for lossy as well lossless video and still image compression. The practical part follows up with design of Java program for simulation of MPEG codec.
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Loudspeaker System for Reproduction of Low Frequencies with Directional Radiation
Skvaril, Šimon ; Husník, Libor (referee) ; Schimmel, Jiří (advisor)
Final product of this work is design of speaker baffle which will have directional radiation at low frequencies. In the course of the work, propagation of sound waves and their beaviour at obstacles are described. The computational method FDTD and the K-wave toolkit for MATLAB, which uses this method, are described. In MATLAB a virtual model of speaker baffle is created and proposed solution is verified. Next step is creation of scaled model of speaker baffle on which agreement of theoretical computations with real-world measurment is verified. Final step is creation of prototype of speaker baffle,, whose parameters are measured, including polar response.
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