Journal Akustika

Dreadnought guitar top plate innovation

Ondřej Jirásek — Mon, 09 Oct 2023 00:00:00 +0200

This paper describes the innovation of Dreadnought guitars, especially braces on top plate. The goal was to increase the dynamic range of the instruments, not only in strength but also in spectral spread. The prolongation of tones in the Sustain and Release phases was also important. Mechanical and acoustic properties of instruments from Furch Guitars' production were measured (Chladni figures, frequency response), numerical simulation of innovated top plate in program ANSYS was prepared (by the matrix) and the changes in organisation of ribs were proposed as following. The new samples of innovated Dreadnought guitars were produced by the factory, again measured, analysed and evaluated.

ACOUSTIC CHARACTERISTICS OF ROAD SURFACES

Petra Marková, Vítězslav Křivánek, Blanka Hablovičová, Jan Machanec — Mon, 09 Oct 2023 00:00:00 +0200

The article is focused on the tyre/road noise and vibration measurements of the motorway network in the Czech Republic between 2012 and 2020. Three different surfaces were measured, namely a conventional stone mastic asphalt pavement (SMA 11S) and two cement concrete pavements with different treatments – burlap drag and exposed aggregate. A basic statistical analysis of the noise values in different years after laying was performed. Cement concrete treated by burlap drag method has lower noise values than SMA 11S. This is to be expected as burlap drag method is considered a low-noise cement concrete treatment. However, it has worse skid resistance properties and so the exposed aggregate cement concrete (EACC) began to be used. SMA 11S and EACC have very similar noise levels in all years tested, suggesting that they behave acoustically in the same way. Vibrations were investigated during field measurements with an accelerometer mounted on the CPX trailer. The noise and vibration results could thus be compared with each other. There is a positive correlation between them.

DETERMINATION OF THE ACOUSTIC POWER LEVEL EMITTED BY A MACHINE COMPONENT BY MEASURING VIBRATION

Stanislav Žiaran — Mon, 09 Oct 2023 00:00:00 +0200

The article applies a methodology for determining the acoustic power of air-borne sound which is generated by the vibration of machinery components or the machine itself. The calculation of the acoustic power level is realized by measuring the vibration acceleration and integrating it to the vibration velocity of the rigid surface of the machinery or its component. The methodology is verified when determining the acoustic power level of operated spinning headstocks on a test facility. Undesirable noise emissions of spinning headstock bearings, as well as their operating condition, can be monitored by measuring kinematic parameters, measuring vibration acceleration and its subsequent integration. The vibration velocity was used to determine the A-weighted level and Z-weighted level of the acoustic power and at the same time to evaluate the operating condition of the two selected spinning units. The article also evaluates the importance of the correct choice of the measuring point of the analyzed spinning headstock on the test equipment when determining the level of acoustic power, which has a decisive influence on the uncertainty of the measurement.

Acoustic Firefighting Method on the Basis of European Research: a review

Jacek Lukasz Wilk-Jakubowski — Mon, 09 Oct 2023 00:00:00 +0200

In the past few years, there has been a search for new flame extinguishing methods that are both cost-effective and environmentally friendly. This article presents a detailed analysis of contemporary techniques for suppressing flames, including the use of fire-resistant materials, traditional firefighting agents, and eco-friendly acoustic firefighting. Among these methods, the acoustic approach seems particularly promising. Unlike chemical products, acoustic waves are safe for the environment, making them an attractive option for extinguishing flames. The article focuses on using acoustic waves to put out fires, taking into account the wave parameters and components. The effectiveness of this method is evaluated and compared to other techniques.