Ray tracing simulation of sound field in rooms is a common tool in room acoustic design for predicting impulse response. There are numerous commercial engineering tools utilising ray tracing simulation. A specific problem in the simulation is the modelling of diffuse reflections when contribution of individual surface is prevailing. The paper introduces modelling of scattering which is interesting when the whole impulse response of a room is not a goal but contribution of certain surface. The main goal of the project is to shape directivity characteristics of scattered reflection. Also, an innovative approach is suggested for converting the energy histogram information obtained by ray tracing into an “equivalent impulse response”. The proposed algorithm is tested by comparing the results with measurements in a real sound field, realised in a scaled model where a diffusing surface is hardware-implemented.

This paper analyses the changes in transfer characteristics of the vocal tract when closed by a mask, i.e. a chamber. The analysis was performed in two ways: by analytical estimation and by measurements in the vocal tract physical model for the case of mask with inner volume V = 430 cm3, corresponding to the oxygen masks used in combat airplanes. It was shown that closing the vocal tract with a mask cavity increases the first formant frequency by about 10% in front and high vowels (/e/, /i/, and /u/) and the frequencies of the first two formants by about 5% in the remaining two vowels (/a/ and /o/). It was also revealed that longitudinal and transversal resonances in the mask chamber can lead to errors in the recognition of the vowel formant frequencies. The results point to the need for additional knowledge about resonances in mask application.

Voice controlled management systems are based on speech recognition techniques. The use of such systems in combat aircraft is complex due to a number of critical factors which affect the accuracy of speech recognition, such as high level of ambient noise and vibration, use of oxygen masks, serious psycho-physical stress of speakers, etc. One of the specificity of the oxygen mask application is overpressure breathing. The results of the simulations presented in this paper show that the presence of overpressure on the order of 1000 Pa in the vocal tract has a significant influence on the first two formant frequencies. The formants discrimination field is significantly reduced when oxygen mask is used, influencing both perceptive and automatic discrimination of spoken vowels.

The aim of this research is to use a simple acoustic method of a very near field recording, which enables measurement and display of oscillation modes, to estimate the velocity of flexural waves, based on the wavelengths of standing waves measured on the sample. The paper analyses cases of 1D geometry, flexural waves that occur on a beam excited by an impulse. Measurements were conducted on two different samples: steel and a wooden beam of the same length. Due to the appearance of evanescent waves at the boundary regions, the distance between the nodes of standing waves that occur deviates from half the wavelength, which can be compensated using a correction factor. Cases of fixed and free boundary conditions were analysed. By quantifying how much the boundary conditions change the mode shape function, it can be predicted how the mode of oscillation changes if the boundary conditions change, which can also find application in musical acoustics and sound radiation analysis.