The occurrence of eigenmodes is one of the fundamental phenomena in the acoustics of small rooms. The modes formation results in an uneven distribution of the sound pressure level in the room. To determine the resonance frequencies and their distributions, numerical methods, analytical methods or experimental studies are used. For the purpose of this paper, an experimental study was carried out in a small room. The study analysed the results of measuring the sound pressure level distributions in the room, with a special focus on the frequency range 20 Hz - 32 Hz, below the first modal frequency in the room. The measurement were conducted in the rectangular grid 9x9 microphones, which resulted in 0.5 m microphones grid resolution. The influence of evanescent modes on the total sound field was investigated. The research takes into account several sound source locations. On the basis of the acoustic measurement carried out, frequency response curves were also plotted. This paper presents a few methods for analysing these curves based on standard deviation, the linear least squares method, coefficient of determination R^2 and root mean squared error (RMSE). The results obtained made it possible to determine the best position of the acoustic source in the room under study. The effect of evanescent modes on the total sound field was also observed.
