When measuring sound insulation according to the standard ISO 10140, the tested sample is exposed to white noise. The noise coveres the whole spectrum of frequencies, contrary, in real situations we are usually exposed only to noise in certain frequency range. Because of that, we study the influence of the sound source frequency on the sound insulation measured on the non-standard measuring setup. All the measurements were performed on non-standard measuring setup developed at CEM. The setup simulates a standard measuring setup but it is built in a smaller scale. The results showed that the frequency of the excitation noise influences measured results. When tested samples were exposed to a lower frequency (500 Hz) measured sound insulation was higher then it ras measured using white noise as sound source. However, when exposing the tested samples to a higher frequency (1000 Hz and 5000 Hz) results did not show any specific trend.