This thesis deals with the creation of a semi-active sound absorbing system. The main part of the system is an electrodynamic loudspeaker, which function as an absorber. In this project my aim is to discover the abilities, and the possibilities of the absorbtion ont he diaphragm. Further aim is to examine the effect of the electrical load on the absorbtion parameters, such as the resonance frequency, the bandwidth and the absorbtion value. If the examination gives the result that the parameters are effectively controlable, it gives the opportunity to adjust the acoustic parameters of a room with this narrow bandwidth semi-active absorber. As we stated above, the electrodynamic loudspeaker is the most important part of the sound absorbtion system. The diaphragm of the loudspeaker works as a resonator, which can absorb sound near the resonance frequency formed by its mechanical elements. During the examination the loudspeaker at the end of a waveguide as a termination, and the absorbtion properties are calculated, by simulating and measuring the resulting reflexion in he tube. The steps of the simulating and measuring method are presented in this thesis, as well as calibrating and standardizing methods in order to achive the required measuring accuracy.