This paper presents an experimental approach for estimating the front-side radiation impedance of a loudspeaker. This acoustic load impedance is the reaction of the sound field on the radiating diaphragm which may affect the loudspeaker response, particularly in the low freqauencies due to the coupling with the room modes. In general, this impedance can not be solved analytically because it depends both on the physical characteristics of the speaker and the complexity of the acoustic field in which it radiates. Conventional measurement techniques require sensors such as microphones and accelerometers. The approach proposed here relies mainly on the the reciprocal mechanism of electrodynamic transduction, making it possible to use the loudspeaker as a sensor simultaneously. This work shows that the front-side acoustic impedance can be derived from the speaker input impedance and the knowledge ot its electromechanical parameters. An analytical model is given and data measured in actual rooms provides proof of concept. Potential applications are also discussed.