## 1 Introduction  
Impact noise in buildings is a problem of major concern for the wellbeing and comfort of their users [1]. In this context, the use of floating floors constitutes a constructive solution to reduce sound vibrations and therefore improve the habitability thereof. To estimate the acoustical performance of these solutions, it is necessary to determine the dynamic stiffness of the materials used as resilient layers [2]. ISO 9052-1 [3] specifies a test method for the determination of the dynamic stiffness of resilient materials commonly used under floating floors in dwellings. Although initially intended for comparing production samples of similar materials used in a continuous layer under floating floors in dwellings, this method has been extensively used for the analysis of many different materials [4]. In this method, the fundamental mode of vibration of a mass-spring system consisting of a loading slab placed over the resilient material under test is excited using a suitable impuser. Once this resonance frequency is determined, it is straightforward to calculate the dynamic stiffness of the specimen using fundamental dynamics formulas [5]. According to the experimental procedure detailed in the standard, the measurements are typically performed through a contact (e.g., piezoelectric sensor or accelerometer) or contactless (e.g., laser vibrometer or microphone) transducer, an impact hammer or a vibration shaker being used as an impuser. Nevertheless, [PERSON] et al. [6] pointed out the uncertainty of dynamic measurements depending on the type of impuser used, hammer or shaker, the former being more influenced by the impact point and the latter by the mounting conditions. Alternatively, electrodynamic actuators can provide a more compact and stable excitation system for the analysis of the dynamic behavior of vibrating structures. These transducers have been widely used as a part of distributed mode loudspeakers [7] or in the active control of vibration in structures [8]. Some authors have dealt with their design [9], the assessment of their performance as self-sensing actuators when compared to piezoelectric technology [10], or their use in thin panels for laboratory vibroacoustic tests [11]. In a recent work by the authors [12], it was shown that electrodynamic actuators can be successfully used to determine the dynamic elastic modulus of materials under a state of simple stresses in beam-type mechanical elements. Similarly to the work by [PERSON] et al. [13], in which a band-pass loudspeaker system coupled to porous sound-absorbing materials was used to determine the airflow resistivity of the latter, the electrical input impedance of the actuator coupled to the beam was measured. By generating a random signal excitation, the fundamental flexural mode of vibration of a beam-type cylindrical element was identified in the electrical input impedance of the actuator, being the dynamic elastic modulus, and then determined using classical beam theory. More recently, some authors have highlighted the usefulness of using an impedance approach for the detection and classification of indoor events by measuring the loudspeaker impedance [14] or for characterization purposes as the determination of the dynamic modulus of elasticity of pine wood [15]. In the present work, a similar approach that measures the electrical input impedance of a mass-loaded actuator coupled to a slab-material system is used to determine the dynamic stiffness of the resilient material. By using an electro-mechanical circuit model, the mechanical mobility function of the system under test can be retrieved from the impedance data and the dynamic stiffness of the material thus obtained. Unlike the standard-based configurations, the proposed approach requires a single transducer, thus reducing the instrumental requirements and further simplifying the characterization procedure. Experiments were performed over different resilient materials, with results showing good agreement when compared to those obtained following ISO 9052-1.