permittivity data to the Vogel-Fulcher (VF) model [1,2] in order to monitor the reproducibility and validity of the physical results. As examples, tetragonal tungsten bronzes (TTBs) with the general formula: Ba6M3+Nb9O30 (M3+ = Ga3+, Sc3+ & In3+, and their solid solutions) [3-5] and the archetypal relaxor ferroelectric PbMg1/3Nb2/3O3 with 10 at % lead titanate (PMN-10PT) [6] were chosen. Restrictions to the VF fit were attempted besides the regular “free-fit” by constraining some of the fundamental relaxation parameters to physically sensible values. We show that Vogel-Fulcher fits are very sensitive to the fitting range resulting in a large range of fundamental parameters for the dielectric relaxation processes, and that the restriction of the frequency domain due to experimental noise or to instrumentation limits has a dramatic influence on the values obtained [5]. Particularly, the effect of B-site doping within the TTB structure on the fundamental dipolar relaxation parameters was investigated by independently fitting the dielectric permittivity to the Vogel-Fulcher (VF) model, and the dielectric loss to Universal Dielectric Response (UDR) [7] and Arrhenius models [8]. The reproducibility of the dielectric data and the relaxation parameters obtained by VF fitting were shown to be highly sensitive to the thermal history of samples and also the conditions during dielectric data acquisition (e.g., heating/cooling rate). In contrast, UDR analysis of the dielectric loss data [9] provided far more reproducible results, and to an extent was able to partially separate the additional relaxation processes present in these materials [8]. Further understanding of these processes and the structural transformations within these materials may be obtained by means of resonant ultrasound spectroscopy, RUS, since elastic constants are more sensitive to structural changes rather than other properties (dielectric permittivity, heat capacity, etc.) and thus supplementary relaxations (accompanying the main dielectric relaxation) are exhibited [10].