Phononic crystal-based noise barriers offer promising solutions for urban noise mitigation, particularly concerning traffic and highway noise, due to their capacity to efficiently attenuate sound while maintaining ventilation. This study advances the state of the art through two key contributions: first, by developing an experimental setup to analyze stopband frequencies and, second, by creating a numerical model that replicates real-world conditions for further validation. Unlike previous studies, which primarily assessed phononic crystal barriers in semi-anechoic chambers with single noise sources, this work introduces a more realistic experimental approach. The setup utilizes an Alpha cabin with a diffuse sound field, where a 4×6 array of cylindrical scatterers is mounted on the cabin door. Insertion Loss (IL) is measured using an external microphone array, capturing the barrier’s performance in practical conditions. To account for production and assembly tolerances, slight variations in the scatterers’ x and y coordinates are introduced into the numerical model. Results show peak attenuation values between 1 and 2 kHz, aligning with critical urban noise frequencies. This study presents a methodology for evaluating ventilated phononic crystals in real-world scenarios, providing valuable insights for designing efficient noise barriers tailored to traffic and highway applications.