The performance of wave energy converters using model scale testing has been assessed primarily using regular waves with limited testing in irregular waves. A viable alternative is the use of polychromatic waves, superposition of discrete regular waves with a definite period. Polychromatic waves allow well proven phase-averaging techniques to be applied to a wave which is more random and therefore representing a more realistic sea-state than regular waves. This paper presents results from model test experiments on a generic forward-facing bent-duct oscillating water column in polychromatic waves from a series of experiments using a wave probe array within the device and secondly with the addition of particle image velocimetry. By adapting phase averaging methodology the results showed that more reliable predictions of the device's operation are obtained when testing in polychromatic waves. Results from wave probe array showed that a longitudinal array is required to capture sloshing within the chamber. Velocity fields revealed a reduction in the proportion of kinetic energy within vortices in polychromatic waves compared with regular waves. This study highlights the importance of performing experiments in sea-states that are more realistic than simple regular waves to ensure an accurate representation of the device's performance and operation.