Most room acoustics simulations and auralization techniques are based on geometric acoustic algorithms, commonly combining image-source and ray-tracing methods for impulse response calculation. This paper investigates the acoustics of a medieval English church and compares a geometric acoustic computer based auralization with measurements obtained from the actual space. More specifically, it focuses on the determination of the influence of different aspects and factors on typical objective room acoustic characteristics. These results are presented and then discussed in terms of how they can be improved and optimized when compared with the measured results.