This study discusses alternative models and methods to be applied in room acoustics estimations for specific room types including disproportionate rooms and rooms with coupled volumes. A recent prediction method, namely, diffusion equation model (DEM) in room acoustic applications is utilized in the methodology, and this method is compared to common models as of statistical theory, image-source or ray-tracing techniques. Both long enclosures as of subway stations and coupled volumes as of multi-domain monumental structures are special cases with specific interior sound fields. Statistical theory is not always reliable in such extraordinary room forms, while ray tracing may tend to over or under estimate certain acoustical parameters. Thus, the application of DEM in a finite element scheme for detailed sound energy decay and sound flow analysis are held over some case structures. The results are compared to field tested data and ray-tracing solutions. Pros and cons of DEM in comparison to different methods are searched in detail considering the efficiency in visualization, computational speed, and reliability of acoustical parameter results for specific room shapes.