Is there an alternative open source software that performs as noise modelling tool compared to Soundplan (Proprietary)? QGIS has a plugin “Openoise” but doesn’t function as compared to Soundplan
This is a highly specialized work field, with really complex software. As a GIS specialist, I have worked with a company that specialized in this type of 3D sound modeling software in (urban) spaces developing tools for our national government. I must admit that it is a long time ago, but I doubt this is the type of setting "open source software" thrives. It requires huge investments with only a limited amount of clients, and there is a strong legal framework (both national and e.g. EU) for this, and tools must adhere to these and be (technically) verified.
Unless there is some research group in a university that releases an open source alternative, finding one "on par" with commercial software, seems unlikely to me.
Then again, as I wrote, it is quite some time I was involved in this, so don't know the current situation for sure.