Do you really know how someone actually pronounced the last name you are researching? One place to find out is from someone who actually has the last name. But there’s no guarantee that someone with the last name today is pronouncing it the way their ancestor did in 1800.
If the name is not in English, find someone who speaks the language and ask them what it sounds like–online genealogy groups may be one place to find these people. For names that are in English are there online genealogy groups from the area where the person or family lived who may be familiar with how the name is pronounced? It is not always necessary to find someone with the last name in order to see how it was pronounced.
The way a name was said matters as it impacts how it gets spelled in records and occasionally those renderings are significantly different from what we would expect.