You need to be be sure that Kopplemann is the actual spelling.Americans misspell many last names if they write them phonetically.So, I recommend you don't limit yourself to this one and only spelling.
For example, my last name, Kappelman, is pronounced in German is if the "a" is a short "o."Additionally, Amercians tend to try to spell it with an "le" instead of "el."So, it is possible that Kappelmann is phonetically spelled as Kopplemann.That is why the Soundex system is so useful when going through U.S. Federal Census.
Lastly, there is no Kopplemann in the German on-line telephone book.