Koppen rhymes with:
alagappan, poppen, alagappan, aspen, campen, capen, cheapen, compean, copen, crippen, crispen, dampen, deepen, deppen, eappen, flippen, happen, hempen, hippen, kampen, karpen, kempen, koeppen, lappen, lupin, mcalpin, misshapen, open, phippen, pippen, poppen, reopen, ripen, rippon, saipan, sharpen, stepan, supan, tappan, tappen, tarpon, thigpen, thomspon, tippen, turpen, vancampen, vankampen, weapon, yaupon, zupan
Koppen sounds like:
kabbani, kaboom, kapaun, kasabian, kassebaum, kauffman, kauffmann, kaufman, kaufmann, kavan, kaveney, kayvon, keaveney, keaveny, kevan, keven, kevin, kievan, koeppen, koffman, koopman, koopmann, koven, kuban, kubena, kubin, kuvin, kvam, kvamme