"sweet" might include qualities like kind, warm, loving, lovely, etc. There are these somewhat related words you can use for someone's voice. 1 달콤해 (달콤하다 - sweet) 2 따뜻해 (따뜻하다 - warm) 3 부드러워 (부드럽다 - soft, tender) 4 고와 (곱다 - clear and beautiful) 5 정다워 (정답다 - loving and caring) 6 사랑스러워 (사랑스럽다 - lovely, lovable)