Purdue Universityâs Chemistry Department gives you examples of noise sources for each decibel level: 1  50 dB (1/4th as loud as 70 dB) - Quiet conversation at home. 2  60 dB (1/2 as loud as 70 dB, fairly quiet) - Conversation at a restaurant. 3  70 dB (upper 70s are annoyingly loud) - Running a vacuum cleaner.