Ambient noise is “the new secondhand smoke.” Like secondhand smoke, excessive ambient noise is not just a nuisance but is a health and public health problem for millions of Americans. Excessive ambient noise causes hearing loss; disrupts sleep, function, and communication; and causes non-auditory health effects including cardiovascular disease and death. The sounds that matter to people are the ones reaching their tympanic membranes, or perhaps the cochlear hair cells or auditory processing cortex. Specific evidence-based noise exposure levels affect human health. 30 dBA (LAeq(8)) disrupts sleep. 45 dB (Ldn) disturbs concentration. 55 dB daily average (Lden) has non-auditory heath effects, including cardiovascular disease and death, due to stress responses including activation of the autonomic nervous system and neuroendocrine axis. Approximately 60 dBA (LAmax) interferes with speech comprehension for the hearing impaired. 70 dBA daily average (LAeq(24)) causes hearing loss, and 70 dBA (LAmax) interferes with speech comprehension for those with normal hearing. 85 dBA (LAeq(8)) is the occupational recommended exposure level in the United States, and 85 dBA (LAeq(1)) is the recommended exposure limit to prevent hearing loss. Acoustic scientists and engineers must be aware of these specific, evidence-based noise exposure levels and must work to reduce excessive ambient noise.