Many hearing loss prevention experts say, however, that people should not be exposed to 100 decibels — the level at the spin class on the Upper West Side — for more than 15 minutes without hearing protection.

“We definitely consider those levels able to cause damage and likely to cause permanent damage with repeated exposure,” said Laura Kauth, an audiologist and president of the National Hearing Conservation Association. “They’re experiencing industrial level noise.”

But at all the aforementioned places, there was nary an earplug in sight.

Hearing experts say ears never get used to loud noise. “Your ears don’t get more tolerant,” said Dr. Gordon Hughes, director for clinical trials at the National Institute on Deafness and Other Communication Disorders. “Your psyche gets more tolerant.”

The background noise is too loud, Dr. Hughes said, if a person’s voice has to be raised to be heard by someone three feet away. Signs of too much exposure include not hearing well after the noise stops, a ringing sound and feeling as if the ears are under pressure or blocked. None of these symptoms necessarily mean the damage is permanent, though even if hearing seems restored to normal, damage may have been done. Yet hearing loss from noise typically takes months or even years to develop.

One waiter at Lavo, who, like several other workers, did not want his name published for fear of losing his job, said he knew his hearing could be in jeopardy. But, he reasoned, slight hearing loss was inevitable, since he had also played in a band. “When it happens, it happens,” he shrugged. “Hopefully by that time they’ll have better fixes for it.”

Rick Neitzel, an assistant professor at the University of Michigan Risk Science Center, said full-time employees subjected to the volumes found at Lavo and Beaumarchais for a year or two could easily incur hearing loss. “Restaurants in the high 90s,” Dr. Neitzel said, “something really should be done.”

Tailoring the Clientele

At the Abercrombie flagship on a recent afternoon, a preteen girl plunged wide-eyed into the darkness as loud beats poured from dozens of speakers. Her mother and her grandmother trailed her. The grandmother, Nancy Hilem, 56, of Bucks County, Pa., said they had been in the shop 10 minutes but it felt as if it had been an hour because of the noise. Normally calm — she works at a funeral parlor — Ms. Hilem found herself jumpy.