The Vox article links to a 2012 NYT article where they posted some pretty amazing numbers.

At Beaumarchais, a nightclub-like brasserie on West 13th Street, the music averaged 99 decibels over 20 minutes and reached 102 in its loudest 5 minutes. “It definitely takes a toll,” a waiter said.

Workers at these places said the sound levels, which were recorded over periods as long as an hour and a half, were typical when they were working.

One spin class at a Crunch gym on the Upper West Side averaged 100 decibels over 40 minutes and hit 105 in its loudest 5. At a Crunch gym in Park Slope, Brooklyn, the noise level averaged 91 decibels. At the Fifth Avenue flagship store of Abercrombie & Fitch, which has designed many of its stores to resemble nightclubs, pulsating music hit 88 decibels, just shy of the limit at which workers are required to wear protection if exposed to that volume for eight hours.

Worthy of note - I told A&F in 2006 that if their staff worked 8-hour shifts they were safe pushing it to 85. Apparently the intervening years actually had them look up the OSHA regs (no noise mitigation if noise dose is 85dBA for 8). 100dB is "give employees muffs or face fines." Granted, that's a Spin class not a restaurant but still. It's hard to converse over 70dB.

People with hearing aids have a hard time with background music.

People with hearing aids lose Haas effect localization, probably because of the processing delay. If a fast hearing aid is 10ms and localization lives in the band between 5 and 20ms, you're going to have a hard time localizing. And localization is what allows us to pick a voice from a crowd.

You're a good man to accommodate them.

It's entirely possible to get a good sound level meter out of a phone. You have to be able to calibrate it, though, and you have to use an external A/D. Both of those things can be done for a few hundred dollars but there will never be a time where phone manufacturers will be interested in offering it as an option.