According to the NHL, the noise level at the end of Hart's performance was 114 decibels - the loudest it has been in either arena during the Finals. By comparison, the records for loudest rock band performances - from Led Zep to the Who to Kiss - hover around 130 dB's. That requires massive amplification, of course.
The conundrum for Hart is obvious. She needs to hear Smith in order to make the performance work; the better the performance, the harder it is to hear Smith.
"I wear little monitors in my ears," Hart said. "They are cranked up, but they only get so loud."
By now, Hart and Smith have become as important a pair for these Flyers as Chris Pronger and Matt Carle. The fans keenly anticipate the moment Smith's image appears on the screen, a moment Hart sets up perfectly by glancing up as if to defer to the woman whose recording became the anthem of the Flyers' 1970s Cup teams.
There is a huge risk here. The novelty has long worn off, and the whole thing could grow stale. It's up to Hart to prevent that from happening.
"That's the pressure," Hart said. "Everyone wants the magic. People want that feeling, and the crowd starts from the beginning of the song. I try to amp it up a notch without changing it too much."
After Game 3, a woman put her arm around Hart and told her how much "I love what you're doing out there." The woman said she was Chris Pronger's mother.
"I looked up at her and said, 'Yes, you are,' " Hart said. "She had that same smile."
Hart, who beat cancer 10 years ago, nails it every time. The Blackhawks have a fine anthem singer, Jim Cornelison, who gestures toward Old Glory on the line "Our flag was still there." The fans in United Center roar at that. Boston's Rene Rancourt does a showy version of the national anthem, too.
But there is nothing anywhere like Hart and Smith - two powerful voices with equally powerful ties to Flyers history.
Hart's father, of course, was Hall of Fame broadcaster Gene Hart, who called the Flyers' championship seasons and many more beyond that. He died in 1999.
"I was too young to know what was happening with the first Cups," Lauren Hart said. "I wasn't invested then. But I know my father waited for years for that magic time to come around again. He didn't see it. I now carry that feeling for him."
This is, after all, a woman with an Australian shepherd dog named Flyer. Hart has worn the same orange T-shirt - an original 1974 Cup champions souvenir a fan discovered in the attic - and black jacket for each game of this postseason. She also wears a pair of lucky socks.
"I have to do laundry a lot," Hart laughed.
It has been a crazy few months. Hart and her husband, Todd Carmichael, adopted three Ethiopian sisters three months ago. The Flyers' run, which caught the whole world by surprise, has gone on for nearly two full months. Amid all that, Hart is hoping to release a new CD - she is a terrific songwriter as well as singer - in the fall.
Her next local show is at Gazebo 9 in Bryn Mawr on June 12 - that would be the day after a possible Game 7.
"I just feel like we have the advantage," Hart said. "The Blackhawks, on paper, may have the edge. But all those little things, those extra special things, give the Flyers the edge."
She should know. Hart, with help from her on-screen partner, is one of them.
Contact columnist Phil Sheridan at 215-854-2844 or email@example.com. Read his recent work at http://go.philly.com/philsheridan.