Science is where you find it, and you can find it these days in the middle of the Montgomery Street BART Station, absolutely free of charge.

A genuine echo chamber is located directly beneath a 15-foot-wide decorative dome that used to adorn a newsstand. The newsstand is gone.

Now a passerby can stand beneath the dome and speak a few words or hum a tune. Reflected back is something eerie — the kind of celestial reverberations that come only in a recording studio, or maybe in that big room where Dorothy met the Wizard of Oz.

“This is pretty cool,” said Bernie Brown, a visitor from Wellington, New Zealand, who paused while passing through the station Wednesday morning to hum a few bars of the New Zealand national anthem. “It’s different. Weird.”

Now Playing:

Hearing your own voice unexpectedly magnified back at you, said BART passenger Doug Cordwell, brings “exciting possibilities to the pedestrian.” By pedestrian, he meant the mundane kind, not the two-legged kind, although he said it works both ways after you get off a train.

“You’re walking through the station, trying to get from the train to your office, and all of a sudden something new and interesting happens,” Cordwell said. “When you’re 69, like me, you don’t get a lot of new things happening anymore.”

The sound is complex and seemingly not of this world. Charlton Heston heard something like it from the burning bush in that movie.

“There’s definitely an echo,” said BART police Sgt. Esteban Toscano, standing in the sweet spot and listening as the word “echo” echoed. “It’s like an exhibit at the Exploratorium.”

Except a ticket to the Exploratorium science museum on The Embarcadero costs $30.

Exploratorium staff scientist Ron Hipschman said the museum does have four similar domes: two inside the museum and two on the outdoor plaza. The indoor domes require a ticket, but visitors also get scores of other exhibits included.

“We call it the God voice,” Hipschman said, quickly adding it’s not the almighty talking but a human hearing his own sound waves “reflected back from the entire surface, like a mirror.”

“It’s magic, but it’s not magic,” he said. “Anything that makes you stop and think about science is a good thing.”

The sweet spot at the Montgomery Street BART Station is precisely in the middle of a small circle of decorative flooring at the east end of the concourse, just a few steps from where the Jehovah’s Witnesses volunteers set up shop. They traffic in the celestial, too. When business is slow, the volunteers have been known to wander over and check out the acoustics beneath the dome.

“It does make your voice sound different,” volunteer Bob Duke said. “It’s reflective.’’

He quickly added that there were even better ways to reflect, and he happened to have a few pamphlets to offer by way of explanation.

From time to time, BART station agent Nathan Ison said, passersby have taken to standing beneath the dome. Street musicians tend to avoid it, he said, because the echo is disorienting. Any listener standing outside the dome doesn’t hear the reverb effect.

“It’s cool for a personal experience, but it might be a bit noisy for a musician,” Ison said.

One homeless man curled up directly beneath the dome the other morning and went to sleep, and his snores bounced off the ceiling and back at him, but he did not awaken.

Tristan Burnside, an Australian living in San Francisco, was on her way home after casting her ballot at the Australian Consulate on Market Street. Voting in an election and listening to your own echo at a subway station are about the only things you can do for free in San Francisco, she said.

“They’re both good things to do,” she added, although she wasn’t certain either would have any lasting effect.

Malik Justin, 25, of San Francisco strolled to the sweet spot and yodeled. The echoes swirled all around him and he grinned.

“Yeah, I stop here all the time,” he said. “I imagine I’m in a music studio.”

Justin tipped his head back and yelled, “Hey, yo!”

“I don’t know what it is that makes it like that, but it’s” — and he gestured all around to take in the stone floor and curved ceiling — “a good instrument. Very nice.”

Steve Rubenstein and Kevin Fagan are San Francisco Chronicle staff writers. Email: srubenstein@sfchronicle.com, kfagan@sfchronicle.com Twitter: @SteveRubeSF @KevinChron