The 75 people milling about the Urban Farm Fermentory in Portland knew they were waiting to hear a concert, but that was about all they knew.

They had signed up for the show online, in some cases months in advance. They weren’t told who was playing and were only given the Anderson Street address the day before the March 24 show. As they waited for some clue about the bands, they were given ground rules that seemed more in line with kindergarten than a night out on the town.

“We ask that there be no talking, and please keep your eyes on the musicians,” Tom Kasprzak, one of the concert organizers, announced to the crowd at 8 p.m. “Feel free to take pictures, but please remember to be in the moment.”

For two hours and three acts, the crowd sat quietly, eyes front, just as Kasprzak had asked. Even the accidental breaking of a bottle of hard cider, one of the fermentory’s products, didn’t distract from the church-like focus on the musicians. The organizers of the show, the Maine chapter of Sofar Sounds, say the unusual setup draws a crowd ready to focus on the music. Who else but people with an intense love of live music would sign up months in advance for a concert without knowing who’s performing?

The Maine group has put on five of these nearly secret shows since the summer of 2014. It’s one of more than 200 chapters of Sofar Sounds around the world. Started in 2009 by three British music fans, Sofar is a for-profit concert organization that links and promotes shows, which are run locally by volunteers and held in atypical concert venues, such as homes or small businesses. People pay a $10 suggested donation for each show, with the money used to hire professional sound engineers and photographers to record videos for the bands, said Dean Davis, global community manager for Sofar Sounds. He said all money taken in is “reinvested” to pay the expenses of putting on Sofar shows.

But Sofar groups, including Sofar Maine, are mostly run by volunteers. None of the local organizers or hosts get paid.

The bands don’t usually get paid much, either. They’re given a choice of $50 or professional-quality videos that might otherwise cost them thousands of dollars. Most take the video. Plus they get a chance to attract new fans who are unusually passionate about music and to play other Sofar shows around the world. Often bands who did one Sofar show get asked to perform in other cities.

An attentive audience at the Urban Farm Fermentory in Portland listens to a local band during an event organized by the Maine chapter of Sofar Sounds – a global member-based network that puts on small shows in intimate and sometimes unlikely spaces.

For fans, the shows eliminate the elements of concert-going that can distract from the pure musical experience: elbow-to-elbow crowds, long lines, late nights, expensive tickets, chatty crowds or general rowdiness. Plus there’s the excitement of knowing you may see a band you’ve never seen before, a band that other hardcore music fans have selected for your enjoyment.

“It’s more fun, more exciting, not knowing what you’re going to hear,” said Christine Rogers, 51, of Portland, as she sat with two friends before the show at Urban Farm Fermentory. “It’s more of a listening crowd this way.”

THE MUSIC COMES FIRST

Sofar Sounds began in 2009 after three music fans – Rafe Offer, Rocky Start and David Alexander – went to see a show by a band called Friendly Fires at a club in London. The music competed with clinking glasses, screaming and laughing at the bar, and people not even watching the show. The three were disgusted with what they saw as a “disconnect” between the artist and the fans, and they decided to host a show with local musicians in a tiny London apartment, said Davis.

Offer and Start had worked in marketing. With Alexander, they came up with a few simple rules to attend: No talking. Support the musicians (applaud and consider buying their CDs). And stay until the end.

The name Sofar was adopted, as a contraction for the phrase “songs from a room.” But Sofar differs in important ways from various house concert movements of the past couple of decades – including a current chamber music house concert trend that’s surfaced in Maine. Sofar shows are kept secret, which helps the artist in several ways. It avoids the audience imbalance that can happen if one act has a considerably bigger following than the other two acts and those fans show up in droves and take over the evening. And, since the audience is coming out to a show blind, they are making a commitment to accept whatever music they hear.

The Sofar Sounds shows grew to other cities, and in each a core of volunteers took charge, picking the venues and the bands. Because of Sofar’s Web presence, including music videos of the performers, word of the new format spread quickly.

Musician Phil Divinsky, left, and Tom Kasprzak, volunteer organizers for the Maine chapter of Sofar Sounds, confer over details before the start of a recent show. Organizers say 70 to 75 people is about as large as they want the shows to be.

In Maine, Kasprzak, a 47-year-old financial adviser who lives in Kennebunk, was intrigued by the concept as soon as he started reading about it online. In 2013, he contacted Sofar Sounds offices and quickly connected with two other Mainers interested in starting a chapter: high school teacher and musician Phil Divinsky and Griffin Sherry, also a local musician, of the Maine band The Ghost of Paul Revere.

With help from others, including business owners and musicians, they put on their first show in June 2014, in the Old Port Wool and Textile Co. on Danforth Street. About 30 people signed up and attended, and that number has grown with each additional show.

Acts that have played Sofar Maine shows have included new and better-known Maine-based acts, including Max Ater and the Marshalls, Sara Hallie Richardson, Lyle Divinsky (Phil’s son), Dark Hollow Bottling Company, the Ghost of Paul Revere, Spencer Albee and Eric Bettencourt. Most have been rock, pop or folk acts. But the performers have also included one string quartet, the Amarantos Quartet. Sometimes touring artists in Portland for a paying gig have also played a Sofar show. Such was the case for Vermonters Kat Wright & The Indomitable Soul Band last year.

“A lot of the Sofar shows (in other cities) are folk-based, but we try to have a range of acts that really represent the scene here,” said Sherry, 28. “We don’t do as many shows as some cities, so we have time to really look for people.”

Griffin Sherry, a founding member of the Maine chapter of Sofar, exhales a plume of tobacco smoke outside the Urban Farm Fermentory just before the start of a recent show featuring three local bands.

When Sofar Maine began, the audience was mostly younger people in their 20s and 30s. But the last couple of shows have attracted an older audience, Sherry said, drawn by the fact that the performances focus on the music, aren’t in crowded clubs, and are over by 10 p.m. A show last October was held in the Think Tank on Congress Street, a business where workers can rent workspace.

Musicians are attracted to Sofar Sounds shows, too, because they can gain new fans who are passionate, and they know they’ll be heard.

“I play a lot of shows where I’m the background music, or the quiet music at a fancy bar. Those shows pay, but I don’t feel very useful,” said Portland guitarist and singer Max Garcia Conover, who has played seven Sofar Sounds shows around the country, including in Maine. “The Sofar shows are like the lifeblood of touring around for me. If the songs I write and perform aren’t impacting people, it feels a little ridiculous and wasteful.”

Plus, Conover said, he sells more CDs at Sofar shows than at other performances.

A ROOM FULL OF GOOD LISTENERS

A day or so before the Sofar Maine show in March, an email went out to people who had signed up after hearing about the program from friends or finding it online. “Please join us between 7 p.m. and 8 p.m.,” it read, then listed the address and mentioned that alcoholic beverages would be sold.

By 7:30 p.m. on the night of the show, the fermentory’s spacious tasting room was filling up. Cider and kombucha were for sale at the bar. People sat on stools near small tables or stood. In one corner there were speakers and soundboards, with a white brick wall as a backdrop. The building, in an industrial area off Marginal Way, has ceilings some 20 feet high and exposed steel beams.

The first band, Max Ater and the Marshalls from Bath, began warming up a few minutes before 8 p.m. After Kasprzak’s introduction, Ater, 23, banged out four or five tunes on his electric piano, backed by Alex Marshall on guitar and David Marshall on drums. He used a deep, powerful voice to sing original songs with a jazz-rock feel. Among the reverential audience, toes tapped or people bobbed their heads, but there was little more movement. Mostly, people listened.

Ater, who has been with this band for six months, was thrilled to be playing what musicians call “a listening room.” He’s not really fond of playing bars, but in southern Maine, there aren’t many other places for a young musician to play and gain fans.

After a 15-minute break, the next band was introduced and silence fell again. Amy & The Engine, a Boston band featuring Mainer Amy Allen as lead singer, began their half-hour set. Allen looked every bit the rocker, her hair tossed to the side as she sang and both hands clutching her aqua blue electric guitar. But between songs, she turned to her audience and sounded more like a grammar school teacher.

“Thanks for being such good listeners,” said Allen. “This is really fun.”

Amy & The Engine – from left, Vinny da Silva, Manuel Ruiz, Amy Allen and Luke Niccoli – performs in a recent Sofar Sounds concert at the Urban Farm Fermentory on Portland’s Anderson Street.

The Dark Hollow Bottling Company, an old-timey folk band, closed out the show.

Allen and her band have also done Sofar shows in Boston and Providence, Rhode Island. She said she had wanted to do a Sofar show “for ages” because of the prospect of playing for such an attentive audience.

“There’s nobody there who doesn’t want to be there,” she said. “Anytime we can play for potential new fans, that’s great. We know we’re playing for music lovers.”

Sofar Maine shows have been relatively small, and organizers say 70 or 75 people is about as large as they want the shows to be.

The next Sofar Maine show is tentatively planned for the end of May, Sherry said. If you want to know where, you’ll have to sign up online. And if you want to know who, well, you’ll have to be patient.

And a good listener.