But the rehearsal struck a confrontational chord afterward when someone at the church found KUER reporter Andrea Smardon audiotaping interviews with a few singers and asked them to leave.
In her report, which aired Monday, Smardon quotes LDS Church spokesman Scott Trotter as saying leaders of the four LDS wards meeting in that space felt it best for all that the choir find another practice venue.
But Trotter went one step further: "We sincerely apologize to the choir and its members for the inconvenience we caused regarding the use of our meetinghouse for their rehearsals. ... Latter-day Saints have a long-standing appreciation for choir music and we wish them all the best as they share their talents with the community."
Horn traces the initial dispute to a misunderstanding about the recording taking place in the meetinghouse.
"The initial statement from ward leadership … was that the choir was conducting audio and videotape recordings at the chapel," he writes on the choir's website, theonevoicechoir.com. Smardon was there, Horn notes, but there was no video. Horn says he also was under the impression that audio recordings were OK in a chapel as long as they were not done during an official church function.
"If I was wrong concerning this," he writes, "I express my sincere apologies to the LDS Church for my failure to contact church officials to clarify the exact policy."
In an interview, Horn says he "just wanted to reassure the church that it was not political there was no challenging doctrine. We were simply there to sing sacred music."
Horn, who is gay, was born into the Catholic faith and once studied for its priesthood before converting to Mormonism and serving a full-time LDS mission. He resigned from the church a few years ago, and today, he says, he has no other faith community.
"I'm still a Mormon. I believe in Mormonism," he says, "but I feel more comfortable praying and reading scriptures on my own."
While the LDS Church preaches against gay marriage, its relationship with the LGBT community has warmed through the years. It has endorsed city ordinances barring job and housing discrimination of gay and transgender residents. Earlier this year, many Mormons marched in gay pride parades in a symbol of outreach and commonality.
The One Voice Choir has found a new rehearsal space at Salt Lake City's Christ United Methodist Church. But Horn hopes the LDS Church will "know who we are, that we're not out to get them."
A bit wistfully, he adds, "Maybe one day we'll perform in a sacrament meeting."
Peg McEntee is a columnist. Reach her at firstname.lastname@example.org, facebook.com/pegmcentee and Twitter: @pegmcentee.