IN 1970, Mildred Krentel bought a toy bell set in hopes of bringing music into the lives of people with intellectual disabilities.

The Melmark co-founder, who died in 2013 at 91, arranged the bells in a line like piano keys and began with simple, one-note melodies. She found that her musicians reacted well to her hand cues instead of sheet music. When it came time to name the handbell choir, the choice was simple.

"It brought so much joy to their lives that they called themselves the Joybells," said Sue Graves, co-director of the group.

The Joybells are the handbell choir of Melmark, a multiservice agency for people with intellectual disabilities in Berwyn. The group is gearing up for the release of its holiday music CD, "Music that Matters," a collaboration with the Chamber Orchestra of Philadelphia. The Joybells will celebrate the release with free shows at the Kimmel Center on Sunday at 10 a.m. and 2 p.m.

The Chamber Orchestra's music director, Dirk Brosse, attended the Joybells' rehearsals multiple times before talk about a collaboration began. Graves said that Brosse wasn't concerned with the performance fitting a particular vision, but rather in expanding on what the bell choir already had in its repertoire.

"He then spent the whole summer writing these exquisite arrangements to go with our songs that we already knew," Graves said.

Although the Joybells were already familiar with the songs, Graves said that playing with another ensemble adds a whole new dimension to their performance.

"For us to take that step, that leap, of preparing our music so we could perform for them, that was like a whole other level or expectation for us," Graves said.

The Joybells' first rehearsal with the group was on Sept. 12. "It was exhausting," Graves said. "Suddenly, we were having to listen very differently." After only one rehearsal, the musicians recorded the CD the next day at the Trinity Center for Urban Life. It was an intense two-day marathon of rehearsing and recording.

"I was never so proud of my ringers," Graves said. Despite the CD's completion, the group has continued to rehearse for the Dec. 7 performances. The show is free, but any proceeds from CD sales will go to covering the costs of the performance and making the album. The CD also will be available on iTunes and Amazon Music. Those interested in making donations other than the CD can do so online or at the concert.

Valerie Barksdale, 29, of Ridley Park, said that she loves performing with the Joybells.

"I just love going on the bell-choir trips, and going on the buses here," Barksdale said.

Barksdale also said that she's excited to perform with the Chamber Orchestra. "I love the orchestra and so does my family," she said.

For Graves, the most fulfilling part of working with the group comes with every performance.

"Every single time they perform, that's my reward," Graves said. "People with disabilities don't have that many opportunities to show the world what they can do. Everyone is always focused on what they can't do, what their limitations are. I think that performing with the Joybells of Melmark is an opportunity for them to shine, for them to show what they've been able to achieve. It puts the focus on their ability and what they can do."

For more information about the Joybells of Melmark, visit melmark.org.