In psychology, the definition of “gestalt” could be summed up like this: The whole is greater than the sum of its parts.

It’s a bit murkier than that, but that’s the essence.

The same concept can be applied to the arts, and classical music lovers will have a chance to hear how it works next Wednesday, July 15, when the Gestalt Quartet performs in Pastorius Park.

“We aim for a kind of playing where the sum of our sound is not just the sum of individual voices, but something greater, something different, a certain blend,” explains violinist Lorenzo Raval.

He will be joined on stage by fellow violinist Alex Link; Shannon Merlino, who plays the viola; and Chen Chen on cello.

“We aim to present to the listener a way of music-making that’s not just playing the notes and playing them well. It’s really high-quality playing, but something greater than that, something that tells a story, something that has a narrative or something audiences can relate to as fellow human beings,” Raval said.

Adds Merlino: “We just all knew that this (gestalt) was going to be it because we all come to the table from different backgrounds and different experiences, but we are not fresh out of the conservatory. It really is like the sum of the parts being greater than the whole.”

All the members of the ensemble do other things, Merlino explained. Raval, for example, is currently playing in the orchestra for the Arden Theater Company’s production of “Dear Evan Hansen.” When she isn’t performing, Chen teaches at Drexel University. Link and Raval work with the Philadelphia Youth Orchestra. Merlino gives private lessons.

The four all knew each other and decided to give playing chamber music as a quartet a try. It seems they were on the right track, from the start. Gestalt Quartet performed the first of its two concerts at The Presbyterian Church of Chestnut Hill in November to critical acclaim. Those concerts, together with the ensemble’s rehearsal sessions, was enough to persuade them that they had happened upon something special, Merlino said.

“I think our quartet is my favorite thing right now,” she said. “I actually, genuinely look forward to our rehearsals and our performances, and even if we have a different gig that’s not the best gig that week, when we come back to the quartet, it’s like coming home.”

For the Pastorius concert, the quartet plans to put its own spin on the 250th anniversary of the Declaration of Independence. Don’t look for deeply patriotic music. The ensemble has something else in mind.

They’ll play a selection from Samuel Barber, who was one of the first openly gay composers, producing stunningly beautiful music. There will be a Dvořák piece, based on Native American themes, and work by Florence Price, drawn from American folk songs.

For Raval, it won’t be his first performance in the park. He once performed in Pastorius with the Joseph Arnold String Quartet — a mix of light classics, pop music and jazz tunes. He’s looking forward to coming back.

A lot of thoughtfulness goes into the quartet’s music programming, Merlino said. “Everything we’ve done before, we’ve had a purpose or it’s like something the music means to us,” she said. “We don’t just approach it like, ‘OK, we’re going to grind out a Beethoven quartet for strings.’ There’s always an in-depth learning of the repertoire that we work on.”

For Raval, too, playing in the Gestalt Quartet is invigorating.

“My heart sings the most in chamber music,” he said. “I think I’m a true chamber musician at heart. There’s no place I’d rather be. Playing in orchestras is great. Playing recitals by myself is great. Playing other formats, in other settings — like the musical I’m doing right now — is tremendous. But this is where I feel most at home. I bring that joy in my playing to other places, too. So, it feeds me. I’m really happy playing in this quartet.”

The Gestalt Quartet concert begins at 7:30 p.m., and it’s free. The performance is sponsored by Independence Blue Cross. Temple Health Chestnut Hill Hospital sponsors the entire concert series. Pastorius Park is at 8177 Roanoke St.