Photo: Alley Lacasse, Belmont High’s Band Director, on stage at the school’s new theater and concert hall.

Alley Lacasse is snapping her fingers as she is standing at the front of the stage of the new Belmont Middle and High School theater. The Belmont High Band Director then begins slowly hand-clapping, all the while listening intently to the sound emulating from the hall.

“I’m listening to how the sound reverberates from the stage,” said Lacasse, in the midst of workers putting the initial finishing touches (there’s a few more touch-ups to come) to the town’s newest performance space.

Last week was a chance for Lacasse to get a feel of the place since, well, neither she or anyone else has had the opportunity to perform in what is the gem of the new Belmont Middle and High School: A spacious two-tier 700-seat theater that is a true concert hall with professional quality acoustics and equipped with up-to-date audio and light systems.

“I have never opened a new performance space as a performer [Lacasse is a professional flutist and chamber musician] or director so it’s going to be so special for all of us,” said Lacasse who is in her third year as

On Dec. 2 at 7 p.m., the theater will hold its grand opening concert featuring the school’s two band ensembles, the symphonic band, and the wind ensemble with special guest artists, Boston Brass. Tickets [General Admission: $15] can be purchased at the POMS website here.

The former auditorium – built in 1970 and demolished in the fall to make way for the new middle school section of the building – was far from the optimum site for holding the myriad of concerts and theatricals that were presented by a music program that has earned multiple local and national honors and awards.

“This space is going to accurately now reflect the quality of music and art in a theater that happens with the Belmont High School, performing arts department all the time. We finally have a space that matches that quality,” she said.

From a design by architects from Perkins+Will which has experience in theater and performance design and construction, the hall’s design and material used – from the wall panels to the fabric upholstered seats – was selected to enhance the listening experience. And getting the right sound begins on Dec. 1 when the bands officially arrive in their new home.

“We’ll start with dress rehearsals where we’ll be doing a lot of sound checks. I’ll have people in the hall listening for me both at the orchestra level and upstairs just to see how balance is working. And it’ll be a lot of adjusting,” she said.

“But it’s kind of fun. It’s the music business. It’s a mystery until you actually do it and the audience is going to hear that for the first time.”

For Lacasse, the concert will also be an opportunity for her students to experience performing with “my personal dear friends,” the five-member Boston Brass, an ensemble with a worldwide reputation.

“They’re known for putting classical music on a concert stage but dressing it up and changing it up and kind of blending genres and giving the audience a really personal human experience. They’re high-energy and very funny. They’re some of the kindest people I know. And they most importantly, truly care about music education, and they love working with students,” Lacasse said.

While the concert will provide the highlight of this primer week, it will be the seemingly ordinary that Lacasse is anticipating.

“It’s gonna be a really magical moment the first time the ensembles steps on stage and we play the first chord or tuning note or just warm up. So it’s going to be a whole bunch of surprises. But it will be a beautiful, beautiful moment there.”