Intensive rehearsal periods aren’t exactly typical for improvised music performances; in fact, the two ideas seem downright antithetical. But that changes a bit when the very room where you’ll be performing is also one of your primary instruments.

For the past two months, musicians/composers Chris Forsyth and Jesse Kudler have spent several hours each week exploring the sonic properties of historic Christ Church. The results of those experiments will be revealed Saturday at “Sounding Christ Church,” funded by a grant from the American Composers Forum’s Philadelphia Chapter, when the duo will perform a loosely structured improvisation taking advantage of the spacious church’s unique acoustics.

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“We’ve had a chance to really sink into the space,” Forsyth says. “We found the most active resonant frequencies of the building and we’re trying to focus on those. It’s just beautiful-sounding instruments in a beautiful space, so you don’t have to do too much.”

The duo worked together once before in Christ Church, but with little time to test the acoustics beforehand found that they’d barely scratched the surface of its possibilities. Unexpectedly, having more time has led to a paring back of instrumentation and activity. Forsyth, who can be found most often leading his much noisier avant-psych  Solar Motel Band, will stick to acoustic guitar; Kudler, a minimalist sound artist who usually works with electronics, synthesizer and prepared guitar, will play the church’s pipe organ.

Forsyth compares the experience to “playing a guitar inside a giant guitar,” and jokes that his collaborator’s increasing facility on the organ could lead to a definite novelty: “We could bill it as ‘Kudler plays melodies,’” he laughs. “We were both surprised by how much we stripped back,” Kudler adds. “To me it feels less sprawling but deeper.”

Besides playing atypical instruments in an unusual space, the two improvisers are also approaching this performance as composers, albeit ones who are compiling a sketchbook of sounds and approaches rather than putting notes on paper. “We haven’t been sitting in a room for 14 weeks writing down something out of our heads, we’ve been mapping the sonics of this room and trying to figure out what our relationship is with it,” Forsyth says. “We’ll be doing a lot of swimming in the sound of it.” ​

Site-specific vibes:

Another appeal of the room is its history. Frequented by the Founding Fathers, Christ Church stakes its claim as the site of one the first acts of treason in the American Revolution, when its pastor ripped the king’s name out of the Book of Common Prayer.

“There’s a good kind of badassness inherent in the place,” Forsyth concludes. “It’s got a good vibe.”

If you go:

"Sounding Christ Church"

Nov. 7, 8 p.m.

Christ Church

Second and Market streets

Free

www.bowerbird.org