At “10 out of 12,” Anne Washburn’s new ambitious, amusing and exasperating backstage play set during a technical rehearsal for a new play, the audience was full of theatrical royalty, including playwright and lyricist Lisa Kron who had just won Tonys for Fun Home. In one of Kron’s Tony acceptance speeches, she had compared Broadway to a big house where until now only a few of the rooms have been used. “This season the lights got turned on in other rooms….Wouldn’t it be great if after this season we didn’t all just go back to the living room.”

“10 Out Of 12” is definitely a previously unused room, even Off-Off Broadway at the SoHo Rep, where it’s just opened. I’m thinking maybe it’s the storage room – the playwright has said she based the play on notes she’s been taking at tech rehearsals over the past ten years. Or it could be the boiler room – everything in the room has some purpose, but you’re not quite sure what.

Those people who are not themselves professional theater artists – a decided minority in the audience the night I attended– are probably most acquainted with technical rehearsals in the theater through the canceled but not forgotten television series “Smash,” when in season one Dev proposes marriage to Karen, and she replies “I’m in tech” – which became a popular catchphrase.

Washburn, justly praised for her bravado experiments and best-known for Mr. Burns, A Post-Electric Play, with its clever use of episodes from The Simpsons TV series, steers way clear of anything resembling Smash in “10 out of 12.” Her play doesn’t seem to be intended as an entertainment nor even an education about backstage life so much as it is a painstaking effort to re-create it — to have the theatergoers feel what it’s like to be part of a tech rehearsal. To that end, each theatergoer is given a headset so that we can listen in on the headset conversations between (the actors portraying) the stage manager and lighting and sound designers and the crew, a standard means of backstage communication.

Some of the impromptu actions and interactions are odd and amusing:

The director wants a total blackout in the opening scene and begs the stage manager to figure out a way to cover up the fire exit light. “Not on my watch,” she replies.

The two actresses ask the costume designer and the director whether they should be “boobier” — have larger breasts. (No details on how this would happen.)

“It doesn’t mess with your mis en scene or anything does it?” one asks the director.

“This is strictly between you girls. Women,” the director replies.

“We must increase our bust,” they start chanting playfully.

“Dear Jesus,” the director says. The conversation ropes in the assistant director, who speculates how the playwright would react.

There are emotional confrontations, mostly involving Thomas Jay Ryan as a prickly member of the cast, who has the juiciest moments and makes the most of them, while the “crew” comment (“Wow” “Yup”) on their headsets, which the audience can hear (on our headsets) but the “cast” cannot.

“I do new plays because I love work which has only just emerged from the present moment,” Ryan’s character Paul says at one point, objecting to a particular scene.  “But — and I mean this with no malice whatsoever — I wish all playwrights would die immediately after writing their script…. I treasure the art, but so often the artist doesn’t have the courage of the art.”

But these shiny moments are like nuggets extracted from a cavernous mine. What tech rehearsal means for most people involved is a lot of waiting while the sets and sounds and lighting and costumes get adjusted and fixed, and the major emotion is tedium. Both waiting and tedium are in abundance in Washburn’s play, which clocks in at close to three hours (including a 15-minute intermission.)

We see how the characters in the play occupy the long stretches of dead time: The director talks to himself in German, a techie breaks out into song, the actors stand around clinking teacups in a kind of makeshift game, the crew talk to each other on the headset about food.  But the audience has no such recourse to amuse ourselves.

“10 Out Of 12” seems influenced by Annie Baker’s “The Flick” in its respect for a real-life rhythm full of pauses, dead moments, random bursts that peter out. But at least in the Flick, we knew what the characters were doing at all times – their activities got no more complex than sweeping the aisles of the movie theater – and we eventually learn about them as people; there’s a solid arc, a story. By contrast, there are only fleeting clues to the lives of the characters in “10 Out Of 12”, a play primarily made up of seemingly random stretches of visual chaos and tech-speak and insider references. Even the title is an insider’s reference, to the union requirement that 12-hour days for rehearsals contain two hours of breaks.

We have to listen carefully just to pick up on that. And, though this tech rehearsal is supposedly a run-through of the play-within-the-play, we never learn its title nor precisely what it’s about; it appears to be a Victorian s&m horror story. It’s a testament to Washburn’s talent that, as cheesy as the drama seemed to be, I wanted more of it.

10 out of 12

at SoHo Rep

By Anne Washburn; directed by Les Waters; sets by David Zinn; costumes by Ásta Bennie Hostetter; lighting by Justin Townsend; sound by Bray Poor; props by George Hoffmann and Greg Kozatek; choreography by Barney O’Hanlon; music arrangement by Dan Mackenzie and Mr. Poor; production manager, Jeff Drucker; production stage manager, Amanda Spooner; technical director, Sara Morgan.

Cast: Quincy Tyler Bernstine (Stage Manager), Jeff Biehl (Technician 3), Gibson Frazier (Ben/Charles), Rebecca Hart (Costume), Nina Hellman (Siget/Old Lady/Lucille), Sue Jean Kim (Eva/Marie), Bruce McKenzie (Director), Garrett Neergaard (Technician 2), Bray Poor (Sound), David Ross (Jake/Richard), Thomas Jay Ryan (Paul/Carstairs), Conrad Schott (Assistant Director), Wendy Rich Stetson (Lights) and Leigh Wade (Assistant Stage Manager).

Running time: About 2 hours and 45 minutes (including 15 minute intermission.)

10 out of 12 is scheduled to run through July 11, which is an extension of the original end date.