I would normally say with a room that size, a Beam (Gen 2), Sub, and two One SLs would be sufficient. But since you are using a 90” screen, I would go ahead and get the Arc. It won’t be too powerful for a 12 x 12 room.

Thanks for your answer! What I don't understand is why, acoustically, it matters that the soundbar matches the width of the screen. I mean, I get why if you had a 5" speaker matching to a 90" screen, but with a Beam (Gen 2), 2 SLs, and a woofer wouldn't that provide adequate stereo experience? Why would a 20" delta between the two matter?

90” is a pretty large screen. You want sound that matches the size of the screen. The Arc has a much wider, and taller, sound stage than the Beam. Will the Beam, Sub, and two One SLs be sufficient? Probably. But if you want the best home theater experience Sonos has to offer, get the Arc. If you are on a limited budget, get the Beam.

Thank you! It's the wait with the Arc, since it's back ordered until at least 12/17.

Actually, nevermind! The package deal with the sub and SLs isn't delayed! Perfect.

You could always get the Beam and test it. If you like it, cancel the order for the Arc. If the Beam isn’t enough, return it and wait for the Arc.

Forums talk about room size but doesn’t help with a specific number (lxb or sq.ft) and hence the question.

Room size 20”x16”. 100” screen with UST projector.

Would the Beam (Gen2) paired with a Sub mini and two rear speakers work fine OR need to invest 2X for the Arc and Sub (Gen3).

Work? Sure.

Give you the best sound possible in that room? Not so much.

Room size is only one concern and really applies to the Sub selection more than the other components. Have to add in room type (open/closed) ceiling height and what you expect from the system.

For the front speaker distance to listening position is a key point, narrow soundbars have shorter distances where the stereo separation is good, wider ones give a longer distance. Also think about dedicated Atmos speakers versus none.

A bit the same for surrounds, the 300s are going to be far superior for Atmos but only if positioned properly. The 100s are a good option if the 300s can’t be set up to take full advantage of their capabilities.

All that said, 100 inch screen, 20x16 room: I’d go Arc and a Gen 3 Sub at a minimum. If the low end disappoints then a second full sized Sub. Then 300s in the rear if possible, otherwise 100s.