Yes, the motor's in the normal place. It's a Genie. And it's LOUD. Can't remember the model but it's not nearly as wellbuilt as the one Woodnet tested here:
There's 29 1/2 inches of height in the box and the vac is about 20 inches high. I believe that's way more than I need. I just built the box from one sheet of ply and it ended up being about 21 inches square and 29 1/2 deep, AFTER the carpet was in.
In my opinion, it's the air flow, not the amount of space available. If the unit can vent the air fast enough it'll be fine no matter if there's no extra space at all. Heat does not seem to be an issue - I've had it running for over an hour and it's no hotter in there than it is after ten minutes.
I've got about ten one-inch holes drilled in the top along one side. You could hear the vac through those holes. Then I fastened a 3/4 strip above them and down the sides, then put a sheet of 1/4 ply over that, so the air was vented almost to the bottom. It made a big difference.
Not this one. They'd hear it. But I think the idea could be taken to a new level if you spent the money and started with the best stuff - a quiet vac and sound-deadening box liner material - you could get your hands on, instead of being like me and spending the least amount of money possible. :-) My budget was much slimmer then.
With mine, if I was in the garage and also shut the garage door, that might work.
But I would have to try it and then ask the neighbors. Actually, I've never run ANYTHING in the shop at that time of day. I know that the neighbor next door - about the same distance as yours - knew when I was using the planer with the doors shut but said it didn't bother either of them. I always take care to do my planing between noon and about 7 PM. The planer is the only one that anyone has noticed - the dust collector, table saw, router, etc, they don't care about. Lawn mowers make more noise than that, and we have a reel mower. :-)
I also note that neighbors really appreciated me asking them which tools they could hear. I got cookies. I like this neighborhood.