Why tilt the baffle? I assume you would use DSP to do any time alignment. And with concentric drivers, it seems even less important. But clearly it was important.
First of all I'd like to point out that this is a prototype thread, and the point of prototyping is of course to test how things work. That means you may see things in this thread (and our other prototype threads) that won't make it to the production models.
When it comes to tilting of the baffle, you are of course correct that the most common reason (or at least stated reason) for this is time alignment. I also suspect some do it just to make their speakers look interesting.
As you indicate, these drivers are basically time aligned by default, since the upper driver is a coax, and the lower driver is an identical size driver from the same manufacturer with almost the exact same dimensions. The timing is also less critical to the lower driver since it's rolling off relatively early. Finally we're using 1.order / async slopes so the phase is linear throughout both crossover points.
So then why tilt the baffle? We're currently testing 4 degrees and 7 degrees. If we choose the latter, on-axis will be roughly half way between a sitting and standing position. So if we optimize the frequency response for 7 degrees off-axis in the vertical plane, we will actually get roughly similar response wether you sit or stand. Based on the testing so far I'm leaning (no pun intended) towards the 4 degrees variant, which will not give the same effect, but nonetheless still leave the standing position closer to the intended listening axis than if it wasn't tilted at all.
(Disclaimer, the following paragraph has some subjective / creative descriptions of the sound, not sure how to put it any other way
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But the primary effect is more about the sound energy as well as imaging and sound stage in the room. These speakers will be designed to have very little toe-in. The recommended toe-in will probably be zero degrees, so none. Thanks in part to the coax drivers, with these speakers you get the benefit of the wide soundstage that little to no toe-in gives you, while still having really good imaging and stereo perspective. At no point does it feel like the sound is coming from the speakers, the different instruments are painted across the entire width of the room and are somewhere in between, or even to the side or in the vertical plane. Slightly tilting them so the tweeter on-axis is slighlty above ear level gives an even wider impression, and also gives an added impression of height, giving for instance vocals a more lifelike sound - you don't want the singer to sound like she's 90cm tall, right?
So all of these things adds up to making the speaker sound "larger than life" which was one of the design parameters of these speakers.
A secondary effect is that when designing for off-axis listening, we have to increase the high frequency energy to get the correct frequency response in the listening position. This subtly increases the total high frequency energy in the room, adding a bit of sparkle and clarity without making them too bright. Tilting them a bit requires us to do that again, further increasing this effect. The result is quite immersive and fascinating - small speakers that sound really large, and they also sound smooth and without a hint of listening fatigue, without losing clarity or attack.