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Here is the latest Luthier Tips du Jour video. In this video I invite Trevor Gore to answer a viewer's question about the difference between using 3 or 4 back braces.
This video as well as all my other videos are available via my website, https://lutherieacademy.com/videos , or on YouTube.
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You can absolutely get a live back with four braces, been doing it since the books came out.

I was shivering just looking at that picture of Antarctica.

But on classical guitars? That was Stephanie's question.

Can be done, but you need pretty skinny braces. Fleta was just about the only "big name" classical luthier to use 4 back braces, specifically, it seems, to make non-live backs on his guitars. Fleta chose to use a strong diagonal dipole, obtained with asymmetric top bracing, to extend the response in the T(1,1)3 frequency area.

So I think I got the right answer out, even though, by the look of the video, I hadn't slept for a week (jet lag!!)

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

With four back braces I make the lower two low and wide, as in Martins. You get the structural strength you need with more mass and not so much added stiffness.