My friend built a pair of open baffle speakers using 15" woofer and coincident mid/tweeter. They work in his space. I've been there 3 times, each time, different content, they sound terrific.
He's driving them with my 1956 Fisher 80az 30 wpc tube amps. Loaned them to him to see if that was enough tube power for them, answer: YES!. Now he knows what size tube amp he needs to buy, i.e. not over-buy, not under-power.