Open baffles existed long before dahlquist I have one from the 1930s as far as DIY I think many look at a OB thinking its a easy build and it can be, but if done right it can be as complicated and material intensive as any other design if not more so. I do know of a good num of OB on market today but the nature of the OB means baffles should be large and large is a hard sell in loudspeakers.
