hi, i finished one cubo 18 (not extended with magnet in horn) today.usualY i do not like 18" speakers and i only built it becuse nobody wanted that eminence sigma 18 pro which was laying around here for years. i was offering it for 80euros allready. i built it with 19mm spahnplatte (the cheapest wood you can get) just to test the design. all i have to say is that im very impresd of this box. it still loads deep enough to be used down to 40hz. unfortunatelly i only had a small car hifi amplifier with me (about 80w rms) but even that was fun. the bass doesnt sound good (still better then most 18" reflex) and should be crossed around 90hz. its biggest advantage is the preassure around 50_60hz. so thanks for sharing your really good plans and greetings from germany.
The ESW1018 is 288 liter, Cubo 18 is 250 liter. Given that they're about the same volume I expect a similar performance as well. Most noticeable difference will likely be the sound and/or transient response. Only after a few reviews in a direct comparison I can say more about that.