I disagree with Marty, will all due respect. When using waveguides, there is just like any other speaker designs, a list of tradeoffs. Bigger waveguides hold pattern lower as also avoid "funkiness" due to mouth diffraction a bit better for a given passband then their smaller brethen. This is why I opted to go with a SEOS18 over the smaller kin even though I was planning to cross around 1khz plus or minus a bit.
1.4" throats will start beaming sooner and most that use larger diaphragms will exhibit a breakup much lower in freq, enough to where I start to think you really need to use a tweeter. Many here will just ignore it, but if we are chasing the absolute highest level of performance, then you can see why I think its needed.
Dr. Geddes which is really the inspiration behind all the SEOS development in the first place has said many times that 1" CDs are the ideal for home use. GIven his set of criterion I see his point. He also had discussed that a 18" round OS would be the ideal mate for a 1" CD (again to my previous posts). I once argued this point on that super huge thread given a set of measurements comparing the 15" and 18" when planning to cross to a 15" but some disagreed. I think if you were to study those graphs hard you will see where we are coming from.
I am not at all against using bigger waveguides/CDs, in fact I am for them, I just think once you go with bigger CDs you except that you are now using a (super)tweeter and make the most of that new system tradeoffs.
I am using 2" CDs on Iwata 300hz and Beyma TPL-150H above them in my audio only system. For lower pattern control in a smallish room and higher sensitivity for tube amps.
I do agree with Marty that if you are going with 1.4" CDs, might as well go for the SEOS24 and then use a tweeter above, otherwise if sticking with SEOS18, I'd opt for 1" hardy CD like the B&C DE250/DIYSoundGroup version and cross ~850-1000hz. Those CDs can handle that in a home environment.
JoshK on most other audio forums