I picked up a 2269H to build a Sub18 clone go with my M2 clones (or close enoughs). The Sub18 specs http://www.jblpro.com/www/products/r...st/sub18#Specs
give the external dimensions which works out to about 9 ft^3 gross (ignores driver, ports, bracing, etc) but no tuning specifics or port dimensions. Guessing from the photo ports are...4" maybe 6"...and let's guess 24Hz for tuning. Let's assume 2400 watts peak (Crown XTi4002 bridged mono)...the iTech 5000 isn't in the budget. Performance below 20Hz isn't a priority, I know this is the wrong driver to go ULF and below 24Hz looks challenging.
I used the 3" Precision Ports on the M2 clone so I figured a pair of the 4" or 6" should do the trick. Long story short...a pair of 4" gives a length of about 12" and the 6" goes about 30" which really doesn't fit in the box without elbows and consumes valuable cubic footage. Unfortunately the port velocity is very high for the 4" ports below 40Hz. As a practical matter, can you hear port noise when you are running >110 dB? I suspect I won't be running near peak power except to show off the system occasionally. Anyone know where to find a 5" diameter flared port?
Haven't done the math on slot ports because the first goal was to match the Sub18 look (if you can call it that). Come to think of it I could incorporate the slot port into a riser to get it up off the floor and eliminate the "problem" of the port consuming box volume (assuming I give up on round ports). Hmmmmm....
Next thought was to look at a passive radiator. I don't know much about them but Parts Express has an 18" model. Any help or advice on optimization would be appreciated. Runs out of excursion between 20 and 30 Hz depending on added mass. What does that sound like? Does it simply not produce the modelled SPL (sort of behaving like a sealed enclosure when Xmax is exceeded) or does it sound like frapping and/or thunking? It does look like the passive radiator does help keep the 2269 out of extreme over-excursion when driven hard below Fs/Fb.
I guess my question really come down to finding the solution that is most tolerant of being driven stupid loud at 20Hz while yielding acceptable SQ.
You guys are a great resource. Thanks!