Questions about SETs and ported enclosures (Paramount + JBL 2215B)

[keto]

Hey all, I'd like to design boxes for some JBL 2215B's (fr 20hz, qts 0.21, dia 13", vas 736.2L or 26ft3). Several calculators point towards 4.4ft3 tuned at 34hz with a pair of 6"-long 4"-dia vents, which is pretty much what the original JBL 4320 boxes were :-). The original boxes were kind of boomy though, which I assume is due in part to their 3/4" walls. I've read here (PJ) that for a sealed enclosure the overall Q will be around 30% less using a typical SET vs an infinitely-low Zout amp. Is there a similar compensation with ported enclosures? Also, is there a way to calculate a minimum "double-dip" in the impedance? A "double-dip" sounds like something that a SET would not really like to drive. I've also looked into a sealed enclosure. In some ways not the best thing for the 2215's since @ Q=1 the Fb would be around 80hz (2ft3 volume), but I'm looking for super SET-friendly. Below is a drawing of the 5ft3 (without driver and port volumes) version (26"-tall) that will fit in the studio. 1.5" walls would be ply and/or MDF, but probably not aluminum :-). It would seem like a good move to go with these dimensions and tune to taste, but if there's a smaller enclosure that would really be a better match for the Paramounts, I'd go with that. Any suggestions would be very welcome. Thanks!

[ssssly]

From my meager experimentation, SETs are more picky about driver specifications than the enclosure. While I am sure there are exceptions I have found that my lower powered amps do not like to drive anything with a large xmax. Have not had issues with ported enclosures specifically though. Though I have found that they are happier in a ported enclosures with low port velocities.

[Paul Joppa]

If I recall correctly, the 2215B is the same as an LE-15B which was designed to boom - JBL marketing out-voted the engineering side. The Lansing Heritage site will have the most and bvest information.

If you adjust the electrical Q for SET drive, then you can use any box design program to find a suitable box; the amp will be comfortable with the resulting impedance function.

Consider a closed box with a QT of 0.5 to 0.7. These well-damped responses roll off very smoothly and slowly and can sound quite deep, especially if there is some room boost.

[keto]

Well, at least I was on the right track -- even if traveling in the wrong direction :-). Okay, just did a bunch of reading. Neat trick adjusting the Qes (increasing the value 20-25%, right?) and then solving for the vented enclosure. With the 2215B that would end up being about 6-7 ft3, which wont fit where it needs to go. It looks like the 4.5-ish ft3 enclosure will work well with a solid state amp when tuned to about 35hz, and that sealed it will have a Q of about .55. Many thanks!