Why so few speakers with Passive Radiators?

I suspect the reason is mostly that ports are cheaper/easier.  I only know of the below three factors.

passive radiator
 - no port noise
 - less sound escapes through the diaphragm than would through a port

port
 - higher efficiency

Wait just a minute, you may indeed be a bozo but not as big a bozo as me.  I've only been at this umpteen years and I don't know vented from sealed.....I occupy the front seat on the bus!

Hey man…all bozos are welcome on THIS bus…Well designed passive radiators do fall into the "venting" category although you'd think they imply a sealed box, but the passive radiator is sort of the "unsealed" part part of the thing. I own a discontinued Mackie HR120 sub that was designed for home use (not the "drag it around to gigs" P.A. stuff), and it has a 12" passive on it, unlike the pro stuff I use in some live sound situations that have a vented/ported design (and generally 1000 watts into an 18" driver)…both work well, but the HR120 with a 500 watt A/B amp driving a very beefy downloaded EAW 12" (92 lbs…you just don't want to move it) is flat to 19HZ. REL does well with their passive radiating little subs (my 2 RELs don't have those, but work anyway), as do many others of course, and it's simply another flavor…personally I prefer raw drivers suspended from fishing wire 2 feet from my head, but that's just me. A bozo.

I consider the passive radiator a special case of a vented design:

1 Sealed enclosures
2 Vented enclosures
    2a Ported
    2b Passive radiator

Keep in mind I'm just a bozo typing opinions on a forum, not an expert!

beetlemania the 3.6 is not vented unless you consider the passive radiator as the vent.  It is a sealed enclosure.

I agree that it is a "successful" trade-off and I am plenty happy with the bass performance of my CS2.4SE. But I think you need to directly compare sealed vs. vented (including passive radiator) designs to fully understand the what the trade-offs are. Most designers have much more experience with this than me and, presumably, you.

In the case of Thiel, it could be instructive to compare the bass performance of the sealed box CS3.5 with the vented CS3.6 (I've never heard either model). I have no idea what Thiel's rationale for the change was but, clearly, he thought the trade-off was worth it. The dearth of other models with passive radiators suggests other designers hear it differently.

Thanks, I’m aware that everything is trade offs, but the passive radiator seems such a successful trade off I’m intrigued that it’s not used more, vs the much more common trade off of, say, ported.

Having owned and listened to many sealed designs, I don’t find the passive radiated Thiel bass remotely describable as "slow." It’s completely the opposite.  I've searched in vain for other speakers with as tight, tonally controlled bass as I hear from this passive radiator design.

Everything is a trade-off in speaker design. If there was one "right" way, all speakers would share that design! Each designer weighs the trade-offs to optimize what they think and feel sounds best.

Sealed boxes tend to give the best definition and resolution but at the expense of extension and ability to play loudly. Ported designs, including Thiel's radiators give better extension but at the expense of low bass timing being a bit slow.

One "good" source of info is the Audio Perfectionist Journal, archived on the Vandersteen website (under Resources, Richard Hardesty memorial). In particular, I suggest Volume 3 for trade-offs of vented and sealed enclosures. (I would add hot links but Audiogon's link feature does not work for me).