Why so few speakers with Passive Radiators?


Folks,

What are your thoughts on Passive Radiators in speaker design?

I've had many different speakers (and like many here, have heard countless varieties outside my home), from ported, to sealed, to passive radiator, to transmission line.

In my experience by far the best bass has come from the Thiels I've owned - CS6, 3.7, 2.7 which use passive radiators.  The bass in these designs are punchy yet as tonally controlled, or more, than any other speaker design I've heard.  So I figure the choice of a passive radiator must be involved somehow, and it makes me wonder why more speaker designers don't use this method.  It seems to give some of both worlds: extended bass, no port noise, tonally correct.

And yet, it seems a relatively rare design choice for speaker manufacturers.

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