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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
tomcarr
530 posts
 
I'm on the bus, too. My Vandersteen 2Cs are a 3-way, with an acoustic coupler on the back of the speaker. Are they considered acoustic suspension? Ported? Sealed?
Thanks for a response, and thanks Prof for this post>

Tom
rodman99999
3,557 posts
 
Systems utilizing passive radiators ARE, "vented" systems. The Thiele-Small parameters and calculations, are identical for both. Only the application(vent or radiator) of the results(mass of port air/size and weight of the radiator), varies. https://itstillworks.com/size-speaker-enclosure-passive-radiators-7918995.html   "Tighter" bass can be realized, by adding weight to the radiator(s).
tomcarr
530 posts
 
Sorry, forgot to ask is an acoustic coupler the same as a passive radiator?

Tom
beetlemania
471 posts
 
The 2Ce and 3A use sealed enclosures (I think the Treo has a downward firing port). From Tom Norton's 3A review in stereophile:
A cutaway photo reveals four drivers and three separate sub-enclosures—the bottom of which is the largest, for the rear-facing 10" driver that Vandersteen refers to as an "Active Acoustic Coupler." It is, as the name implies, actively driven [though it shares some of the characteristics of a passive radiator—Ed.]. Since the AAC is designed to cover primarily the range below 35Hz, I would be inclined to call it an integral subwoofer; but perhaps Vandersteen chose to give it another designation to distinguish it from the company's dedicated, outboard subwoofers. 
I think the crossover is designed as a 3-way, so not sure how this thing works - and I ran 2Ce Sig IIs for 10 years! Maybe the filter for the woofer has a sub-network for the AAC?
timlub
1,649 posts
 
Hi guys,   Well,  a lot great info, a few minor inaccuracy's... Even the Richard Hardesty post is more opinion and not cast in stone. 
Yes,  A passive radiator is more of a vented or ported design.  When we do a ported speaker,  Lengthening the port lowers the frequency of air moving through the port so changes the frequency the woofer peaks at.  Where Richard was not quite accurate in his description is that it is completely feasible to port/vent a driver to be very smooth and accurate bass, it is then a function of a well damped amplifier to control it. There are many ported speakers out there that are great. A passive radiator works similarly in that as you add mass to the radiator,  it will like a port, change frequency where there is a peak or dip and by how much. Every driver does change spec as it is used over the years and fact is,  a sealed box comes much closer in keeping its original sound as it wears and a ported box is the same.   Oddly enough in my own speakers at home right now, I have 3 pair built. A 10 inch 3 way in a sealed box,  an 7 inch mtm in a ported box and a 12 inch 2 way (big Heil amt) in a passive radiator box.  All 3 are flat, accurate and fast with the right equipment in front of them.  
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