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What is a Passive Radiator in a Speaker

I am interested in figuring out something about the Vimberg Amea speaker. It has a passive radiator woofer in the rear. I was wondering what that meant. Here is a quote from a the Canadian Vimberg distributor.
The woofer at the back is actually a passive radiator. It’s using the air pressure inside the cabinet to move so you can put it close to the wall without any problem.
Anyone care to chime in with an explanation of a passive radiator woofer. What is the benefits and negatives of this design. What are other speakers using such a design? I was under the impression Thiel used this design.
yyzsantabarbara
yogiboy's avatar
yogiboy
5,718 posts
 
Here ya go!
http://www.centerpointaudio.com/PassiveRadiators.aspx
delkal
110 posts
 
Most of the early Polk speakers used a passive woofer.  This design extends the bass response and you don't have to worry about port chuffing.

The only negative I can think of is that the speaker needs to be airtight.  If someone messed with the gaskets or was sloppy putting the speaker back together it will effect the bass.   You can easily test for this by gently pushing in on the passive and hold it in.   The drivers should move out and take a few seconds (the longer the better) to return to normal.   If they push out but immediately start to go back in you have a leak somewhere.
twoleftears's avatar
twoleftears
5,318 posts
 
Thiel has used this design, as has/does Klipsch.  No doubt others.  I've always thought of it as a kind of half-way compromise between sealed box and ported/vented.  Achieving in theory a sort of half-way mix of the advantages and disadvantages of both of those designs.
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