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will someone explain this to me? what is it, and what advantages/disadvantages does it have?

i cant find any resources on the net to explain this...

Basicly it just a cone and surround mounted inside a frame.

I personally wouldnt ever use one. Out of time for today though....

so there is no advantage in power usage or spl? right?

They are usefull for adding more feeling in the car. They won't add much SPL to you because they are not doing work. They will assist in moving a little more air and proportioning the airwaves (multidirectional 'firing'), but my guess is it will take away from the active driver's efficiency.

They are basically the sub minus the magnet and voice coil. They do have spiders.

I have a little bit of know how about them, but I have never used them.

I would assume William is right though. If one driver is pushing out then the passive is sucking in. Which will lower the efficency.

With the passives they both have to be in the same airspace.

I have heard you can gain about 2 dB (pretty sure thats what I read) if you can properly build/setup a box for them.

alright. my specualtion was that they had no overall advantage. but someone was insiting that it did....and i have never read anything about them. so i wanted to see if anyone knew anything.

i guess the Infinity BassLink system uses a passive woofer, i didnt know that, till now.