Odd passive radiators

[Shel-e-bean]

I was cruising through thrift stores the other day and saw a pair of 2 way tower speakers with odd passive radiators. They were flat and porous!? If you pushed on the woofer cone, the radiator would push out, then sink back to it's neutral position.
Has anyone ever seen these type of radiators before? I couldn't tell which manufacturer it was because the large paper labels were ripped off the back. They sort of reminded me of Energy speakers, but I'm sure Energy would label their speakers better.
The idea of a porous passive radiator is sort of interesting. It must have been fun playing with the design.

 

[Nat]

That actually sounds like perfectly normal behavior, though depending on what you are describing, it may not be what you want. If what you are saying is that when you push the woofer in, the passive moves out, and then reverts to normal even though you have not let go of the woofer, there is a leak in the system. This is,unfortunately, normal after a while. Passive radiator systems should be absolutely air tight, but aren't always. particularly if they have foam surrounds (which can degrade as they get older or as they are exposed to UV or aerosols), or if the drivers vibrate themselves loose from their mounts. In that case, repairs are needed if the PR is going to produce tight, deep bass. On the other hand, if you let go of the woofer, its correct for the passive to go back also.
There may have been foam on the front of the passive radiator -- that's common, but doesn't mean the radiator itself is porous. Usually its foam over cardboard of some sort.

 

[RayW]

(said in my best Cliff Clavin voice...) Actually Norm, a PR system can't be totally airtight. If the speaker were totally airtight then changes in ambient air pressure would cause physical offset of the PR (and to some extent the active driver). If there were a storm coming your PR would be sticking out.
You have to have some way to equalize the internal pressure with the external.

Ray

 

[Shel-e-bean]

There may have been foam on the front of the passive radiator -- that's common, but doesn't mean the radiator itself is porous. Usually its foam over cardboard of some sort.

Ahh. That makes sense. It took about a second or two for the passive radiator to reseat when I pushed on the woofer. I guess the cabinet is just a little leaky.