I saw some aluminum cone passive radiators from Parts Express which I haven't got around to enter into box software to simulate yet.
But what drives the choice of cone material for a passive radiator? Is it advisable to match an aluminum cone woofer with an aluminum cone passive radiator, paper woofer with paper PR, poly woofer with poly PR? Or is everything a resounding "it depends" with no characterization possible without actual simulation/experimentation/measurement?
But what drives the choice of cone material for a passive radiator? Is it advisable to match an aluminum cone woofer with an aluminum cone passive radiator, paper woofer with paper PR, poly woofer with poly PR? Or is everything a resounding "it depends" with no characterization possible without actual simulation/experimentation/measurement?
I would base it on aesthetics. 
For a passive radiator without a weight in its center it does not matter too much. The weight is evenly distributed along the full surface. It is also driven from it's full surface, so I expect there is not much excitation of cone resonances. Those resonances are way above subwoofer territory anyway. Flexing of the cone is also less important due to the same reason.
When a weight is mounted at the center, things become different. Now the same rules apply as for the woofer: stiffer is better. I expect that most passive radiators have a sufficiently stiff cone, so I would not worry about it.
A system for suppression of rocking modes and a highly compliant and low loss suspension are other performance related parameters to look for. The former is done by using for example both a surround and spider as the suspension, the latter can be examined by looking at fs (including added weight, must be below operating range) and Qms or Rms (if you increase Qms of the passive radiator in a simulation, efficiency around the tuning frequency should remain constant). Most passive radiators available for hobbyists are fine in those aspects. And of course, look at whether it is possible to add enough weight to obtain the desired tuning frequency.
For a passive radiator without a weight in its center it does not matter too much. The weight is evenly distributed along the full surface. It is also driven from it's full surface, so I expect there is not much excitation of cone resonances. Those resonances are way above subwoofer territory anyway. Flexing of the cone is also less important due to the same reason.
When a weight is mounted at the center, things become different. Now the same rules apply as for the woofer: stiffer is better. I expect that most passive radiators have a sufficiently stiff cone, so I would not worry about it.
A system for suppression of rocking modes and a highly compliant and low loss suspension are other performance related parameters to look for. The former is done by using for example both a surround and spider as the suspension, the latter can be examined by looking at fs (including added weight, must be below operating range) and Qms or Rms (if you increase Qms of the passive radiator in a simulation, efficiency around the tuning frequency should remain constant). Most passive radiators available for hobbyists are fine in those aspects. And of course, look at whether it is possible to add enough weight to obtain the desired tuning frequency.
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