Passive radiator design from scratch

Are there any guidelines to design a custom passive radiator from scratch?

My intentions are to make a honeycomb passive radiator membrane, resulting in a known Sd and mass (Mmd). I've several idea's for the suspension that I'd like to try out, that hopefully ends up with a ball park Xmax of 10 mm for the passive radiator.

My first try would be a 33 x 33 cm square membrane (1089 cm^2) with an Mmd translating to the equivalent of a port that is between 100 cm - 150 cm long (40 - 60 inch). This will be used in combination with a 12" PA driver, in an enclosure tuned to 50 - 60 Hz.

What I do not know at this point are the resulting Fs, Vas and Qms and the effect these will have on the performance of the passive radiator.

I've seen mention of the effect of the Fs on the passive radiator performance but nothing on the effect of the Vas and Qms. Any guidance is welcome ;)
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Indeed. The relevant parameters for tuning are the cone area and moving mass. Vap and Qmp are limited by the desired property than the passive cone should not be able to move in any way other than forward / backwards, which usually is solved by using a suspension. Rocking modes can be a problem if no spider is used.
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You're looking at 2 x 6" in a push-push configuration, to cancel out vibrations, both are in a cavity just large enough to fit the driver. The passive radiator is a diy 10", weighing approximately 75 - 80 gram (Mmd), with the ability to add weight to it via a M6 bolt.

Showing the impedance and phase response:

Adding 48 gram of weight to the passive radiator shifts the small bump between 40 - 50 Hz down by 5 - 7 Hz, all else stays pretty much the same:

I do have some questions because I'm not entirely sure what is going on:
  1. Is the impedance plot inverted (giving peaks where there are dips and vice versa)?
  2. Does this mean the passive radiator is hardly working? Follow-up, how can this be improved?
  3. What the frick is going on in the next plot?


Best regards Johan
OK, so this is what I get with the impedance-rig connected to the right LINE-OUT of my sound-card, with the with the leads shorted together at the point where the drivers (the load) are attached:

And this is what I get with the impedance-rig connected to the left LINE-OUT of my sound-card, all else equal:

With this new information I get this impedance plot, for 0 gram added (red), 25 gram added (green) and 48 gram added (blue):

Does this mean I've got a passive radiator tuned to roughly 70 - 80 Hz?