Needed R for driver as passive radiator

Hello there.

I've read in a few different posts how by adding a resistance to oppose a driver movement it can be used as a PR.

When I simulate a box with a PR I can add grams.

Is there a formula to get the equivalent in grams that I would get by adding a resistance to a driver?

Best regards.
 
Thanks @AllenB .

I can use trial and error and measure the response. I wonder what is the max damping I could get so that I don't waste time building the box. Say, if I just short the coil with a 0-ohm resistor.

The real solution is to use passive radiators. But I'd like to find use for some drivers I do not plan to use otherwise.
 
Thanks @AllenB .

I can use trial and error and measure the response. I wonder what is the max damping I could get so that I don't waste time building the box. Say, if I just short the coil with a 0-ohm resistor.
A shorted motor turns the driver into a piece of stiff cardboard.

The real solution is to use passive radiators. But I'd like to find use for some drivers I do not plan to use otherwise.
The fs of the drivers is likely too high to be used as a passive radiator. Adding resistance would raise the fs, the opposite of adding weight to a pr.
 
There's no way to change the Fs of a driver electrically. The driver's Fs is determined by solely by its moving mass (primarily the cone and the voice coil and former) and its suspension (spider and surround). You'll have to either add or remove mass (the latter is a lot more difficult to do, LOL), or modify the driver's spider (~80% contribution) or surround (~20% contribution).

Fb, the resonant frequency of the driver when mounted in a box, will depend on the driver's parameters and the size of the box. This also can't be changed electrically, but you can electrically modify the driver's behaviour around Fb, e.g. changing the resistance attached across the voice coil's terminals will change the Q of the resonance at Fb.
 
Using old drivers for passive you would have to add weight.
Fb can be confirmed by measuring the impedance curve.

For low distortion, which passive unfortunately does quickly.
You need usually at least 2x the passive area as woofer area.

Older somewhat basic way to determine Fb is a salt test.
Woofer cone movement is very little at Fb.
So you do a frequency sweep and watch the salt you place on the woofer cone.
When you have least movement your at Fb.