Passive Radiators

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Good day to all,

I have a pair of nice 10" driver I salvaged except that the voice coil is gone in one. I was going to put them in the rubbish bin when I realised that I could possibly use them in subwoofer that I need for a satelite system. I want use the blown driver as the passive radiator. I have the parameters for the working driver, does anyone know how to get the parameters for the other driver as a passive radiator to put in the software to get the right box volumes and etc.

This is my first stab at a passive radiator box. So anyone with experience in this area I am all ears:)

Surf, Sun & Sound
As a general principle the same type of driver can't be used as a drone cone.
It will have too little output at a too high frequency to work with the driver that works.
With added mass on the drone cone the resonanse frequency gets lower, but so do the output.
When propely loaded the output will be around 12dB lower than the driver, and even if that will give slightly deeper bass it isn't a good solution.

Please post Qts, Qes and Rf so we can say what the driver can be used for.


Thank you for your replies.

Hedlund - here are the parameters:

Qts - 2.898

Qes - 1.057

Fs - 27.5Hz

AE - I have already removed the voice coil and could easily remove the spider if needed. I have no problem using the defective driver as a PR with a 8" driver if that is better.
I just hate throwing out stuff if I can put it to use.

I have ran some preliminary figures with my software(Unibox) and have been a bit disappointed with the results. Not much lower Fs than the good driver in a sealed box. Of course, I am sure that I have put in some wrong numbers since I not at all familiar with passive radiators.

Surf, Sun & Sound
I assume you have mixed up the numbers.
The Qts can't be 2.898, but Qms can.
Qts should be in the range 0.25 to 0.6 or so.
Qes is a little high too. Are you sure you have gives the right numbers ???
With that Rf, Qes should be in the range 0.3 to 0.7 for any 10" driver.

Mixed Up the Numbers


You are right, I really messed up those numbers. Not sure where I found them out. Let's try again.

Qts - 0.347

Qes - 0.364

That is better!!

I am not guaranteeing those numbers are perfect, since I am not an expert speaker designer. But they are real close.

Surf, Sun & Sound
With those numbers the driver is well suited for bas reflex if placed as a normal speaker.
If placed in a corner a passive radiator is the best choice.
The drone cone should have a Qts around 0.45-0.5 if you want a 10" driver as drone cone and around 0.4 if you use a 12" driver.

Your broken 10" driver will only suite a 8" bass with about the same parameters that the 10" bass have.

When tuning, add mass to the drone cone until you get a suitable balance of depth and punch in the bass.

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