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You shouldn’t wire anything like the above pic, it won’t give the same power to each driver, and the guy who said he did just that is wrong also…

3 is a really odd number unless you can run a 1 ohm stable amp

Put bluntly you have the wrong subs for your amp

With three subs you need either all subs in parallel or all subs in series

So 4ohms a sub is either 12 ohms or 1.33

2 ohms a sub is 6 ohms or 0.667

That’s it for three subs to get the same power to each driver 👍🏼 You can’t series/parallel 3 coils and get equal power to each ever

 

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US8761433B2 - Variable impedance voice coil loudspeaker - Google Patents

A variable-impedance electro acoustic transducer having multiple voice coils is disclosed. In one implementation, the loudspeaker includes a coil former around which three coils are wound, and a switch in communication with two of the coils such that when the switch is in a first position the...

patents.google.com

Three coils indeed, quite simple but clever

 

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And seems like it would reduce efficiency, correct? They have extra mass that is not contributing to motor force. I'm not discrediting the sub or the novel approach, simply discussing a design consequence.

Edit: I own one of their shallow roofers with the switch. Again, not dogging the design.

It depends, if they use the same weight of coil it’s very possible to acheive the same impedance of each, with thinner wire of a longer length then there would be no extra moving mass

That’s how they make d1 and d2 coils with the same moving mass as an example, it depends how the coil is made up with regard to wire diameter and length