How to model dual VC drivers in MTM configuration?

[dhieber]

I have a pair of the satellites from Joe D’Appolito’s “Swan IV” speaker design published in Speaker Builder magazine way back in 1988. The system biamplifies the satellites and the bass speakers using an active LP filter for the bass. I would like to use the satellite’s drivers in a MLTL cabinet as a full range speaker. If I keep the cabinet width the same as the satellites, I hope to avoid the need to modify the satellite’s passive XO.

The satellites use the Focal 5N412DB, a 5” dual voice coil driver, in an MTM configuration. The VCs of each driver are connected in series with the corresponding coil of the other driver. The series connected VCs are then wired in parallel. One series pair is used to compensate for diffraction loss by using a series inductor.

My problem is figuring out how to model the box response when the dual VCs are connected as described. I have the manufacturer’s specified T/S parameters for the driver, which I presume are for parallel connected VCs for a single driver since Re is listed as 3 ohms. I need to know the corresponding changes in the T/S parameters for the case in which the VCs of each driver are treated separately—i.e., series connected to the corresponding VC of the “other” driver.

Maybe at low frequencies, the configuration used by D'Appolito is equivalent to some more easily understood configuration, but I’m not knowledgeable enough to know. I would appreciate any help you might offer.