[Vintage-Audio] Dual Voice Coil For Woofer?

[Duane Fischer]

Hi All, 	
	
The single DBX SW-15 with bottom firing 15 inch woof woof uses something I
am not familiar with. Are any of you?	
	
It has an input for the left and right channels from the amplifier. The
signals are run through a crossover network and those from 250 Hz down sent
on to the speaker and those above 250 Hz are sent to terminals on the back
of the cabinet. The left and right speakers are connected to these
terminals.	
	
The 15 inch speaker has two voice coils, one for the right channel and a
second one for the left channel. Somehow the two signals are put in phase
and fed to a single speaker. 	
	
How did they cause the two voice coils to work with one speaker? 	
	
Was doing this common or unusual?	
	
Thanks for your assistance.	
	
Duane W8DBF	
dfischer at usol.com