Your battery test only tell half the story
http://www.mcintoshlabs.com.ua/files/products_documents/135.pdf
•Special Crossover
At frequencies below 350Hz both Low Frequency Drivers operate in-phase; above 350Hz both the Low Frequency Drivers and Tweeters operate out-of-phase thus providing the desired diffused surround effect. Both the Low and High Frequency Drivers are crossed over at a 12dB per octave rate.
http://www.mcintoshlabs.com.ua/files/products_documents/135.pdf