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This starts to get “interesting” when you build [url=http://en.wikipedia.org/wiki/Isobaric_speakers]isobaric[/url] loaded speakers. In one example, 2 drivers are connected face to face and wired out of phase with each other. The air cavity between the 2 drivers stays at a constant pressure and essentially couples them together allowing the pair to act as a single driver. This causes Vas to be half that of a single driver allowing the enclosure to be half as large. The down side is the driver pair is 3dB less efficient than a single driver. Of course, if you have the amp wattage to spare, simply load 2 isobaric pairs of drivers into an enclosure sized for one driver and you can attain 6dB higher peak output than a single driver. Of course that requires 4 times the wattage, but who’s counting…
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