Since I bought a pair of Kef 104abs years ago, I've always wondered how passive radiators work, and now I've got a pair Audio Physic Virgos that have them, I want to understand. I initially thought it effectively increased the size of the bass speaker, so basically you want a strong magnet on the active cone, and the pressure inside the speaker drives the passive cone. But then I thought surely the passive is out of phase with the active so there will be cancellation rather than an increase in bass. The air pressure in the speaker should travel at the speed of sound and the distance between the cones is not far enough to mean the back pressure from the active driver is at 180degs at say 50hz once it gets to the passive so it will push it out as the other driver is pulled in by the magnet. Then I read it does the same thing as a port and that got me wondering how ports increase rather than cancel the bass. So who can answer the question, in terms of what the air molecules are actually doing?

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