Mwalsdor, best let your family doctor look in your ears first. It might just be a case of too much wax distorting & dampening every sound that tries to reach your tympanum. Cadman, you have a very interesting problem. Have you ever measured the +ve pressure? It should not affect free standing diaphragms like electrostatics or planars. Guess only totally sealed woofer boxes would be affected, and to lesser extend the ported boxes be affected. Please post soon as you know the pressure at which your sound is audibly degraded. As a possible quick solution, suggest you leave a small vent open somewhere in your listening room when running the aircon to prevent pressure built up. Good luck.
