I wrote an email direct to Irv asking this exact questions, regarding variation in atmospheric pressure or air transport issue. No answer back from him at all. I suggested him to install some spring loaded pressure relieve valve in the back so that user Can equalize inside and outside air with a single push. Imagine the burden presented to an amplifier if air pressure inside and outside is different, and multiply by cone surface area. That is a lot of air load presented to amplifier. Toga
Here is my post from 2012 discussed exactly about this.
http://www.audioaficionado.org/gener...-speakers.html