What is it exactly that is under so much pressure?

[ChalleB]

• hermetic woofers that function under high pressure
  
• pressure sealed to give ”levels associated with a rocket launch"
  
• “If you could get inside the Phantom, it would be like standingnext to a rocket during launch.”
  
• To name only one, the maximum air pressure inside the enclosure is 20 times higher than in a conventional speaker box. This pressure is equivalent to 174dB SPL,which is the acoustic pressure level associated with a rocket at launch... 
  
• Devialet uses a modified version of the sealed-box design where the drivers fire into the unit's hemispheric resonance chamber (which takes 1.2 tons of compression force to seal, by the way). Because it's blasting a speaker each into only 3 liters of air, the sound pressure in each chamber reaches levels which Devialet claims to exceed 174dB. That's roughly the sound pressure level of a rocket firing from 1 meter away, and 20 times the pressure inside the typical sealed-box subwoofer.
  
  Sorry, but could someone please explain to me exactly what it is that is under so much pressure?
  Is it the casing which is under pressure? or is it the speakers? 
  and will it explode if i try and open it  ?