I have borrowed a pair in flight, by the way.

Could you provide a source for 30db? I am skeptical. Would love to see credible sources.

Edited to add: IIRC, each 10db reduction is roughly equivelant to a 50% drop in the percieved sound level. For example, to the average person, 60db sounds twice as loud as 50db. 110db sounds roughly twice as loud as 100db. Therefore a 30db reduction would result in a sound level roughtly 1/8 of the percieved sound level before reduction.

The human perception of volume does not follow a linear relationship like the db level.