Andrey,

If I remember correctly, there was a frequency/attenuation chart on the
back of some foam earplugs carton I saw once in a drug store. I'm sure
ANR manufacturers have plenty of charts for their products. So, data is
obtainable, at least theoretically.

A chart alone means nothing. It all depends on how you measure that chart.

But that doesn't mean much, since
noise perception is a very psychological thing (think of all those crazy
psycho-acoustic models for Hi-Fi audio noise reduction),

Not sure about that.

--
Thomas Borchert (EDDH)