M,

From a hearing protection's
perspective a good passive headset is more than enough to reduce the
noise to a level that's not harmful to hearing.

Uhm, some people have different opinions.

The cabin noise level
in my Grumman Traveler is around 91 db at high power cruise. A 21db
reduction drops it down to 70db and it's a very safe noise level for
100hr a year.

At what frequency?

--
Thomas Borchert (EDDH)