flightsimer From United States of America, joined Aug 2009, 494 posts, RR: 1 Reply 2, posted (9 months 3 weeks 2 days 14 hours ago) and read 1796 times:
You have two types of noise reduction, passive and active. The below is just a basic understanding, I'm sure someone else will have the specifics to the Saab's system.
Passive noise reduction is a physical action such as using sound absorbing material or vibration dampeners
Active noise reduction does not rely on physical noise reduction like passive but instead uses opposite sounds to reduce sounds. So with an active noise system, their will be microphones placed throughout the cabin and fuselage which will measure the sounds being heard from the engines, props, airflow, etc. The system will then send out sounds that are the exact opposite of the sounds being generated by the engines, props, airflow, etc which are supposed to cancel out the sounds.
The problem with the active systems is that they break down, often ( at least the older systems did) whereas with passive noise reduction, it's always working and requires little to no maintenance. The King Air family used to have active noise canceling for while, until Beechcraft decided to replace it with a passive system because of the countless issues with the active system. The Q series is also seems to have lots of issues with its active noise canceling based on posts here of people always complaining about it.
You're right, my mistake. ATRs have only passive noise dampeners. I guess I always thought they had active noise reduction too since I haven't noticed much difference in cabin noise between the -500 series and the Q400. Interesting--thanks.