The Q400s are a lot noiser outside having one of the biggest props on the market, inside they are the only commercial turboprop available today to make use of an active noise cancelling system, with which the average cabin noise of 77-79dBA is lower than that in an Airbus A318/319, and around 2-4dB quieter than the ATR72′s cabin. There are 40 microphones in the plane, the system measures these vibration frequencies throughout the cabin, this frequency is analyzed and an equal frequency 180 degrees out of phase is sent to Actively Tuned Vibration Absorbers (ATVAs) which are placed between the exterior and interior walls, and they push back against this vibration with the out-of-phase frequency to effectively “cancel” the vibration. Since the vibration is cancelled, noise generation is also eliminated right at the source.