Speed and Noise
Jet noise doubles with each 25% increase in exhaust speed
Airframe noise doubles with each 26-32% increase in speed.
When people look at reducing noise, they often think of raising altitudes. Most people don't realize that speed is also a huge component of airplane noise.
The best example I could find on speed and airplane noise was a study that was done at Mather Airport in Sacramento.
This airport had been used by the Air Force until 1995, then was re-purposed for commercial (cargo) aviation in May 1995. They were receiving many complaints with arrival procedures and studied how to reduce the noise.
They found that by reducing speed and keeping engines on idle they were able to get a 5 db reduction in noise. However, when speed brakes are extended noise increases by 7 or 8 db.
To reduce noise they followed these parameters:
- Reduce speed earlier than normal
- Reduce speed by utilizing flaps
- Avoid speed brakes under 7000'
- Keep engines idle