Noise from rocket

For all but the very smallest sizes, rocket exhaust compared to other engines is generally very noisy. As the hypersonic exhaust mixes with the ambient air, shock waves are formed. The sound intensity from these shock waves depends on the size of the rocket as well as the exhaust speed. The sound intensity of large, high performance rockets could potentially kill at close range.

The Space Shuttle generates over 200 dB(A) of noise around its base. A Saturn V launch was detectable on seismometers a considerable distance from the launch site.

Generally speaking, noise is most intense when a rocket is close to the ground, since the noise from the engines radiates up away from the plume, as well as reflecting off the ground. This noise can be reduced somewhat by flame trenches with roofs, by water injection around the plume and by deflecting the plume at an angle.

For crewed rockets various methods are used to reduce the sound intensity for the passengers as much as possible, and typically the placement of the astronauts far away from the rocket engines helps significantly. For the passengers and crew, when a vehicle goes supersonic the sound cuts off as the sound waves are no longer able to keep up with the vehicle.