Sound below 20 Hz (infrasound) receives little attenuation traveling through air, barriers or any other means that may be used to reduce audible noise

78 dB at 0.5 mile (from previous chart gas turbine)

Decreases approximately 6 dB for every 2x distance

At 1 mile from source – 72 dB

At 2 miles from source – 66 dB

At 4 miles from source – 60 dB

85 dB at 0.25 mile (Siemens SGT-800 45 MW gas turbine with “best available” damping)

Decreases approximately 6 dB for every 2x distance

At 0.5 mile from source – 79 dB

At 1 miles from source – 73 dB

At 2 miles from source – 66 dB

At 4 miles from source – 60 dB

Undamped sound from SGT-800 gas turbine 45 MW electric generator is 130-150 dB, Siemens data indicates damping to 85 dB is possible.