Gunfire Noise Analysis

• Sound from guns: 150dB to 170dB; See http://www.freehearingtest.com/hia_gunfirenoise.shtml
• conversational speech is approximately 60-65 dB
• This article: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/db.html#c1 describes the Decibel, which is used to express sound intensity.
  • 0 Decibels (dB) is the threshold of hearing I_o, and is 10^-16 watts/cm²
  • 40 dB is 10,000 times more sound power per unit area than I_o
• To estimate the sound level at a distance further from the source, the inverse square law
  • I₂/I₁ = (d₁/d₂)²
• Assuming one gunshot at 150dB at 1m, the sound will be at loud conversational level (70 dB) after 10Km (6.21 miles)
• If 300 trainees are firing guns at the ranges, assuming 3 ft for each shooter, then the sound should be significantly higher, and continual.
• The placement of the shooting ranges against the far hills will cause the sound to reflect off the mountain and be directed back toward Potrero. This may double the sound intensity, meaning another 3dB.
• To get the sound down to 62dB, you need to be 25Km away. This assumes reflection off the mountain and no unusual dissipation, and assumes the quietest firearm loudness (150dB).
• Assume the intervening mountains dissipates the sound by half. Then, we are back to eliminating the reflection, and still need 17Km to get it down to 65dB.

-- Raymond Lutz - 09 Apr 2007