Ballistic Shockwave
Definition
An N-shaped pressure wave produced when a supersonic projectile displaces air faster than the air can move out of the way. It is a Mach cone trailing behind the bullet and arrives at a receiver from a direction that points back along the bullet's flight path, not from the shooter's position.
- Field
- Forensic gunshot audio analysis
- Wave shape
- N-shaped pressure wave
- Cause
- Supersonic projectile displacing air
- Directionality
- Points back along bullet flight path, not shooter
Common questions
Why does the ballistic shockwave direction matter for estimating shooter position?+
Because the shockwave arrives from the bullet's Mach cone rather than directly from the muzzle, a microphone or witness near the bullet's path can hear the crack of the shockwave before or independent of the muzzle blast, and misreading this as coming from the shooter's location can lead to an incorrect estimate of where the shot originated.
How can an analyst tell a ballistic shockwave apart from the muzzle blast in an audio recording?+
The shockwave typically produces a short, sharp N-shaped transient distinct in waveform and arrival timing from the longer, lower-frequency muzzle blast, and where both are captured, the time difference between the two arrivals at a known recording position can be used to help estimate the bullet's trajectory and the shooter's approximate position.
Does every gunshot recording contain a ballistic shockwave?+
No, a shockwave is only produced when the projectile itself travels faster than the speed of sound and only reaches a given microphone if that microphone lies close enough to the bullet's flight path; a subsonic round, or a recording position well off the bullet's path, may capture only the muzzle blast.
Related terms
- Confounder
- A non-gunshot acoustic event that shares characteristics with a firearm discharge: vehicle backfire, fireworks, industrial tools, and tyre bursts are the most...
- Impact Transient
- The acoustic energy released when the projectile strikes a surface. Its character depends on the target material (wood, concrete, soft tissue) and...
- Muzzle Blast
- A broadband impulsive pressure wave generated when high-pressure propellant gases exit the barrel behind the projectile. It radiates roughly omnidirectionally and is...
- ShotSpotter
- A commercial urban acoustic gunshot detection and localisation network that processes impulsive events from distributed microphone arrays to estimate shooter location and...
- TDOA (Time Difference of Arrival)
- The difference in arrival time of a sound at two spatially separated receivers. Each measured TDOA constrains the sound source to lie...