MovieChat Forums > Quigley Down Under (1990) Discussion > Sound delay

Sound delay

posted 19 years ago by rogerc210
6 replies | jump to latest

It's highly commendable that this fictional movie owns up to something even documentories refuse to do. Namely the fact that sound is not instantanious over distance but there's a delay as it's enroute from the source. THat being said, I'm still a little puzzled by the delay b/n when the bullet of Quigglie's rifle struck & hearing the report of the gun, w/ silence in b/n. The bullet reaching them b/4 the gun report means it must be supersonic, which means it would be making sonic bangs enroute. Seems like just because the bullet stops doesn't mean the shockwaves do, thusly, shouldn't we start by hearing the impact, then shockwaves made by the bullet enroute in the reverse order in which they were generated, then finally the muzzle blast? Delay according to the bullet's lead on the muzzle sound? Doesn't the bullet of a long barreled gun make more noise at it's higher velocity, than the more energy-spent explosion in the bore? My impression is that even a supersonic bullet never outdistances the sound of the shot, because it automatically takes some of the sound with it. In the goof section, it said the bullet wasn't supersonic long enough to have a sufficient lead on the sound. My question is different, because the goof section doesn't outwardly rule out the potential of a sound delay after a supersonic bullet hits.

There's only 1 Yogi Bear. They tried a 2nd time, & they made a Booboo!HeyeyeyhEY!

[–] beevee-1 19 years ago

A super-sonic bullet creates a sonic boom (The "crack" of a rifle) the instant it leaves the barrel as it is exceeding the speed of sound. The sound heard at the target (the delay) after the bullet arrives lags, whether super-sonic or sub-sonic. The sound of a sonic boom doesn't travel faster than a regular sound, but at identical speed. HTH.

[–] ranb40 19 years ago

The 45-110 round used in the rifle is a 550 grain bullet moving at 1360 fps. The speed of sound in air at sea level is 1116 fps, depending on temperature. Using a ballistic coeffecient of .500, the bullet would be moving about 1100 fps at only 300 yards. At 600 yards, it is moving 960 fps and at 1000 yards, only 846 fps. Flight times at 300 yards is .74 seconds, 1.6 seconds at 600 yards, and about 3 seconds at 1000 yards. The sound of the muzzle report lags behind the bullet only .07 seconds at 300 yards, and is .3 seconds ahead of the bullet at 1000 yards. As you can see, the sound of the muzzle blast and the impact sound of the bullets are never far apart in ranges less than 1000 yards, and the muzzle report stays ahead of the bullet at ranges past 700 yards.

A person standing next to the intended target will hear the impact, muzzle blast and and air noise all at about the same time.

Ranb

[–] beevee-1 19 years ago

Thanks for the great clarification. Do you frequent the FAL Files Forum?

[–] ranb40 19 years ago

Just started lurking there.

[–] rogerc210 19 years ago

My general understanding has been that the supersonic bullet is continuously producing sonic booms throughout it's SS trajectory, therefore, the sound of the bullet never lags behind it. The SB is not only where the bullet leaves the barrel.That means you hear nothing until the bullet arrives, then you hear the nearest SB at about the same time as you hear the impact(if that's the part of the trajectory you're closest to-the terminus), then you hear a trail of crackling as shockwaves arrive from uprange. Not a series of repeated sonic "booms", but a continuous stream of sound. Seems like the track of a supersonic bullet can be compared to a lightning bolt, in that it's a geometrically distributed source of sound where parts of the otherwise instantainious bang reach your ear at different times.

Still, it's good to have a movie which at least aknowledges sound lag over distance. I even saw at least one documentory that I could tell was edited to make it seem like sound was instantainious regardless of distance. It was "Air Disasters" which showed some real footage of planes crashing. The crashes sounded realistic, except I could tell the crashes were videoed from 1/2 mile or more away, so there should have been at least a 2 second lag. Moreover, the reactions of nearby spectaters sounded suspiciously familier. In documentory footage, I don't want to hear anything they didn't hear.

There's only 1 Yogi Bear. They tried a 2nd time, & they made a Booboo!HeyeyeyhEY!

[–] ranb40 18 years ago

You are correct that the sonic boom is produced throughout the flight. But the muzzle blast is many times louder than the sonic boom. The sound of the impact and the sound arriving from the rifle's muzzle are what I was comparing in my first post.

Ranb