Posted: 5/30/2010 9:31:23 PM EDT
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If I were to set a digital voice recorder exavtly between me and a steel target, record me shooting it. Now taking the audio, use a program (pictured below) and measure the distance between the two noise peaks to see how long it took the bullet to travel the distance, therefore telling me the velocity by taking distance in feet / seconds= velocity in fps?
Picture below is a test run with an airsoft gun... 
So would this work with .223 at 100 yards?? |
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Quoted: Quoted: It would just give you average velocity over the distance. But also, you would have to account for sound travel time. Im thinking that placing the digital recorder in the middle would cancel that, or not? if you subtract the time it would take cound to travel from the gun and then subtract the time it would take sound to travel from the target you will have an accurate count. doesn't really need to be in the middle though. you could just put it by the gun and account for the time it takes the sound to travel from the target to the recorder. |
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It would just give you average velocity over the distance. But also, you would have to account for sound travel time. Im thinking that placing the digital recorder in the middle would cancel that, or not? if you subtract the time it would take cound to travel from the gun and then subtract the time it would take sound to travel from the target you will have an accurate count. doesn't really need to be in the middle though. you could just put it by the gun and account for the time it takes the sound to travel from the target to the recorder. So if the target is 300ft away, and the speed of sound is 1125fps, that means its takes .267 seconds for the sound to get from the target to me? Now i would take the time in the recording of how long it takes the bullet to hit the target and subtract .267 seconds, then i would use that time? |
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Quoted: Quoted: Quoted: Quoted: It would just give you average velocity over the distance. But also, you would have to account for sound travel time. Im thinking that placing the digital recorder in the middle would cancel that, or not? if you subtract the time it would take cound to travel from the gun and then subtract the time it would take sound to travel from the target you will have an accurate count. doesn't really need to be in the middle though. you could just put it by the gun and account for the time it takes the sound to travel from the target to the recorder. So if the target is 300ft away, and the speed of sound is 1125fps, that means its takes .267 seconds for the sound to get from the target to me? Now i would take the time in the recording of how long it takes the bullet to hit the target and subtract .267 seconds, then i would use that time? You subtract .267 to get the total time if you have the recorder at the muzzle, and add .267 if you have it by the steel. |
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Quoted: yepQuoted: Quoted: Quoted: It would just give you average velocity over the distance. But also, you would have to account for sound travel time. Im thinking that placing the digital recorder in the middle would cancel that, or not? if you subtract the time it would take cound to travel from the gun and then subtract the time it would take sound to travel from the target you will have an accurate count. doesn't really need to be in the middle though. you could just put it by the gun and account for the time it takes the sound to travel from the target to the recorder. So if the target is 300ft away, and the speed of sound is 1125fps, that means its takes .267 seconds for the sound to get from the target to me? Now i would take the time in the recording of how long it takes the bullet to hit the target and subtract .267 seconds, then i would use that time? |
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It would just give you average velocity over the distance. But also, you would have to account for sound travel time. Im thinking that placing the digital recorder in the middle would cancel that, or not? if you subtract the time it would take cound to travel from the gun and then subtract the time it would take sound to travel from the target you will have an accurate count. doesn't really need to be in the middle though. you could just put it by the gun and account for the time it takes the sound to travel from the target to the recorder. So if the target is 300ft away, and the speed of sound is 1125fps, that means its takes .267 seconds for the sound to get from the target to me? Now i would take the time in the recording of how long it takes the bullet to hit the target and subtract .267 seconds, then i would use that time? You subtract .267 to get the total time if you have the recorder at the muzzle, and add .267 if you have it by the steel. Which is why i think that if i were to put it at 150ft, i wouldnt need to even worry about the difference in time. If at one extreme i add .267, and at the other i add -.267. Then in the middle i would add 0, right? |
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Quoted: Quoted: Quoted: Quoted: Quoted: Quoted: It would just give you average velocity over the distance. But also, you would have to account for sound travel time. Im thinking that placing the digital recorder in the middle would cancel that, or not? if you subtract the time it would take cound to travel from the gun and then subtract the time it would take sound to travel from the target you will have an accurate count. doesn't really need to be in the middle though. you could just put it by the gun and account for the time it takes the sound to travel from the target to the recorder. So if the target is 300ft away, and the speed of sound is 1125fps, that means its takes .267 seconds for the sound to get from the target to me? Now i would take the time in the recording of how long it takes the bullet to hit the target and subtract .267 seconds, then i would use that time? You subtract .267 to get the total time if you have the recorder at the muzzle, and add .267 if you have it by the steel. Which is why i think that if i were to put it at 150ft, i wouldnt need to even worry about the difference in time. If at one extreme i add .267, and at the other i add -.267. Then in the middle i would add 0, right? I think you're right. |
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One thing that will probably be a problem is that the recorder will record muzzle report, bullet impact, and the sonic shock wave.
So, you'll have three peaks, which may overlap, maybe making it hard to find out the actual data you want. Also, you need to have good temperature measurements to compute the speed of sound (maybe already said) In theory your idea seems good but the details will be the key to getting good numbers. You also have to consider the effect of the microphone being offset from the line of flight (which might be negligible but should be calculated beforehand) Another factor is the sample rate of the recorder since that is a limit on the accuracy of the measurement. Over long ranges you will probably get a good average speed for the projectile. But you won't get muzzle speed since the basic measurement techique averages things over the total flight from muzzle to impact. Edit: make sure you measure the distance yourself; don't rely on the '100 yard range' signs for the distance. If the distance is 103 yards, it won't matter to the average shooter but it will make a big difference in your results. |
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Quoted: no. you are measuring sound. any place you put the mic in the line of fire you will need to subtract that .267 Quoted: Quoted: Quoted: Quoted: Quoted: Quoted: It would just give you average velocity over the distance. But also, you would have to account for sound travel time. Im thinking that placing the digital recorder in the middle would cancel that, or not? if you subtract the time it would take cound to travel from the gun and then subtract the time it would take sound to travel from the target you will have an accurate count. doesn't really need to be in the middle though. you could just put it by the gun and account for the time it takes the sound to travel from the target to the recorder. So if the target is 300ft away, and the speed of sound is 1125fps, that means its takes .267 seconds for the sound to get from the target to me? Now i would take the time in the recording of how long it takes the bullet to hit the target and subtract .267 seconds, then i would use that time? You subtract .267 to get the total time if you have the recorder at the muzzle, and add .267 if you have it by the steel. Which is why i think that if i were to put it at 150ft, i wouldnt need to even worry about the difference in time. If at one extreme i add .267, and at the other i add -.267. Then in the middle i would add 0, right? I think you're right. |
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Quoted: Quoted: no. you are measuring sound. any place you put the mic in the line of fire you will need to subtract that .267 Quoted: Quoted: Quoted: Quoted: Quoted: Quoted: It would just give you average velocity over the distance. But also, you would have to account for sound travel time. Im thinking that placing the digital recorder in the middle would cancel that, or not? if you subtract the time it would take cound to travel from the gun and then subtract the time it would take sound to travel from the target you will have an accurate count. doesn't really need to be in the middle though. you could just put it by the gun and account for the time it takes the sound to travel from the target to the recorder. So if the target is 300ft away, and the speed of sound is 1125fps, that means its takes .267 seconds for the sound to get from the target to me? Now i would take the time in the recording of how long it takes the bullet to hit the target and subtract .267 seconds, then i would use that time? You subtract .267 to get the total time if you have the recorder at the muzzle, and add .267 if you have it by the steel. Which is why i think that if i were to put it at 150ft, i wouldnt need to even worry about the difference in time. If at one extreme i add .267, and at the other i add -.267. Then in the middle i would add 0, right? I think you're right. Suppose you're shooting supersonic .223 at steel. Assume 3000 fps, giving 100 ms time of flight over 300 ft, and 267 ms sound travel time. Put the recorder at the muzzle. What sound arrives first? Well, the report, of course, at 0 ms. 367 ms later, the impact sound arrives. Subtract 267 ms, and that gives actual time of flight, report-to-impact. And remember what we're subtracting from what: impact minus report minus speed of sound. Now put the recorder at the steel. What sound arrives first? Impact, because it's supersonic, at 100 ms. Report arrives 167 ms later, at 267 ms. So, using the "anywhere in the line of fire" equation, subtracting 267 ms, we get 100 ms - 267 ms - 267 ms = -434 ms time of flight. That doesn't make any sense. The operation on speed of sound depends on where the recorder is. |
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Quoted: Quoted: Quoted: no. you are measuring sound. any place you put the mic in the line of fire you will need to subtract that .267 Quoted: Quoted: Quoted: Quoted: Quoted: Quoted: It would just give you average velocity over the distance. But also, you would have to account for sound travel time. Im thinking that placing the digital recorder in the middle would cancel that, or not? if you subtract the time it would take cound to travel from the gun and then subtract the time it would take sound to travel from the target you will have an accurate count. doesn't really need to be in the middle though. you could just put it by the gun and account for the time it takes the sound to travel from the target to the recorder. So if the target is 300ft away, and the speed of sound is 1125fps, that means its takes .267 seconds for the sound to get from the target to me? Now i would take the time in the recording of how long it takes the bullet to hit the target and subtract .267 seconds, then i would use that time? You subtract .267 to get the total time if you have the recorder at the muzzle, and add .267 if you have it by the steel. Which is why i think that if i were to put it at 150ft, i wouldnt need to even worry about the difference in time. If at one extreme i add .267, and at the other i add -.267. Then in the middle i would add 0, right? I think you're right. Suppose you're shooting supersonic .223 at steel. Assume 3000 fps, giving 100 ms time of flight over 300 ft, and 267 ms sound travel time. Put the recorder at the muzzle. What sound arrives first? Well, the report, of course, at 0 ms. 367 ms later, the impact sound arrives. Subtract 267 ms, and that gives actual time of flight, report-to-impact. And remember what we're subtracting from what: impact minus report minus speed of sound. Now put the recorder at the steel. What sound arrives first? Impact, because it's supersonic, at 100 ms. Report arrives 167 ms later, at 267 ms. So, using the "anywhere in the line of fire" equation, subtracting 267 ms, we get 100 ms - 267 ms - 267 ms = -434 ms time of flight. That doesn't make any sense. The operation on speed of sound depends on where the recorder is. no it doesn't the boom from the rifle has to travel at the speed of sound to the mic. the sound of the impact on the target does the smae no matter what side you put the mic on you have to subtract the time it takes BOTH sounds to reach the mic. unless the mic is placed well outside the line of fire you will have to subtract the .267 |
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Quoted: Quoted: Suppose you're shooting supersonic .223 at steel. Assume 3000 fps, giving 100 ms time of flight over 300 ft, and 267 ms sound travel time. Put the recorder at the muzzle. What sound arrives first? Well, the report, of course, at 0 ms. 367 ms later, the impact sound arrives. Subtract 267 ms, and that gives actual time of flight, report-to-impact. And remember what we're subtracting from what: impact minus report minus speed of sound. Now put the recorder at the steel. What sound arrives first? Impact, because it's supersonic, at 100 ms. Report arrives 167 ms later, at 267 ms. So, using the "anywhere in the line of fire" equation, subtracting 267 ms, we get 100 ms - 267 ms - 267 ms = -434 ms time of flight. That doesn't make any sense. The operation on speed of sound depends on where the recorder is. no it doesn't the boom from the rifle has to travel at the speed of sound to the mic. the sound of the impact on the target does the smae no matter what side you put the mic on you have to subtract the time it takes BOTH sounds to reach the mic. unless the mic is placed well outside the line of fire you will have to subtract the .267 No. Here is the timeline if the recorder is placed a negligible distance from the steel plate. 0 ms - bullet leaves the barrel, report is produced 100 ms - bullet arrives at place, clang is produced and recorded 267 ms - report is recorded Now, we only know about the peaks at t = 100 ms and t = 267 ms. If we're going to generalize this into a simple equation, we need to have a different equation for when the recorder is at the muzzle and when it's at the plate. At the plate, add 267 ms: Time of flight = clang - report + sound = 100 - 267 + 267 = 100 ms Now, at the muzzle, you're right. Subtract 267 ms: Time of flight = clang - report - sound = 367 - 0 - 267 = 100 ms |
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no. if mic is at the muzzle it will take 0 seconds for the sound from the muzzle to reach the mic and .267 for the sound from the plate to reach the mic. therefore subtract .267 from the time between sounds. if the mic is at the plate it will take .267 seconds for the muzzle sound to reach the mic and it will take o seconds for the impact on the plate to reach the mic. therefore you subtract .267 from the time between sounds. put the mic in the middle and you subtract .1335 from both sounds as that will be the time for both the muzzle boom and the plate impact to reach the mic. therfore subtract .267 from the time between both sounds. the only way you would add any thing is if the soundwaves somehow traveled faster than sound which is not possible. |
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Quoted: no. if mic is at the muzzle it will take 0 seconds for the sound from the muzzle to reach the mic and .267 for the sound from the plate to reach the mic. therefore subtract .267 from the time between sounds. if the mic is at the plate it will take .267 seconds for the muzzle sound to reach the mic and it will take o seconds for the impact on the plate to reach the mic. therefore you subtract .267 from the time between sounds. put the mic in the middle and you subtract .1335 from both sounds as that will be the time for both the muzzle boom and the plate impact to reach the mic. therfore subtract .267 from the time between both sounds. the only way you would add any thing is if the soundwaves somehow traveled faster than sound which is not possible. You aren't differentiating between steel and muzzle noises. That's the only difference between our methods, I realized once you clarified. Both arrive at the same answer. Subtracting negatives has a net additive effect.
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no. if mic is at the muzzle it will take 0 seconds for the sound from the muzzle to reach the mic and .267 for the sound from the plate to reach the mic. therefore subtract .267 from the time between sounds. if the mic is at the plate it will take .267 seconds for the muzzle sound to reach the mic (which will occur AFTER the sound of the clang is recorded) and it will take o seconds for the impact on the plate to reach the mic. therefore you subtract .267 from the time between sounds. Sign convention is key in this problem as well as the exact distance from rifle, recorder, target. Also good to get the temp, elevation, pressure and humidity to get a really accurate speed for sound at your location. put the mic in the middle and you subtract .1335 from both sounds as that will be the time for both the muzzle boom and the plate impact to reach the mic. therfore subtract .267 from the time between both sounds. the only way you would add any thing is if the soundwaves somehow traveled faster than sound which is not possible. |