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I have seen a lot of commercial electronic shooting targets. Most of them seem to use microphones to "triangulate" the position of the projectile. If I wanted to do a diy version of this what kind of math would I need to determine the location of a projectile shot at a metal target?

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Attempting to guess as the function of commercial products is not productive as there could be 100s of answers that are "rigth" but only one is true. – Kortuk♦ Jul 4 '12 at 20:54

closed as off topic by Kortuk♦ Jul 4 '12 at 20:54

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I haven't had an opportunity to look at any of them from a technical stand point. But my understanding of the ones used @ Blair Atholl (Scotland) when we visited last year for an invitational (going back as far as 1233yds) was that their target system used some sort of rubber membrane behind the target face, and a series of sensors attached to the membrane around the perimeter sensed the location of the shot to within a fairly accurate position (less than 1mm error).

I believe both this system and the ones utilizing microphones use some sort of triangulation to determine the location of the bullet as it passes through what ever sensor network is used.

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That is the same explanation that I have gotten when I have been using them. Rubber and several microphones listening towards the rubber membrane and listening for the sound of the round passing through it. – Jontas Jun 4 '12 at 19:25
My understanding was the microphones were for targets that have no physical medium for the projectile to pass thru (other than a paper aiming point in front); the rubber membrane I thought was physically attached to some sort of transducer, not necessarily a microphone. The sound-type targets are more for disciplines where the bullets are likely to go very closely thru the same hole (say, indoor smallbore). The rubber membrane targets seem to be more for disciplines where the intervening range/atmo conditions (like 1000yd Prone) make that somewhat unlikely... ;) – memilanuk Jun 4 '12 at 20:35
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(As for how they work, see memilanuk's answer)

For the math you need some sort of triangulation too see where several distances intersect.

Use several microphones, time the difference between when they heard the round hitting your target - by using the speed of sound you will get the distance between the microphone and the hit.

By having several distances you need to figure out where they intersect on the target; all mics will have heard the sound at different times (as the are placed on a line by the base of the target - in order to eliminate the possibility of them all reacting at the same time).

We are talking about the speed of sound and distances of about a meter (a few feet for you imperialists;) so use the same length of wire for all the microphones to rule that out as a variable and keep in mind that the accuracy of the sampling is crucially important for this sort of thing.

Another reason these sort of targets are so expensive is that they are made to be placed on a range, side by side (maybe as close as a feet in distance from each other) so they need to disregard if the target next to it was hit at the same time.

Also keep in mind that if you use metal (or any sort of "non healing" target) you might end up with a hole larger than the bullet - and if the bullet would pass it then no sound and thus nothing to hear.

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