Acoustic chronograph?

[dfrois]

Hello all,

Has anyone here tried to use a laptop as an acoustic chronograph? I want a chronograph to better evaluate my bows and limbs, but I can`t afford one. I read smoething about using a PC sound card with a microphone to record the sound of firing a firearm and then the sound of impact on target, and figuring the mean speed by accurately measuring the time between sounds (to the milisecond) and knowing the precise distance between weapon and target. I figured out the maths and created an Excel file to do the calculations, where you only have to input the distance (feet or meters), and the time, in miliseconds, between release sound and impact sound.

Then I wondered...perhaps someone here has already played with this, and found more than I can imagine.

I will try it tonight when I get home, but, if someone has any thoughts on this, or has played with similar ideas, I would like to know what you know or think about it.

My idea is that this could, maybe, be useful, not only to assess speed, but also to find about limb sync, arrow impact, etc., on a real shooting condition. I have only made two glass bows and a pair of limbs, but I`m ready to start my third bow, and, if this works, could be useful to progress.

DF

Any input is welcome.

[psychmonky]

It would work to determine average speed, BUT when a bow manufacturer (or gun manufacturer for that matter) lists a speed, that speed is measured right at the weapon or just a bit in front. The arrow slows down quite a bit between bow and target.

The reason I mention this is that different weight projectiles will slow at different rates. This will cause an arrow that's light and fast that loses speed quickly to have an average speed that may be fairly close to a heavier slower arrow that maintains its full velocity longer.

That's theory, and may not matter at 20 yards anyway, so I'd actually encourage you to try it and see if it works  

[dfrois]

Now there`s another idea...average speed. If the time resolution is enough, it can be measured at, say, 10 yards (multiple shots for averaging), then at 30 or 40 yards...and it would tell how much speed is lost along the distance of the shot...assuming linear deceleration. This could work well to compare arrows, or fletching, etc...

Now I`m even more worked up to try it!

I`ll keep you posted. And, even if it only results in you lot laughing at me, then it`s all good...I have learned so much lurking in TG that entertaining you is the least I can do!

Who knows? Maybe something useful will come out of this...

DF

[k-hat]

You could probly find some rough figures of the deceleration and figure that in to find the approx speed at release.  If you're just comparing your own bows though, avg speed would be fine, long as you use the same arrow on all your tests.

[k-hat]

the mic would have to be equidistant from the bow and the target, otherwise the delay will throw it all off.

[Gundog68]

Achrono  works very well. Just about 5 fps overrated compared with a real chrono. My measure distance is 16 yards.

[dfrois]

Didn`t know about Achrono, but then again, I don`t have a smart phone. k-hat, your reasoning is a little way off. An equidistant mic would suffer delay from the release sound and the impact sound. The way I planned it is to place the mic at one end (bow or target), and then subtract from the total time between sounds the time it takes for sound to travel from one end of the distance to the other, thus cancelling the delay.
Last night I tried to put an old laptop to work, but I couldn`t find a sound recording program that worked there. I`ll try to fix this during the day, so that I can finally try this tonight. I`ll keep you posted.

DF

[eflanders]

dfrois,

I find your experiment to very interesting.  You may have found a way to prove or learn what the effective killing/shooting distance is for hunting humanely with a certain poundage bow as well.  

I realize that I am probably going to get flamed for this but I personally have always believed that just because you might be an accurate shot even with a 40 lb. bow (let's say 50 yards), the bow has lost so much energy and the ability to penetrate at this distance that the shot is far less effective at killing humanely.  Note: I have heard stories of people that say they have successfully killed elk with a 35-40 pound bow and a 50 yard (or more)shot, by I personally find it hard to believe this would be a humane kill with a fairly short tracking job.

[eflanders]

Originally posted by eflanders:
dfrois,

I find your experiment to very interesting.  You may have found a way to prove or learn what the effective killing/shooting distance is for hunting humanely with a certain poundage bow as well.  

I realize that I am probably going to get flamed for this but I personally have always believed that just because you might be an accurate shot even with a 40 lb. bow (let's say 50 yards), the bow has lost so much energy and the ability to penetrate at this distance that the shot is far less effective at killing humanely.  Note: I have heard stories of people that say they have successfully killed elk with a 35-40 pound bow and a 50 yard (or more) shot, but I personally find it very hard to believe that this would be a humane kill with a fairly short tracking job.

[dfrois]

Well, I got the laptop working, so I can try things tonight. I do hope this works, to some extent, and that the numbers will give some insight on how my gear (mostly made or assembled by me) performs. I can only try distances up to about 18 meters at home, but that, combined with my 3 bows and several different types of arrows, should begin to show something. Especeially since 2 of the bows are only 30# (one longbow, one recurve). Before testing, though, I have to say that I expect much of the speed loss to depend strongly on the arrow: weigth, diameter and feathering should show noticeable variance. I`m lucky there too: I have a bit of everything, from 300gr carbons to hunting aluminiums a little over 500gr...and some wood arrows to mix. What I don`t have (haven´t got there yet) are really heavy hunting arrows, 600grs or more.

I have the day off tomorrow. Next sunday, I will go to the local shooting field, where I can try larger distances (that`s why it had to be a laptop).

Now I will tell you my own little secret agenda: I want to prove that the recurve I built is at least as fast as my wife`s fancy target recurve, even being only 29# against 32#. I might be wrong...stay tuned!

DF

[Swissbow]

If you're still looking for an audio recording tool, then I would recommend Audacity. It's free and it offers great functionality. You can download it here...

 http://download.cnet.com/Audacity/3000-2170_4-10058117.html

If your computer has a built in microphone then you're ready to go. The program is easy to use and you can also use it to measure the time from the release to the impact of the arrow. Put the computer right between the point from where you shoot the bow and the target and you don't even have to calculate the effective time, because the two delays equal themselves out of the equation. The calculated value is only a mean value but it gives you an idea how your bows perform and it works well to compare different bows.

----------
Andy

[k-hat]

Originally posted by dfrois:
Didn`t know about Achrono, but then again, I don`t have a smart phone. k-hat, your reasoning is a little way off. An equidistant mic would suffer delay from the release sound and the impact sound. The way I planned it is to place the mic at one end (bow or target), and then subtract from the total time between sounds the time it takes for sound to travel from one end of the distance to the other, thus cancelling the delay.
DF

Good point, i knew it mattered and was thinkin in a hurry, that's what i get  

[dfrois]

Well, the first results are in...but there`s a long way to go.

swissbow, you´re right, about audacity and about the mic placement. k-hat was closer than I thought. Actually, Audacity was the software that I had set up on my home PC, and the one that didn`t work initially on the old laptop. It really is great for this, and it will even allow playback at reduced speed...but we`ll get to that in a moment. First, my initial results:

Bow: Glass laminated longbow, 61" ntn, 31#@28"
String: Dynaflight 10, 6-strand
Arrows: Easton Jazz 1816, 29", 393gr.
Four shots:
147.9
147.6
150.9 fps ????

Bow: Glass laminated takedown recurve, 62" ntn, 29#@28"
String: Dynaflight 10, 6-strand
Arrows: Same as above
3 shots:
156.2
159.7
167.3 fps (different measurement method)

Bow:Glass laminated takedown recurve, 62" ntn, 48#@28"
Arrows: Easton XX75 2016, 27", 446gr, feathers.
String: BCY B55 14-strand
3 shots:
174.3 fps (original measurement method)
204.5 fps (different measurement method)
201.3 fps (different measurement method)

Now, the initial values seemed, to me, quite a bit too high, so I thought I had to check and refine the method. The maths are solid, so it must be the other big problem: how to determine, from the sound file, where to measure beginning and end. I even included arrow length, since release is at the nock end and impact is at point end. but it is still too high.

[dfrois]

Now, the sound, as recorded in Audacity, does not have a clear point for release, nor impact. Initially I measured from the first BIG sound on release to the first BIG sound on impact - that`s the first measurement method. Playing it back at 0.01 speed, it was clear that there were, at release, not one, but two big sounds at release, and only one at impact. My guess is that the release is heard by the mic, first when the fingers let go of the string (first big sound), then when the arrow nock releases itself from the serving (second big sound). If so, then measurement should begin when the arrows lets go, since that`s when energy transmission ends. So I did the "different measurement method" like that...but it was still faster, since time was shorter.

I still have a lot to work out on this, but at least I have somet time today.

DF

[dfrois]

Forgot to say, all these were at a very short distance: 6.8 meters, or 22.3 ft. Later on I will do more at longer distances.

Df

[Onehair]

Can you also use this to determine a measurable  level of bow noise. Maybe assist in silencer placement and such.

[dfrois]

OneHair, I think so, but it would have to be done in a very carefully controlled fashion, so that it would allow valid comparisons. Audacity allows easy measurement of wave amplitude, but the capture would have to be very strictly performed. Also, the direction from which the sound is captured would matter a lot, which is not the case for measuring speed. Something to try later, I guess...

I have been sidetracked...by myself! I got distracted listening to the sound captures at 1/100th the normal speed...spent hours there! It is fascinating! I tried a few shots at 18 meters, but the mic could not capture the sounds clearly. If it doesn`t rain tomorrow, I will try again with the mic closer to the bow. The impact is always louder than the release. Did a few more shots indoors, but the results were the same as before...I still think they`re too high.

DF

DF

[Onehair]

Something to play with I guess. Thanks for the info.