# Poor Man's Chronograph



## Maine Iceman (May 30, 2012)

So I was sitting at home last week, snowed in and left to entertain myself with my bow in my 50' barn. I have been curious lately of approximately just how fast my bows are shooting and so I started thinking about how I could measure the speed of my arrow traveling the 43' foot distance I can shoot in my barn. That's when I realized that instead of measuring the length of time it takes for an arrow to pass by (like a real chrono) I could measure the length of time between sounds (sound of arrow leaving bow and sound of arrow striking target).
This is how I did it:
Materials:
-Laptop
-Microphone (if one is not built in to the laptop
-Audio recording program (I used Audacity and it is free and safe)
-Something to set the laptop on (I used a stool)
-tape measure

Steps:
1. Measure the exact distance from the face of the target and your shooting position
2. In a quiet setting, position the laptop/microphone half way between your shooting position and the target and start recording
3. Fire one shot past your laptop/microphone and at the target.
4. Stop the recording and find the spike where the arrow left the bow and the spike where the arrow struck the target
5. Find the difference in the time from one spike to the next (for one of my bows it was .136 sec.)
6. Divide the distance in feet by the time taken (43'/.136 sec.= 316fps)

I'm not claiming this is super accurate, but this will help give an idea to those of us that don't see the use in spending hundreds of dollars on a chrono.

Have Fun!


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## Brendon_t (Aug 12, 2013)

I'm pretty sure a chrono is cheaper than the laptop * )

I would love to see the actual chrono speed readout to compare.


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## Apohlo (Feb 18, 2013)

I like the idea! I think i will have to try this some day. Seems straight forward, and there really isn't any cost to it!
Thanks for the post


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## Fury90flier (Jun 27, 2012)

there is a time delay that needs to be dealt with (difference in distance between a (Bow)-b (mic) and b-c (target) unless the mic is exactly in the middle of launch and impact


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## owl (May 28, 2004)

Another way to do this might be to use the free android sound meter, and just measure the graph between the twang and thump. Of course you would need to calibrate, and you would need a fairly quiet area.


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## Fury90flier (Jun 27, 2012)

checkout the DIY chrono thread here...ceap, easy to build, free software.

no need to worry about ambient sounds or atmospheric conditions


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## Dartonpro55 (May 16, 2011)

There is an app for iPhones that does the same thing I think it cost like $2


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## pragmatic_lee (Jan 19, 2008)

Dartonpro55 said:


> There is an app for iPhones that does the same thing I think it cost like $2


AChrono - works great!


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## Maine Iceman (May 30, 2012)

Brendon_t said:


> I'm pretty sure a chrono is cheaper than the laptop * )
> 
> I would love to see the actual chrono speed readout to compare.


Yes, however more people tend to have a laptop or have one available than a chrono. That was the point of this.


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## Maine Iceman (May 30, 2012)

Fury90flier said:


> there is a time delay that needs to be dealt with (difference in distance between a (Bow)-b (mic) and b-c (target) unless the mic is exactly in the middle of launch and impact


I stated that the mic needed to be in the middle of the bow and target. Not too diffucult. If one is shooting 40', place the mic at 20'. regardless, there is no time delay.
Also, the point of this is to chrono a bow for free. I get that one can make their own, but that still costs money ($23.46).

Try it before criticizing it.


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## b0w_bender (Apr 30, 2006)

Maine Iceman said:


> Yes, however more people tend to have a laptop or have one available than a chrono. That was the point of this.


I think what he meant was that the $2.00 iphone app mentioned in the previous post was called "AChrono". "AChrono" is the name of the app, I looked it up and yes it's available for the I phone.

Now that we have that out of the way your system is perfectly sound. (so to speak) As long as you put the laptop exactly half way as you described it this should be relatively accurate. I too would like to see the comparison I'm betting it would be real accurate especially at 20 yards. Of course the crono would give you the arrow speed at the bow but the sound based system would give you the average speed over the entire distance so they should be slightly different. Great idea, way to use your knoggin!


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## titan-chaser (Nov 18, 2011)

Op, cool thread.


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## aread (Dec 25, 2009)

This may not be as accurate as the best, most expensive chronographs, but I bet it's as accurate as the consumer level chronographs that many of us have.

How would you compensate for the drop in speed over the 20 yards? Not an issue for comparing bows, but may be of interest for the more OC among us.

OP, Thanks for posting this idea!

Allen


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## Maine Iceman (May 30, 2012)

aread: First, thanks for the response, my good ideas only come around once in a blue moon, haha. Secondly, Yes, you're right, I have no doubt in my mind that a real chrono will measure differently than this style. It is to be expected. However, I felt that this gave us a more realistic idea especially for hunters. We all know that when these bows are measured for their speed on a chrono, the thing to do is stand directly behind and shoot as close as possible, thereby giving us the initial velocity when first leaving the string. unfortunately we all also know that an arrow, like any other projectile, loses it speed the moment it is fired. I think this method might help in determining the actual average speed of an arrow when traveling a distance longer than 10". Not only can this work at 20 yrds, but with the right mic, this could work at 40 and even 50 yrds if folks really wanted to know. One of the bows I own is a Bowtech Insanity CPXL and it is fairly fast, but the only speed I know is its chronoed speed at point blank range and I dont get the chance to hunt many animals at point blank range . This method gives me the opportunity to understand its overall speed at distances for things like 3D shoots and hunting. With that short story made long, of course this method isn't flawless, after all, what really is.


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## Maine Iceman (May 30, 2012)

b0w_bender said:


> I think what he meant was that the $2.00 iphone app mentioned in the previous post was called "AChrono". "AChrono" is the name of the app, I looked it up and yes it's available for the I phone.
> 
> Now that we have that out of the way your system is perfectly sound. (so to speak) As long as you put the laptop exactly half way as you described it this should be relatively accurate. I too would like to see the comparison I'm betting it would be real accurate especially at 20 yards. Of course the crono would give you the arrow speed at the bow but the sound based system would give you the average speed over the entire distance so they should be slightly different. Great idea, way to use your knoggin!


Thank you. And I really ought to check out that app, you folks aren't the only ones I have heard speak of it!!


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## aread (Dec 25, 2009)

Giving it a little more thought, this may actually be a better method than a standard chronograph.

Set up at various distances, you can get a better idea of the effect of any changes to your bow. I'm not going to set up my chronograph to figure out how fast my arrow is going at 60 or 80 yards. Chronographs have been killed trying to measure down range speed. 

Getting the average speed over 20yds, 30yds, 40yds, etc, will provide a sense of how your bow is performing. There is probably a formula for that will allow you to figure out initial arrow speed and arrow speed at each distance. Maybe one of the engineers here will provide this.

Allen


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## Maine Iceman (May 30, 2012)

EXACTLY!!!!! I could not have written that better, myself. :teeth: I will see if I can try to come up with a formula or get some help. I feel we could really be on to something more accurate for longer range shooting and the affect on an arrow at longer shots. Do you know any engineers on here??


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## Irish Sitka (Jul 2, 2009)

Thanks Maine Iceman, 
Have downloaded the programme and will put to the test over the 9yds across my kitchen and into utility room.
I will post result.
Storm blowing here at the moment so will wait for calm day.


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## Maine Iceman (May 30, 2012)

Great!! Cant wait to get them. Let me know as much detail as you can, I have a math professor friend working on a formula for long range estimations (bow, draw weight, draw length, weight of arrow, distance shot, time taken, etc.) Good Luck!!


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## cbmac (May 24, 2006)

Just saw this thread and like the idea. I found an android app designed to do this for pellet guns shooting at 10 to 20 yards. It's a free app called *Chrono Connect*, looks like it should work but I won't have a chance to try it for a few days. May be other options available also.


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## crawdad (Jul 21, 2008)

hey can someone report on using the Achrono app and how the numbers compare to the chrono at your local bow shop?


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## pwssyz (Feb 24, 2014)

that's awesome,can't wait to try that !!


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## notz (Mar 4, 2013)

Post is prolly dead but here is your initial velocity equation.... I found it for you lol


By the way you don't need to have the much dead center..... just factor in the distance from mic to target and mic to bow


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## MJForce (Sep 30, 2013)

Microsofts Excel would be a good program for formulas. Once your factors are determined you could map just about anything. Speed, drag, deceleration, trajectory. Different arrow weights or size, types of vanes etc. could all be factored in.


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## MJForce (Sep 30, 2013)

Here is a site with the formulas.

https://sites.google.com/site/techn...rag-coefficients-of-bullets-arrows-and-spears

This type of chrono would work well in determining velocity changes of an arrow thus giving a drag coefficient of a particular arrow. Once a drag coefficient is determined all other factors could be applied (such as mass, avg velocity, kt energy) to determine arrow trajectory, time/distance to the target etc. 

Different fletching or shaft sizes would yield different drag coefficients. 

Could be useful if your experimenting with different arrow configurations.


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## MJForce (Sep 30, 2013)

And one more thing regarding the AChrono app or laptop program for measuring average velocity. 
Factoring in the time in which the sound of execution and impact takes to arrive at the microphone if the speed of sound is considered would give a more accurate average velocity value. But I think speed of sound may change with altitude and temperature. 
More importantly I think I need to work on my OCD when it comes to this stuff. Lol. Idk, I find it fascinating.


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## notz (Mar 4, 2013)

MJForce said:


> And one more thing regarding the AChrono app or laptop program for measuring average velocity.
> Factoring in the time in which the sound of execution and impact takes to arrive at the microphone if the speed of sound is considered would give a more accurate average velocity value. But I think speed of sound may change with altitude and temperature.
> More importantly I think I need to work on my OCD when it comes to this stuff. Lol. Idk, I find it fascinating.



over such a short distance ther speed of sound really isnt very relative to be honest. sure it would make it more accurate but really is down to the 0.000001th place really needed?


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## b0w_bender (Apr 30, 2006)

MJForce said:


> And one more thing regarding the AChrono app or laptop program for measuring average velocity.
> Factoring in the time in which the sound of execution and impact takes to arrive at the microphone if the speed of sound is considered would give a more accurate average velocity value. But I think speed of sound may change with altitude and temperature.
> More importantly I think I need to work on my OCD when it comes to this stuff. Lol. Idk, I find it fascinating.


As long as the laptop is centered between the target and the archer the speed of sound is not a factor. The delay in time for the sound to hit the microphone from the bow is offset by the delay in time for the arrow strike to hit the microphone. It's OK If there is a one second delay before the sound gets to the mic from the bow because there is a one second delay for the arrow report to hit the microphone 1-1 = 0 i.e. not a factor


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## MJForce (Sep 30, 2013)

notz said:


> over such a short distance ther speed of sound really isnt very relative to be honest. sure it would make it more accurate but really is down to the 0.000001th place really needed?


I agree. 
That was my OCD speaking there. 

However, if an algorithm was used in a program such as excel, so much ballistic information could be determined by using a poor mans chronograph. More so than a typical chronograph.


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## MJForce (Sep 30, 2013)

b0w_bender said:


> As long as the laptop is centered between the target and the archer the speed of sound is not a factor.


It may not be a critical factor. But it is a measurable factor. 

Imagine if the same test was preformed over a 1 mile distance. An accurate measure of speed could only be determined if you factor in the speed of the sounds relative to the source and the microphone.


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## notz (Mar 4, 2013)

you are correct but we are talking yardage


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## huntfish25 (May 29, 2004)

i had the paper some where. you stand 10 yard in front of a target and aim straight. walk back 20 yards shoot three walk back 30 yards shoot three and 40 yards. and measure the drop and that will give you fps. i look for the info if i find i will post it


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## MJForce (Sep 30, 2013)

notz said:


> you are correct but we are talking yardage


Point taken. (no pun)

So basically in order for the poormans chrono to be accurate, the speed of sound could be factored in quite easily into an algorithm formula.


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## Texanjohn (Apr 16, 2007)

b0w_bender said:


> As long as the laptop is centered between the target and the archer the speed of sound is not a factor. The delay in time for the sound to hit the microphone from the bow is offset by the delay in time for the arrow strike to hit the microphone. It's OK If there is a one second delay before the sound gets to the mic from the bow because there is a one second delay for the arrow report to hit the microphone 1-1 = 0 i.e. not a factor


Aren't the delayes to be added? they are both DELAYES ,I just don't understand how they offset each other, I feel the delay time should be added together and then subtracted from the total arrow flight time. Someone correct me if I'm wrong, maybe I'm the one with OCD. LOL


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## MJForce (Sep 30, 2013)

Texanjohn said:


> Aren't the delayes to be added? they are both DELAYES ,I just don't understand how they offset each other, I feel the delay time should be added together and then subtracted from the total arrow flight time. Someone correct me if I'm wrong, maybe I'm the one with OCD. LOL


Yes you have OCD too!

Yeah, the sound delays from both distances are added then subtracted from the time of arrow flight. Which gives the corrected time between the given overall distance. V=D/T right?


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## Texanjohn (Apr 16, 2007)

MJForce said:


> Yes you have OCD too!
> 
> Yeah, the sound delays from both distances are added then subtracted from the time of arrow flight. Which gives the corrected time between the given overall distance. V=D/T right?


Thank GOD, Thought I was losing my mind!!!


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## MJForce (Sep 30, 2013)

huntfish25 said:


> i had the paper some where. you stand 10 yard in front of a target and aim straight. walk back 20 yards shoot three walk back 30 yards shoot three and 40 yards. and measure the drop and that will give you fps. i look for the info if i find i will post it


I used this method long ago. You only needed to know the drop and weight, and distance. I think?


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## huntfish25 (May 29, 2004)

found it
d.	Drop of speed from 20 yards - 40 yards
Speed in fps inches drop
190 19.3
210 15.8
230 13.2 
250 11.1 
270 9.5
290 8.3 
310 7.2	
330 6.4





huntfish25 said:


> i had the paper some where. you stand 10 yard in front of a target and aim straight. walk back 20 yards shoot three walk back 30 yards shoot three and 40 yards. and measure the drop and that will give you fps. i look for the info if i find i will post it


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## klean1 (Jan 14, 2012)

Maine Iceman said:


> I stated that the mic needed to be in the middle of the bow and target. Not too diffucult. If one is shooting 40', place the mic at 20'. regardless, there is no time delay.
> Also, the point of this is to chrono a bow for free. I get that one can make their own, but that still costs money ($23.46).
> 
> Try it before criticizing it.





Dartonpro55 said:


> There is an app for iPhones that does the same thing I think it cost like $2





notz said:


> over such a short distance ther speed of sound really isnt very relative to be honest. sure it would make it more accurate but really is down to the 0.000001th place really needed?


Sound travels at 1125 FT/sec. At 20 yards, this would add on. 0.053 seconds for delay at sealevel anyways


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## zu! (Feb 19, 2014)

huntfish25 said:


> found it
> d.	Drop of speed from 20 yards - 40 yards
> Speed in fps inches drop
> 190 19.3
> ...


This is an interesting way to go about it...almost like the ballistic charts that we use to calculate bullet drop. However in ballistic charts, we take into account things such as the bullet ogive, weight and charge. In archery terms, would these correlate to type and number of fletches, arrow weight and FOC ratio? 

FWIW, I have an old Browning recurve that Achrono says its 211 fps if that's even possible! I have used a decibel meter quite effectively to calculate brace height though, but that's another story altogether ;-)


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## MJForce (Sep 30, 2013)

klean1 said:


> Sound travels at 1125 FT/sec. At 20 yards, this would add on. 0.053 seconds for delay at sealevel anyways


Interesting. I wonder if they factored that into the app. Not that it would affect the fps too much. But exact numbers help when calculating drag coefficients and trajectories in ballistics.


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## klean1 (Jan 14, 2012)

I applied the distance into your numbers and it said your bow was 400fps! Im not sure if they dont cancel out. My brain is fried currently


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## klean1 (Jan 14, 2012)

The chrono connect app looks legit


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## Stab 'em (Dec 26, 2008)

This is a really good idea. Thanks for sharing. 

Placing the microphone at one end or the other of the shooting range and then actually subtracting the speed of sound over that given length of distance from your recorded time would be more accurate a measurement of average speed. This is because the arrow speed is not a constant over the entire length of the range; especially if you are measuring speed over a fifty+ yard range, for example.


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## b0w_bender (Apr 30, 2006)

Texanjohn said:


> Aren't the delayes to be added? they are both DELAYES ,I just don't understand how they offset each other, I feel the delay time should be added together and then subtracted from the total arrow flight time. Someone correct me if I'm wrong, maybe I'm the one with OCD. LOL


Yes of course this is true
now with the device in the center as the original poster stated the delays are equal. OK so in the example I gave earlier for easy math the release time is reported a second late, the impact of the arrow is also a second late both events are recorded the exact same time apart just at a later time interval. Here I'll draw a visual. You can see the 2 events are the same distance apart on the time line (5 Seconds) So as long as the delays are the same i.e. the recorder is halfway between the 2 points 1 mile or 2 feet the speed of sound does not matter!


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## MJForce (Sep 30, 2013)

b0w_bender said:


> View attachment 1918001


That's an excellent illustration. Well done!

.....and how should I cook my crow?


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## Texanjohn (Apr 16, 2007)

MJForce said:


> That's an excellent illustration. Well done!
> 
> .....and how should I cook my crow?



Put salt and pepper on my Crow please MJForce, and to bOw_bender Thanks for the explanation, told ya I had OCD !!!!


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## MJForce (Sep 30, 2013)

Texanjohn said:


> Put salt and pepper on my Crow please MJForce, and to bOw_bender Thanks for the explanation, told ya I had OCD !!!!


Truth be told, I was awake at 3:00am fretting about bOw_bender's illustration. Could not sleep. Or it was because of my dentist appointment at 7:00am. Regardless, both felt agonizing for different reasons. 

But you know...if we hadn't debated so eloquently on the wrong principle, bOw_bender would have never create a strong illustration that definitively shows that a laptop and microphone works well as a chronograph. 

TexanJohn, pass the pepper please. 👊


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## b0w_bender (Apr 30, 2006)

Texanjohn said:


> Put salt and pepper on my Crow please MJForce, and to bOw_bender Thanks for the explanation, told ya I had OCD !!!!


To be perfectly frank I sat and scratched my head over it for a good ten minutes before I managed to convince my self it didn't matter.


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## Maine Iceman (May 30, 2012)

Holy Cow. I never thought that this thread would spread the way it has. I can't help but to extend my gratitude to you incredibly intelligent individuals for your work in proving the usefulness of my theory. I would like to further extend my thanks to bow_bender and MJForce for their eloquent explanations and detailed observation of this style of a chronograph.


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## kerrye (Sep 1, 2010)

I don't think I saw anything about it in going through this thread but you will also have a slight loss due to the speed of sound factor. In the OP's case, you would have 43' worh of 1100fps loss. Not much but would slightly improve the accuracy.


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## MJForce (Sep 30, 2013)

kerrye said:


> I don't think I saw anything about it in going through this thread but you will also have a slight loss due to the speed of sound factor. In the OP's case, you would have 43' worh of 1100fps loss. Not much but would slightly improve the accuracy.


Oh boy! Get your dinner plate handy. Of course my OCD would love to visit this theory again. 

kerrye, could you please elaborate?


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## kerrye (Sep 1, 2010)

OK, Remember, I said slight loss. To keep it close to round figures, let's use 40 feet distance with mic at 20'. It takes 1/55th of a second for the sound of the shot to get to the mic and another 1/55th second for the sound to return to the mic from the arrow hitting the target.


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## MJForce (Sep 30, 2013)

kerrye said:


> OK, Remember, I said slight loss.


I attempted to come up with a formula which would correct this slight loss and give an accurate result. I could not come up with a logical or scientific algorithm which would apply. 

Then Mr. Smarty Pants with his fancy illustration showed us why the speed of sound differences between the release and impact sounds essentially cancelled each other out. Thus causing us nay sayers to fold. 

However you may have a different approach and I'm interested to see it and mathematically test it.


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## Maine Iceman (May 30, 2012)

kerrye said:


> OK, Remember, I said slight loss. To keep it close to round figures, let's use 40 feet distance with mic at 20'. It takes 1/55th of a second for the sound of the shot to get to the mic and another 1/55th second for the sound to return to the mic from the arrow hitting the target.


Exactly. Refer to page two and you will see that b0w_bender drew us an example to show that the speed of sound cancels itself out. With that being said, if you have an alternative theory, like MJForce, I am eager to see it.


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## kerrye (Sep 1, 2010)

Maine Iceman said:


> Exactly. Refer to page two and you will see that b0w_bender drew us an example to show that the speed of sound cancels itself out. With that being said, if you have an alternative theory, like MJForce, I am eager to see it.


Nope. Not a cancel out. It takes 2/55th of a second to cover the forty feet regardless of where the mic is.


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## MJForce (Sep 30, 2013)

At what time intervals would the mic hear the release and impact? Given the mic is centered over 40yds? Could you create a theoretical timeline that could show the missing fps. That missing fps would then become a 'factor' which could then be applied to the results for correcting the allowances for speed of sound?


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## Maine Iceman (May 30, 2012)

b0w_bender said:


> Yes of course this is true
> now with the device in the center as the original poster stated the delays are equal. OK so in the example I gave earlier for easy math the release time is reported a second late, the impact of the arrow is also a second late both events are recorded the exact same time apart just at a later time interval. Here I'll draw a visual. You can see the 2 events are the same distance apart on the time line (5 Seconds) So as long as the delays are the same i.e. the recorder is halfway between the 2 points 1 mile or 2 feet the speed of sound does not matter!
> 
> 
> View attachment 1918001





kerrye said:


> Nope. Not a cancel out. It takes 2/55th of a second to cover the forty feet regardless of where the mic is.


As compelling as your argument is, you have provide no evidence to support your theory or disprove the theory provided.


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## MJForce (Sep 30, 2013)

To add some more brain bending to this; 
What if the microphone was setup at different intervals along the plane of release and impact rather than centered between the two measured sounds? Would the results differ?

If the mic was setup at exact impact, or visa versa, what effect or factor would sound travel have on the timing of the two events (release and impact)?


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## Maine Iceman (May 30, 2012)

Give me a little time to think about that one. Now you got MY OCD all fired up!!........................... My hypothesis is that we could still use b0w_benders timeline, however we would have to find the difference of the greatest length of time sound took to travel and the shortest length of time. As a result, I believe in a case like this, we would have to factor in the speed of sound. With that being said, would the end result still wind up being the same?


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## MJForce (Sep 30, 2013)

Maine Iceman said:


> Give me a little time to think about that one. Now you got MY OCD all fired


Haha, know how you feel.


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## richl35 (May 15, 2013)

Maine Iceman said:


> So I was sitting at home last week, snowed in and left to entertain myself with my bow in my 50' barn. I have been curious lately of approximately just how fast my bows are shooting and so I started thinking about how I could measure the speed of my arrow traveling the 43' foot distance I can shoot in my barn. That's when I realized that instead of measuring the length of time it takes for an arrow to pass by (like a real chrono) I could measure the length of time between sounds (sound of arrow leaving bow and sound of arrow striking target).
> This is how I did it:
> Materials:
> -Laptop
> ...


Haha... for what you used in equipment (laptop, mic, cables etc..) you could of probably bought 10 Cronys.. about $100.


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## DEdestroyer350 (Dec 31, 2013)

What if you just set up a mic at the bow and a mic at the target? That would eliminate all travel time and show a pretty clean time frame from shot to impact with no delays


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## Veni Vidi Vici (Jan 23, 2011)

kerrye said:


> Nope. Not a cancel out. It takes 2/55th of a second to cover the forty feet regardless of where the mic is.


Bowbender is exactly right, and his diagram is a good way to show it. Just to restate things a bit .....

IF the microphone is positioned exactly in the middle of the shooter and the target, then the time it takes for the sound of the release to reach it is the same amount of time that it would take for the sound of the impact to reach it. Because sound does not travel instantaneously, the microphone will not hear the release of the arrow at the exact moment that the arrow is actually released. There WILL be a delay. Once the sound actually reaches the mic, however, the timer will start. Fortunately, the mic will also be delayed in hearing the impact, and by the same amount of time. This means that the timer will get to run for just a little longer. The timer running longer at the end makes up for the fact that it didn't start quite on time at the beginning.



MJForce said:


> To add some more brain bending to this;
> What if the microphone was setup at different intervals along the plane of release and impact rather than centered between the two measured sounds? Would the results differ?
> 
> If the mic was setup at exact impact, or visa versa, what effect or factor would sound travel have on the timing of the two events (release and impact)?


Yes, if the mic is positioned anywhere other than the center between the release and the target, the speed of sound will have to be accounted for. When trying to think about things like this, it is often best to evaluate the limits of the problem. For example, what would happen if the mic is positioned right next to the shooter? The timer would start as soon as the arrow leaves the bow, but it wouldn't stop until the SOUND from the impact travels all the way back. This delay would have to be accounted for (by subtracting the time it took for the sound to travel back). Likewise, if the mic is positioned at the target, the timer could not start until the sound of the release reaches it, but it will stop as soon as the impact occurs. In this case, you would have to ADD the sound travel time in order to correctly determine the arrow's true flight time.


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## MJForce (Sep 30, 2013)

Veni Vidi Vici said:


> IF the microphone is positioned exactly in the middle of the shooter and the target, then the time it takes for the sound of the release to reach it is the same amount of time that it would take for the sound of the impact to reach it.
> 
> ...if the mic is positioned anywhere other than the center between the release and the target, the speed of sound will have to be accounted for.


Elvis has left the building!!!!!

And there it is! It must be exactly centered to be accurate. Making this microphone-chrono very accurate for determining the average speed of an arrow over a given distance. 

If fact, taking speed measurements over different distances would help determine the drag coefficient of that arrow. 

And since typical chrono only shows arrow speed at a given point and are impractical at showing speed at 40yds, a mic-chrono shows speeds over any distance. If the drag coefficient is applied, you would know the exact speed at release and/or impact. If arrow drag is important to you?

I'll sleep well tonight.


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## MJForce (Sep 30, 2013)

DEdestroyer350 said:


> What if you just set up a mic at the bow and a mic at the target? That would eliminate all travel time and show a pretty clean time frame from shot to impact with no delays


As long as the microphone wires were the exact length. If they weren't, then the speed of an electron would have to be factored in. Or if you were using a laser, the speed of light could be a factor if the two laser device were not exactly centered. And so on....


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## MJForce (Sep 30, 2013)

Even two Warp-speed measuring devices would have to be exactly centered...


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## Veni Vidi Vici (Jan 23, 2011)

DEdestroyer350 said:


> What if you just set up a mic at the bow and a mic at the target? That would eliminate all travel time and show a pretty clean time frame from shot to impact with no delays


I actually tried this before I switched gears and came up with the DIY Coil Chrono. The problem I had was that the sound of the shot is not as instantaneous as you might think. I could not find a consistent point in the shot signal that identified exactly when the arrow had left the string, and that was enough to induce several fps worth of inconsistency. I was trying to make something that worked over a short distance, though. The further apart you place the release point and the target the less significant finding the exact release point becomes.


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## MJForce (Sep 30, 2013)

There are many sounds made at the release interval. Slice up the release sound wave and you would have the sounds of; mechanical release, limbs, string vibration, cam stop, arrow rest, nock release, vanes...

The arrow travels up to 30" during this period.


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## MJForce (Sep 30, 2013)

Identifying the nock release would be difficult but not impossible.


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## b0w_bender (Apr 30, 2006)

MJForce said:


> As long as the microphone wires were the exact length. If they weren't, then the speed of an electron would have to be factored in. Or if you were using a laser, the speed of light could be a factor if the two laser device were not exactly centered. And so on....


OK now we are starting to split frog hairs but yes a cables of the same length would solve the problem.
:icon_1_lol:


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## MJForce (Sep 30, 2013)

b0w_bender said:


> OK now we are starting to split frog hairs but yes a cables of the same length would solve the problem.
> :icon_1_lol:


Is that the African or European Frog? Lol

Ahhhhhhhhhhhhhhhhhhh!


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## Maine Iceman (May 30, 2012)

richl35 said:


> Haha... for what you used in equipment (laptop, mic, cables etc..) you could of probably bought 10 Cronys.. about $100.


Wow, like I haven't received this exact same response about a million times so far. The POINT is, that more people have a laptop in their home than a chronograph. Especially considering a chronograph can do one thing. and a laptop can do innumerable things. Why buy a chronograph that you use, what, a few times a year, than use a laptop you have kicking around the house.


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## Maine Iceman (May 30, 2012)

MJForce said:


> Elvis has left the building!!!!!
> 
> And there it is! It must be exactly centered to be accurate. Making this microphone-chrono very accurate for determining the average speed of an arrow over a given distance.
> 
> ...


YES!!!!!! Thank you! Mic-Chrono: 1 Chrono:0 

MUWAHAHAHAHA


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## temujen (Dec 2, 2014)

So after reading this thread, I stopped by Radio Shack on the way home to pick up a mic ($13 bucks!), and downloaded Audacity on my laptop when I got home.

I can confirm that it does produce consistent results, within a few FPS, and this is with a distance of only 26 feet total, from the bow string to the target. I ran a bunch of tests with my own bow, as well as my friends bows.

I am having some trouble with one thing, however, and hopefully somebody here with some knowledge of audio interpretation can help -


I'm trying to understand how to read/interpret the audio waveform on Audacity. I've zoomed in on the part of the graph that covers everything, from trigger release to the arrow impacting the bag target. 

I'm trying to better understand where in the wave to count as the initial point of impact on the target, as it's not nearly as clear-cut as where we can interpret the arrow starting to move-










As you can see in chart above, the trigger release is pretty clear-cut, however the point of impact is harder to determine. You can see that for the impact portion, the increase in the size/height of the wave is significant, and the ramp up can certainly affect the calculation - in this case, the range can be from anywhere from ~277fps to ~288fps. I'm assuming the smaller, in-between waves (if you can even call them that) are the sound that's generated by the fletchings as they fly over the mic.


For reference, the bow in this shot was a 2015 Hoyt Charger, set at 28 in. DL, and 60# DW. 400 grain arrow with straight fletching.


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## CarbonTerry (Jan 8, 2003)

a Blue Moon in Feb and a Blue Moon in March......This only happens once in a Blue Moon ;>)


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