Velocty testing using PC and mic

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hotsky
Posts: 319
Joined: Wed Sep 07, 2005 7:28 pm
Location: ON, Canada

Velocty testing using PC and mic

#1 Post by hotsky »

I posted this a while ago on a the Airgunscanada forum, thought some ‘new’ people might find it usefull :wink:

Might be a good idea for a sticky :)

You need 3 things

1. PC (or a Mac)

2. A Microphone (not to be build in) - I got mine from a dollar store

3. A sound rec/reading software

I use Audacity program (free from http://audacity.sourceforge.net/)

You need to set up a backstop (pellet trap) something that is not too soft, ‘cause you need the pellet to make some noise when it his it.

Measure a distance between the gun and a backstop, make sure you measured it accurately or your results will be off ( I used 10ft). Place a Mic half way between the gun and the backstop (this is important too).

When everything is set up, Open the software (Audacity has a REC button so you can do everything with in that program) set up your Input Volume (on the top right corner beside a mic icon) somewhere from 0.1 -0.5 (worked best for me). Start recording, fire the gun and press the stop button.

You will see a wave of sound, delete the parts where the wave is flat (no noise) - you don’t have to do it but it’s easier that way. Zoom in on the part where the gun shot happens. You will see two major waves; first from the gun shot, second from the pellet hitting the trap/backstop.

Write down the time (shown at the bottom of the screen) at the beginning of the first wave rise and of the second one (you might need to play with the zoom tool to get the best view). Subtract the lower number from the higher one

--Or simply hightlite the difference, it will tell you the number at the bottom of the screen :)--

.Now divide your distance (in my case 10ft) by the number you just got. This number is your velocity is fts. (If you want it to be in m/s bust multiply it by 0.3048)

Is might sound really complicated, but trust me it’s not. You might mess up a couple of shots to figure it out, but it’s pretty easy stuff.


if you try it post your results here
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airgunfun
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#2 Post by airgunfun »

I'll leave it as a sticky for awhile so that it gets some attention that it deserves.
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Equuleus
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#3 Post by Equuleus »

I wonder if this is close to the accuracy of a Chrony...
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webstien
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#4 Post by webstien »

Equuleus wrote:I wonder if this is close to the accuracy of a Chrony...
Its a ghetto chrony ;) me likes!
shoot
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#5 Post by shoot »

i got:
666
481
550
5 times 500

The gun is still new so its still dieseling/settling in.

I found that 10 feet is not enough since the 2 bangs are really really close toqether so i used 20 feet instead (around 0.3 seconds to 0.4 to make the distance).

I placed my mp3 player on record at mid-distance and then imported files in audacity.
hotsky
Posts: 319
Joined: Wed Sep 07, 2005 7:28 pm
Location: ON, Canada

#6 Post by hotsky »

10 feet should works great for 300-500fps guns, anything above might need a larger distance.
I placed my mp3 player on record at mid-distance and then imported files in audacity.
maybe that was the problem...why not just use the Audisity from the start?


Equuleus, the method is very accurate right down every foot once you get the hang of it. :wink:
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I_HATE_PAL

#7 Post by I_HATE_PAL »

A very useful sticky. Thanks for putting it on!
shoot
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Location: Montreal

#8 Post by shoot »

hotsky wrote:10 feet should works great for 300-500fps guns, anything above might need a larger distance.
I placed my mp3 player on record at mid-distance and then imported files in audacity.
maybe that was the problem...why not just use the Audisity from the start?


Equuleus, the method is very accurate right down every foot once you get the hang of it. :wink:
The file was recorded in mono with 16 bits and 8khz sampling rate. The problem with 10 feet is that there is not enough time to reach 0 level between the 2 bangs and with the echo from the gun it is difficult to see where the new bang starts and the echo finishes.

Personnaly I have achieved better result with 20 feet since you have more time space to properly discern the beginning of the impact.
hotsky
Posts: 319
Joined: Wed Sep 07, 2005 7:28 pm
Location: ON, Canada

#9 Post by hotsky »

when using Audicity you have to lower the input volume all the way till 0.2-0.0 (also depends on a mic) if it's all the way up to 1.0 it will be impossible to tell what's going on.
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