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Old 05-05-2012, 10:11 PM   #1
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Default Info for people new to NFA and Suppressors.


We made this for the questions that people have when they get the addiction.


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Last edited by sub; 05-14-2012 at 06:43 PM.
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Old 05-06-2012, 08:09 PM   #2
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Good post for the new folks.
This chart may also may prove useful.
I have noticed that even Std. Vel. and Subsonic may be transonic below 50F depending on brand.

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Old 05-07-2012, 07:45 AM   #3
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I tacked this thread. I think it will prove to be something that might be required reading for new people...

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Old 05-09-2012, 12:43 PM   #4
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Nice Vid Dave! Is there any data on how altitude affects the speed of sound? I would think higher altitude(and the resulting lower atmospheric pressure) would equate to a higher speed of sound since the air is less dense up here. BUT that's just speculation on my part.
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Old 05-09-2012, 01:42 PM   #5
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"Implications for atmospheric acoustics"

"In the Earth's atmosphere, the most important factor affecting the speed of sound is the temperature (see Details below). Since temperature and thus the speed of sound normally decrease with increasing altitude, sound is refracted upward, away from listeners on the ground, creating an acoustic shadow at some distance from the source.[2] The decrease of the sound speed with height is referred to as a negative sound speed gradient. However, in the stratosphere, the speed of sound increases with height due to heating within the ozone layer, producing a positive sound speed gradient."

Copied from Wikipedia directly, I did not write this.

Link to page:

Speed of Sound

I really thought it had more of an effect that it does though.

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Old 05-10-2012, 03:34 PM   #6
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Quote:
Originally Posted by DoctorSolo View Post
Nice Vid Dave! Is there any data on how altitude affects the speed of sound? I would think higher altitude(and the resulting lower atmospheric pressure) would equate to a higher speed of sound since the air is less dense up here. BUT that's just speculation on my part.
The speed of sound gets lower as the pressure decreases. It has to do with the mean free distance of the fluid. Lower pressure means longer distances between collisions of particles, thus slower transmissions of pressure waves. But like Dave/Wikipedia said, temperature is the key factor in the speed of sound.

The equation a=sqrt(gamma*R*T)
where:
a=speed of sound
gamma= 1.4 (for all diatomic gasses, and since air is almost all N2 and O2...)
R=specific gas constant of air=1716 ft-lbf/(slug-Rankine)
T=absolute temperature=Temp F + 459 (converts from Fahrenheit to Rankine)

If you like Metric, then:
R=287 J/(kg-K)
T=Temperature in Kelvin (Temp C + 273)

The chart above basically takes gamma and R out of the square root, but is still the same basic equation.

Elevation will change R ever so slightly, as will humidity (along with changing gamma). However, we can't breath at the conditions that will change either property enough to make a noticeable difference. Therefore- gamma and R are constants and only variables we (as gun guys) need to worry about is temperature.


*No I didn't stay at a Holiday Inn Express last night, but Gas Dynamics was one of the coolest classes I've taken. Hope this helps.
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Old 05-10-2012, 06:52 PM   #7
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Awesome. What kind of engineering are you majoring in, Mechanical?
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Old 05-11-2012, 12:07 AM   #8
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affirmative.
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