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Signal Delay- Math anyone?

C

c2thej2theizzo

Mar 14, 2011
219
2
Milwaukee, WI
www.milwaukeejam.com
#1
Just Wondering, using traditional signal processing. How many ms does it it take for your signal to go through the stage mixer then to the snake 100ft to the FOH mixer, to the board and 100 ft back to FOH amps.

How bout for the actual sound to reach the FOH engineer - asumming lets say 50ft cable runs to speakers?

looking for a general estimate of course.
any calculators anyone know of ?
 
#2
The signal travels through the wires at the speed of light, more or less. So there is no measurable delay in terms of the cable lengths. What slows down sound is air resistance, so it's the distance between the speakers and the ears that needs to be accounted for. I don't know the math for that, and it's a good question. Surely there must be a reference text for this, and I'd be interested in reading it.
 
#6
c2thej2theizzo said:
yes obviously air is the main issue, but just in case I plan on breaking the guiness book of world records by organizing a concert for 20 million people and was running sound a mile away from the stage, I just want to account for every factor. :)
Click to expand...

The speed of sound, at sea level, at 68 degrees F, is 768mph, or 1126fps. Since there are 5280 feet in a mile and you are one mile away, the sound waves will take 4.689165 seconds for the sound to travel from the stage to you. :p

Good luck with the show!
 
#8
I think the OP's initial question is solely concerning the delay caused by electromagnetic propagation, disregarding speed of sound delays.

As mentioned above, an electric current propagates at the speed of light, or as near enough as to make no difference.
Electric current itself actually travels much slower, but that is a different matter.

Consequently, using 983,571,056 as the speed of light in feet per second, we can figure this out.

So, signal to 100ft snake to FOH to snake to amp to mains.
The way the signal path is phrased is very confusing ("to the FOH mixer, to the board". What is the difference between FOH mixer and "board"?) but I shall assume a 250 foot total signal path.

I believe this works out to approx. 0.000254175841 ms (rounded), for a signal to travel 250 ft. Note that this is disregarding processing, latency, etc.

Hope this helps. (Would someone like to check my math?)
 
#9
In addition, I should like to mention that concerning the speed of sound, the elevation does not affect the speed of sound.
Specifying "at sea level" means nothing.

Humidity and temperature do however affect the speed of sound.
A useful figure is the speed of sound in air at 20ºC: 1126.038 feet per second. (Humidity can be disregarded because the affect is slight.)

F-Clef-Jef's figure of 4.689165 seconds is very close to my figure of 4.6890069429273257208016070505613487289061292780527832
:hiding:
 
#13
projectMalamute said:
This is totally wrong.
Click to expand...

I do apologize if this is in fact incorrect, however, this is what I gleaned from numerous references found on the web.

Because air is not an ideal gas, I suppose altitude does factor in, but perhaps not very much?

See here: Speed of sound - Wikipedia, the free encyclopedia
Also, see here: Invalid Link Removed
And here: Acoustics/Sound Speed - Wikibooks, open books for an open world

If I am in some way misinterpreting these sources, I apologize and would appreciate correction of my error. However, these sources do state that the speed of sound is unaffected by altitude.
 
#14
At higher altitudes the temperature tends to be lower, and the temperature does affect sound speed. So while technically there is nothing inherent to the distance from the surface of the earth, within the first layer of the atmosphere anyway, that alters waves--the practical reality is that the air is thinner as you go up, which means fewer collisions between molecules, which means less heat, which means slower speed of sound.
 
#15
Hactar said:
I do apologize if this is in fact incorrect, however, this is what I gleaned from numerous references found on the web.

Because air is not an ideal gas, I suppose altitude does factor in, but perhaps not very much?

See here: Speed of sound - Wikipedia, the free encyclopedia
Click to expand...

Here's a direct quote from that link:

"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."
 
#18
Hactar said:
Hrmmmm. I am now rather confused.

So altitude does not directly affect speed of sound, but indirectly due to a lower air temperature?

:confused:
Click to expand...

Sort of. The dominant factor that influences the speed of sound in any medium is the density of the medium; the lower the density, the lower the speed.

Lower temperature increases the density of air, which increases the speed of sound. Higher altitude decreases air density due to lower pressure, which decreases the speed of sound. Higher humidity increases air density, which increases the speed of sound. At very high altitudes, the density of the air is essentially zero and so is the speed of sound, i.e., sound does not propagate in a vacuum.
 
#19
bongomania said:
The signal travels through the wires at the speed of light, more or less. So there is no measurable delay in terms of the cable lengths. What slows down sound is air resistance, so it's the distance between the speakers and the ears that needs to be accounted for. I don't know the math for that, and it's a good question. Surely there must be a reference text for this, and I'd be interested in reading it.
Click to expand...

What's interesting is that the electrons in the cable don't travel at the speed of light, but the signal does. It's like turning on a faucet with a hose attached. The pressure at the far end increases almost instantaneously, but the water travels through the hose at a few feet per second.
 

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