Seeing Sound Waves - 1130 ft/second @ Obama Inauguration

"I noticed something interesting during Garth Brooks' performance at the pre-inauguration concert on Sunday: I could actually see the sound waves. No, I wasn't hallucinating. To see the sound for yourself, check out this little video I made:"

from Control Geek. John Huntington's Entertainment Technology Site


1) there will be speekers at multiple points down the line , with the aditoinal tv screens as well

2) it is far more likely that it is actually the reaction time of people who see people in front doing an activity and then feal forced to participate.


^Are you a sound engineer? If so, maybe you should read John Huntington's blog and learn a few things. Here's what he had to say:

"And so, when we have a sound system where we want people to hear some distance away from the stage, sound system engineers have to take this into account. Speakers at a distance from the stage (like at the concert pictured in the video) must be intentionally delayed to get them to line up in time with the sound emanating from the stage. This happens because the electrons in the cables transfer the audio signal out to the delay speaker positions effectively, for our purposes, "instantly", while the sound waves, vibrating air molecules, can take many seconds to travel. And if the "delay" speakers, remote from the stage, are not aligned in time (even milliseconds matter), the audience will hear either destructive interference called "comb filtering", or perceive an echo. (Interestingly, from what I saw on screen, it appears that the large video displays on the mall were actually delayed to match the slowness of the sound.)"

adn here are some of the comments on the thread. (some of these are really cool)

-"Very cool way to show this "lag".

To geek you out further. Since heat rises, many sports arenas can have a 10degree or greater temperature difference from floor to ceiling during a show. Sound traveling through the top of the room to the balcony's gets to the last row before the sound on the floor.

This is not a constant. During sound check the room is much more balanced. But put 5,000 excited dancing people in the room. Now try and calculate your delays."


-"I know the effect well. When I mixed sound for outdoor rock festivals and they'd often times have the mixing booth a 200 - 300' from the stage.
I'd always have to slip the headphones on and mix that way when timing was critical. It was the only way you could time changes properly.

Most sound engineers didn't know this trick and they would always screw up the timing and couldn't figure out why.
The same engineers used to criticize my use of the headphones as they said you have to mix for the audience not for the headphones.
Well you can't mix for the audience if you have a 1/4 second time delay."


There's no way to absolutely know if the engineers delayed the speakers the further they were from the stage, so it's impossible to comment on this part. Judging by the audience, it does look like they didn't do their job properly.

But to think that this concept is only known to well-seasoned sound engineers is ridiculous. There are these computer thingies that have these application thingies that take the distance of speakers, and come out with the proper delay equation down to milliseconds. A lot of this is automated these days as well, so hardly an old-skool task for anyone anymore.

My gf does this all the time, and her theater only seats around 800 people, oh and she didn't go to engineering school.

[defunct] 2pornot2psays...

My first instinct was to say the crowd was intentionally doing the wave, like they do during baseball games, but then I realized how fast was actually happening, almost too fast for cooperation between people. This is cool shit.


Why does this say 1130 ft/s like that is (a) the speed of sound and (b) we didn't know the atmoshperic conditions on that day?

It was cold and probably less than 100ft above sea level. You could probably get the barometric stuff. It should have been 5% faster based on how cold it was.


While we're being super technical, I might add that this is not an example of "actually see[ing] the sound waves." Rather, this is merely the secondary effects of the sound wave.

Interesting nevertheless.


Like anything else, anybody CAN know it. "Sound Engineers" are the most predictable group to know it professionally. No one's claiming to make absolute statements here. It's a cool video demonstrating a cool concept. I didn't know about delaying remote speakers, and I'm glad to have the chance to see it in practical application.


ok i agree if thay just had speakers realying the stage then yah maby thay delay it so synk it up , but as there were multiple screens on the way down as you would not see anything i bet thay synked the sound with each tv screen not the stage,

i still think crowd reacting to crowd in front,

and ether way i believe my assumption to be far less of an assumption that what the guy in the video is saying.

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