Lightening?

Posted: Fri Jun 13, 2008 7:50 am

Hello all,

Forgive me if this seems like a dumb question, but has anyone ever done any research into the acoustic properties of thunder? I am not talking the general nature recordings, I am talking truly analyzing the different sounds of thunder.

I noticed last night during a local rainstorm that we had more lightening (and thunder) than usual and it seemed that bout 3-7 seconds there was a lightening strike (with resulting thunder sound). I noticed that when further away form the lightening I felt more of the lower rumble, but when closer to the lightening (say 50-100ft) I got the loud crack but not so much of the lower rumble.

I know most are thinking "we all know this" but from a research standpoint I am wondering if anyone has studied this aspect of lightening/thunder and attempt to re-create the actual sound of thunder?

Thanks for any input.
Nick~

Posted: Fri Jun 13, 2008 8:02 am

Tried to record thunder once. Levels either to low or to high. The proximity of the source keeps moving.
The farther away the more low-end(actually less highs) but also the echos between clouds/ground and buildings and such increase the duartion of the sound.
Stereo SDC's in carport to avoid rain but the floor/ceiling created weird echos and phase cancellations... [/img]

Posted: Fri Jun 13, 2008 8:13 am

Hmm, interesting.

Now I know this would be unsafe (and I am sure it will bring images of Franklin and his kite) but what about placing a mic-array on top of a building during a thunderstorm?

I know it is risky and could loose the equipment, but just a thought.

Posted: Fri Jun 13, 2008 11:10 am

I've had to record thunder before. It was for a planetarium production soundtrack, during the summer here in Florida, the world's capital for lightning strikes. I used an E-V RE20 to do it, feeding a Grace 101 into an ADAT HD. The rig was on my back porch, so power was not an issue. I've also used a Sennheiser 421 into a Yamaha portable recorder. The important aspects are that you use a mic that can reproduce a strong low end, and that you get close enough to capture the rumble while being far enough away from the lightning. Experts say to stay away from lightning strikes that are closer than 5 miles to you. This means that you want a 25-second delay between the actual lightning strike you SEE and the associated rumble you hear. That is kind of distant-sounding, I've been less than 2 miles. but that's a bit scary. I like that "crack" noise it makes in the summer night, and you have to be closer than 5 miles to capture that. And remember- no shiny mic stands!

Posted: Fri Jun 13, 2008 11:14 am

Thunder is really a sonic boom; the heat from the lightning almost instantly expands the air through which it travels, and then the surrounding air collapses back into the vacated space.

Basic science - high frequencies travel faster than low frequencies. That's why you first hear the crack and then the boom sound from thunder. High frequencies lose energy faster (and are more easily deflected) than low frequencies, that's why when thunder is many miles away you only hear the rumble. The more frequencies you hear, the closer the lightning strike.

Here's a link about lightning and thunder (lots of cool pix):

http://science.howstuffworks.com/lightning.htm/printable

Posted: Fri Jun 13, 2008 11:20 am

UncleBob58 wrote:

Basic science - high frequencies travel faster than low frequencies.

What?
Frequency has nothing to do with speed.

Posted: Fri Jun 13, 2008 12:51 pm

Thanks for all the information guys.

I know the basics of sound and wave theory. The thing about frequencies and speed is wrong, but I know what you are saying.

A higher frequency takes more energy to travel the same distance as a lower frequencies. Same thing applies in wireless signals. For example 900MHz has better distance and object penetration than say a 2.4GHz.

Anyway, why the recommendation of 5 miles? Unfortunately around here thunder/lightening isnt common and is usually accompanied by rain so any thoughts on how to capture that?

Did you just set to record and let it go and listen to the results later?

Posted: Fri Jun 13, 2008 3:51 pm

Yeah, I would just sit on the porch and sip a "refreshing beverage" while the sonic booms ran their course...And many times I've been closer than that 5 mile thing. I remember one time where an errant strike hit a next door neighbors' tree. It really overloaded the recorder, but it could've been a lot worse. Like a dead PC (or ME!).

Posted: Fri Jun 13, 2008 4:46 pm

Gentlemen,

I can only speak with some limited authority about lightning, and it's counterpart, thunder.

As I was struck by lightning 14 years ago, I can assure you that the amount of audio spectrum energy is more than enough to cause one to go deaf, so capturing a true bolt of lightning on any type of recording device in a close proximity would easily destroy any microphone diaphragm.

I will also tell you that there are several "valid" schools of thought about the nature of the audible component of a lightning bolt.

One says that it's the void created by the rapid expansion of the air. Supposedly, that's not completely possible. How can you create a void in an expanse of an air column, unless the air molecules are moved, or destroyed? There has been no measured expanse of an air column.

So another school indicates that the visible light from the lightning is actually the air column as it's being burned. But if the air column is burned, then why is it that lightning is in a narrow white color band, and not a wide variety of colors; dependent upon the quantity of differing chemical values in a given volume of air? e.g. He (Helium) burns at a different frequency than O2, etc...

The argument goes on, and on.

When I was struck the 2nd time, I was deaf for almost 16 hours and suffered from severe tinnitus for almost 5 years. However, the first time I was "struck" (the lightning was within 50 ft) prior to the flash, I heard a burning and sizzling sound that was in a phasing envelope that went from extremely high pitched (possibly above the human range of hearing) and grew louder and and lower in frequency until the exact moment of impact. At that point, the sound was an incredible rush of what I would call pink noise. After that, there was a long, 2-3 second, period of decaying audio that grew lower in frequency as time moved forward... e.g. doppler effect.

Another school of thought is that the low frequency component is related to the length of travel that the stepped leader, stroke and return strokes make. e.g. the average distance a lightning bolt travels is 2 miles. So the low frequency component would have a fundamental wave that long, and is accompanied by the short (several meters long) stepped energy paths.

I don't really care to get into any kind of discussion or debate as to which hypothesis is close, vague, right or wrong. I went through an exasperating and humiliating 36 month ordeal attempting to have this very discussion with some of the "worlds leading authorities" on the subject of lightning. I found them to be some of the most pompous, pretentious, snide and arrogant bastards I've ever dealt with in my life.

Posted: Fri Jun 13, 2008 5:34 pm

MadMax wrote:

... When I was struck the 2nd time, ...

F^#%

double F^#%

TWICE
Confused

that's intense

errr
speachless
Confused

Posted: Fri Jun 13, 2008 8:30 pm

Kev wrote:

TWICE

that's intense

Well... there's some question (even in my own mind... what's left of it that is...) as to whether I was truly struck the first time, or not.

According to the scientific data that's been gathered, in most instances, the energy from a typical lightning bolt "puddles" or "ripples" outward for a distance of 150 to 200 ft radius. The amount of energy dissipated is inversely proportional to the square of the distance. If there are say 1 million Joules in a bolt, the energy at 100' is fairly benign, with the typical kill zone being within 25 feet.

The first time, I was running, trying to carry my chubby little butt cheeks home as fast as I could. When the strike occurred, my forward momentum and the fact that I would have had very little body contact with ground... There's some doubt that I actually took any of the real energy discharge. I'm pretty sure I took the brunt of the energy from the rear, as I'm pretty sure the bolt struck behind me. Everything was completely white, and couldn't tell you where it actually was.

The second time I had a run in, I KNOW I was struck... there can be no doubt by the fact that I went into cardiac arrest, respiratory arrest and had both an entrance wound and burn marks... more like lightning patterns all across my body that resembled palm frongs or ferns. They were pretty much a strong 2nd degree burn.

As an interesting side note... before the first run in with lightning, I was a drummer and percussionist... after the 2nd time... people thought I'd be a guitar player because of drane bammage. Confused

But I ended up starting to run sound and operating a studio... so the damage is obviously far worse than anyone could have imagined!

Posted: Fri Jun 13, 2008 11:14 pm

Powder...

Freaking me out.

I was once standing 2 feet from a clothesline that was hit. I know what you mean by all white, it was daylight for a split second then just as it was fading to black the sound hit me. I got up from the grass so happy to be alive. It's why I try not to get too uppity lest someone try to smote me again.

Posted: Sat Jun 14, 2008 7:04 am

I was in my car about 200 feet from where a lightning bolt hit the ground -that was scary enough for me. Previously my close encounter came with a friend on a golf course when we saw a tree a long way away being struck by lightning and split in two pieces. We both dropped to the ground and waited until the storm passed before we got off the course. I use to record the Cleveland Orchestra at Blossom Music Center. There were many recordings of thunder recorded along with the Orchestra. In one instance the CO was doing the 1812 when a thunderstorm came out of nowhere. Everyone on the grassy hill came inside to the pavilion and the Orchestra finished up the evening with a naturally occurring battle in the background. They did not shoot off the cannons due to the danger of having someone out side in a lightning storm but the effect was the same with the thunderstorm.

Some interesting reads

http://www.wisegeek.com/what-causes-thunder.htm

http://www.sciam.com/article.cfm?id=what-causes-thunder

http://www.weathereye.org/cadet/lightning/thunder.html

but the correct answer is that a reaction takes place during lightning strikes because of the intense temperature between nitrogen and oxygen forming different oxides of nitrogen this reaction results in the loud cracking sound as its nearly and explosive reaction. - from the web...

Be safe!

Posted: Sat Jun 14, 2008 10:38 am

Be Safe is right...

The 3030 Rule:
30 seconds from flash to bang - Seek substantial structure or a vehicle.

Wait 30 minutes after the last clap of thunder or flash of lightning before resuming outdoor activities.

If you are outdoors and cannot find shelter;
DO NOT stand near or under a tree.
Crouch down on the balls of your feet and only touch the fround with your fingertips for balance... e.g. minimize your height and ground contact.

Here's a few links...
Lightning Strike Survivors
National Lightning Safety Institute
National Lightning Safety Awareness Week

Posted: Sat Jun 14, 2008 11:05 am

Counting after the flash is cool. 3 seconds per kilometer (approx).
So if you see a flash, and 30 seconds later you hear the thunder the lightning struck just over 10kms away.
The 3030 rule is smart, storms can generate lightning over an enormous front.
I've been thinking about how to record it. I suppose using two mics, one very capable of reproducing bass set up with a reasonably high gain on something with a limiter so after the "crack" maxes things out you can still get clear "boom" and "rumble". The other mic better suited to high SPL and rather lightly driven to give a clear picture of the "crack".
I'm just reasoning, anyone with some logic chime in.

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