Established Member
I recently watched this video of the launch of Apollo 11 on Saturn V. If you listen closely, there is a crackling sound that starts just as the rocket clears the tower. I am assuming that is the sound the engines make, however, why would it sound like that?
Thank you for your help.
Banned
Followed your link and, herd the sound you mention. My interpretation of that clicking sound is ' There are a number of feeds suppling sound to that video stream. Audio controllers switching mic feeds from one to the next would make that sound. The sound recording equipment was never going to reproduce a true sound of the lift off as the decibels produced are the from the loudest sound on Earth. Accurate reproduction of that sound is still a big ask.
Established Member
If you're talking about the sound I think you are (and it's much more prominent in the night launch a bit past 5 minutes), it's the microphone being unable to respond to the pressures it's being given; the range in which the vibrating part inside can vibrate is limited, so, when pushed hard enough, it slams into one extreme end of its range or the other, because it just can't vibrate loosely enough to really keep going with the flow as it would with lighter pressure (quieter sounds or less wind). It's the same thing you get when you see a weather reporter standing in a hurricane to tell us that it's windy, and the wind hits his microphone so you can't hear him saying it.
Established Member
Ok, that works!
I guess now you would have to pop on a couple of those Bose Noise canceling headphones if you were under the rocket when it went off...
Order of Kilopi
quick toast...
foreignkid; I can see it now....don't try this at home, laying on your tungsten liquid-cooled lawn chair with asbestos suit covered with ablative heat shield....OUCH!Originally Posted by foreignkid
Ok, that works!
I guess now you would have to pop on a couple of those Bose Noise canceling headphones if you were under the rocket when it went off...
Order of Kilopi
I couldn't hear the audio on the recording clearly enough to make
out the crackling sound, but I've heard it plenty of times elsewhere,
and I heard it when I listened to a Space Shuttle launch with my
own ears in March 2002. It sounded like 10,000 drummers all doing
manic riffs on 10,000 snare drums simultaneously. I was a bit less
than 6 miles from the launch pad. I would think the SRBs would
sound different from the Saturn's kerosene-oxygen F1s, though.
-- Jeff, in Minneapolis
http://www.FreeMars.org/jeff/
"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"
"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves
Order of Kilopi
You can hear it really well in this video. Clearly, it isn't entirely microphone artifacts though if it is audible to a live observer...
Established Member
it's the same effect. and you can actually get a similar feeling in your ears. basicly your ear drums only move so far, if you max them out, it sounds really weird, and thank your lucky stars (astrology?) that they didn't break.
Order of Kilopi
Guys, doesn't this also and mainly have to do with the shock diamonds in the exhaust, especially when hearing it live?
Order of Kilopi
Not as far as I know, as several smaller hobby rocket motors have mach diamonds (shock diamonds), and yet do not make that sound.
KingNor: I'm not entirely sure that is correct. I can guarantee you that the space shuttle is nowhere near loud enough to do that from 6 miles away. It is certainly loud, but nowhere near the limits of the ear. It has to be some other effect...
Order of Kilopi
Indeed, they sound more like opening a soda bottle, but amplified a bitNot as far as I know, as several smaller hobby rocket motors have mach diamonds (shock diamonds), and yet do not make that sound..
Can it also be interference; the sound waves of multiple engines periodically amplifying and reducing the total sound level, giving rise to the hammer like sound without any clipping of pic or ear involved?
Order of Kilopi
That means that it can't be a microphone artifact. Somebody on youtube wrote that it was a series of sonic booms, I guess from the expansion of the exhause. It sounds fairly reasonable. I think thunder sounds crackling for the same reason. But I don't know very much about it.
As above, so below
Order of Kilopi
cjl, Jens,
Right. The Shuttle launch sounds very loud from six miles away, but
not painfully loud. Not loud enough to make me want to plug my ears.
A fire truck siren or the cannons fired while playing the 1812 Overture
do that. (Luckily I happened to be behind the cannons rather than
in front of them.) The sonic boom thing is something I've read or
heard about before. No question that the expanding gases inside
the engines are moving at well above the speed of sound.
-- Jeff, in Minneapolis
http://www.FreeMars.org/jeff/
"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"
"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves
Order of Kilopi
But then the only reason that model rockets, which also show mach diamonds and hence have supersonic exhaust, don't feature this sound would be the limited strength of their mach shocks. Possible.
In that case, I was right all along!
Order of Kilopi
Well, it also depends on the model rockets...
For example, this one weighed almost 200lbs at liftoff and had over 1500 pounds of thrust. No crackling was audible:
If sonic booms are the correct explanation (keep in mind, by the way, that not all supersonic exhaust flows contain mach diamonds, only the ones that are not properly expanded), it must take one heck of a lot of power to create enough of them that it is audible.
Established Member
ok so i think i was mistaken then. so some of you are hearing this crackling while watching a launch in person? NOT while watching a recording, right?
how very odd.
Order of Kilopi
It's not so much the amount of shocks as the strength of them that depends the noise.
But I'm not sure it are the mach diamonds that make the crackling noise.
Posting Permissions
Reply With Quote