The PING is supersonic. So why do we hear it?

[Quagmire]

I cant get enough of the Fleet Type Submairne manual at this website: http://www.maritime.org/fleetsub/ I have read to the Sonar operators section now and the more I read the more I cannot wait for SHIV! Those uboots are in the stone age compared to the average USN fleet boat!

Anyway the manual describes echo ranging or "pinging" as supersonic meaning that the ping cannot be heard without receiving gear. So why do we hear it when we are crapping our pants in the control room?

Also the manual states that escort vessels ping constantly due to the noise they make at high speeds? This doesnt seem to happen in SHIII. They only seem to ping when they detect you.

Or am I missing something???

Here are the links that I am referring to:

Supersonic listening: http://www.maritime.org/fleetsub/sonar/chap5.htm#5A

Single Ping Echo Ranging: http://www.maritime.org/fleetsub/sonar/chap6.htm#6A

[Drebbel]

Those uboots are in the stone age compared to the average USN fleet boat!

Then why where new designed post-war subs around the world mainly copies of the German type XXI ?

[Quagmire]

Well the XXI was a whole new class of boat. When I say stone age I am comparing the average VII or IX to the average USN fleet boat.

From the air and surface search radar to the ice cream machine I would rather be in the USN for sure!

[Keelbuster]

Kindof a cool question. Not sure, but - from the single-ping echo ranging link:

4. Keep your eyes on the revolving slit and listen intently for the echo. Disregard the rolling reverberations, and concentrate on catching the clear note of the returning echo from the target. At the instant it comes, note the reading on the scale. This is the range.

But this 'audible' ping is through a transducer - i.e. a hydrophone of some kind. So why do we hear it inside the sub? Well, I think long-range sonar pings are high amplitude. The hull probably acts as a kind of transducer (like a big drum) and you get some kind of sound from the transformed ping energy - even if it was originally a frequency that humans can't hear audibly, the hull may act as a low-pass filter/transducer that warps a high frequency ping into the audible range. Not sure - just a guess. I know that modern subs also use High-frequency sonar that doesn't travel a long distance and is not detectable except at close range. I feel like the ping-echo we hear has something to do with the amplitude of signal required to travel long distances. But I'm not sure. I don't even know how a hydrophone works.

Edit: Also - think of diffraction of light - when it passes from a good conductor to a poor conductor, it's frequency gets warped downward (i think). So the good sonar medium is water, carrying a high frequency signal, and the air inside the sub is a poor medium, resulting in the high frequency signal being warped into a lower frequency signal that happens to be in the audible range.



Kb

The most common description I've read of hearing the ping inside the boat is "it sounds like someone throwing gravel against the hull".

[Quagmire]

A logical enough explanation Keelbuster. However can any ex-navy guys give us any hard facts? Any ex-sonar operators with us?

Thanks!

[Vikinger]

Iam not an sub crew but there is difference between active and passive sonar.

Active sonar is much more lauder and use a frequency that human ear can detect.

It was surface weasels that used active sonar and today also used by helicopters.

No submarine is using active sonar coz of the risk of detection today.

Difference is also that active sonar works like a radar. It detect objects by bouncning sound. While passive sonar is more listen to the surrounding like propchafts, engines etc.

If u want to know about sonar u can check it out here:

http://en.wikipedia.org/wiki/Sonar

[Konnrade]

Originally Posted by Vikinger

Iam not an sub crew but there is difference between active and passive sonar.

Active sonar is much more lauder and use a frequency that human ear can detect.

It was surface weasels that used active sonar and today also used by helicopters.

No submarine is using active sonar coz of the risk of detection today.

Difference is also that active sonar works like a radar. It detect objects by bouncning sound. While passive sonar is more listen to the surrounding like propchafts, engines etc.

If u want to know about sonar u can check it out here:

http://en.wikipedia.org/wiki/Sonar

Also used by helicopters? Do they drag a sonar probe through the water beneath them?

[Cerberus]

Originally Posted by Vikinger

Iam not an sub crew but there is difference between active and passive sonar.

Active sonar is much more lauder and use a frequency that human ear can detect.

It was surface weasels that used active sonar and today also used by helicopters.

No submarine is using active sonar coz of the risk of detection today.

Difference is also that active sonar works like a radar. It detect objects by bouncning sound. While passive sonar is more listen to the surrounding like propchafts, engines etc.

If u want to know about sonar u can check it out here:

http://en.wikipedia.org/wiki/Sonar

Active sonar sends out a loud 'ping' which is like holding up a big sign saying 'I am Here!' - but does allow you to get (fairly) accurate range & bearing data on your target of interest.
Passive sonar produces no noise but doesn't give any range data & (sometimes) only approximate bearing data. You need to plot stuff over time to develop a picture of what it is, where it is & where it's going.

Subs all carry active sonar but never use it, except possibly in the last few seconds before firing on their target.

Surface ships are so noisy that subs already know where they are, & hence using active sonar is a practical measure.

The operating frequency of an active sonar is determined by it's purpose.
High frequencies don't propagate as well, so for long range detection, the optimum frequency is slap bang in the human audio range.
(The sound frequency that propagates best in water, is the frequency to which the human ear is most sensitive. The light wavelength that propagates best in water, is the wavelength that the human eye is most sensitive to - coincidence or evolution at work?)
For shorter range stuff (like an echo-sounder) higher frequencies are useful because shorter wavelengths allow you to 'see' finer detail and the transmit/receive transducers can be smaller.

[BigBadVuk]

Huh...First when i stumbled upon this topic i was confused but after few seconds i realised what are you trying to say and ask...Let me try to explain:
1st..There is no supersonic sound..lol..sound has variable speed of traveling wich depends on many factors, so i will stick to water as enviroment.In sea water sound speed depends on many factors like salinity,temperature,depth...etc..BUT sound can`t be supersonic supersonic is a word for something traveling FASTER than sound like jet fighter..You probably was talking about infrasound(below human capabilities of detect <60Hz) or ultrasound ( above human capabilities of hiring,greater than 19kHz)

Now,the greater the frequency of sound(pitch) the greater is definition of "image" u can get as echo becose u have lets say higher resolution of image.But there is a problem:Higher frequencies dont travel far enough to be useful in most cases.For ASDIC purporse u cant use infra sound becose u need high definition,to see where is the Uboat.So u will most probably use freq.around 7kHz or more..up to 15kHz and that is within the human hearing range.Infra sound u can detect on modern subs up to 20nm or even more but u cant hear them, u can only see them on sonar waterfall screen.
As for NAVY Helicopters ,yep ,they use dipping sonar,but u cant hear much if u drag that little thing becose of the nose of water run over hydrophones.That is why (in most cases) hello has to be stationary while dipping and pinging or just listening...

P.S. sory for bad english but my english start to sucks when technical things are about

[Vikinger]

Originally Posted by Konnrade

Also used by helicopters? Do they drag a sonar probe through the water beneath them?

Hehe No. its very common in most navy that they use helicopters for submarine hunt. Helicopters hover (or how it is spelled ) and drop the sonar probe into the water and then listen for sounds.
A typicaly picture how it can look like can u se here:

http://svt.se/content/1/c6/13/92/50/Ubaatsjakt.jpg

If they find something they can then drop either depth charges or torpedoes. ( If they have that kind of weapon fitted)
Or call in reinforcement.

[caspofungin]

british ww2 asdics used pings in the range 14-20Hz -- well w/in the hearing range of humans.

re constant pinging -- that's true, in ww2 escort vessels constantly had the asdic operating. unfortunately, that's not implemented in sh3 (although i seem to recall it in silent service 2).

[mheil]

I haven't totally read the link you post about supersonic, but my guess is that by supersonic is that the sound waves travel faster through the water than through the air and at a frequency that humans can't hear (dolpins, any one?). When these sound waves hit the poor doomed submarine hull, the hull then vibrates into sound waves that can be heard by the ear.
Great link to the manual. I'm ckjeckin' it out now.

[theluckyone17]

From "Iron Coffins" by Herbert A. Werner (p.293):

... However, the thunder of the barrage was not nearly as frightening as the noises that preceded and followed the attack. At first it sounded as if something like a chain or an iron net were being dragged along the hull; then came a wild clattering, as if a great load of pebbles were bing dumped upon the boat. These were brand new sounds to all of us - and a terrifying turous experience... But I concluded - correctly, as I later learned - that the British were using a new search device akin to the Asdic.

If I've got the dates right, that would've been March 19th, 1944. I imagine that at some point prior to that, the Allies started playing around with sound frequencies higher than previously used, causing the shift from the high pitched ping that could be heard earlier to that "load of pebbles" sound.

Possibly better picture for dipping sonar.

Basically, to do this, the helo stops and hovers a few meters above the water, then lowers the sonar probe, and listens. If they hear something susupicious, then they go active, and try to immediately locate the sub. If they don't hear anything, they winch in the probe, fly over a few hundred meters, and try again (usually also being given steering commands by the ship they're operating from; the ship's sonar, being a lot bigger is also a lot more sensitive, and between the two they can pinpoint a sub pretty quickly). Usually helos in this mission are armed with 2 homing torps.