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Quick back story... On my drive home, I drive next to a fairly busy train track on an otherwise unused road -- the track is about half a mile either direction from any crossings, so I won't have to worry about the train's horn in a stereo pass-by. I plan on recording the pass-by sometime soon (it's been far too cold lately to sit out and wait for the train), but I was also thinking about ways to maximize the single experience.

One of the thoughts was using contact mics on the rails, to get the sound of the train approaching from as far away as I can. My biggest fear from this is if I'm recording hot, will the signal from those mics damage my h4n as the train passes (which I suspect will be enough to damage the mics), or is this relatively safe to my equipment?

Just to clarify, I plan on being probably 30+ feet away as the train passes, with the h4n set up on a gorillapod 15-20 feet away, or as far away as I can with the contact mic's cord.

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Not sure about that - I remember reading years ago of guys recording onboard F1 engines, the SPLs were so high the dynamic mics they were using were generating volts rather than millivolts, which I dont imagine preamps would like too much. They had to pad them down LOTs to get a recordable signal... But I dont imagine your normal distortion/over level sitations would damage your recorder...

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Thanks, Tim... that makes a lot of sense, and now I'm inclined to look up how a microphone works. Ahh, the things we take for granted. –  Dave Matney Feb 28 '11 at 20:11
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You may get a distorted recording, if it is too hot, but it won't damage your recorder.

The ways I have damaged equipment has been through physical violence, powersurges or sea water. Oh and also the occasional loudspeaker from playing too loud...

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Nice to see normal water has never damaged your equipment. :p –  Dave Matney Feb 28 '11 at 20:10
    
Well my english may not be the best, but I have had some rain on recording equipment a lot of times without damage, but I have had equipment break down because of sea water, due to the salt in sea water which quickly corrodes the electronics... –  Morten Green Feb 28 '11 at 20:23
    
I've dropped mine a few times, cosmetic damage only though luckily :) –  Adrian Millington Feb 28 '11 at 20:56
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I've used contact mics to record trains, and if I recall correctly I did make some recordings with the mics attached to the rails. Didn't harm the recorder, and in fact the levels were ok too provided the gain was low enough. Sticking contact mics onto the heated pipes of a running steam engine was probably a bit more dicey!

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While I have not used contact mics, I have used this recorder before with an external mic capturing many a Union Pacific freight train at distances of about 5-8 feet (further away too). And Tim is correct, you'll face signal distortion via the mic if it's set too hot, but the recorder should be fine. The ONLY thing which may come to mind is ultra low frequency which could possible disrupt the recorder on occasion, especially if the unit itself is very close to a train engine. I cannot confirm this or deny this, although it's the only remote possibility which comes to mind, especially since it's below our hearing range yet can have an effect on the electronics - much in the same way a 3G cell phone data connection makes no sound whatsoever to our ears, although hold it close enough to a mic when it is transmitting or receiving data, and you will in fact pick up a very strange burst of static and beeps.

If it's of any help, I have found that a setting of about 24-26 on the H4n recorder is a good sweet spot when doing a close train bys, including the horn blasts (this was when I routed in a Rode NT4). Give you a robust enough signal without quite going into dangerous territory - plenty of headroom to work with in post.

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