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Old February 24th, 2009, 08:10 PM   #1
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Recording an engine bay without destroying a mic?

I would like to get some recordings of various engines from within the engine bay itself. The only mic I have that would be practical for this is an AT943 cardioid lav.

The big thing I'm worried about, really, is heat. I'd like to get at least a few minutes of solid audio from each car but I'm afraid of cooking the mic. I can deal with the vibration and environmental goo... Any ideas on how I could keep it alive during hot laps with big engines? If I could just trash this mic and go out and get a new one, it wouldn't be a problem. That's not in the cards though....

--Andy P
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Old February 24th, 2009, 08:40 PM   #2
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Go buy an inexpensive dynamic mic and use that instead. Sensitivity is NOT an issue in this application -- instead, you want a mic with the sensitivity of a damp brick. Even with a suitably "cold" mic, you may still have to wrap it in a few layers of foam rubber to deaden the levels down. Omni, cardioid, who cares? In that environment (under the hood), the sound comes from EVERYWHERE.

Dynamic mics are designed for high-ambient noise and sound level environments, like on stage at a heavy metal concert. The vocalist has to choke right up to the mic screen (and in a lot of cases actually "lips" the mic) to get enough level. I'd check out Radio Shack or maybe hit a few pawn shops to see what mics they have. I couldn't see spending more than $50 to get a mic that worked, maybe TWO at that price.

Martin
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Old February 24th, 2009, 09:43 PM   #3
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What kind of engines are you talking about? Cars and trucks or race cars?

One 'regular' engine won't be a problem for most mics. A race car on the other hand could create some high decibel-age.

Two ideas: a shotgun from a safe distance or a EV 635, better yet an RE-20--designed for bass drums and real high SPLs. I believe PZMs will also take high SPLs too.

I think a shotgun will give you the sound you want without being right in the engine compartment.

Or are you talking about while driving? Then a 635 will do the trick.

I doubt that cheap Radio Shack mics will handle high SPLs.
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Old February 24th, 2009, 09:47 PM   #4
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I'd be willing to be it gets very drafty in there, too. So some sort of effective wind protection should be considered.

And keep in mind that part of that engine sound comes out the tail pipe. You might want to mic that, too.

Would that be a cool 5.1 sound for a home theatre?!
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Old February 24th, 2009, 10:02 PM   #5
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The cheap Radio Shack mike may not be a crazy as it sounds. In years past I used Radio Shack $5.00 tape recorder mikes to run sound trippers for remote cameras set up at the Shuttle launch site...that is some serious sound pressure. Of course, all it had to do is send a signal, no idea of how good it might have been..../ Battle Vaughan /miamiherald.com video team
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Old February 24th, 2009, 11:03 PM   #6
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Some of us have actually used earphone elements as microphones. Cheap, disposable, and very NOT sensitive-just what you need for engine compartments...
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Old February 25th, 2009, 06:35 AM   #7
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Great suggestions guys. Thanks a lot.

I especially like the idea of using cheap mic's and seeing what happens.

My intentions are to get three tracks really. One from the engine bay, one inside the cockpit, one from the exhaust. That way I can cut the sound between different shots, getting the sound I'm looking for.

And yeah, these are race cars. 6+ liter engines running over 8k rpm on road courses. Some street cars will be interspersed as well, but the intention is capturing the "big boys".

I'll start the experimentation phase within the week or so. It's gonna be a good time =)

Any more ideas or anyhting please do let me know!

Thanks

--Andy P
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Old February 25th, 2009, 01:08 PM   #8
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A Shure SM-58 or the cheaper 48, or Senny e-835 may be a good choice, The metel windscreen may help protect the element from the heat and they handle high SPLs. In any case I would use an additional windscreen, shield the body of the mic with some kind of heat shield if your expecting excessive heat and mount away from the exhaust manifold. Under normal (moving) street or highway driving conditions there's usually enough airflow so you won't cook it.
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Old February 25th, 2009, 02:38 PM   #9
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I've recorded some street cars' engines while parked and revved. We found the exhaust noise to be attractive, and engine noises to be very unattractive. In the engine bay, you mostly hear belts and pulleys. When driving, you'll also hear wind.

I agree about using a cheap dynamic mic. You need insensitivity, not fidelity.

Use good mounting. In 150 mph winds, a human can barely stand up while holding a rope!

FWIW, here's where I used our exhaust recordings (of the actual cars on screen - except for the sound effect clip in the "previously" review.) As I recall, we used a shotgun, 45 degrees off axis from the exhaust at a distance of about three feet. We used lots of EQ and panning for scene changes. Colonel Crush - Sword in the Stone OF ACTION!
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Old February 26th, 2009, 10:46 AM   #10
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I bought I secondhand Electrovoice 635a as a backup mic but have never used it yet, so I'm no expert.
It's a classic dynamic reporter's mic that has a reputation for being as tough as old boots.
When doing the research I read something about a guy using one of these, I think for dragsters or something similar.
It was the only mic he had that would handle the high sound levels without being damaged.
I see that Andy T suggests this too.
Secondhand, they are very cheap.
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Old February 26th, 2009, 04:07 PM   #11
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Quote:
Originally Posted by Jon Fairhurst View Post
I've recorded some street cars' engines while parked and revved. We found the exhaust noise to be attractive, and engine noises to be very unattractive. In the engine bay, you mostly hear belts and pulleys. When driving, you'll also hear wind.
That's right. Long ago I tried it with giant aircraft piston engines inside the cowlings and found it was a waste of time. Even if the result was useable, no one recognised it. Better from the exhausts or where folk would stand to hear it.

Cheers.
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Old February 26th, 2009, 04:26 PM   #12
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Quote:
Originally Posted by Allan Black View Post
That's right. Long ago I tried it with giant aircraft piston engines inside the cowlings and found it was a waste of time. Even if the result was useable, no one recognised it. Better from the exhausts or where folk would stand to hear it.

Cheers.
The one exception might be if you could get the sucking sound of the intake. It wasn't feasible on the street cars we recorded, due to their small displacement, and might not work on moving race cars, since the intake is usually plumbed to make use of the wind. That said, I own an older Turbo Esprit (that wasn't running when we did our recordings) that has a mean hisss from the intake once the turbo spools up. It doesn't sound like your typical engine, but has a visceral feel.
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