Mic recommendations

[mofo22]

I need a mic for a specific task and would like to know what the experts recommend. The mic would be mounted on a motorcycle, towards the rear, to record sound coming out of the exhaust system on a mini-DV camcorder, thru the MIC jack. I would like something compact and non-obstructive, and good quality audio. The film will be on DVD dolby digital 2 tracks. How much should i expect to pay and do you have any suggestions? Thanks.

[Cornucopia]

Since a motorcyle exhaust is going to put out quite a loud level, and because your DV camcorder mic inputs probably don't have phantom power. It would make sense for you to use a dynamic mic. You still might have some trouble with the max sound pressure level (SPL), so you may want to have a physical cover/barrier/filter to lessen the signal before it actually gets to the mic. Or, you can get an in-line filter/attenuator so you can dial-down the signal before it gets to the camera. Even though it will be referenced to mic level, it'll probably be quite "hot".

Next thing to consider is the form factor. How bulky do you want this thing? Do you worry/care about wind noise? Also, VERY IMPORTANT--depending on where it's situated how hot could it get?
Me, I'd try to find a very rugged lavalier (clip-on) mic and fashion a heat-resistant screen around it (the regular nylon ones will melt in seconds) and also fashion a coat-hangerlike elbow to go slightly below and infront of the mouth of the exhaust (remember-heat rises, and exhaust puts out alot of heat and wind). Also, you'll have to experiment to see what gives you the most appropriate balance between direct sound and ambient noise (which may or may not contribute to the quality of the effect). Distance is the critical factor here.
Also, make sure the cable is protected and away from the exhaust.

A good mic that fits the bill is probably gonna cost ~$100-$400 US, depending on you source and whether it's new or used, etc. That's not counting the extra accessories/attenuators, etc you'll need to fashion /buy.

Good luck,
Scott

[mofo22]

The gases coming out of the exhaust are really hot, so i don't want to place the mic right behind the muffler, but maybe 20-25 inches closer to the front. I tried it last summer and you could still hear the exhaust sounds very loud, maybe too much still. The biggest problem was when the bike was leaned over in a curve, then you could hear a lot of wind noise hitting the mic from the side of the bike. It wasn't as big of a deal when the bike was straight up, as the mic was better protected from the wind at this angle. I tried putting some foam around the mic but that didn't help much if at all. I noticed the tv crews are using those long hair wigs around mics when they shoot outside, maybe this is what i need? Where do you get these wind protectors for the mini clip-on type microphones?

[Cornucopia]

AFAIK, they don't make them for clip-ons. You'd have to make one yourself--shouldn't be too hard.

Actually, 20-25 inches seems a big distance. Is it possible to get closer without heat being a problem (or the level being too loud)? I was thinking more along the lines of 8-12 inches, and along side or below, but more forward.

Making a movie? Tell us about it...

Scott

[mofo22]

Even at 25 inches away from the muffler, it is REALLY loud, so i don't think i want to move it any closer. What i need is wind protection. I used the type of foam you can get to make pillows, kinda like those cheap mattresses you put underneath your sleeping bag when you go camping. I wrapped the mic in it, but it didn't help much if at all.
I'm not shooting a Hollywood production, but still the quality needs to be decent enough for tv broadcast. We're shooting a few motorcycle races (roadracing) and want to use onboard videos to complement the trackside cameras. It's all being shot on Betacam SP, and the onboard stuff i will use bullet cameras with the Sony EX-view CCD, pretty good quality if you ask me. Don't know of a better bullet camera in this price range. The onboard recorders will be mini-DV camcorders. I've got some great footage from last season, but i need to work out the audio bugs.

[dphirschler]

Don't laugh, but I read that some pros recommend stretching a condom over the mic for severe wind protection. OK, you can laugh, but it's true.


Darryl

[Cornucopia]

Think of it this way:

Quiet---------------------------------------Loud
A. .............WindNoise.......Exhaust............. @ 25 inches
B. .............WindNoise.................Exhaust... @ 10 inches
C. .....WindNoise.................Exhaust........... @ 10 inches*


You want (C). You get that by taking (B) and *attenuating it (volume down), with an in-line attenuator.
This will simultaneously make the balance between the the main signal (the Exhaust) and the noise (wind) more favoring the exhaust, and it will lower the overall level to comfortable recording levels. The only reason this wouldn't work would be that the actual output from the exhaust is well beyond the Max SPL capability of the mic and is overloading it anyway. If that were the case--find a different mic. Try a Green Bullet (blues harmonica mic).

And yes, condoms do work. They are known to be quite useful for underwater work (mic can be made waterproof, but sound wave aka "pressure wave" still penetrates--pun intended 8) ).


Scott

[mofo22]

Any good sources for in-line attenuators?

[dphirschler]

www.soundprofessionals.com $7.

Also, Radio Shaft has one for $5. It's called a headphone volume control or something like that. I have the Sound Professionals one and it works well.


Darryl

[Cornucopia]

Try Markertek, for starters.

Scott

[Cornucopia]

Vol. controls that are meant for headphones --may-- work, but they aren't the best choice. They are set up for headphone voltage levels and 8 ohm impedance. Standard mics usually have 600 ohm (pro) or 10,000 ohm (consumer) impedance, which appears a whole lot different to the electrical circuit than an 8 ohm would.
Note: Impedance is like resistance, except that varying the impedance can vary the frequency response.
This means that you likely get a change in the tonality of the sound when you adjust the control.
Plus, the signal-to-noise is not optimal when the impedances don't match.

If simple vol. controls were easily useable, audio engineers would be using them all the time. Instead, however, they buy more expensive attenuators. Haven't looked recently, but I would guess the cost to be $30--$180 US, depending on quality and features.
But,in a pinch, headphone vol controls would probably do.

Scott

[dphirschler]

I used the Sound Professionals attenuator with my gear and it worked out great. It was an experiment but it turned out beautiful. My setup is as follows:

Audio-Technica 831-B mics with battery box (x2) -->
home-made XLR (x2) to stereo 1/8" mini stereo plug -->
Sound Professionals attenuator -->
Sony M1 DAT recorder

I set the attenuator at about half volume and recorded a Stryper concert. It was extremely loud, but it recorded perfect (better than my ears could hear). Before I got the attenuator, the DAT's preamp was getting overloaded. The M1 is famous for having a weak preamp. The D7 had a much stronger preamp which could handle the load of a loud concert. The mics have always handled the load.

Without the attenuator, the signal would do what I call "brickwalling" during the loud parts. In other words, the signal levels would not bounce around but instead hit the maximum (the wall). I could adjust the level lower on the DAT recorder, but it was just a lower volume distorted signal. What I had to do was attenuate the signal before it entered the DAT recorder.

I can send a sample mp3 out to anyone interested. It did a great job. Perhaps the attenuator I bought was made just for my application (stealth recording) which is why it performed so well.


Darryl

[mofo22]

If an in-line attenuator is similar to a headphone volume controller, i have this very small pre-amp for a mini stereo mic that i was planning on using. It has a knob for volume control on the side, so if i lower the volume manually is this like getting the same result as if the signal would go thru the attenuator?

[Cornucopia]

Yes, sounds about right...

Good luck,
Scott

[mofo22]

thanks again.

[vcdforme]

Believe me, I'm being sincere.
Now I've never tried this, but, I think it's worth a shot.
Radio shack makes some very inexpensive piezo mics,
and they're small too.
Get one and try puttiing it up your ass.
You won't have worry about attenuation.
Wind won't be a factor.
And, if you fart, people will just think it's
the motorcycle.
Fact is, the farther you get away from the muffler the better
it will sound.