Shotgun Microphones

      • Anybody know how these things work, or where there’s any technical diagrams or info on the net? I want to make some directional shields for a pair of mics I use for recording, but can’t find any info on how shotgun mics are made. I am guessing it’s a cylinder closed at one end and lined with sound-absorbing material, with the mic set inside near the closed end. They often have ports in the sides near the closed end, so I figure that I can try it without ports first and then make some ports if it sounds lousy…
        ~
        Note: a shotgun mic is more “directional” than a unidirectional mic, but not so much as a parabolic reflector mic, -which is too much for my purposes. - DougC

Some links

http://hyperphysics.phy-astr.gsu.edu/hbase/ph4060/p4060.html

http://hyperphysics.phy-astr.gsu.edu/hbase/audio/mic.html#c1

http://www.core-sound.com//

http://www.harmony-central.com/Other/mic-faq.txt

http://www.locationsound.bc.ca/Specialty.htm

http://www.tfwm.com/twm/articles/audio/0101_Taipale.html

http://www.governmentvideo.com/issues/2001/0501/0501.prod.shtml

To a limited extent, what you suggest will work. Put them in the end of tubes, and close off the ends nearest the mikes. Make sure there’s no play between the mike and the tube, any brushing movement between the two will pick up loudly.

You should know the pickup pattern of your mike before you start. If is already directional, you should orient the mike so the tube is aimed along it’s pattern. Duct tape and a paper towel roll. Just leave the paper on the roll.

Could you explain what you’re trying to mike? As noted in Astro’s post, the range of a shotgun mike is not significantly farther than any other. Only the noise coming from other directions is reduced in comparison. In other words, al the design expense in shotgun mikes goes into what you are proposing to replace with essentially a cardboard roll (actually, I have seen shotgun mikes use cardboard). The secret is in the design of the diaphram inside the mike, and how the cartridge around it allows in sound. If your mike is omnidirectional, don’t expect great results. Work instead on a better location for it, or greater control over the ambient sound environment.

I have doubts this will accomplish what you hope, but it is certainly cheap enough to be worth trying out. And experimentation is alway to be encouraged. Just don’t modify the mikes in any ways that you can’t unmodify later.

      • I plan to eventually get a pair of $50 (each) condensor mics, but all I’ve got now is PC mics, and even I can afford to ruin a few of them. The shields I am making won’t require permanently mounting the mics: the mics will clip in with the lapel clips on them.
  • The idea was to record instruments or vocals (separately, that is). The problem is that even though it sounds quiet, the mics are picking up lots of background noise, sort of a roaring/whooshing/screeching noise, almost like a jet plane was circling low overhead. I am using a PC soundcard and a minidisc recorder, but you generally get the same result with any cheap casette recorder, so I doubt any of my current equipment is the culprit. I can use a param-EQ to get most of it out, but I’d like to keep it out as much as possible.
  • We have also tried using low-priced uni-directional mics as well, and got results about the same as the omnidirectional PC mics. It’s probably poor acoustics of the house, but that I cannot cure. All I can do is attempt to zero in on the intended sound sources… - DougC

Try this experiment: Sit quietly in the space you’re going to be using and LISTEN, while you record ambient sound. If YOU can’t hear the “sounds” the mikes are picking up, then there is a problem in your system. If you CAN hear those sounds, some of them can be identified and eliminated.

Likely culprits: your computer, specifically the fan and the monitor(you’ll have to move them away from the mikes); flourescent lights, furnace, waterheater, etc. You’d be surprised what you can get rid of.

I suggest, with such small mikes, trying the earlier paper towel roll idea. Pack some paper towels around the mike to keep it centered in the tube, then slide it in about half way, and pack in more paper towels behind it.

The let it sit for at least 15 minutes. The paper will be rustling and resisting its new shape in the tube for a while, noisily.

Do not touch or move the mike, tube or wires while you are recording.

Good luck. Let us know how it works.

If you turn off your fridge, don’t forget to turn it back on.

Are you using the PC soundcard and the minidisc at the same time? I don’t understand.

You might turn off the PC and record straight into the minidisc (thereby avoiding noise from the PC fans), then run the output of the minidisc into the computer.

Another thing to check in the recording level. Send the recording device the strongest signal you can without distortion. Your goal is to improve the signal to noise ratio. If you can’t reduce the noise, boost the signal. Get the mic as close to the source as possible.

And once you have recorded a .wav file, there are ways to reduce noise besides EQ. I use Cool Edit Pro, which has noise reduction. You might find cheaper (or even free) noise reduction software at www.sharewaremusicmachine.com.

Ultimately, getting better mics will be the best solution IMHO. And if you ever plan on buying a mixer, get one with decent mic preamps. Then you’ll no longer need to use your soundcard or minidisc to amplify the mic signal.