Loud Cockpit

[sprucemoose]

Try A200 was notorious for coming from the factory with the microphone gain set way to high for our high-noise airplanes. I'd start with that.

[Mike S]

Originally Posted by BobTurner

Noise cancelling mikes (you do not want anything less) work by having two mikes, back to back. The signal is differenced (subtracted). Noise from sources more than a foot or two away tend to be about equal on both sides, so after subtraction you get zero.

I used to make up paired mics for the theater at the college I worked at back in the late 1960s by building a "Y" cord wired out of phase.

Works quiet well for canceling out background noise-----anything more that 3 times the distance between the two mics was attenuated rather well, yet you could talk into one mic and all was normal.

Little trick taught to me by the folks from Altec Lancing who did the Acousta Voice setup for the theater.

[rv7charlie]

But I was a sound engineer in one of my past lives. Bob's right; differential mics do exist, and have for a long time. Find some old video of Grateful Dead concerts from the '70s when they had their 'wall of sound' PA system. You'll see two identical looking mics in front of each vocalist, one above the other. All the PA speakers fired directly into both mics, but the singer only sang into the top one.

Now, that technique is pretty rare in the 'mobile' world; not sure I've ever seen a headset that used that technique. Virtually all current headsets, and most vocal microphones used in live PA type settings, use 'unidirectional' mics. This link
http://www.soundonsound.com/sos/sep0.../direction.htm
has a pretty good diagram of how one works, about 1/2 way down the page. (Or just google the term; you'll learn more than you ever wanted to know.)

Reading your original post, you kinda have the solution embedded in the question. The headphones block the high ambient noise, but the mic can't help picking it up. (Unidirectional mics do have their limits.) Turning down the mic gain is a good suggestion; it increases overall signal to noise (ratio of the mic's perception of your voice's volume to its perception of the ambient noise. (Voice gets louder than the noise, from the mic's perspective.) Next step is reducing ambient noise, as you suspect, but the biggest offender, and easiest thing to fix, hasn't been mentioned.

As strange as it may sound, in most planes like RV's the biggest contributor to noise that affects communication is wind noise. If you haven't already done it, spend whatever time it takes (shouldn't take much money) to seal up all the air leaks around the canopy, wing roots (aileron pushrod boots, etc) and into the tailcone. I'll bet you'll see a dramatic improvement.

Quick test before taking any action: What's the noise/intercom squelch like while doing a runup on the ground? If it's significantly less bad, you probably have a wind noise issue.

Hope the above is useful,

Charlie

[flightlogic]

"Works quiet well".... now yu are pulling my leg Mike!
I am headed down to the thrift store in search of Grate Full dead equipment... be back in a while.

[Neal@F14]

Dunno if I'd want to have any equipment onboard my RV that has the word "Dead" in its name.

[rv7charlie]

Reckoning??

[Pat Stewart]

I have the RV12 with the Garmin 200. I have been fighting a squeal in the headset every time I key the Mic that goes away once I speak. I assumed it was a ground so I took the airplane apart, wings off to gain access to the headset jacks, floor panels out and started looking for the problem. After finding everything perfect I was ready to start making calls to Stein and Garmin. I then remembered a comment someone made a few weeks earlier about how loud my radio was when I was in the pattern and it started me thinking. I put the radio in setup mode and checked the Mic Gain. It was set on 10.I keyed the Mic and turned it two clicks left to 8 and the noise was gone. Looks like it was so high that the Mic was able to feedback to the headset.

I lot of work chasing grounds for something I should have checked first. The positive result was that I will never again need to remove the wings to get to the headset jack wiring. That design issue was corrected.

[snopercod]

I had the same problem a couple years ago. Besides the noise in the intercom, my mic picked up the cockpit noise and transmitted it when I was talking to ATC; The cockpit noise was so loud that ATC could barely understand me. I used a multi-pronged approach and finally solved the problem. I haven't had any complaints from ATC since doing these things:

1. I added sound insulation to the cabin and improved the canopy seals
2. I bought a Sigtronics S-20 headset with a noise-cancelling mic
3. I added a Mic Muff over the microphone
4. I adjusted my Icom A-210 as follows:

INCOM LVL = 051
MIC 1 GAIN = 10
MIC SQL = 026

5. I added down turns on my exhaust pipes

[flightlogic]

Just a quick note to relate how we solved a high noise cockpit. This is in OV-10 Bronco's. Lightspeed mic and headset. We found installing not one... but sometimes two or three of the little leather covers from David Clark fixed the issue. Cheap and easy. And yes, they still need the hole in the back AND the front for the passive noise cancel to work. (CAL Fire working planes)

[Xkuzme1]

There are intercoms expecially made for open cockpit airplanes. I'd start with that. Could probably pick one up for cheaper than you could buy insulation.

SigTronics SPA-400N