---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Wed 05/15/13: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 12:40 AM - Microphone gain tuning (Holger Selover-Stephan) 2. 05:40 AM - Re: Microphone gain tuning (Ken) 3. 08:02 AM - Re: Microphone gain tuning (Robert L. Nuckolls, III) 4. 09:26 AM - Re: Microphone gain tuning (Robert L. Nuckolls, III) 5. 10:30 AM - Re: Pre-oiler system controls (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 12:40:25 AM PST US From: Holger Selover-Stephan Subject: AeroElectric-List: Microphone gain tuning Hi all, I seem to have a microphone gain tuning problem on the second DIY headset, following these instructions: http://n999za.com/2011/02/04/roll-your-own-in-ear-headset/ For the first headset I slaughtered an old GA headset and used its wires and microphone. Works beautifully. Now on the second headset I am using new shielded wires and this microphone (packed into a wind screen): http://store.acousticom.com/m7a-amplified-electret?keyword=5720-CA&categ ory_id=0&description=1&model=1 The microphone is now overly sensitive and picks up everything. In a quiet environment, my transmissions are crystal clear, but in flight the surrounding noise pretty much drowns out my voice. I tried it with two radios: an ICOM IC-A6 (on the ground) and in the air with a KX-135A through an RST 422 intercom. In the hangar with everything quiet but a radio playing soft music 20 feet away that music makes it into the transmissions. Since I bought the microphone new, I asked the vendor, and Joel writes back: What you will need to do is adjust the microphone gain control within your radio to adjust it to fit the microphone properly. All radios are different and require proper tuning when replacing the microphone. Please refer to your radio's manual for adjustment procedures. We do sell a microphone that allows you to tune the microphone with a screwdriver. This is a common occurence that microphones need to be adjusted to the radios to perform properly. Your mic currently is set too high in sensitivity/gain. I can see how the combination radio and microphone needs to be tuned, I don't want to tune the radio to just this new microphone, and thus make all other headsets unusable in my plane. Their adjustable gain microphones apparently need a 9V power supply - not ideal. Should I try this trick posted to this group a while back: Got a great idea from somebody, and the cost is free! Get the plastic 35mm film containers. Cut an "X" in the lid and slide it on the mic arm. Then wrap some foam around the mic and slide on the 35mm can after you have drilled a 1/4" hole in the side. Line up the hole with your mouth. Better than sliced bread. Just keep the hole tight against your mouth to keep out engine noise. My engine noise keeps my intercom open, but makes for a pleasant ride with me as the tour guide. walt evans NX140DL ============ Oscar Zuniga Medford, OR Air Camper NX41CC "Scout" A75 power But this probably addresses mostly wind noise, and I'm in an all enclosed cabin. Any other thoughts? Thanks! Holger ________________________________ Message 2 _____________________________________ Time: 05:40:53 AM PST US From: Ken Subject: Re: AeroElectric-List: Microphone gain tuning Oscar I've played a version of this game. I adjusted the radio to work well with a David Clarke non adjustable mic. Then I adjusted the mic on a Lightspeed to match. While the light speed uses batteries to power the active noise suppression, I often did not have batteries in it and the mic worked fine anyway. I'm suspicious of the claim that the adjustable mic needs a separate power source. All radios feed a DC bias voltage to the mic anyway. Makes little sense to me that any would need additional power. I'm sure others are more familiar with that but it would greatly curtail the usefulness of such a mic. I have found that the foam cover on the mic helps a bit but note that most mics also sense background noise from the backside so that they can cancel that out of the signal going to the radio. Makes me wonder if the film canister you mention would work all that well although it would certainly reduce the signal strength. Ken On 15/05/2013 3:38 AM, Holger Selover-Stephan wrote: > Hi all, > > I seem to have a microphone gain tuning problem on the second DIY > headset, following these instructions: > > http://n999za.com/2011/02/04/roll-your-own-in-ear-headset/ > > For the first headset I slaughtered an old GA headset and used its wires > and microphone. Works beautifully. Now on the second headset I am using > new shielded wires and this microphone (packed into a wind screen): > > http://store.acousticom.com/m7a-amplified-electret?keyword=5720-CA&category_id=0&description=1&model=1 > > The microphone is now overly sensitive and picks up everything. In a > quiet environment, my transmissions are crystal clear, but in flight the > surrounding noise pretty much drowns out my voice. I tried it with two > radios: an ICOM IC-A6 (on the ground) and in the air with a KX-135A > through an RST 422 intercom. In the hangar with everything quiet but a > radio playing soft music 20 feet away that music makes it into the > transmissions. > > Since I bought the microphone new, I asked the vendor, and Joel writes back: > > /What you will need to do is adjust the microphone gain control within > your radio to adjust it to fit the microphone properly. All radios are > different and require proper tuning when replacing the microphone. > Please refer to your radio's manual for adjustment procedures. > > We do sell a microphone that allows you to tune the microphone with a > screwdriver. This is a common occurence that microphones need to be > adjusted to the radios to perform properly. Your mic currently is set > too high in sensitivity/gain./ > > I can see how the combination radio and microphone needs to be tuned, I > don't want to tune the radio to just this new microphone, and thus make > all other headsets unusable in my plane. > > Their adjustable gain microphones apparently need a 9V power supply - > not ideal. > > Should I try this trick posted to this group a while back: > > /Got a great idea from somebody, and the cost is free! Get the plastic 35mm/ > /film containers. Cut an "X" in the lid and slide it on the mic arm. Then/ > /wrap some foam around the mic and slide on the 35mm can after you have/ > /drilled a 1/4" hole in the side. Line up the hole with your mouth. Better/ > /than sliced bread. Just keep the hole tight against your mouth to keep out/ > /engine noise./ > /My engine noise keeps my intercom open, but makes for a pleasant ride with/ > /me as the tour guide./ > /walt evans/ > /NX140DL/ > /=============/ > /Oscar Zuniga/ > /Medford, OR/ > /Air Camper NX41CC "Scout"/ > /A75 power / > > But this probably addresses mostly wind noise, and I'm in an all > enclosed cabin. > > Any other thoughts? > > Thanks! > > Holger > > * > > > * > ________________________________ Message 3 _____________________________________ Time: 08:02:07 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Microphone gain tuning > >I have found that the foam cover on the mic >helps a bit but note that most mics also sense >background noise from the backside so that they >can cancel that out of the signal going to the >radio. Makes me wonder if the film canister you >mention would work all that well although it >would certainly reduce the signal strength. >Ken Porous envelops and enclosures are simple attenuators of sounds. They can also present tailored effects upon the frequencies of sound allowed to pass. A 'noise canceling microphone' is another critter entirely. The following is purloined from Wikipedia: The development is a special case of the differential microphone topology most commonly used to achieve directionality. All such microphones have at least two ports through which sound enters; a front port normally oriented toward the desired sound and another port that's more distant. The microphone's diaphragm is placed between the two ports; sound arriving from an ambient sound field reaches both ports more or less equally. Sound that's much closer to the front port than to the rear will make more of a pressure gradient between the front and back of the diaphragm, causing it to move more. The microphone's proximity effect is adjusted so that flat frequency response is achieved for sound sources very close to the front of the mic ' typically 1 to 3 cm. Sounds arriving from other angles are subject to steep midrange and bass rolloff. Commercially and militarily useful noise-canceling microphones have been made since the 1940s by Roanwell,[1][dead link] Electro-Voice and others. As you might guess, the mechanical differential microphone presents some real design problems that get more difficult as the size of the microphone is reduced. There are electrical differential configurations that simply places two identical microphones back to back amplified by circuits that balance the two signals against each other in opposite phase so as to achieve a degree of cancellation. Then, my speaking closely to one of the two cartridges, the differential balance is upset and the voice predominates over background noise. When we ran the airport, I had head-sets that could be loaned to renters. I did some tests with the various brands we had hanging on the pegs and found marked differences in their ability to reject background noise. David Clarks were always good . . . but a bit pricey compared to the Telex Echelon headsets that were about half the price and still quite effective in their ability to cancel noise and only $120 a pop in 1990 dollars. A note of caution about adding 'stuff' to the outside of a microphone . . . if it is a true noise-cancelling design, then adding external features may work against the original design goals for the product. If the mic is not noise-canceling design and achieves improvement of signal-to-noise ratio by proximity of the speaker's lips, then added features are less problematic . . . Foam socks are most useful in the reduction of wind noise . . . REALLY important for open-cockpit flight. But the nature of the foam's 'bubbles' can produce unexpected results. Use a 'sock' crafted by a supplier of microphones that is advertised for the reduction of wind noise. Balancing the ship's audio system to the differences between brands is a separate issue. Not all microphones are the same but as long as the airplane is fitted with two or more of the same model, those differences are a wash. >>We do sell a microphone that allows you to tune the microphone with a >>screwdriver. This is a common occurence that microphones need to be >>adjusted to the radios to perform properly. Your mic currently is set >>too high in sensitivity/gain./ >> >>I can see how the combination radio and microphone needs to be tuned, I >>don't want to tune the radio to just this new microphone, and thus make >>all other headsets unusable in my plane. EXACTLY. When dealing differences between microphones, the 'fix' is to attenuate the hotter microphones to a level consistent with the cooler ones. >>Their adjustable gain microphones apparently need a 9V power supply - >>not ideal. But the nature of the beast. If you want a mic with the greatest applicability in the market, you deliberately design for 'hot' and then provide controls for attenuating the mic down to system friendly levels. >>/Got a great idea from somebody, and the cost is free! Get the plastic 35mm/ >>/film containers. Cut an "X" in the lid and slide it on the mic arm. Then/ >>/wrap some foam around the mic and slide on the 35mm can after you have/ >>/drilled a 1/4" hole in the side. Line up the hole with your mouth. Better/ >>/than sliced bread. Just keep the hole tight against your mouth to keep out/ >>/engine noise./ What ever works for you . . . assessment of 'elegance' is in the eye of the beholder. There ARE electronic solutions transparent to the appearance of the thing hanging out in front of your face. Bob . . . ________________________________ Message 4 _____________________________________ Time: 09:26:44 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Microphone gain tuning > >http://store.acousticom.com/m7a-amplified-electret?keyword=5720-CA&category_id=0&description=1&model=1 > >The microphone is now overly sensitive and picks up everything. In a >quiet environment, my transmissions are crystal clear, but in flight >the surrounding noise pretty much drowns out my voice. I tried it >with two radios: an ICOM IC-A6 (on the ground) and in the air with a >KX-135A through an RST 422 intercom. In the hangar with everything >quiet but a radio playing soft music 20 feet away that music makes >it into the transmissions. > >Since I bought the microphone new, I asked the vendor, and Joel writes back: > >What you will need to do is adjust the microphone gain control >within your radio to adjust it to fit the microphone properly. All >radios are different and require proper tuning when replacing the >microphone. Please refer to your radio's manual for adjustment procedures. > >We do sell a microphone that allows you to tune the microphone with >a screwdriver. This is a common occurence that microphones need to >be adjusted to the radios to perform properly. Your mic currently is >set too high in sensitivity/gain. This off-the-shelf cartridge is a two-wire 'electret' device that contains what ever electronics are necessary to make it look like the legacy, radio-powered, aviation carbon microphone. You cannot reduce it's audio output with a potentiometer in it's leadwires. While the pot would indeed adjust the audio output FROM this device, it would adversely affect the DC power being conducted TO the device. You can place a resistor-capacitor network ACROSS the microphone's leads thusly. Emacs! Adjust the resistor value such that the microphone produces a signal commensurate with others in your system. The capacitor keeps the audio attenuator resistor from shunting the DC power. I'm guessing that a value in the 100 to 1000 ohm range will prove satisfactory. You might temporarily wire a potentiometer into the resistor's slot, adjust the pot for desired gain, then measure with ohmmeter. Substitute a fixed resistor of the appropriate value. Bob . . . ________________________________ Message 5 _____________________________________ Time: 10:30:14 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Re: Pre-oiler system controls At 01:20 PM 5/8/2013, you wrote: >Bob, > >Thanks for the prompt and informational response. >I agree with your concerns, and thank you for your interest. >My reasons for adding pump: >Accumulator is already installed on aircraft. >Accumulator will also provide transient protection from low oil >pressure during maneuvering. >Pump and plumbing will only add about 5 Lbs to gross weight. >The a/c is a Stewart 51, 500 HP, 2 pax (I weigh 150Lbs, my >Lady-Friend 130Lbs), minimal baggage capability. Therefore this >addition will barely be noticeable:) > >The pump and the valve are both simple on-off circuits. Is there a >wiring diagram in your book to show how to wire this switch? > >Thanks very much for your time and experience, >Neville You need a 2TL1-50 toggle switch http://tinyurl.com/azcswed wired thusly: Emacs! Emacs! Emacs! 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