---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Thu 05/16/13: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 12:47 AM - Re: Microphone gain tuning (Holger Selover-Stephan) 2. 12:53 AM - Re: Microphone gain tuning (D L Josephson) 3. 07:44 AM - Re: Microphone gain tuning (Robert L. Nuckolls, III) 4. 05:39 PM - Z13/8 all electric airplane (Mauri Morin) ________________________________ Message 1 _____________________________________ Time: 12:47:01 AM PST US Subject: Re: AeroElectric-List: Microphone gain tuning From: Holger Selover-Stephan Hi Bob, Ken, Many thanks for the very detailed explanation of the situation. A slap on the forehead is in order: I have covered up the front-facing side of the microphone, and thus might have disrupted the noise reduction mechanism. Interestingly, I mentioned this to the vendor, but it wasn't commented on in their response. Let me first run tests with the front side uncovered. Then try your resistor-capacitor network solution, Bob. I really like the simplicity of the latter, just what I was hoping to hear from you! I'll report back with further findings. Once this is figured out yet another DIY headset is going into production for the daughter. The pooch stays on Mutt Muffs as he rarely contributes anything useful to the conversation. Thanks again! Holger On May 15, 2013, at 9:25 AM, Robert L. Nuckolls, III wrote: > You can place a resistor-capacitor network ACROSS the > microphone's leads thusly. ________________________________ Message 2 _____________________________________ Time: 12:53:50 AM PST US From: D L Josephson Subject: Re: AeroElectric-List: Microphone gain tuning Nearly all noise-canceling microphones in aviation headsets these days (including the Acousticom mentioned) use a single diaphragm electret capsule with front and back ports just as described in the Wikipedia entry Bob quoted (I know, I wrote it...) There's a simple circuit, usually one or two transistors, to interface with the aircraft radio's carbon mic circuit, provide some gain, and power the FET in the electret mic. You need to be able to adjust the gain of this circuit. There is a version of this same mic, the Acousticom 5715, that is adjustable. It would really be better to get the adjustable version rather than try to kludge an attenuator. A resistor and capacitor across the mic output could cause some distortion, as the mic would then be loaded with a lower impedance than just the radio input. Trying to muffle the microphone with some thick material over it is seldom successful as the frequency response and noise cancelling properties will be altered significantly. -- David Josephson ________________________________ Message 3 _____________________________________ Time: 07:44:58 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Microphone gain tuning > > >A resistor and capacitor across the mic output could cause some >distortion, as the mic would then be loaded with a lower impedance >than just the radio input. I've not found this to be the case. The artificial lowering of radio input impedance has no non-linear contributions. The amplifiers common to electret- to-carbon interface are pretty high output impedance to begin with and 'adjustment' of loading to bring two microphones into agreement with each other is not severe. To be sure, having an adjustable mic cartridge is the ideal condition, but when a non-adjustable is what you have in hand, then a little 'jiggering' of the gain is a low risk experiment. >Trying to muffle the microphone with some thick material over it is >seldom successful as the frequency response and noise cancelling >properties will be altered significantly. To be sure, effective noise cancelling design is not a trivial task. Exploiting the designer's skills is not well served by altering the environment that the designer targeted. Even so, I've seen some wide variation in the levels of noise-cancelling success. I think the best cartridges I've ever encountered were the very low impedance, dynamic cartridges common to military headsets. We were working with aviation headsets and intercoms on the Cessna O2A and T41 programs back about 1968. I did a dynamic-to-carbon interface module to connect the military mic to a 121.5 emergency transceiver on the T41. Those were VERY good microphones but with an output in the 1-2 millivolt range. An interesting task. Bob . . . ________________________________ Message 4 _____________________________________ Time: 05:39:53 PM PST US From: "Mauri Morin" Subject: AeroElectric-List: Z13/8 all electric airplane Bob, I'm using your Z-13/8 diagram wiring my RV-8 and want to use a CB Switch combo to replace the individual circuit breaker and switch for the AUX ALT ON/OFF SWITCH. The circuit breaker has two terminals labeled line & load. Which one do I hook to GND? Mauri Morin ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.