---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Tue 10/04/11: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 07:37 AM - Audio systems and "output impedance" (Robert L. Nuckolls, III) 2. 03:45 PM - Headsets Redux-was "Warning - New Bose Line Power Cable (jonlaury) ________________________________ Message 1 _____________________________________ Time: 07:37:55 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Audio systems and "output impedance" At 10:53 PM 10/3/2011, a reader wrote: >Bob, the audio out on this beast is rated at 500 ohms. I don't >think my Bose headsets are the same? What's the best way of tying >this into my audio system, I have a cheap aviar intercom I was >planning on using but open to suggestions? I also have your Audio >Isolation amplifier. See the description of audio systems and the concept of 'output impedance' in the audio chapter of The Connection. There's not a single audio device with a real output impedance of 500 ohms . . . or any similar value. By definition, a source of energy with an output impedance of 500 ohms would see a drop in output by 50% when loaded with a 500 ohm headset. Two such headsets in parallel would drop the output further to 33%. So when an audio output is 'rated' for 100 mW into 500 ohms, they're only speaking to the ability of the amplifier to deliver a VOLTAGE along with a citation as to POWER delivered into a typical load. Interestingly enough, the same output, when presented with TWO headsets of load would deliver 200 mW. My audio isolation amplifier has an output impedance of less than 1 ohm . . . but it's capable of delivering about 8 volts pk-pk into what ever load you wish to tie onto it. The smaller the resistance . . . the higher the current . . . the higher the power. Further, because the true output impedance is so low, you can drive 1, 2 or 10 headsets with no perceivable drop in ouput. Your radio(s) and intercom are similarly configured. Just know that the term "output impedance" is quite often used in a manner that does not contribute to understanding. Bob . . . Bob . . . ________________________________ Message 2 _____________________________________ Time: 03:45:23 PM PST US Subject: AeroElectric-List: Headsets Redux-was "Warning - New Bose Line Power Cable From: "jonlaury" Bought 2 pairs of Beyerdynamic HS 800 headsets by 8/31/11 to make it through the $200/set trade-in window they offered. Got the BD's and they are a very nice German-built headset. In the back of my mind, I figured that I would go through the motions of due diligence comparison and probably buy Bose, then return the BD HS 800's in the 30 day trial period. I went to a Bose store to compare headsets with the Bose display simulating cockpit noise in a single engine piston plane. First, the Bose earcups were not as generous as the BD cups and were more difficult to get a good seal. I did manage to get them on correctly. I felt that the Bose head band was awkward in using a multi-segment, pivoting mechanism and it didn't feel secure on my noggin, and caused doubt about it's ability to stay on if encountering heavy turbulence or rapid head movement. The BD uses a traditional spring steel type band, with slightly more clamp pressure than Bose and felt very secure on my head. Inspite of Bose specs claiming lighter weight by an ounce, the BD felt lighter when wearing it. The BD earcup seals also seem to seal around my wire frame sunglasses more effectively than the Bose. The actual noise reduction comparison was interesting. When switching back and forth between brands with the simulated noise on, the Bose was obviously quieter...initially. After doing this a few times, I noticed that when the BD's were on for about 3-4 seconds, the noise attenuation would increase from the initial covering of my ears. BD calls their system Digital Adaptive NR and I attribute the attenuation lag to that "adaptive" feature. Once internal earcup sensors adapted to the particular frequencies being sensed and subsequently reduced the sound level, I found the sound of the BD's more natural than the Bose. The Bose had less sound, but I found that I prefer a little aural feedback. The sound level difference between the two is pretty minor, but detectable and in favor of Bose. To explain what I mean by aural feedback, I can give you the analog of my choice in cars. When I was deciding brand and model the last time I bought one, I chose one that gave me more road feel at the expense of minor cabin noise. I found that driving a car that isolated me from the road, both in feel through the steering wheel and tomb-like quiet in the cabin, made me slightly nauseous, and imparted the feeling of a slight lack of control over the car. Moving on, the BD electrical cording is high quality and about 6' long. The audio box is about the same size as Bose but much simpler and BD provides the various adapters for music players and cellphones to plug right in to the audio box. I confess that I don't use a cell phone much and I hardly think of an aircraft cockpit as a concert hall, so having Bluetooth is not much of a selling point for me. After my brief comparison, I'd opt for the BD's even without the $200/headset trade-in for my 24 year old DC's. With it, it was a no-brainer. Thanks to Gerry Van Dyk for turning me on to the BD's John Read this topic online here: http://forums.matronics.com/viewtopic.php?p=354062#354062 ------------------------------------------------------------------------------------- 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.