Runtoeat Posted July 31, 2014 Report Share Posted July 31, 2014 Hi Anticept. We're both saying the same thing. An easier way might be to think this way. A 4 cylinder 4 cycle engine has two firings per revolution. Each revolution, two cylinders will go into compression then fire while the other two will exhaust then intake. Revs/minute divided by 60 = revs/sec. Times 2 = firing pulses per each revolution. 5250 divided by 60 = 87.5 which is 1st order rotational frequency. Multiply this by 2 to get engine firing (2nd order rotational) frequency. 87.5 X 2 = 175 hz. This is the excitation frequency caused by engine firing. Link to comment Share on other sites More sharing options...
FredG Posted July 31, 2014 Report Share Posted July 31, 2014 Dick, NIOSH recommends that whatever the passive attenuation rating, first assume only 75% true effect (fit, real world, etc). Then, subtract 7 dB from that value (a conversion from dBC to dBA), then use the final value for the actual decrease from ambient. An example, Suppose passive attenuation for a headset is 24 dB and ambient sound is 90 dB. First, take 75% of 24 dB, which would be 18 dB. From that value, subtract 7 dB, which results in 11 dB. Using that headset would result in exposure to 90 dB - 11 dB, for a value of 79 dB. Active noise reduction headsets are more complicated and may need simultaneous sound measurement inside the ear cup and outside the ear cup. Fred Link to comment Share on other sites More sharing options...
Anticept Posted August 1, 2014 Report Share Posted August 1, 2014 Hi Anticept. We're both saying the same thing. An easier way might be to think this way. A 4 cylinder 4 cycle engine has two firings per revolution. Each revolution, two cylinders will go into compression then fire while the other two will exhaust then intake. Revs/sec divided by 60 = revs/sec. Times 2 = firing pulses per each revolution. 5250 divided by 60 = 87.5 which is 1st order rotational frequency. Multiply this by 2 to get engine firing (2nd order rotational) frequency. 87.5 X 2 = 175 hz. This is the excitation frequency caused by engine firing. Yeah I looked over what we said and agree! Where we differed was you said 2 pulses per rev, I said 2 rotations per firing. You said dark, I said absence of light. Link to comment Share on other sites More sharing options...
Runtoeat Posted August 1, 2014 Report Share Posted August 1, 2014 Fred G, thanks for the info on headset attenuation measurement. It looks like using a set of ear plugs for added sound attenuation in combination with passive noise cancelling headphones may be warranted for those who run their Rotax engine at max throttle most of the time. This discussion made me wonder how my A20 stacks up for sound attenuation. I looked for attenuation specs for Bose A20 but could not find any. One would think that Bose would provide this information if it truly feels their headset offers better attenuation than the competition. Link to comment Share on other sites More sharing options...
FredG Posted August 1, 2014 Report Share Posted August 1, 2014 Dick, I'm also curious about the A20 headset. If you find anything, please post it on the forum. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted August 4, 2014 Report Share Posted August 4, 2014 I usually use a Zulu headset. The other day a friend gave me a ride in his Avid Flyer with a Rotax 582 (cruise RPM is 6000!). I snatched the passenger headset from the CT for the trip, which is a non-ANR MGL Avionics headset. Holy smokes, that was loud. I might need a Sierra or other ANR for my passengers, so I don't subject them to that kind of noise in my airplane. That much noise really lessens the joy of flying. Link to comment Share on other sites More sharing options...
FredG Posted August 5, 2014 Report Share Posted August 5, 2014 Hi Andy. I took the plunge and got ANR for my passengers. I think it improves the quality of their flying experience. Link to comment Share on other sites More sharing options...
Runtoeat Posted August 5, 2014 Report Share Posted August 5, 2014 Agree that ANR greatly improves the flight experience. I might look into playing with the earbud ANR setup I linked earlier in this thread. I've got a reconditioned pair of David Clark's that would be nice to set up with this. For $100 + shipping, it would be a low cost way to get a second ANR headset for my CT. Link to comment Share on other sites More sharing options...
Jim Meade Posted August 5, 2014 Report Share Posted August 5, 2014 Earbuds and short flights. Earbuds and passengers unfamiliar with using them. A couple of reasons to have a conventional ear muff headset around if only for contingencies. Not saying conventional is better, just saying they might be more familiar to an occasional guest. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted August 5, 2014 Report Share Posted August 5, 2014 Hi Andy. I took the plunge and got ANR for my passengers. I think it improves the quality of their flying experience. When I got the airplane my wife bought her own Zulu 2, so she's covered, but that is HER headset...all my airport bum friends have to use the MGL. I will probably spring for a basic pax ANR once the sting of my recent autopilot install subsides. Link to comment Share on other sites More sharing options...
Runtoeat Posted August 5, 2014 Report Share Posted August 5, 2014 Considered usage of the earbuds being a hassle. My plan was to let passenger use my Bose and I'd use the earbud setup, if I ever get around to trying this. Plan B is to win the lottery, get a new CTLSi which comes with dual Bose A20's. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted August 5, 2014 Report Share Posted August 5, 2014 I would not ask a pax to use an earbud-type headset that might have been in somebody else's ears. Link to comment Share on other sites More sharing options...
Tom Baker Posted August 5, 2014 Report Share Posted August 5, 2014 I think I have a ANR noise cancelling kit that can used to convert a older David Clark or DC clone headset, that I would sell cheap. I used to use one and they did pretty good job. They work even better with gel ear seals. Link to comment Share on other sites More sharing options...
Anticept Posted August 5, 2014 Report Share Posted August 5, 2014 Anyone know of a noise canceling in-ine device? I am kind of thinking about something that i can include in my plane for renters to use with their cheap headsets Link to comment Share on other sites More sharing options...
Tom Baker Posted August 5, 2014 Report Share Posted August 5, 2014 Anyone know of a noise canceling in-ine device? I am kind of thinking about something that i can include in my plane for renters to use with their cheap headsets I don't know of any. I think most sample noise inside the headset to provide the cancelling solution. Link to comment Share on other sites More sharing options...
Anticept Posted August 5, 2014 Report Share Posted August 5, 2014 I don't know of any. I think most sample noise inside the headset to provide the cancelling solution. I would think that would cause a feedback loop. Then again if you know what sounds you are compensating for, you can include the sound solution in an exclusion algorithm to prevent it from creating the loop. I should research the subject. Link to comment Share on other sites More sharing options...
Doug G. Posted August 5, 2014 Report Share Posted August 5, 2014 I know the PFX samples inside and outside the muff plus both sides of the boom mic. Link to comment Share on other sites More sharing options...
Znurtdog Posted August 5, 2014 Report Share Posted August 5, 2014 I use QT Halo ear buds and love them. My Zulu II's are for pax only. And if I'm feeling decadent I'll put the Zulus over the QT's. Now THATS quiet. Link to comment Share on other sites More sharing options...
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