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01-27-2006, 08:47 AM | #11 |
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What is a fair test for in the air sound levels. It would seem the frequency plays as big a part as DB ratings?
For example: A DA-50 with a can muffler sounds much quieter than a 2 stroke with a lower static DB rating. In this example it seems unfair to ground the DA-50 because the static test was higher. Electrics can be loud but also seem to have a lower frequency. For you smart engineering guys the question is: Does Higher frequency sound travel farther?
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01-27-2006, 09:36 AM | #12 |
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Just me two cents but I think noise requirements are rediculous. A lawn mower is just as loud and you should hear the traffic noise behind my house. That's constant. I also should mention the Cessnas that fly over my house with no mufflers. What's so bad about our little engines while the others don't seem to count?
Fortunately the field I fly at is near a busy street corner so noise isn't a concern except on Sundays, due to a near by church. I fear that once the houses creep up, that's going to change. *-ing developers.
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01-27-2006, 09:37 AM | #13 |
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Here is a condensed version material submitted as part of a re-zoning application concerning the effects of distance and frequency on noise intensity.
Attenuation of sound waves Sound waves that spread into the atmosphere loose more of their intensity, i.e. the sound amplitude decreases. One reason is the geometrical spreading since the emitted sound energy is distributed over a larger and larger volume. Therefore the local sound energy flux (sound intensity) decreases with growing distance. If the sound originates from a point source (e.g. a single car), the waves are spherical and spread into all directions. In this case the sound level reduces by 6 dB as the distance from the source doubles. If, on the other hand, the sound originates from a line source (e.g. a busy road), the waves are cylindrical and the sound level reduces only by 3 dB as the distance from the source doubles. A further effect that leads to an attenuation of sound pressure is the atmospheric absorption. As the sound waves propagate through the air, sound energy is lost due to friction between air molecules and because of further properties of the molecules. This loss depends on the air temperature und humidity. High frequencies are much more affected by atmospheric absoprtion than low frequencies. Therefore, one can hear only the bass tones at greater distance from an open air concert. Attenuation by air absorption at 20 °C and 70 % relative humidity (after ISO 9613-2) 125 Hz 0,3 dB/km 250 Hz 1,1 dB/km 500 Hz 2,8 dB/km 1000 Hz 5,0 dB/km 2000 Hz 9,0 dB/km 8000 Hz 76,6 dB/ As can be seen from the table immediately above, frequency does have a profound effect on sound level attenuation. What may sound loud and/or irritating at close range may be practically inaudible at distance. An on line distance to noise calculator is available at: http://www.mcsquared.com/dbframe.htm (This calculator does not include the effects of frequency). Dennis
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01-27-2006, 09:54 AM | #14 | |
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Quote:
My glow powered 1.4 pattern model spining a 16x13 prop @ 8200 rpm tested 89-90 dB @ 3 meters.....my electric powered pattern model spinning a 21x13W at 5900 rpm measured 92-93dB @ 3 meters.....however you cant hear the electric in flight, and the glow retains a lot of its noise during the ground test the electric is just replacing engine noise with prop noise. I have seen changes of 5-6 dB from a windy day testing to a calm day....so its really tough to get decent ground test results unless everyone is tested on the same day. Lowering the diameter and upping the pitch, combined with a good muffler and flying with the appropriate throttle setting for the manuver will have significant impacts to the amount of inflight noise generated. Using low pitch big diameter props, which is very commonly done is about the worst thing you can do if you have a noise problem. @ 6 meters a modern pattern model would be down into the mid to low 80 dB's.....all of them have not lost an inch of performance It can be done if you want to. |
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01-27-2006, 11:24 AM | #15 | |
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Quote:
We had a couple show up at the feild last year and you sure couldn't hear any airplanes..... Paul
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01-27-2006, 11:29 AM | #16 |
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What Chad said about props has more effect than many realize. Once you start talking about exhausts, a more integrated approach needs to be taken. A good example is the YS engines with the muffled pipes in the tunnel - lots of time has been spent here to come up with a specific combination of engine/header/pipe that produces excellent results.
Also, I bought one of these for a ZDZ 80 to improve performance: http://www.rcshowcase.com/html/acces...carbitems.html What I found is not only better performance but also lower noise!!! It's amazing how much noise from a gas 2 stroke comes from the intake. ON this set-up I had a CF prop and a Bisson pitts style muffler. Paul
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01-27-2006, 07:10 PM | #17 |
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Thanks for all the input so far. This is stressing me out I lost sleep last night. I love my toy airplanes and want to fly them. So while construction noise will mask us from the new neighbors for this season, after that
The opinion expressed about people make more noise with there lawn mowers is true, but it is also acceptable noise. If you bought a $450 - $750,000 house on a new golf coarse would you put up with model aircraft noise 10hrs a day on the weekend?
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01-27-2006, 07:19 PM | #18 | |
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Dont stress...it will all work out Just be proactive and demonstrate that you are making the effort...and hopefully all will understand. I think a lot of clubs have found that making good relationships with neighbours through invitations to the field etc goes a long way to improving their tolerance level!! |
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01-27-2006, 07:53 PM | #19 | ||
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01-27-2006, 08:07 PM | #20 |
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I posted this at All E Flite some time ago...
Some further thoughts on model noise. The sound of a model engine is quite tonal (a few select frequencies dominate) and not broadband (like pink or white noise). Tonals are more prominently percieved by the human ear. The human ear has a very characteristic (and un-flat) frequency sensitivity. The Fletcher-Munson equal loudness contours attempt to quantify this. For example, In order to block out what would normally be a very annoying amount of body noise (beating heart, thumps from walking etc.) human hearing is very insensitive to low intensity low frequency sound. See http://www.norsonic.com/web_pages/correlation.html . By nature, human senses are more sensitive to change than steady state. Stare at one spot in a picture long enough and the whole picture eventually dissappears. This is no less true of sound. Steady state sound is easier to ignore. The siren of an emergency vehicle with its varying pitch is more effective at attracting our attention. In my opinion, the characteristics described above make the sound of model airplanes unwanted noise to more people. A small two-stroke IC engine produces most of its acoustic energy in the form of tonals in the frequency range the human ear is most sensitive to. As the throttle setting changes and the loading on the prop changes in flight the RPM and consequently the frequency of sound produced by the engine changes. Add to this that the model is moving at high speed and in the human brain this is perceived as additional change in the form of directional information processed by the brain. Electric models are not immune to making "annoying" sounds. As an example, (and no offense to Zagi pilots!) but a Zagi with its prop next to the trailing edge of the wing generates a considerable amount of tonal energy. Fortunately, it isn't particularly loud by measurement, but is the same type of noise described above that loses flying fields. In contrast, a lawnmower engine is lower in pitch, relatively constant in pitch, relatively constant in position (or at least, slow moving) and is a socially accepted necessity of suburban living. The attitude that "my neighbour's lawnmower is just as loud as my model so I have every right to fly my model" doesn't hold water when the above factors are considered. Rob |
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