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Noise measuring

Old 09-09-2008, 03:31 PM
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lamarrc
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Default Noise measuring

What is the normal ambient noise level is various flying fields?
Old 09-09-2008, 09:45 PM
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flyfisher431
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Default RE: Noise measuring

That is a very interesting question. Are you running afoul of a group like our club did?

see http://www.rcuniverse.com/forum/m_70..._1/key_/tm.htm

Abient noise is very subjective. If the flying field is located in a remote rural area it can be very low. So low that the mere act of talking will raise the noise level 15 to 20 db.

Ben
Old 09-09-2008, 10:03 PM
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CoosBayLumber
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Default RE: Noise measuring

Although you mention "Flying Field" not mention as to if anything is in the air, people around, autos moving, being near to what type of a highway. I have done urban planning and that is the sort of facts that have to do into a report, before quoting any levels.

Thus your known "ambiant" noise level could be anything from 10 to 45 in background, depending upon the area and the conditions.


Wm.
Old 09-10-2008, 05:29 AM
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bkdavy
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Default RE: Noise measuring

We measured noise levels at our field last year in anticipation of new noise regulations by the county. Just standing in the pit area, no oplanes running, no one talking, we had levels around 55-60 db. We're approximately 1/2 mile from a 4 lane highway, and on the approach path for Dulles and Baltimore Washington International Airports. For reference, 60-65 db is considered a normal conversational level.

Brad
Old 09-10-2008, 06:00 AM
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da Rock
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Default RE: Noise measuring

I believe there are guidelines for judging the loudness of a single model, and it's with the model on the ground (and what kind of ground cover is specified, I think) and at a specific distance from the model and in a specific orientation to the model.

And I think their threshold is in the 90s.

I think both the pattern boys and the IMAC guys have recommendations published, or did have 'em at one time. Anybody know for sure?
Old 09-10-2008, 08:01 AM
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Red B.
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Default RE: Noise measuring

For F3A (internatianal aerobatic competition class) the following noise limit applies:

"The maximum sound/noise level of the model aircraft and its propulsion device, shall be 94 dB(A)
measured at 3m from the centre line of the model aircraft with the model aircraft placed on the
ground over concrete, macadam, grass, or bare earth at the flight line.

The tolerance of the sound/noise level measurement, is the specified tolerance of the manufacturer
of the measuring instrument.

With the propulsion device running at full power, the measurement will be taken 90 degrees on the
right-hand side, with the nose of the model aircraft pointing into the wind. The Class 1 SLM (Sound
Level Meter) microphone shall be placed on a stand 30cm above the ground in line with the
propulsion device Other than the helper restraining the model aircraft, and the sound steward, no
persons or sound/noise reflecting or sound absorbing objects shall be nearer than 3m to the model
aircraft or the microphone. The sound/noise measurement shall be made immediately prior to each
flight. The sound test area must be located in a position that does not create a safety hazard to
officials and other competitors." (Source: [link=ftp://www.fai.org/sporting_code/sc4/sc4_f3_aerobatics_08.zip]FAI Sporting Code F3A[/link])
Old 09-10-2008, 09:32 AM
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lamarrc
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Default RE: Noise measuring

Thanks for the replies. I am working on project where we are measuring the amount of noise generated by propellers. We just want to get an idea of what the lowest possible ambient noise could be. Where we have been testing, the ambient noise ranges from 50-60 dB and and we feel that this could be too high.
Old 09-10-2008, 10:18 AM
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David Bathe
 
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Default RE: Noise measuring

If you follow the FAI advice suggested by Red B (and why not as it's the definitive competition method) and stay with that sound level you'll end up with a very quiet model.
Every F3A plane I've seen in competition has been VERY quite compared to even the quietest models used a club level. My planes often appear completely silent during vertical flight at the ends of the box. This can be somewhat concerning as the only indication that the engine is running is the exhaust smoke!
What you'll experience is that different propeller produce a great deal of difference in the noise level. Brand to brand and pitch to pitch.
Also a great deal of ambient noise that you hear is generated by the airframe and not the engine. Wheels, push rods rattling etc. beleive me, you'd be seriously surprized just how much you can quiet'en down a model by changing to a tight set of wheels!
Do what Reb B said. Don't experiment with other methods of measuring. That's the one.
Old 09-10-2008, 10:51 AM
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Red B.
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Default RE: Noise measuring

ORIGINAL: lamarrc

Thanks for the replies. I am working on project where we are measuring the amount of noise generated by propellers. We just want to get an idea of what the lowest possible ambient noise could be. Where we have been testing, the ambient noise ranges from 50-60 dB and and we feel that this could be too high.
Are you concerned that the ambient noise will affect the result when measuring aircraft noise?

IMHO this is not a problem because sound is measured on a logaritmic scale. The sound intensity associated with a sound intensity level of 60 dB is 1000 times lower than the sound intensity associated with a sound intensity level of 90 dB.

In practice this means that if an aircraft gives a reading of 90.0 dB in an absolutely quiet surrounding, the reading will still be 90.0dB if measured in in a surrounding where the ambient noise level is 60dB. In theory the difference in readings would be 0.043dB, which is much less than the uncertainty of the measurement.

FYI, I did a quick and dirty calculation that may be of some help when correcting measurements for ambient noise (see figure below). Make two measurements, engine on (A) and engine off (B). Calculate the difference (A-B) and find that value on the horizontal axis of the diagram. Use the graph to find the corresponding correction. The difference (A - correction) is the approximate noise level of the engine. An example: If the reading with the engine running is 95 dB and the reading with the engine shut off is 88 dB, the difference is (95-88)dB=7dB and according to the figure below the correction is approx 1dB. Then the noise level of the engine is (95-1)dB = 94dB.

Edit: Added a figure
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Old 09-10-2008, 03:27 PM
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TexasAirBoss
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Default RE: Noise measuring

Years ago, there was some standard mentioned in the industry. Glow engines with mufflers should be no louder than 90db at 3 meters. I haven't heard that standard mentioned in years. I forget where it came from. And I don't know if exists today.
Old 03-21-2009, 07:26 PM
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mmiller1
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Default RE: Noise measuring

I am interested in casting a net out their regarding noise limitations. I have read some topics on this topic in RCU as well as having conversations with AMA. As I understand it the 3 meter standard at 30 cm off the ground with measuring devise pointed perp. to the fuse a reading of no more than 96dB should be the limit. Greg Hahn with AMA indicated to me in an e-mail that those figures are correct for contests sanctioned by AMA. He did suggest that clubs may have a revision to this dB reading at 25 feet. However, each club needs to evaluation its location in relation to the surrounding area. The club in Choachella Valley (near P.S.) is very far away from any housing and is probably not a big issue.
According to Greg Hahn (AMA) they are taking up this issue and should have some information(re-evaluation?) by the end of the year. The real folks that should be helping us out is the manufacturers. But they have concerns with keeping costs down. I think that is not savy. I can't think of any club member that wold not be willing to pay a bit more for an engine if it meant losing their flying site. I also understand there are some after market mufflers that are available, but thus far I have not seen a web page for them. I actually have not looked to hard, either. If someone has opinions on this topic, suggestons, after market makers of mufflers for glow and gas, that would be a start. It would be helpful for as many members to joing in on this topic so keeping our flying sites does not become an issue.
I am all ears.
Tim in Tacoma

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