<div>The formula is:</div> <div> </div> <div>20 * Log ( d1 / d2)</div> <div> </div> <div>where d1 and d2 are the distances involved, and "log" is log base 10 (not the natural log).</div> <div> </div> <div>For 10ft and 25ft, the difference should be close to 8 dB, assuming no effects from nearby reflecting objects, (like the ground!). :-) Doubling the distance changes the level by 6dB.</div> <div> </div> <div>A club I belonged to years ago instituted a noise rule. Some planes would not pass on the ground, but were quiet in the air. Part of that problem was due to some propellers being stalled on the ground, particularly planes with very high pitched props. We had limited success with trying to measure the in-flight noise, with the pilot flying over the centerline of the runway at full throttle. We extrapolated the noise limit using the formula above, and did get correlation with some models. OTOH, there are the models that unload in the air
and the prop tips start developing shock waves, making that classic giant-scale OOOOOWWWWAAAAAAAHHHHHH sound that some people think is the whole point of flying giant scale. They are much more of a problem in the air than what any sound reading on the ground may indicate.</div> <div> </div> <div>While it is important to the future of model aviation, sound rules are a real PITA to enforce.</div> <div> </div> <div>Bob R.<BR><BR><B><I>Joe Lachowski <jlachow@hotmail.com></I></B> wrote:</div> <BLOCKQUOTE class=replbq style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px solid">>From what I measured a quite a while ago, I believe the equivalent at 25 ft <BR>to that at 10ft is about a 7db difference.<BR><BR><BR>>From: "Lance Van Nostrand" <PATTERNDUDE@COMCAST.NET><BR>>Reply-To: NSRCA Mailing List <NSRCA-DISCUSSION@LISTS.NSRCA.ORG><BR>>To: "NSRCA Mailing List" <NSRCA-DISCUSSION@LISTS.NSRCA.ORG><BR>>Subject: Re: [NSRCA-discussion]
Noise rules<BR>>Date: Wed, 21 Jun 2006 22:53:36 -0500<BR>><BR>>I'm not sure if there may be a perception that measuring at 25 feet is <BR>>somehow more palatable than at 10 ft. If this is the feeling in your club <BR>>then go for it. However, I know from experience that all influences on the <BR>>measured result (wind, hard/grass, fences, proximity to a covered pit echo <BR>>chamber, cars, etc) are exponentially amplified with distance. I measured <BR>>the same Extra330 with a large gas engine in every way possible and found <BR>>the results varied from 101-105 db. This is a huge variation. <BR>>Upwind/downwind in about 10 mph winds is worth 2-3 db. At 10 ft the <BR>>variation was from 102-103 db. If you have a guy with a plane near the <BR>>limit he may argue your measurement result. If you say the lmit is the <BR>>highest value measured then you are really restricting some guys with loud <BR>>planes to less than the nominal. If
you provide leeway, then your limit is <BR>>effectively raised. It opens a can of worms.<BR>><BR>>Lance<BR>> ----- Original Message -----<BR>> From: Glen Watson<BR>> To: 'NSRCA Mailing List'<BR>> Sent: Monday, June 19, 2006 10:52 PM<BR>> Subject: Re: [NSRCA-discussion] Noise rules<BR>><BR>><BR>> Links below are to a RC club in the Houston market who implemented a <BR>>noise standard.. My club has adopted the same standard. In 2004 we had <BR>>complaints from a nearby neighbor regarding noise. Since implementing this <BR>>noise standard we've had zero complaints.<BR>><BR>><BR>><BR>> http://fortbendrc.com/<BR>><BR>><BR>><BR>> http://fortbendrc.com/Field/Field%20Noiselevel.htm<BR>><BR>><BR>><BR>> Regards,<BR>><BR>><BR>><BR>>
~Glen<BR>><BR>><BR>><BR>><BR>><BR>><BR>><BR>><BR>>------------------------------------------------------------------------------<BR>><BR>> From: nsrca-discussion-bounces@lists.nsrca.org <BR>>[mailto:nsrca-discussion-bounces@lists.nsrca.org] On Behalf Of John Ferrell<BR>> Sent: Monday, June 19, 2006 8:09 PM<BR>> To: NSRCA Mailing List<BR>> Subject: [NSRCA-discussion] Noise rules<BR>><BR>><BR>><BR>> If someone out there has a set of noise rules for a general purpose RC <BR>>club? Especially a set that works.<BR>><BR>><BR>><BR>> I cannot expect the masses to conform to pattern numbers, but I need <BR>>something to start with. "Reasonable" does not seem to mean the same thing <BR>>to every one.<BR>><BR>><BR>><BR>><BR>><BR>> John Ferrell W8CCW<BR>> "My Competition is not my enemy"<BR>>
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