sound meter

[David Lockhart]

To me, the bottom line on the current noise rule (largely unchanged since
introduced) is that we no longer have 105 db planes that offend the
neighbors.  And from my experience over the past 15 years working with
"quiet" setups - an honest 94 db on pavement is not that difficult to
achieve.

In practice, application of the noise rule is not without problems - but it
is not that difficult to copy setups that are known to be quiet, and
following some basic rules of thumb will keep the noise under the limit -
and avoid noise test failures at major contests.

The last thing I would want to see is a shift from a quantitative noise
measurement to a qualitative noise measurement - I'd hate to see placement
in a contest determined by a bonus or penalty assigned by a judge to a plane
that sounded "nice" or "loud" - especially considering the relatively
uncontrolled background noise present at most contests (other planes in air,
engines running in the pits, etc).

Regards,

Dave Lockhart
DaveL322 at comcast.net




----- Original Message -----
From: "Adam Glatt" <adam.g at sasktel.net>
To: <discussion at nsrca.org>
Sent: Monday, April 26, 2004 3:44 PM
Subject: Re: sound meter


> Earl Haury wrote:
>
> > Generally even the sound meter calibrators are +- 0.5 dB. Makes the
> > flight zero for >94 (F3A) really a tough rule (even flying behind the
> > flight line only zero's the maneuver)! Albeit, a fail isn't official
> > until verified by a second meter - but generally both are calibrated
> > with the same device, so the calibrator offset will be present at both
> > meters. Calibrator equipment itself should be re-certified pretty
> > often (yearly), want to bet when the Nats equipment was last certified?
> >
> > The only way to be sure is to use known accuracy equipment and target
> > a number that allows for equipment variance. The air density at the
> > time you make measurements will vary the results also, both from an
> > engine output (more/less rpm) and a sound transmission standpoint.
> > This can amount to a couple of dB, and the Muncie site is usually
> > better air density than soggy Houston - so the noise measured is
> > higher in Muncie. Again, allow for this in your noise plan.
> >
> > The good news is that the Nats meters seem to be on the liberal side
> > and the display is analog - making it difficult to discern the
> > difference between 94 and 94.xx. Also the 96 dB AMA limit is much
> > easier to attain and the penalty for missing a little not too bad.
> >
> > Earl
>
> Good idea, but terrible rule.  They should give a 5% score penalty to
> the noisiest 10% of planes in a class (either by ear or by sound meter),
> imo.  Measuring a plane on the ground, with someone holding it, people
> standing around, wind blowing, and the prop a few inches from the
> ground, and from a distance that doesn't represent the problem of noise
> (i.e. Shulman's electric being one of the loudest planes on the meter
> due to low clearance and gear box noise, but one of the quietest in the
> air) is a dumb way to do it.  The only noise that matters is what we
> hear while the plane is in the air.
>
> It was obvious in Poland the FAI officials knew the sound rule was
> implemented wrong, as well.
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