Sound Level meter requirements

[Dean Pappas]

Here's an excerpt from the FAI Sporting Code.

The maximum noise level will be 94 dB(A) measured at 3 m from the centre line of the model aircraft with the
model aircraft placed on the ground over concrete or macadam at the flying site. With the motor running at full
power measurement will be taken 90 degrees to the flight path on the right hand side and downwind from the
model aircraft. The microphone will be placed on a stand 30 cm above the ground in line with the motor. No
noise reflecting objects shall be nearer than 3 m to the model aircraft or microphone. The noise measurement
will be made prior to each flight. If a concrete or macadam surface is not available then the measurement may
be taken over bare earth or very short grass in which case the maximum noise level will be 92 dB(A).
In the event a model aircraft fails the noise test, no indication shall be given to the pilot, and/or his team, or the
judges and both the transmitter and the model aircraft shall be impounded by the flight line official
immediately following the flight. No modification or adjustment to the model aircraft shall be permitted (other
than refueling). The model aircraft shall be retested by a second noise steward using a second noise meter and
in the event that the model aircraft fails the retest, the score for the preceding flight shall be zero.
The flight time will be interrupted while the noise check at the flying site is being made. The competitor shall
not be delayed more than 30 seconds for the noise check.


Here's the AMA version of same:

* 4.2. Noise limit. Each reciprocating or rotary
piston internal combustion engine shall be equipped
with an effective silencer. The maximum noise level
for all classes shall be 96 decibels measured at three
(3) meters from the center line of the model with the
model standing on concrete or macadam, and 94 dB
if an earth or short grass surface must be used. All
measurements will be taken perpendicular to the
fuselage centerline on the right-hand downwind side
of the model with the motor running at full power;
the microphone to be placed on a stand 30 centimeters
above the ground and in line with the motor. No
noise reflecting objects shall be nearer than three (3)
meters to model or microphone. A score penalty of
five (5) percent of the raw flight score shall be
assessed for those models registering over 96 dB, and
a 10 percent penalty for those registering over 98 dB.
The Contest Director shall have the option of deleting
the noise level requirement at any sanctioned
event


As you can see, they both measure things the same way, though FAI actually bothers to tell you the weighting, explicitly.
"C" weighting is the standard, though and the frequency range is built-in.
Come hear the noise-abatement seminar I'll give at WRAMs on Saturday.

Later

Dean Pappas
Sr. Design Engineer
Kodeos Communications
111 Corporate Blvd.
South Plainfield, N.J. 07080
(908) 222-7817 phone
(908) 222-2392 fax
d.pappas at kodeos.com


-----Original Message-----
From: discussion-request at nsrca.org
[mailto:discussion-request at nsrca.org]On Behalf Of John Pavlick
Sent: Tuesday, February 15, 2005 1:20 AM
To: NSRCA Discussion
Subject: Sound Level meter requirements


Does anybody know the requirements for a sound level meter capable of
testing for AMA noise requirements? I've found a few that measure A and C
weighted response. Some are IEC Type 2 compliant. Is this good enough for
AMA standards? Also, there's no spec. for the measured frequency range
requirement. All meters specify a range (i.e. 30Hz - 12KHz). What range does
an AMA approved measuring device have? There must be a list of requirements
somewhere, otherwise it's going to be a guessing game. It's not like buying
a tape measure.
 I've been thinking of getting one for several reasons. First, I want to
test some of the planes at my club field to get an idea of how much noise
the average sport model generates compared to a lawnmower or a weed whacker.
Second, I would like to include a noise measurement for the airplanes that I
write magazine reviews for. I think it would be a good idea for the general
public to see that most pattern planes are VERY QUIET - I don't think they
realize this.

John Pavlick
http://www.idseng.com

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