Originally Posted by pro bro steve
+1 kody got me hooked a long time ago
I went to BOD meeting last night .
Went over the DB testing and how to use the DB meter and fill out the proper paperwork .
+1 on Kody the 3D machine.
Thank you for representing all of us at the MARC.
Looks like I can't keep my mouth closed on the db issue.
Steve or Joe is there anyway you can possibly influence the MARC board to standardize there db test to be consistent with the AMA test protocol?
MARC current Test Protocol: The sound meter will be used in the “A” weighting position and “Fast” switch position. Momentarily press the “Hold” button so that the meter will retain the maximum dB level; following the test, show the level on the meter to the flyer. Position it 25 feet from the model in the plane of the prop at a height of 2-3 feet and with no noise reflecting objects within three feet.
Point it directly at the model and have the engine run at full power.
Link to MARC sound Abatement Rule:
The issue and inconsistency with MARC's db test protocol is that the tester is holding the db meter while performing the db sound level test. This causes sound reflection of roughly 1db which in turn lowers the passing db threshold to 89db instead of 90db which is the intended sound abatement target db.
1 db doesn't seem like much however keep in mind db's are exponential in nature not incremental. i.e. the higher the db number means exponentially more noise.
Here is AMA's competition db rule. Note they use a stand for testing thus eliminating the sound reflection issue.
4.2: Noise Limit: Each internal combustion engine shall be equipped with an effective silencer. The maximum noise level for all AMA classes shall be 96 decibels measured at three (3) meters from the centerline of the model. All measurements will be taken perpendicular to the fuselage centerline from the right hand side of the model. The nose of the model will be pointed directly into the wind and the microphone will 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 the model or microphone.
The measurement will be made while the throttle is at full power.
Link to AMA competition rules:
"Don't get caught up in the db threshold difference between MARC at 90db & AMA at 96db." As I understand it the 90db target was chosen to be consistent with traffic noise on 520. This will be a difficult to change without getting all legal-beagle sighting King County Park Ordnance precedence and this is not advisable because of the relationship fall out that would incur with MARC board members.
Focus on recommending the missing testing stand component which should allow some two blade props to pass with cans at true 90db