Noise
As defined by state and federal law, vehicle sound is measured by a
decibel meter 20 inches and 45 degrees from the exhaust outlet.
For
ATVs and motorcycles, the test is performed at 50% of the
manufacturer's
RPM recommendation. For Class II or full size vehicles, the test
is performed at 75% of the vehicles maximum RPM.
The limit is 93 dB (check current regulations, it may be
less!)
Practical observation #1:
You can do this test yourself using a Radio Shack sound meter.
The Forest rangers have indicated that they are accurate enough.
The technicians often have a calibration sound source you can use to
check
the calibration of your meter. For VW based sandrails, they use
3,000
RPM. They carry a portable tachometer. The test results are
much more a function of RPM than your muffler. It's almost
impossible
to pass, regardless of your muffler, if they hold you to a true 3,000
RPM.
During the baseline measurements, they often held the RPM just under
3,000
in order to allow people to pass the test. As a result, there are
hundreds of records showing that it's possible to pass the test.
It is not. As soon as you are required to hold to the true 3,000
RPM or the reading is taken while the RPM is increasing,
you will fail (you pass the $100 ticket test, though).
Practical observation #2:
If you have a conventional automotive oval type muffler on your
sandrail,
no one will probably bother you. This is assuming it's not blown
out or you have violated one of the many other regulations to draw
attention
first. Conversely, if you have a stinger or a stinger with a
Super
Trapp, you may stopped and measured regardless of other reasons.
Practical observation #3:
All this noise reduction isn't so bad, really. Once you get a
good muffler setup, it's rather pleasant. 93 db is plenty low
enough
and just barely achievable.
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