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KevNC

Sound level - enduros...public lands...etc

7 posts in this topic

I got ahold of a good quality sound meter. How do I test the bike? I've read conflicting things while searching these forums, and elsewhere. Anybody with some real experience with race officials or park ranger types?

I'm looking for 1) distance from the bike, 2)orientation to the bike, 3) throttle/RPM level while measurement recorded (and how do they verify throttle position/rpm?)

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Taken from the FMF Q-series thread:

Scoobydoo, I've posted to tell you that the MMIC uses and SAE sound test procedure which is standardised, is the one that has been used in magazine articles, is used at races etc and came into existence to solve the problem of "meaningless" such as you described. A little research on your end would help how your posts are viewed.

In short, it's dBA scale weighting, slow meter response, no obstacles near the bike to cause reflections, not raining or drizzling (attenuates greatly), meter at 45 deg out right from the rear tip of the muffler, 20" from the rear tip of the muffler, pointed at the muffler, level with the ground, engine revved to proper rev and held there (I'm guessing about 5000 rpm for the YZ/WR 400/426 bikes, I haven't found a published "accepted" rpm yet).

The general impression of it being not quite as quiet as a stock WR pipe, but much quieter than a stock YZ or opened up WR pipe is quite reasonable.

If someone in Toronto has a Q series muffler, bring it on over and I'll test it. If it turns out good I might just buy one myself.

Brian

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Bonzai,

Let's just say that it's a bit different out here in CA...... I doubt that it will be long before those rangers start checking you for noise compliance.

Brian

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The group I ride with goes to numerous state and national forests throughout the Southeast. Mostley WR 400's and 426's, we always ride uncorked and have never had any problems with park rangers or any other law inforcement types....On the contrary it seem like they're always stopping us because they think our moto's sound awsome.... :)

Bonzai......... :D

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Well, I checked out 2 bikes with the sound meter and the main thing I noticed was that any levels posted anywhere are going to be hard to measure or benchmark against.

The standard is 20" from exhuast tip, same height, 45 degree angle.

However....extremely small differences in distance/angle from the bike make large differences in the measured sound level...up to 5-8 db for just a few inches of delta distance. Also, what is half throttle? This makes a big difference too. A 5-10% change in rpm can also make a 5-10 db change.

This can add up. Do a couple things "wrong" and you've made 94db into 115 or vice-versa.

[This message has been edited by KevNC (edited 07-12-2001).]

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Hi KevNC,

I've never found a large sensitivity to +/- 1" of 20" in the reading. I've also not found much directionality to the meter response, i.e pointed at the exhaust tip say +/- 10 degrees giving the same numbers. I would bet that your variation came from trying to hold a throttle position vs holding an rpm. If you hold the rpm constant, you'll find quite repeatable results, where the variation of rpm is by far the dominant factor in varying your reading. Yes, you need a tachometer to do the test. If you get rpm +/- couple hundred, use a cheap meter and don't even account for environment (surrounding terrain and weather conditions) you should still be within a few dB of "true" reading. So your 94 could read as 92 to 96 with non-picky testing procedures. Take a few radings with a tachometer and you'll see what I mean.

I'm sure a marginal bike (within a dB or two) could be sweet talked past a Ranger, explaining that your muffler packing just wore out or some other excuse, or promising that you'll have it ship shape next time out etc.

Hint: get a Briggs and Stratton resonant wire tachometer, about $20.

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Most of the Dual Sport rides, and Turkey Run's, they hold the unit from tip of the fingers to the elbow away. seems to work for them.

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