KDXRIDER.NET

An aside...

Limit on the Oregon coast is 92db. Note how many aftermarket pipes make that threshold. Not many.

It's like..'Sure, you can ride here. SPL limit is 60db. Tech check in the parking lot!'

Gee. Thanks.

60db !!! I've ripped 60db farts !!!

intersting how all the kdx's with stock pipes had variable dbs. 84-92
seems like you could just take the test until you pass it. i guess different jetting and pipes may make the difference. i may go ahead and get that FMF, i thought my stock was more quiet than that.

I'd guess it to be the tester that was the difference...not so much the bike.

In local tech checks my bike has been not found in the spec sheets, tested at 1/2 throttle, tested at 1/4 throttle etc. etc.

Certainly pipes make a considerable difference..but the TesterMan does, too.

Excuse me....TesterPerson!!

I think the FMF "Q" might be the quietest aftermarket silencer currently available. I use the stock muffler, but I am concerned that my pipe (ProCircuit Platinum regular thinwall rev type) is making too much noise. I don't mean out the back, I mean because it is thin and emits more noise because it is. I am going to buy a Platinum II and hopefully the thicker wall will reduce the noise. Everybody should be concerned about this. It is one of the major contributing factors in the closing of lands to OHRV'rs as well as motocross tracks.

Please read this story before buying a pipe or silencer.

http://www.sharetrails.org/index.cfm?page=41[/url]

Scroll down to: Quiet Please--Two Bikers Tell a Tale of Sound

What?! ... and eliminate the #1 KDX forum question of all time:

Which pipe - FMF Gnarly/Rev/Woods/Fatty/Gold Series/K-30 or K-35??



But seriously, that's a good article.

Thought I'd resurrect this thread for a moment with my personal experience

Was at an organized ride last weekend with my boys and they were conducting sound tests. Never been down this road before myself and had never seen it done. Had the following results

XR 80 completely stock, no test required (no surprise) pretty much quiet as a mouse
DRZ 125 completely stock, tested at 92
KDX 220 dynoport pipe, airbox drilled, stock silencer. Guy wasn't going to test because it had stock silencer, but I asked him to test, result was 96

Their procedure was to use a "thingy" to locate the position where the meter should be and to rev up to 4k rpm and take a reading with the meter. I was surprised it was 96 (so was the tester) but I'm not really sure if they followed the correct procedure. Guy with the meter wasn't necessarily holding steady in the right spot. Seems to be lots of room for testing errors, as far as I could see.

Said he had never tested a basically stock kdx that went 96

Don't know what any of this means, just my experience. Seemed like there were lots of 4 strokes there that made alot more noise than mine though. I didn't see anybody that was told to go home because of noise either.

I used to work in the Health and Safety field which meant that I had to take sound pressure readings on a regulator basis. People who are commenting that it is likely the testor which makes the difference - are correct IMO. Although I certainly think jetting, pipes, oil saturation of silencer, air box mods, etc,; play a role.

There are a variety of microphone pick-ups that are used on various instruments. The meters should be properly calibrated prior to the actual test by a calibration procedure applicatable to that sound pressure analyzer and to the particular microphone being used. (This is one area where I believe many mistakes are made).

Also the microphone type determines whether it should be held perpendicular to the sound source (tail pipe outlet) or parallel (highly unlikely) or at a 45 degree angle to it. (Second area of common mistakes) The test protocol being followed must be adhered to.

If, for example, the test is called out for at 20 inchs from the tail pipe outlet with the bike at 6350 rpm then this should be followed as clost as practical. Its hard to hold a particular rpm on a 2T bike more than a couple of seconds without some floating of the rpm. Typcial low cost test meters like I've seen used take a few seconds to generate the SPL onto the meter display. In reality the meter is taking the sound pressure level at different frequencies then applying a sound correction factor (-dB) to the different lower frequencies then combining the frequencies dB readings to give an output on the display which it typically an Slow A-Weighted db average. This A-weighted average is suppost to mimic the human hearing response. (If the testor is using the B-Scale or C-Scale the readings will be completely different.)

Then of course is the vibration rpm meter which I've seen used for determining the rpm on the given motorcycle. I'm not sure of how it excately functions but I seem to detect changes in rpm sometimes before the rpm meter shows a significant change and then other times it is just the opposite leading me to believe there may me some problems with this analytical tool also.