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Sound check!

AJ Waggoner

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#1
The article is out,or soon to be in most DR subscribers hands-
Since sound is a very important issue in keeping land open and our rights to ride..and being an AMA District president and having been personally involved in the land issues and legislative battles for a couple decades ....
I understand well the sensitivity on this issue!

So I wanted to clarify the sound/ dB things brought up on the DRN bike entry..

The bike was built and shipped with a manufactuers specified and forest service approved *96dB compliant* exhaust system chosen by the voting DRN membership.
Specifically chosen to be more quiet , and compliant.

We did not test it here, but these units normally sound check at 96dB with this system or very very close.

DR mag tested the bike at 97.2dB after some riding and testing.
yes i wish it had been 96dB , and with 20/20 hindsight should have tested it, and made any corrections needed,if possible.

I think it is important to note:
While the off road limit is 96dB , there is a variance allowed by the California testing procedure, and the bike would pass inspection by officers testing in these riding areas.
It's why DR noted in the article that even though it was slightly over 96dB - " no ticket"

plus it was significantly under the 99dB standard set for MX models.

This is not a defense , or justification of of loud bikes in anyway..

Just a clarification that the bike was built with what was manufactuered , and Forest Service approved, to be a 96dB compliant exhaust, by a very reputable manufactuer.
and if tested by an officer in those sound sensitive riding areas, would have passed....

Unfortunantly it would be on the edge..
and yes , we need to keep the noise down!!!

I applaud Dirt Rider magazine ,
DirtRider.Net ,and loudsucks.com,
for taking a strong stand on this important issue.
 
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BSWIFT

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#2
:cool:
 
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#5
Sound check

I built a large silencer for a modified CR5 a few years back. Yes, it was kinda a garage hack job. But it was engineered and constructed quite well. I am not proud of how it looked, but it worked.

If I remember correctly, about 91db at full throttle was all we could get out of it. It was very quiet indeed. It would have easily passed the sound check.

If you are interested, I still have a few pics of it on the bike.

It was large, oval and had 3 distinct sound attenuation methods. The internal flow area was huge, so exhaust restriction was not a problem. It had a unique exhaust tone too.

If I remember correctly, It weighed about 4 pounds. I really should have built more of them.

Chris
 
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#6
Cujet, I'm interested in a drawing of the internals...

In fairness to the silencer manufacturer, they really couldn't (or shouldn't) promise any particular sound level on a hybrid bike.

The difference between 97.5 dB and 96 dB is huge. I'm surprised the Kali standard allows such a large fudge factor. Of course the sound limit I test to here in Washington is 98 with no fudge so I guess it's pretty equivalent.

It would have been great if DR had said "bugger, you're over" and then a dB snorkel had been fitted to save the day. In fact I believe the snorkel was actually initially built by it's inventor to make a CR500 pass sound.

Please don't misunderstand me. I love the DRN bike (and the whole AFX concept) - The bike is stunning. It's just that the sound issue is one of my few hot buttons. If the AFX was 92dB it would be the greatest bike in the woods.

I wish one of the forums had made stealth a top priority. I really tried to get KTMTalk to go that way.
 

MACE

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#7
BTW, I'm a bit out of touch with DRN these days. Is RideStealth.com a DRN production? It seems to have a bit of that Okie / Thump style.
 

AJ Waggoner

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#8
In fairness to the silencer manufacturer, they really couldn't (or shouldn't) promise any particular sound level on a hybrid bike.
MACE, not trying to nail the manufactuer, but this entire exhaust system was designed exclusively for this model,the CR500AF and CR500AFX.
We should be able to expect it to meet the sound 96dB standards it was designed for?
The porting could effect it , and that would not be thier responcibilty.
Stock it should certainly meet the state 96dB standards it was intended and designed for, without further testing.
 

AJ Waggoner

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#9
I agree the snorkle added on would be a quick and easy fix..!!
 
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#10
Hey Mace,

I will try and get you a drawing.

In case anyone is interested, here is how I did it:
Glasspack FMF oval silencer, into a large chamber. Through a baffle with standpipe. Into another large chamber of different volume. Standpipe into a glasspack of larger diameter and on a bias. Out a downspout.

The airflow path gets larger downstream. This helps keep pressure to a minimum.

Like I said, kind of a hack job, but tough and quiet.

Chris
 
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#11
Hi Chris,

I've had a project like this on my to-do list for a CR125 for a long time and never had a good start point to shorten the possible iterations to make it work right, so I never really tried. However, with your success, I'm very interested to see diagrams, drawings, amd/or pictures. It's also of interest what materials were used where. Yes, I want to copy it, if you're willing. Consider it a compliment. You could P.M. them to me or whatever - let me know what's good for you.
 
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#12
I hesitate to post this as the unit looks really bad in the pics. In fact, it looked better than this in person. http://hometown.aol.com/cujet/index.html

Link to pics and drawing. The internal flow path drawing is by memory and is not to scale. Remember, I made the internals free of restrictions of any sort. So it was quite large inside. The flow passages were all over 1.5 inches inside diameter.

Chris
 
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#14
Hey Vic!

That is so funny! I totally forgot about that thread. You are right about my useless memory:)

But I do remember that in my original drawing, I forgot to include the internal baffle and standpipe. It is in there, somewhere. If you look at the line of pop rivets, you will see where it is.

Chris
 

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cujet said:
I hesitate to post this as the unit looks really bad in the pics. In fact, it looked better than this in person. http://hometown.aol.com/cujet/index.html
Chris
To a great extent, this design looks like a large boom box and a second muffler added after a standard muffler.

So since we - being vain pretty boy bikers - are so concerned with asthetics, can we envision the second muffler and boom box being made concentric around the outside of the primary muffler and exiting forward behind the riders boot?

Maybe not well described...

Good work on your prototype cujet. :cool:
 

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