Sound check!

[AJ Waggoner]

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.

 

[BSWIFT]

:cool:

 

[RichBaker]

The only thing "Forest Service approved" about ANY exhaust system is the spark arrestor....

 

[Okiewan]

The only thing "Forest Service approved" about ANY exhaust system is the spark arrestor....

Yes ... and then there are 96dB rules all over the country. Your point?

 

[cujet]

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

 

[MACE]

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]

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]

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]

I agree the snorkle added on would be a quick and easy fix..!!

 

[cujet]

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

 

[techman]

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.

 

[cujet]

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

 

[Vic]

Hey, Chris! I have a better memory than you! :nener:

Lookie here.

http://www.dirtrider.net/forums3/showthread.php?t=26002

 

[cujet]

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

 

[MACE]

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:

 

[cujet]

Yup! there are some really cool things one can do to quiet things down. Your packaging idea is excellent.

While it looks like 2 absorption mufflers placed end to end, that is not the exact way it works.

In fact, there are chambers seperated by a baffle and standpipe. The standpipe in not along a wall or edge where sound pressure level is highest. This is a tried and true method. By the way, both chambers have different volumes. Also the 2 standpipes have different tuned lengths and diameters.

In fact, there are a couple of things I forgot to add. The first muffler aims directly into a concave reflector. This is supposed to help. Not sure if it does.

An Idea I have for my wifes 2t modified scooter: Use a center bleed for the expansion chamber. But drill many small holes, instead of just one big. Connect these in linear fashon with an wrap around tube. Make the silencer integral with the tapered end of the expansion chamber. This would keep size down. It would also reduce some of the expansion chamber noise.

The advantage of the center bleed is less noise.

Chris

 

[zigmx614]

Nice! you guys are on the sound thing for sure. This is Jesse from Dirt Rider Magazine. I wrote the test on your forum's bike and have some input about it's sound. First, most of the sound from that bike that is pushing it close to the limit is not coming out of the exhaust. The 500's exhaust system was adequate and acceptable to our standards. It was close, and a ranger would give us a warning, but it still passed. A lot of the bad noise (bad according to a sound meter) is resonating from the expansion chamber, airbox and engine as that beast eats air and spits dust. For this test we did it as a ranger would. It was done in a parking lot and that's not the best setting for a 2-stroke to shine. The 2-banger sound is a little unfairly tested in these scenarios since we all know their noise doesn't carry nearly as far as a four-stroke. Plus, the more rapid, sharp pulses of 2-stroke sound bounce around the small area of a sound test and sort of gang up on the meter. It's great that you're taking the sound issue so seriously and I'm glad this bike and project brought the topic up again. So, realize that even though the bike was the second loudest in the test, it's sort of at a disadvantage with it's noise and looks worse on paper than it sounds on the trail.

Wouldn't a legit 96db bike be sweet? Keep up the good work!

-JZ

 

[Patman]

So maybe some foam between the engine and skid plate? Perhaps there is some room for improvement by changing up the expansion chamber guard? Some kind of standoff or honey comb design on the back of the CF guard to help muffle things :think:

 

[AJ Waggoner]

Jesse , Thanks for the input!
I was thinking i had once heard a CR500 put out almost 100 dB at the airbox with the exhaust levels completely taken out ..
I'm sure that was an exaggerated number , but seeing how all engines are a
big air pump, an engine making the hp's of a CR500, is sure to be louder in both airbox and exhaust, than a bike making far less hp. *can't get something for nothing* comes into effect?
That said, i'm sure a CR500 can be made 96dB compliant!(looks like cujet got it down below that )
but yeap might also have to look into other areas than just the silencer!

cujet, that exhaust looks very cool! i'd like to hear what material(s) you used in the filled chambers? regular silencer packing material?

anyway nice job!

 

[gwcrim]

I like Cujets muffler too. Looks like a mini Flowmaster or something. Ya know, there could be a market for that sort of thing.

And I agree that the porting sure could have made a change in the sound level. That's pretty common. But as Jesse reported, lots of noise came from elsewhere. Some sort of sound deadner around the expansion chamber would be interesting.

 

[zigmx614]

I'm no sound professional, but I think you encase the engine in one of those styrofoam beer coolers you get at the grocery store (you know, the ones that explode when you try to sit on them), that should quiet down the atmospheric noise a little. That or a double-walled, insulated expansion chamber (like stove pipe).

As far as mufflers go, I often wondered why MC exhausts weren't designed like automotive systems ala' flowmaster, etc.. I'm sure size and weight are the big factors. But really, I think there are just too many spodes out there that think a lot of noise means a lot of speed. Until the market changes (and it slowly is) development will be left to the geniuses like cujet

-JZ

 

[Vic]

I'm no sound professional, but I think you encase the engine in one of those styrofoam beer coolers you get at the grocery store

That would certainly contain much of the sound. Unfortunately, it would also contain quite a lot of heat. :nod:

 

[gwcrim]

But really, I think there are just too many spodes out there that think a lot of noise means a lot of speed.

More than just spodes. It's about every gearhead on the planet. And I bet we've all been there at one point or another. Old habits die hard.

 

[zigmx614]

That would certainly contain much of the sound. Unfortunately, it would also contain quite a lot of heat. :nod:

not if we bought enough ice. :)

 

[cujet]

Hey AJ, I used silent sport glass fiber. Thanks for the nice comments!

The CR5 I used was also a ported engine. With a taller and wider exhaust port. That did hurt the noise output some. BTW, the chamber was putting out the most sound, as has been suggested.

The double wall OEM chamber on my husky really cuts down on chamber noise. But the exhaust note is the same. And the double wall chamber is very heavy.

I truly like the idea of a center bleed, with the silencer around the aft part of the chamber. This would cover at least half the chamber, reducing chamber noise. It would be easy for me to fabricate. Maybe out of Ti?

The bolt on silencer was more effective than you might have expected though, chamber noise and all.

In my mind, it is easier to quiet the big two strokes than the big 4 strokes.

I took my OEM Husky silencer and modified it in a similar fashon. However I did not change the size of the unit. It is quieter than stock, but no where near as good as that big can.

Chris