Sound check!

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#16
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
 
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#17
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

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#18
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

Crash Test Dummy
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#19
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

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#20
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.
 
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#21
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

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#22
zigmx614 said:
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

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#23
zigmx614 said:
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.
 
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#25
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
 

MACE

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#26
Jesse, how about next time you are sound testing, you throw a moving blanket over the bike with just the silencer sticking out and see what the delta dB would be.
 

DougRoost

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#27
I agree this borrows nicely on automotive muffler design, but more on the turbo mufflers than Flowmaster (though the deflectors Chris mentioned are of that thought process). Really great work, especially since you did it some time ago. And I think the workmanship is pretty amazing for a prototype you were developing...looks a lot like some of those welded drag car mufflers.

I actually asked the Flowmaster guys a few years ago why they didn't build bike mufflers and they shared they had but they failed. Said they initially targeted Harley's and there were 2 issues. The first was what was mentioned, those people want the loud pipes. The other they claimed was this is a much harder problem with a single cylinder engine (we were talking thumpers) than a multi-cylinder due to less pulses that can cancel each other out.

Doug