Author Topic: Any Way To Get This Exhaust Down To 95 Decibels Or Lower Yet Keeping Good Flow?  (Read 377 times)

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nicholastanguma

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Is there any way to get this exhaust's decibels down to 95 or lower without utterly destroying good flow characteristics for a wide powerband, maybe using some kind of internal baffles that can work miracles?

No more length can be added to what you see here, nor changes from the shape seen here, nor a muffler added to the end.

However pipe diameter can be changed, and stepped diameters can be included in the length, if somehow this allows for miracle working internal baffling while keeping good flow characteristics across a wide powerband and limiting decibels to 95 tops.

What I'm dreaming of is an exhaust with this ultra shorty I'm-going-to-punch-you-in-your-face appearance and the performance to match...but without the I'm-a-Harley-pirate-pay-attention-to-me sound level.





« Last Edit: June 02, 2021, 02:22:23 pm by nicholastanguma »


ace.cafe

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Sure.
You could use a much much larger diameter pipe that goes around the existing pipe, terminate the back end of the big pipe, allow the small pipe to have its outlet inside the terminated big pipe so the exhaust gases reverse direction to go back towards the front, and put an exhaust dump up near the front of the engine.
In other words, make the entire pipe into a muffler.
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nicholastanguma

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Sure.
You could use a much much larger diameter pipe that goes around the existing pipe, terminate the back end of the big pipe, allow the small pipe to have its outlet inside the terminated big pipe so the exhaust gases reverse direction to go back towards the front, and put an exhaust dump up near the front of the engine.
In other words, make the entire pipe into a muffler.


Sarcasm?

Kind of a wacky idea, but I suppose it might actually work...

But what about a Helmholtz resonator in addition to some kind of minimal internal baffling, Ace?










ace.cafe

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No sarcasm. You specified a pretty tight set of parameters to do a monumental task which normally requires 15x displacement.

Those photos are terminated Helmholtz resonator chambers which assist wave functions in the exhaust.
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nicholastanguma

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No sarcasm. You specified a pretty tight set of parameters to do a monumental task which normally requires 15x displacement.

Those photos are terminated Helmholtz resonator chambers which assist wave functions in the exhaust.


I suppose the megabomb header design is probs more akin to what you had suggested?





ace.cafe

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None of those things will do anything to reduce the sound levels. They are all wave function products. Unless that red piece is terminated at the tail end, and even then it has insufficient internal volume to muffle anything.
« Last Edit: June 02, 2021, 05:50:22 pm by ace.cafe »
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AzCal Retred

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https://en.wikipedia.org/wiki/Active_noise_control
History
Electronic noise management test in Vienna, 1973
The first patent for a noise control system was granted to inventor Paul Lueg U.S. Patent 2,043,416 in 1936. The patent described how to cancel sinusoidal tones in ducts by phase-advancing the wave and cancelling arbitrary sounds in the region around a loudspeaker by inverting the polarity.


Build a Dual section pipe constructed to create a standing (+) pulse and (-) pulse at the exit hole. Gas flows, sound ceases or is reduced.

Excellent opportunity for a young mind to bask in the mystery & wonder of acoustics & PV=nRT. A welder, grinder, a selection of various tubing diameters, some elbow grease, some calc's & soon you're there.
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NVDucati

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'''
But what about a Helmholtz resonator in addition to some kind of minimal internal baffling, Ace?







YES! I made one for my V-strom 1000.
That is a straight pipe with a bit of expansion and the goofy looking down spout. It is more quiet than my SV650 with a fully baffled 2-Brothers.
You can find the formula on the internet and if need be make two of them with different lengths. Absolutely works.
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AzCal Retred

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Kudo's to NVDucati! Here's some theory & calc's. I'm not seeing continued interest/interaction/learning by the original poster though...?

https://www.sciencedirect.com/topics/engineering/helmholtz-resonator
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nicholastanguma

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YES! I made one for my V-strom 1000.
That is a straight pipe with a bit of expansion and the goofy looking down spout. It is more quiet than my SV650 with a fully baffled 2-Brothers.
You can find the formula on the internet and if need be make two of them with different lengths. Absolutely works.



You're being serious, not just yanking my chain?  Your Strom's straight piped exhaust w/ homemade resonator is actually quieter than your SV w/ fully baffled silencer?

Don't play with my emotions, friend...


NVDucati

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You're being serious, not just yanking my chain?  Your Strom's straight piped exhaust w/ homemade resonator is actually quieter than your SV w/ fully baffled silencer?

Don't play with my emotions, friend...
I take motorcycle emotions seriously and would never toy with yours. ;)
To be clear neither of those bikes are as whisper  quiet as the OEM vacuum cleaner sized mufflers.
But they are not what anyone would point out as a loud motorcycle. Sound waves and exhaust gases are two separate entities which happen to travel in the same tube as they leave your engine. Sound waves behave very much like ripples in water do. So expansion and dispersement reduces the sound level. Essentially, once the resonator is pressurized the exhaust gases pass on by and out the back. The sound waves which are always expanding move into the capped Helmholtz tube, reach the end and bounce back at nearly the original frequency and collide with the new sound waves entering. This is a known behavior since the 1850s. The formulas can seem overwhelming but once you break it down to engine displacement and a target RPM (I chose 4500) its like riding a unicycle. What surprised me the most was the visceral reaction people have to the exit downspout. It seems to violate a sacred code. But it is a final, zero-flow-resistance, smashing against the ground of the sound waves. Next time I'll hide it inside a larger cone ;). Thanks for the comment. 
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nicholastanguma

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The formulas can seem overwhelming but once you break it down to engine displacement and a target RPM (I chose 4500) its like riding a unicycle.


Did you simply Google something along the lines of "Helmholtz resonator exhaust formula" or similar?   :o


What surprised me the most was the visceral reaction people have to the exit downspout. It seems to violate a sacred code.

It is ugly indeed.   ;)


But it is a final, zero-flow-resistance, smashing against the ground of the sound waves. Next time I'll hide it inside a larger cone.

I'm not sure I understand the wording of this statement.  You're referring to hiding the offensively unattractive exhaust tip inside a larger exhaust cone, I assume.  But what does "it is a final, zero-flow-resistance, smashing against the ground of the sound waves" exactly mean?

Apologies if I'm being obtuse.


Thanks for the comment.


Most welcome.  But thank YOU for your comment!
« Last Edit: June 12, 2021, 01:34:58 pm by nicholastanguma »


zimmemr

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I take motorcycle emotions seriously and would never toy with yours. ;)
To be clear neither of those bikes are as whisper  quiet as the OEM vacuum cleaner sized mufflers.
But they are not what anyone would point out as a loud motorcycle. Sound waves and exhaust gases are two separate entities which happen to travel in the same tube as they leave your engine. Sound waves behave very much like ripples in water do. So expansion and dispersement reduces the sound level. Essentially, once the resonator is pressurized the exhaust gases pass on by and out the back. The sound waves which are always expanding move into the capped Helmholtz tube, reach the end and bounce back at nearly the original frequency and collide with the new sound waves entering. This is a known behavior since the 1850s. The formulas can seem overwhelming but once you break it down to engine displacement and a target RPM (I chose 4500) its like riding a unicycle. What surprised me the most was the visceral reaction people have to the exit downspout. It seems to violate a sacred code. But it is a final, zero-flow-resistance, smashing against the ground of the sound waves. Next time I'll hide it inside a larger cone ;). Thanks for the comment.

Kudos on the downspout! A few of the guys in our off-road club have fitted similar downspouts, especially the guys riding big bore bikes, even with no other mods to the exhaust it quiets them right down, and in at least two cases that I know of lowered the boom of aftermarket piped 450's enough to get them thru NETRA sound tests. I like the way it looks, and it also keeps the exhaust out of my face when I'm following someone, which is a big plus. Besides you'll never see it from you're sitting.  :)


ace.cafe

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The downspout redirects the sound downwards, away from the ear. It has an effect like standing aside a bullhorn instead of in front of it.
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zimmemr

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The downspout redirects the sound downwards, away from the ear. It has an effect like standing aside a bullhorn instead of in front of it.

+1 It also directs it away from the sound meter. As an aside when you see the puff's of dust and dirt that the downspout kicks up you begin to realize  how much energy is in the exhaust. It's also why downspouts aren't allowed in dirt track, they don't want the kicked up dust to blind the riders. When I was dirt tracking you'd feel the impulses on your chest as you closed in on riders in front of you.


NVDucati

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Did you simply Google something along the lines of "Helmholtz resonator exhaust formula" or similar?   :o


It is ugly indeed.   ;)


I'm not sure I understand the wording of this statement.  You're referring to hiding the offensively unattractive exhaust tip inside a larger exhaust cone, I assume.  But what does "it is a final, zero-flow-resistance, smashing against the ground of the sound waves" exactly mean?

Apologies if I'm being obtuse.



Most welcome.  But thank YOU for your comment!
Yeah, your search for a usable, more simple formula will come from sites dealing with factory noise and the muscle car crowd. They get "droning" at specific speeds. They have various formulas that you can scale to. The audio speaker crowd will just drive you crazy and you can pretty much ignore them.
   In a practical sense, the photo of the bike you are working on has a straight shot to the rear. That's handy. You can get some sections of pipe from a place like Cone Engineering and a exhaust pipe expander to form a slip fit. Have a couple of them for experimentation. The Akripovic guys use the same size pipe for their tubes. I had a hard time getting myself to second guess the exhaust gods but I disagree with that approach. The horizontal section of my tube is smaller than the exhaust pipe and the "connector" tubes (perpendicular) are smaller again. My, un-provable, theory is that I get the same "collision factor" as they do but two extra expansion moments. (might not even matter)
It also comes down to space available. You have plenty of space so you might decide to have two resonator tubes, one for 4000RPM and another for 11,000RPM.
    As for the downspout, setting aside some fractional gas friction at the turn, having the exhaust gas (really the sound waves) aimed at the ground breaks them up yet again and the crevices in the pavement act as additional baffles to scatter the sound waves further. Think of it as a flashlight beam reflecting off a carpet. And those same sound waves are also having to survive the air turbulence created locally by your tire. So there you have it. Start welding. ;)
« Last Edit: June 12, 2021, 05:59:13 pm by NVDucati »
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ace.cafe

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Its will be difficult to get enough air mass and diameter in such small resonators to have much effect on anything but higher frequencies.

A fishtail tailpipe is aimed at shaving high frequencies if that is the goal.
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AzCal Retred

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This Zontes R310 single cylinder sport bike seems to have grafted on enough extra pipe, maybe that's about what a functional factory resonator might look like.

So the basic open fishtail mainly takes the "crack" out when spinning the motor up a bit? How does the Brooklands fit in here, it's "sort of" a fishtail, but with perforations and a resonator section.
« Last Edit: June 13, 2021, 08:17:11 pm by AzCal Retred »
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ace.cafe

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This Zontes R310 single cylinder sport bike seems to have grafted on enough extra pipe, maybe that's about what a functional factory resonator might look like.

So the basic open fishtail mainly takes the "crack" out when spinning the motor up a bit? How does the Brooklands fit in here, it's "sort of" a fishtail, but with perforations and a resonator section.
The Brooklands silencer has the expansion chamber to trade velocity for pressure, and then the fishtail to tame the high freq's.
If the expansion chamber is at least 15x displacement, the engine sees it as if it were exiting the exhaust into free air.
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Richard230

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The Brooklands silencer has the expansion chamber to trade velocity for pressure, and then the fishtail to tame the high freq's.
If the expansion chamber is at least 15x displacement, the engine sees it as if it were exiting the exhaust into free air.

That is interesting. I always wondered how those Brooklands silencers worked. And now I know. Thanks, Ace.
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