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Old August 25th, 2017, 09:18 PM   #1
DannoXYZ
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How do noise-reduction inserts work?

So I was exploring options to quiet my bike down for Laguna Seca. I can't figure out how noise-reduction inserts can possibly work? I have one similar to this for the Yoshimura RS-5 exhaust on my CBR600RR.



And one for an Akra



It would appear to me that these would reduce the effective internal volume and baffling surface-area inside the muffler? How does that reduce loudness? Imagine having an even longer solid tube go all the way through to remove ALL off the baffling and this would be maximum loudness, not less? I don't get it.

Meanwhile, on the auto front, extreme measures are needed.



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Old August 26th, 2017, 08:12 AM   #2
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it changes the air flow, usually involves fiberglass to absorb sound. the silencers also convert wide airflow to a more narrow air flow. I am in the process of building a silencer for my 250 as I run straight pipes and no muffler. I cut my stock exhaust head and got the baffle out, and need to weld some pieces together. Wrap the baffle with fiberglass and then insert it back into the "stock" pipe in order to slip it inside my exhaust.
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Old August 26th, 2017, 11:54 AM   #3
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Except these inserts don't change any of the packing material. I just don't get it. Anyway, I left the innards alone and rotated the muffler 180-degrees so the outlet aimed upward awards. Then welded on 90-degree bend from Autozone.



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Old August 26th, 2017, 02:39 PM   #4
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what is the db level at laguna?
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Old August 26th, 2017, 03:13 PM   #5
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what is the db level at laguna?
I think 92, might be 90 sometimes :/
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Old August 26th, 2017, 03:20 PM   #6
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What we perceive as noise is actually sound pressure. If you can modify the apparent sound by tuning the harmonics then you get an apparently lesser or greater sound.

Straight through performance exhaust create a distinct sound wave, the baffle changes the tone, by both volume & area reduction this is usually enough to reduce it enough to defeat he dab meter, but not reduce performance to much, they can help in certain parts of the rev range netting you a little more torque.

YMMV
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Old August 26th, 2017, 03:36 PM   #7
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Quote:
Originally Posted by jrshooter View Post
what is the db level at laguna?
Quote:
Originally Posted by Singh2jz View Post
I think 92, might be 90 sometimes :/
I think today is 90db !!! I can confidently say that Tyga full system passes!!! No inserts needed, I just flipped muffler upside down and welded on 90-degree exhaust bend from Autozone!

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Old August 26th, 2017, 04:25 PM   #8
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a little 300/250 with a exhaust sys, will go over the 90 db?
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Old August 26th, 2017, 05:17 PM   #9
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It very well could. Certainly sounds louder than some of big bikes with FACTORY exhausts that were getting black-flagged. Then again, it actually sounds louder to me because the sound isn't aimed backwards any more. My left ear's taken a beating even with ear-plugs. Need to get some of those silicone ones.
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Old August 26th, 2017, 05:57 PM   #10
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sorry to hear this. do you get to test your bike before your session?
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Old August 26th, 2017, 06:50 PM   #11
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I've been going up hill full-throttle past the sound-monitoring station all day and didn't get black-flagged, so I think it's working !!!
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Old August 26th, 2017, 10:31 PM   #12
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here is the baffle in from my el cheapo ali muffler. works quite well.
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Old August 27th, 2017, 03:06 AM   #13
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Glad it worked out!

Did the possibility of getting flagged distract you throughout your run? Lol..cuz I'd go ham on that track at which point they'd need some spike strips to stop me hahahaha
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Old August 27th, 2017, 11:59 PM   #14
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sorry to hear this. do you get to test your bike before your session?
Track organizer said that would put you on their radar! It's like dragging a 100-lb bag of weed to the airport and asking them to have their dogs sniff it to see if you did a good enough job of sealing bag!!!
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Old August 28th, 2017, 05:36 AM   #15
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Track organizer said that would put you on their radar! It's like dragging a 100-lb bag of weed to the airport and asking them to have their dogs sniff it to see if you did a good enough job of sealing bag!!!
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Old August 28th, 2017, 08:00 AM   #16
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Glad it worked out!

Did the possibility of getting flagged distract you throughout your run? Lol..cuz I'd go ham on that track at which point they'd need some spike strips to stop me hahahaha
Hahahahah! Knowing I get three strikes helped. At first, after T5 i weaved to left and hugged shoulder to go up hill past sound-booth as far away from it as possible. Then move back to right and set up for T6.

Each lap I'd gradually move closer and closer to right side after T5. Eventually I was on racing line on right side closest to sound-booth, no black-flags!

Some other Ninja 250R's sound-reduction efforts.



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Old August 28th, 2017, 08:03 AM   #17
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thats just crazy, as much as i would love to ride that track, i probably wont now.
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Old August 28th, 2017, 09:41 PM   #18
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thats just crazy, as much as i would love to ride that track, i probably wont now.
It's not that bad, a factory muffler would totally pass. My buddy rented one of the FLAP Ninja 300s so he wouldn't have to worry.

I think this track is totally worth it! More challenging than Thunderhill. No walls to worry about like Sears/Sonoma. And it has The Corkscrew!!! And due to all the corners, you actually have better chances against the big bikes!
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Old August 29th, 2017, 08:18 AM   #19
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Quote:
Originally Posted by Mohawk View Post
What we perceive as noise is actually sound pressure. If you can modify the apparent sound by tuning the harmonics then you get an apparently lesser or greater sound.

Straight through performance exhaust create a distinct sound wave, the baffle changes the tone, by both volume & area reduction this is usually enough to reduce it enough to defeat he dab meter, but not reduce performance to much, they can help in certain parts of the rev range netting you a little more torque.

YMMV
thanks for info! So you're saying it changes frequencies of helmholz resonance? A little more restriction and slower flow can certainly move torque-peak around. More would certainly beef up mid-range. Kinda like what Kawi did in going from pregen to newgen.
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