How do you make an XR200R sound good?

**Wingnut** · 14th October 2008, 19:52

ARJ127 - God I could watch your avatar for hours. Hmmmmmmmmmmmm

Anyway - I have nothing decent to add so - catch ya

**oldskool** · 14th October 2008, 19:52

Well I paid $750 for the bike, but that included a helmut, the manual, 2 pairs of boots and a Fox skivvy. So anything more than $200 for a new can wouldn't add up in the scheme of things, specially when I know of someone who scored a mint supertrapp for $30! - speaking of supertrapps I'm wondering if the idea is similar to 'pulse width modulation' (PWM) in that the can gives out max dB but in quick doses. You adjust the volume by changing the frequency/duration of the max dB output. In this way you get a huge pulse of subsonic sound each time the plates open. dunno just a random thought.

**motorbyclist** · 14th October 2008, 20:41

now i have no idea how a supertrapp works, but:

aren't deciBells a measure of amplitude?

as i'm sure you know, PWM just achieves an easily controlled average power output while using only one voltage/amplitude.

so a sound tester would measure the same amplitude, and i suspect it would just sound deeper at same volume. unfortunately, stopping the noise from the motor for PWM would require you to stop the motor/sound source

a more likely method of quietening (or loudening) a bike would be tuning the pipe for destructive (or constructive) interference of the sound waves

most stock mufflers use baffles to smooth out the peaks/valleys thus giving a lower (and therefore legal) dB rating. most aftermarkets just use fibreglass to absorb the sound energy to acheive the end effect without as much backpressure and thus higer flow, which the market demands.

so think of the muffler as an inductor/capacitor to smooth out the loud pulses from the motor, with a resistor to absorb the sound energy... or something like that...

correction welcome

**motorbyclist** · 14th October 2008, 20:47

here's what supertrapp has to say on the matter:

Originally Posted by http://www.supertrapp.com/technology/index.asp

Removing discs decreases the exhaust opening and increases backpressure. This effectively decreases the powerband to create more low-end torque. It also decreases exhaust tone and enriches carburetion.

Adding discs increases the exhaust outlet and decreases back pressure. This widens the powerband at the top end. It also increases exhaust tone and leans out carburetion.

which is basically what i've said in earlier posts

and it's exactly how my tunable muffler worked, albeit by a different mechanism... which basically means even a spotty teenager could've come up with this "patented technology"

imo, moving parts in a muffler are a very bad idea, which would rule out your pwm idea unless they stuck a spring steel reed in there for some reason

**motorbyclist** · 14th October 2008, 20:51

and on further thought:

PWM of sound would just acheive a change in the timbre (quality) of the sound

same amplitude(volume) and same frequency(pitch), just "sounds" different

**oldskool** · 15th October 2008, 08:48

I had Custom Chambers make one for my XR250 years ago. An awesome muffler and a fair price to i thought.

I followed up ARJ127's suggestion. Custom Chambers over East Tamaki way will do a black can for $180 (usually same day) and add an extra $30 (and 4 days) if in silver. Not bad really, but would be a hassle to leave the bike over there on a working day tho'.

**oldskool** · 15th October 2008, 09:00

@motorbyclist
wow amazing where a random thought may lead!
Yeah I follow you, your R/C filter analogy for a muffler sounds sane enuff!
For a sec there I half expected yah to allude to interference waves and phase shifting like what Mazda looked at in their electronic noise cancelling mufflers. I think they got it to the stage where you could dial up your own sound wave?

Anyway, do you reckon you can resurrect that curved pipe leading into the muffler?

**motorbyclist** · 15th October 2008, 18:21

Originally Posted by oldskool

Anyway, do you reckon you can resurrect that curved pipe leading into the muffler?

seriously i doubt my welding is up to the task, but i'm sure there's people who could.

if i were you i'd go get some steel pipe of correct diamter and excessive length, figure out what bends you want, trace it out, and take it to a car muffler shop and pay a few bucks to have them do it on a hydraulic press for you.
which is basically what i did for the pipe in my square muffler.

then perhaps cut the pipe so it can slip over the conical part of my muffler and i'd be a fair bit more confident stick welding that on. more weld to hold it against fatigue and less likely to just burn away the end of the pipe trying to weld it

or buy one. that usually works.

**oldskool** · 15th October 2008, 18:42

Yeah like I originally figured, good intentions but in reality too much effort for my precious spare time. It's all do-able and we know it, but the time saved for a few hundy spent on a guy who does it for a living is well worth the expense. (as long as I earn more than he does

)
The question remains on trusting a guy to come up with a sound I will like. Seems to me this part is a lucky dip on what is prob a standard can he will pull from the shelf. I guess I could go with the flock and get what the market dictates...not.
Still, that ARROW on an XR200 I heard on youtube sounded pretty good.

**motorbyclist** · 15th October 2008, 18:55

Originally Posted by oldskool

Yeah like I originally figured, good intentions but in reality too much effort for my precious spare time. It's all do-able and we know it, but the time saved for a few hundy spent on a guy who does it for a living is well worth the expense.

yeah pretty much

it makes a fun project, but once you account for time taken it's often cheaper to get the pros to do it

although, if you DIY there's only one person to blame if it doesn't work

**oldskool** · 15th October 2008, 19:07

LOL, being a proud and patriotic Kiwi, DIY is my middle name! Mind you when it comes to something like my DIY motion simulation platform, theres not a lot of pro's in NZ that could tackle the project and if there were I'd be looking at costs well into the mid 5 figures. So sometimes DIY is the only option!