Decibels

[Freakshow]

LEt the games begin.

I will be interested to see all the aussie inginuity and ideas posted in future on the hunt for not HP but -DB.

There must be an easier way to quieten the bike, in theory does the DB rate change out at a flatter neutral Rpm ? if so in theory, if you can tune the bike to be quiet in that static test RPM zone the other sides dont matter right ?  you now when you build up revs it goes quiet in a sweet spot where it harmonises before it picks up again.  IF your really luck and that spot is in the rpm test zone would it be possible to tune up or down , pipes etc, to get that zone into the test area or is that just pie in the sky ?

[Rosco400]

Ive got an idea Freaky that will defeat the db limits,

1. We all push our bikes to the start
2. Push them for one lap around to the finish line, rolling down table tops and helping each other on the up ramps (except for the guys leading, they are automaticaly sent to the back of the field)
3. Push them back onto the trailers,

At no time do we get to start them, we have now brought the bikes under the 96db, will eventually feel fitter than we ever have before,
eliminates the need for mixing of fuels, still get to see some great looking bikes, never have to buy wear parts, win win situation alround and the governing bodies are happy

[Tony T]

I remember a guy writing to Dirt Bike asking if wrapping old inner tubes around the pipe/muffler would help reduce the noise......................

I think the answer was that the noise from the bike would definitely be less noticable................... over the sound of the fire sirens................. 

[huskyrider78]

Rosco,
Not sure that would work - dropping the tailgate on my trailer makes a godawful racket! 

And my metal tie-down hooks make a horrible rattling sound against the eyelets! (although I'm looking into having them shrinkwrapped in soundproofing nylon sleeves - will let everyone know).

[Freakshow]

i remember it was all the rage to run heat cloth wrap on the front header pipes on the roadies for a while back, cant remeber why but most teams did, could have been heat deflection or inflection, but then again we didnt run fairings so it may have been to do with somthing else, we ran it too,  but cant remember if it had a reason or was like the Sweat bands on the brake cylinder faze.

Anyone ?

[yzhilly]

I just picked up a late model cr80/85 alloy  muffler with down turned exit for $50 on ebay so hopefully that will fix one .

[evo550]

Tony,
I remember reading a similar article where an aussie isde rider failed a test at an isde event, he wrapped the muffler with tubes and passed the second test.

[pokey]

My 240WR Husky had a heatproof cloth strapped chamber and another metal skin. not sure if it was for the noise abatement or the heat  but it looked stock.was secured by worm clamps.


Just like this one


http://img71.imageshack.us/img71/3330/explorar0010ai0.jpg

[Wombat]

Despite my opposition to this 'Law' I'll no doubt be impressed with the many varied and ingenious ideas you'll come up with to muffle your bikes.
What's that saying, "Necessity being the Mother of invention"?
Heat wrap, inner tubes (??!!)...and what better than a car muffler to slot beautifully over the arse end of bikes pipe.
How gracefully the Vintage ideal is taking it's place in the 21st Century.
And what a shame only the Garage Queens/Museum pieces will maintain the look and essence we all love. 

These ideas may all work - and a few Forum Members have expressed support for the 96db rule.
But I have a question:

Is there anyone so keen to support the rule that they will not sign the proposed petition?

[Lozza]

Finally you are starting to think Freaky as this is exactly what Dave Morris did to his CZ.The inner tube goes inside the stinger/end can and then packed with fibreglass matting.Hardly rocket science innit.No need for whinging ,masters degrees or anything else. 
Just digesting the details of side resonant chambers in John Bradley's book.Since the test occurs at an rpm according to stroke, we can determine what frequency noise needs to be attenuated.eg 50mm stroke 2 stroke 7600 rpm so 7600/ 60 = 127 Hz the fifth harmonic* is the loudest so 127 x 5 = 637 Hz will be the frequency the noise meter will see the most of.A side resonant chamber is an extra chamber placed at the exit of the stinger usually about 80mm long same diameter as the silencer.The centre pipe has 2 holes in the side of between 5-10mm in od.The holes are designed only to filter out the specific test rpm noise nothing else as the bike simply has to pass the test. I'll have some better explanations from a sound engineer I am doing some work for.
*Don't ask me.

The wrap on pipes was to equalise pipe temps on V twins and to add heat to some 125's nothing to do with noise.Now out to the shed.

[All Things 414]

God I hope Geoff can make me a muffler. If I have to work out stuff like Lozza does I think my head will implode!

[Rossvickicampbell]

I agree with 414 - where are you Geoff???  My 250 Elsinore has a GMC pipe with something like an 18inch silencer packed to the max and should be OK - my YZ360 on the other hand has a bloody 3 inch pickle!!!!!  Geoff - what ya got for my 360 mate!

 

Rossco

[Nathan S]

The RPM that the test is done at is interesting...

up to 85cc  8000 rpm
85cc to 125cc 7000 rpm
125cc to 250cc 5000 rpm
251cc to 500cc 4500 rpm
over 500cc 4000 rpm

What would a BSA or Triumph normally rev to?
& what were these limits based on?

4500 RPM for an open class bike.
A TT500 would maybe be at 3/4 throttle where as a CRF450 would be at 1/2 or 1/3 throttle.
A CZ 360 or Maico 350 would also be at 3/4 throttle??

125cc to 250cc 5000 rpm
How high would a MX 250 rev, or an Elsinore 250? They would also be around 3/4 throttle compared to a YZF250 being around 1/2 or 1/3 throttle

And the 250 f's run with the 125's so are they measured as 125's or 250's?

So instead of chasing lower decibels for the older bikes maybe we should be pushing for the readings to be taken at a lower RPM.
This lets MA brag they have lowered the noise limits to keep the greenies happy & in effect it would make the levels more achievable for the older bikes.

Quoted because I reckon its the best post I've read on the topic.

[Tim754]

The Fifth Harmonic using a guitar as sound devise
cents
2    octave    P8    1200.0    0.0
3    just perfect fifth    P8 + P5    1902.0    702.0
4    just perfect fourth    2P8    2400.0    0.0
5    just major third    2P8 + just M3    2786.3    386.3
6    just minor third    2P8 + P5    3102.0    702.0
7    septimal minor third    2P8 + septimal m7    3368.8    968.8
8    septimal major second    3P8    3600.0    0.0
9    Pythagorean major second    3P8 + pyth M2    3803.9    203.9
10    just minor whole tone    3P8 + just M3    3986.3    386.3
11    greater unidecimal neutral second    3P8 + just M3 + GUN2    4151.3    551.3
12    lesser unidecimal neutral second    3P8 + P5    4302.0    702.0
13    tridecimal 2/3-tone    3P8 + P5 + T23T    4440.5    840.5
14    2/3-tone    3P8 + P5 + septimal m3    4568.8    968.8
15    septimal (or major) diatonic semitone    3P8 + P5 + just M3    4688.3    1088.3
16    just (or minor) diatonic semitone    4P8    4800.0    0.0

Shit that clears it up !!!!!!   Wikipedia.................................. Tim

[Wombat]

Jet Plane 98db - are you sure??