Street Bike Sound Test - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 9 Old 09-07-2009, 04:55 PM Thread Starter
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Street Bike Sound Test

The latest issue of the American Motorcyclist (AMA) has an article on the latest streetbike sound test (J2825). While mostly easy to understand I have a question that someone "out there" may be able to answer. SAE J2825 calls for a 92 dBA limit at idle for all bikes but it has different limits for the Set RPM or Swept RPM tests depending on the number of cylinders. It calls for a 100dBA limit for three or four cylinder bikes (at 5,000 RPM or 75 percent of maximum RPM whichever less) and 96 dBA for one and two cylinder bikes AND bikes with more than four cylinders (at 2000 RPM or 75 percent of maximum RPM whichever less).
Any idea why they have two sets of limits split the way they are?
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post #2 of 9 Old 09-07-2009, 05:32 PM
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Disclaimer: I don't know WTF I'm talking about.

It makes some sense to me that the one- and two-cyl bikes are in a different class than the 4cyls: thumpers and twins have "large" cylinders moving thru a "long" distance. The 4's (at least the inline sporty ones that come immediately to mind) have much shorter strokes and therefor make their hp up higher in the rpm range, and have much, much higher redlines as a result - imagine a KLR with a big 650 jug at 12,000rpm - it would fly apart.

Again, I want to point out that I don't know WTF I'm talking about, just thinking out loud because I have some time to kill.

On one hand, if an engine's design means it's naturally going to be louder and little can be done about it, it seems fair to have different standards for them. OTOH, screw that: presumably the law is what it is because society has chosen a particular "this much, and no more" limit on noise. Making exceptions is ridiculous - it would be like having a "Harley law" that only American cruisers can wake up the neighborhood. Your peace is disturbed regardless of the badge on the bike (or the # of cylinders).
post #3 of 9 Old 09-07-2009, 09:06 PM
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flat spot

its also the reason some bikes have a dip in HP at the rpm they are tested for sound

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post #4 of 9 Old 09-08-2009, 08:09 AM
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Just to clarify, this is not a LAW, but an SAE design spec. Odds are some municipality somewhere will base a law on the spec, but even then, it's almost un-enforcable at the street level as the test results will vary based on a whole lot of other factors.

As for why the specs differ based on number of cylinders, My best guess is that since they have differing numbers of sound sources (two versus three versus four) more pistons generate more noise (or at least more intense noise).

I recall having to use a similar test spec for our FormulaSAE car several years back...

The kicker? None of those tests are performed on a dyno under a load. They're all free-revving. The sound a 4-banger sportbike makes at 9000 rpms with no load is a whole lot different than it makes under load. (I know... we tested it). The other rub? The environment the test is performed in makes a huge difference in the outcome as well. Measured on a concrete slab in an alleyway will net MUCH louder results than in an anechoic chamber. The specific angle and distance from the pipe, and the orientation of the sensor can make a difference too. Measuring it to the side yields a different result than measuring it above the bike... Again, too many variables to even remotely be enforced on the street.
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post #5 of 9 Old 09-08-2009, 09:15 AM Thread Starter
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Originally Posted by gijoecam View Post

As for why the specs differ based on number of cylinders, My best guess is that since they have differing numbers of sound sources (two versus three versus four) more pistons generate more noise (or at least more intense noise).
Yet they group six cylinder bikes with singles and twins.
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post #6 of 9 Old 09-08-2009, 09:18 AM
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Gents, this subject can be debated till the proverbial 'cows come home'. Now being almost 65 years old I grew up with bikes in the early chopper years, late 60's and early 70's. My buddies and I rode everything, BSA twins, Triumph Tiger Cubs, Honda 305 scramblers etc. We would get stopped for handlebar height checks, broomstick in the pipes and anything else they could think of. My one buddy had what they called 'snuff r nots' in the pipes of his 305 Honda. For those who don't know what they are they were washers with a hole in the center. The end of your 'straight pipe' was cross drilled and these were inserted with a pivot shaft, spring and knurled nut. They could be rotated for somewhat quiet use or turned for straight pipe use. The bottom line is we as a motorcycling community feel we always have our riding rights being infringed on but why should we be any different than the automotive sector. I can't imagine what it would sound like to have every second car go by with glass pack mufflers installed. I enjoy a bike with nice sounding pipes but when was the last time you saw a baffle in a set of Two Brothers 'mufflers'? They can make any laws they want but until the police get out and do something other than sit with a radar gun in their hand we can make all the noise we want but the writing is on the wall. Motorcycling venues are closing, cities are enacting noise ordinances and enforcing them, laws are being made that only stock exhausts can be replaced and many others. In case you haven't figured it out, we are bringing this on ourselves.
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post #7 of 9 Old 09-08-2009, 09:38 AM
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Interesting post. I have three bikes and they all have stock pipes and seem to me at least to run just fine? I can blow past the speed limit on any of them in a few seconds and they just don't make much racket? Personally I dislike the "Bully Dog" set ups on the diesel pick ups more than any other noise makers. The have an exhaust pipe about 4 or 5 inches in diameter and just pour out a cloud of dark black smoke that almost chokes me to ride through and nothing is being done about that? If it is really the "Noise" they wanna raise a stink about then why not get the real noise makers like all them little 4 cylinder
cars with a huge pipe and booming subs pounding away?

I think that the bikes are just very easy to pick on because every motorcyclist has this ego thing that his particular brand or style or set up of bike is the only really "cool" one and he just can't or won't join forces with "ALL BIKERS" to save the motorcycling sport if it means he has to be seen with a guy on a Harley or a Vespa?


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post #8 of 9 Old 09-08-2009, 10:21 AM
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I'm just speculating as well, but I think the classification has something to do with Harleys and other cruisers, as they are the ones that tend to run straight pipes. I've heard some loud "mufflers" on sportbikes, but never anything as loud as a straight-piped Harley.
I agree with gbritnell. The few are ruining it for the many. Common sense has to prevail, or else we are going to be stuck with bikes that sound like a Honda Civic (cough... WeeStrom... cough).
What's really strange is how different stock pipes can be. My Triumph has quite a loud idle with stock pipes, but it is quiet at RPM. I'm not sure how they managed that, but it's noticeable. My friend's wife commented that it sound like "a dustbuster on steroids" on the road. It does, actually, but it sounds good when you're riding it. I wish they could have pulled that off with the WeeStrom. It sounds bad from any angle, and is the quietest bike I've ever (not?) heard.
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post #9 of 9 Old 09-08-2009, 06:42 PM
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Just guessing here. The "A" suffix indicates a specific filter, that peaks around 3000Hz (the peak sensitivity for most human ears) and tapers off above and below that. Singles and twins put out more low-frequency sound, which the filter would tend to attenuate (reduce). The lower limit for those bikes may indicate an attempt to 'level' the playing field by allowing a higher limit for bikes (and frequencies) that the "A" filter tends to accentuate. Kinda odd they didn't use an unfiltered spec.
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