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The "new" sound levels are not as quiet as you think. 99db to 94dba is not a full 5 db more quiet, they are slightly different standards.
Unless the surface can absorb sound (very tall thin grass) the sound is just reflected at a nearly identical intensity.
conversely if I had a muffler with a 1" outlet (but no perforations in the core and no packing to absorb sound energy) I would be OK?
I think (as previously mentioned)checking some bikes at the line before practice or race would go along way to curtail cheating. They regularly do this at AMA pro ATV races.
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Tests have to be done in a controlled enviroment and can be affected by a lot of variables like temps, wind, ambient noise, and anything nearby that can reflect noise.
An ID limit along with a maximum DB level (instead of a measurement at 1/3 throttle) along with fixing the holes in the system that let mechanics use double air filters, remapped ignitions, and other measures used to circumvent testing is what will be required to fix the problem.
Other competitors should be allowed to protest another rider who they suspect is voilating the noise limit just like they can protest displacement or modifications done to machines being raced in the stock class,
Pay the protest fee, let the officials do the test and if the rider fails they are DQed.
I guess it will take an organization that is serious about enforcing the rules AND protecting the future of our sport to make it happen.
The AMA has failed so miserably it is embarrassing.
And for those of you suggesting that the problem can be solved by simply turning the pipe down towards the ground, I would suggest going to an ATV National.
A lot of those machines do exactly that and you will find that it makes very little difference in the sound levels.
If a machine is blowing 120 Db it is going to be loud no matter what bandaids you come up with.
The ground will dissipate some of the sound, and more importantly, the sound will be reflected more upwards, instead of across property lines to piss off neighbors. If you doubt this, just listen to a speaker facing straight towards you, then listen to it again at the same distance once it's been pointed down to terra firma. You will notice at least a 3db reduction even at close range, and a more dramatic change at longer distances (which is what we are concerned with here). Lastly, those waves that do get bounced off the ground, will be lengthened, helping to put the tone into a less sensitive range of human hearing.
Let's say a bike being tested is putting out 100 db of sound at a distance of 1 foot from the exit of the exhaust.
Let's say the ambient noise at the track (including lets say a tractor discing, other bikes warming up, track PA system ect) is 90 db.
For the ambient to effect the reading of the bike being tested, the ambient noise will have to be at least 100 db. If it is not, it will not give the bike a higher reading.
For instance, if you have a speaker putting out 100 db all by itself, you can introduce a second speaker at 90 db and you will only hear the 100db speaker. To even hear the second speaker, it will have to be at least 100 db. The pair then together will register 103 db.
Now, let's say you are testing bikes on the line. If the bike you are testing is actually putting out 100 db, but a second bike right next to it fires up and is putting out 100 db, and the mic being used for measurements is not focused tightly enough on just the first bike, then you will get a false reading of 103 db. But generally, with a good B &K mic, using C-weighting, measured a short distance from the exit of the exhaust, it would be extremely hard to have a false reading unless something very close by is extremely loud.
The current method of testing here in Australia is similar to what you guys use in the US use and my acoustic engineer refered to it as the biggest joke he had ever heard of. There are to many vairables and it realy only tests the skills of the those that need/ want to cheat. For noise testing to be consistent and quantifiable the bikes need to be tested in real world situations.
The reason that the current sound testing methods are used is that it is cheap. You do not need expensive equipment to measure the way they currently do. Before you say that the dB readers they use cost a couple of grand, when we had some noise testing done the acoustic engineer had 3 meters. The cheapest was $15000 and was the reference meter. The meter he used to test the bikes was over $30 000 and it fitted in the palm of your hand. I can't see the regulatory authorities going to this expesnse to monitor noise but if you want to minise impact then we have to drop the max dB's of a bike to 94, not the scrutineering test.
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Our noise issues have a built in contingency to allow bikes to peak at 105 dB. If they exceed 105 we have issues with compliance from the local Council. This is where it gets technical. Our Noise walls have an STC rating of 47 and in order to comply with regulations individual bikes must not exceed 105.
The positive thing though is that there are moves to make bikes quieter. Most people are getting the message but there are still the ignorant ones that think noise = power.
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