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How loud is it? - CA has the answer.....

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Look at the variances in even the stock pipe...88.0, 94.8, 88.0, 91.0, 91.0, 88.0, 89.0, 97.0,88.5, 94.5

I wouldn't really take this pdf as gospel by any means.

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Totally ridiculous. They have the same make, model, year, stock, at different decibel levels. I think too many stoned tree huggers typed that list!

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Look at the variances in even the stock pipe...88.0, 94.8, 88.0, 91.0, 91.0, 88.0, 89.0, 97.0,88.5, 94.5

I wouldn't really take this pdf as gospel by any means.

Actually, those are pretty good results if you disregard the 97.0 reading. A 6 db swing is actually pretty tight and I find it somewhat impressive. Since I assume these readings were from different bikes, there are alot of variables that will account for the range they measured. Unless they were all measured in the same controlled environment, here are some things that will affect the reading:

1. hardness on the ground, grass will absorb more sound, hard pack will reflect sound back to the meter.

2. atmospheric conditions, cold dense air will carry sound better than thin dry air.

3. silencer packing condition

4. jetting, air filter, air box mods, fuel, these will all have a slight effect

5. I seriously doubt the sound meters they use are kept in calibration or are extremely accurate. A precision meter such as a B&K will cost about $1,400, they probably use something in the $300 range.

6. operator variances, the distance and angle from the pipe will never be exactly the same in a field measurement. Height and girth of the operator and different clothing will reflect sound back to the meter differently.

The list goes on, all of which have a minor effect on the db reading. However, the pdf certainly gives a good indication of the sound levels you can expect from the different pipes so I do think it has some valuable data, plus it shows the range you can expect when you get a sound check in the field. An example, my Husky WR250, FMF gnarley and turbine core II was measured 11 times last year at different events. Readings ranged from 88 db to 96 db. I'm sure that if it was always measured in a contrlloed anachoic enviroment, reading would have been within 1 db.

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Wow, pretty neat compilation. First thing you learn in science classes is that you're not going to test 15 things and get less than 15 results. Everything being the same would actually be evidence of a test being bupkus ;]

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This proves that sound testing

is more of an art than a science... :bonk:

The listed values are interesting in that they're obviously actual test results done in the field...

...and were performed under wildly varying conditions... with instruments, some of which had to have been dropped... and by people who had also been dropped. :naughty:

The variance on the stock exhausts is telling...

...although I have some *stock* pipes that vary from 88 to 97 decibels, too. :D

Greg

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Another thing to consider is that there is no way brand new bikes will yield the same result at the factory. If they specify the new bike has an 88 db sound pressure level (SPL), that spec has upper and lower control limits which I would guess would be maybe +/- 6 db (could be +/- 3 db or whatever that particulay manufacturer specifies). That would mean they would pass production tests anywhere in the range from 82 db to 94 db. There is simply no way, without fine tuning each indivdual exhaust system after it was installed on said bike, that they could produce an SPL of exactly 88 db, just too many variables within the complete system of intake, combustion, exhaust, et.

I do see some value in the PDF data. For example, if you were planning to convert your mx bike to an offroad racer for enduro and hare scrambles, you will need to meet the 96 db spec in most arenas. Therefore, you can certainly rule out the ehaust systems that consistantly exceed the 96 db limit. It would be valuable to see more data published on this issue. At our next club meeting, I will propose that we collect data for alll the events that our club puts on this season. Don't expect to see any results until late October and only if I can convince them that there is alot of value in the data, especially as we are currently attempting to get MX racers interested in competing in off-road events when there racing scedules permit. You can check out the club at http://www.norsemenmc.org/

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A 6 db swing is actually pretty tight and I find it somewhat impressive.

Sorry, I don't agree. With properly calibrated equipement and taking the reading x3 a 6dB swing IMO would be unacceptable.

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Sorry, I don't agree. With properly calibrated equipement and taking the reading x3 a 6dB swing IMO would be unacceptable.

I used the 6 db as an example and I don't really know what each manufacturer uses, but I'll guarantee that a 6 db swing will be acceptable for most applications.

I work for one of the predominant manufacturers of acoustical components that supplies the US military. A typical MIL-SPEC for these products is +/- 3 db and some products are speced as much as +/- 8 db. These products are deemed as life critical, meaning that comunication must ALWAYS be reliable and intelligable under any environmental condition. Same goes for commercial aviation products. A motorcycle, on the other hand......... well let's just say that +/- 6 db seems reasonable to me.

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I used the 6 db as an example and I don't really know what each manufacturer uses, but I'll guarantee that a 6 db swing will be acceptable for most applications.

I work for one of the predominant manufacturers of acoustical components that supplies the US military. A typical MIL-SPEC for these products is +/- 3 db and some products are speced as much as +/- 8 db. These products are deemed as life critical, meaning that comunication must ALWAYS be reliable and intelligable under any environmental condition. Same goes for commercial aviation products. A motorcycle, on the other hand......... well let's just say that +/- 6 db seems reasonable to me.

Is that for a single reading or a 3x reading? Also, if a 6dB swing is OK, does that mean that at one of the Norsemen clubs trail rides/enduros with a 96dB limit is going to accept a bike blowing 99dB (96dB +-3) or 102 dB (the full 6 dB swing)?

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Is that for a single reading or a 3x reading? Also, if a 6dB swing is OK, does that mean that at one of the Norsemen clubs trail rides/enduros with a 96dB limit is going to accept a bike blowing 99dB (96dB +-3) or 102 dB (the full 6 dB swing)?

Not sure what you mean by a 3x reading, but a given piece of product will test the same in a controlled environment if you test it 1 time, 3 times, or 100 times. If it is tested today, next week, next month, or next year, it will yield the same result. If it doesn't, then there is something defective with it such as it's performance is degrading at an unacceptable rate. However, the acceptable variance will occur within multiple units coming off the assembly line. Of course, motorcyles will change with time due to factors such as silencer packing condition, engine wear, and fuel differences. If a motorcyle manufacturer was required to hold +/- 1 db, the reject rate would be so high that the cost of a machine would increase perhaps 10 fold.

As far as the Norseman testing, they do calibrate thier equipment several times throughout the season. Could they test a bike at 96 db and have someone else test it and read 102 db? Certainly, because of condition changes, equipment and method variances. As I stated, different events I participated in yielded readings from 88 db to 96 db. I'm thinking that in a controlled environment, it would be somewhere in the middle at about 92 db.

Anyway, that's my story and I'm stickin' to it unless some other acoustical engineer convinces me otherwise.

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One thing I forgot to mention. If a machine is required to meet 96 db, say for the US Forest Service, the manufacturer would make that the upper limit. So if they had a +/- 6 db test standard, the test spec would be 90 DB +/- 6.

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I would say that the .pdf is more of a guide than anything else. No one knows the circumstances of the readings when they where taken so we can't know for sure why the db's are off.

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Sorry, I don't agree. With properly calibrated equipement and taking the reading x3 a 6dB swing IMO would be unacceptable.

I have to disagree with Sundog. If youve ever done sound measurements without a tach, you know how much the levels can change, even with just a couple hundred rpms! Im sure that they are not measuring the distance to the muffler exactly, either. Even an inch variance in distance to the muffler can make a measureable difference! (it also matters how pi**ed off the Ranger was that made the measurement)

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