Cycle News - Archive Issues - 1970's

ROFSILENCE: ~~~Test I ,; o By Ron Schneiders Several weeks ago we ran an article advocating the use of silencers and spark arresters. Our most cogent argument was that if we don't stop irritating people with noisy bikes, we won't have any place to ride. We blandly stated that there were a number of good silencers and spark arresters on the market and that they didn't cost much, either in money or power. Afterwards it occurred to us that we ought to test the' devices that we were recommending and see just how good they were. We contacted a number of manufactureu and asked for one of everything that they made in this particular field. Here is what we got. quality of sound varies greatly. A cement mix", and a symphony orchestra might produce the same volume of noise as measured on a meter, but what a difference! You might make the same sort of a comparison hetween a Triumph and a Hodaka. Almost anything that is stuck on the end of an expansion chamber' will improve the quality of the sound, but unfortunately this doesn't count with the Highway Patrol. It does count in the neighborhood popularity contest, however. To ensure accuracy, each test was hearing is such that if you double the intensity of a sound. a person does not hear it as "twice as loud." If he did, he would quickly go insane because there is a lot of noise that is more than 1,000,000' times as intense as a soft whisper. In order to bridge the gap between physical fact and physiological fact (and for other reasons as well), the measurement of sound is generally expressed in decibels. Three db is the magic figure to remember: It is about the smallest discernible audible difference, between sounds. Three db also represents a doubling of the Considering the meaning of the term "decibel", it becomes clear that even the worst of the silencers cut down the volume of noise quite a bit because none of them are worse than 3 db down from the open pipe lever Several other things are also apparent. First, none of the devices meet the CHP standard of 88 dbA (The small J&R/Horstman· K rizm an spark arrester on my Sachs does, but it's like a cork in the end of the pipe). Some of the silencers would probably get by on the street if a good helping of discretion was used, but they don't make a bike street legal. Period. ~.~I'~ These are ,the devices we tested. Since thiS is a .relatively new field, many of the products are still in the design or prototype stage. Some of those that we tested that are not yet production items but will be in a period of weeks. Some probably'will never be. The first job was to determine how effective th e various devices were as silencers. Since spark arresters do some quieting, we tested them right alongside the silencers. In. order that other people could (hopefully) duplicate our tests if they so desired, we followed the California Highway Patrol Measuring Procedure. The procedure may be found in the California Administrative Code, Chapter 2, Title 13, Article 10. This procedure specifies the type. of instrument to be used, the pb,ysical conditions, the method of vehicle operation, and the levels required for operation of various vehicles on California Highways. For motorcycles, the maximum noise level (under test conditions) is 88dbA. A precision noise meter was required so we rented two General Radio units, Models 1565 A and 1551 C. We set up the test as precisely as p'ossible, following the CHP specifications. We found that the test is scientifically somewhat sloppy and humanistically invalid. Maximum noise from a motorcycle occurs when it is producing maximum power which can only occur when the machine is operated under full load. The test specified that the machine was to he operated under load, hut under the prescribed conditions there was no way to put the machines under maximum load! It would-be better to run the bikes up a pretty good hill or through some deep sand. As it stands, however, the measurement works in favor of bikes so we'd better not complain! Humanistically, the test works against us. As everyone knows, the Darryl Bassani, Ron Fry and Rick Vesco were willing helpers in the test. Author is on bike, Editor Bob is supervising. repeated three times and occasionally, when it was felt that the rider wasn't getting on it hard enough, it was repeated several more times. Present at the tests were, myself, Bob Sanford Cycle News Editor), Mike Jackson Norton Villiers), Ron Fry U&R Products), Darryl Bassani (Bassani Engineering), and Rick Vesco (Hooker Headers). With that crowd, you can bet there wasn't any hanky·panky! We had four motorcycles; my Sachs with a K & G Engineering Expansion Chamber, Bob's Yamaha with both a Bob Bailey pipe and"an A & A pipe, An AJS with a factory silencer on the stock pipe, and Ron Fry's 400 Husky with the stock pipe. l When all the tests were run, 1 averaged the three loudest in each case. The results are listed in table 2. In order to understand the measurement, the meaning of the term "decibel" must be understood, at least intuitively. Human intensity. A ten db change in a sound level seems like double the loudness but it is about eight times the intensity. Twenty db sounds like four times as loud, but it is 1,000 times the intensity. Sixty db represents an intensity change of 1,000,000. TABLE I To Fit Sachs, Yamaba Husky Sachs, Yamaha silencers Husky silencer prototype Sachs silencer A&A about $9.95 Sachs, Yamaha (their own pipes) Spark arresters Sachs Jerry Bases 113.95 Husky Austin & Graydon Sachs, Spark arrester/ Jerry Bases $14.95 Husky silencer combinations Austin & Graydon Sachs Spark Arrester/ prototype Yamaba Silencer combination Spark Arrester prototype Sachs silencer combination Manufacturer J&R Device silencers Bassani Mfg. Torque Eng. A&A J& R J& R Hooker Headers Torque Eng. I I : 13 ! 1 Distributor Price Jerry Bases $9.95 Austin & Graydon Bassani $9.95 ' i'i\.·" " 'L' ~ '2 f--f'--i-'_ I I : -- i' 11I---+l---!-'-,;'_., ,o~.--:-_L- " 9 L.+- ": --;--- I.. _-I-~ I" B_ _ • I ._.+_. , 'i ' - :' _ _ 1_ :/,'_ , I " B •• _ . , 1 .. 5 - _.. --f-- I / ~ :: --: __, SACHS WITH J81 R ~ • ~_ .. _ I 21 ~ ~ 3 S'LENCER/SPARKARRESTER APPROVED, YES PRODUCTION ITEM: YES " ..l-..-QUIETING:·lO DB I I NOISELEV~L' 9D DB r ; 2 ~PM xtDllD' C.R. Axtell did the verv orecise dynomomePaer testina. Here the Sachs is runnina at 'ft-'-'~l 1>J.'(W,1UV·. ~. ., j,,,,, .... 1 1 fu mron e.' armuTTS were reqUlr"", 10 spIte T silencers. . . " . . . ...uu, u..J.w:i"l .,.1 Secondly, you can not expect the same amount of quieting, or the same level of noise when you take one device and put it on another machine. For instance, the same J&R silencer that produced 8 db of quieting on the Sachs, produced 15.3 db of quieting on the Yamaha. Some ! 5 B I I f-~ • 10 bikes are much harder to quiet than others. Quieting of 16 db was achieved on the Yamaha, while not even 6 db was achieved on the Husky. One fact cannot be emphasized too strongly: The exhaust notes of all the tested bikes had a sharp, biting sound. The silencers removed the bite. The bikes were still loud, but they were no longer really irritating. FOT those of you who are around bikes a great deal, particularly if you don't like to wear a helmet all the time, a silencer can make the difference between hearing and deafness in later years. Noise in excess of 100 db can cause permanent hearing loss; we measured noise in excess of 100 db at a distance of 50 feet. Every bike tested was over 100 db at a distance of five feet whenever the engine speed was above an idle. When the noise tests were completed, we took the Sachs and the Yamaha to C.R. Axtell's Dynomometer shop in Glendale. There we ran tests to determine just what the various devices did to the performance of the two bikes. The results are shown graphically This J&R combination silencer/spark 'arrester was the best device fitted to the . Sachs.. Note horsepower gam thro~gh the mld·range. Graphs of others deviCes lite e~4~~" ,. '~.',I. I. ", .Hi • ,':JiJaf:.,";rJul;"~'Ji(Pf~~ttJ'tli.I'io) Z ~ w Z W ..J C,) > C,)

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