This might end up being thread drift but I've recently learnt that "loud" is a very slippery concept. I have been trying to reduce the decibel level of an aircraft to meet noise requirements. With the original exhaust system it was measured at just over 70db. The measurement involved flying over the mic at a specified height with full power applied in climb configuration, The result was about half a db over the limit for the class of plane. With a very small extra muffler - a German design and it seems very clever and weighs about 250 grams - attached to the exhaust pipe we have reduced the db by about 3db. It doesn't seem like much but the noise levels in the cockpit are considerably reduced and we are now within the law. A decibel is a tenth of a bel and the Bel is a nod to Alexander Graham. So a reduction of 3 db is very significant regarding the loudness that one perceives. Others who know more about this might jump in here.
But what I want to know is - how do motorcycles get away with the enormous noise they produce while a slightly loud Morgan would not pass the test? I suspect it has something to do with where the throttle opening is as one passes the mic. i.e. accelerating or decelerating. And yes I'm a bit bitter about all of the bother and expense of conforming when my planes' noise is way less than the 125 cc Vespa down the street. Like most Morgan 4/4s. Even those with Librands side exhaust.
