You left out the part where that noise is heard by the driver, but does not confer any directionality, at all. This is a major problem with Emergency vehicles, you can hear the sirens, but you have no idea if the vehicle is in front, behind, or to the side.
The system to tell where something is coming from is built into your hearing and brain. (posted earlier in the thread) I know what you are saying, but there still needs to be a standard. I understand some people will have NO problems locating a sound source, where as others will have some difficulty, or it will just take them longer. There are factors that contribute to this (age, genetics, abusing your ears, drugs, alcohol). Being able to tell where something is and the speed at which you can detect where the sound is coming from are individual, and only by doing tests with many many (I'd say in the 1000's) people can you form a baseline avg. (which has been studied)
So of course there will be differences between individuals but it still does not take away the noise stimulus argument. Its the fact that the drivers have become aware of a bike in any form - is all that really matters. (for this argument) The bikers themselves will have to ride appropriately with traffic to reduce their risk of course, but
assuming the rider is being responsible (not speeding, or lane splitting or ANYTHING ELSE). The sound emitted from the bike will increase overall awareness to all the other road users around them. It may not be as important as actually learning to ride well and safely, BUT it does what it does. I suppose along the way it annoys a few people, but that doesn't take away how the science behind it all works.
The horn upgrade is a great idea as well, but that would be reserved for those "oh *****" moments.. whereas a louder exhaust is just a telltale sign that there is a biker around. Its up to the drivers of cars to drive their vehicles responsibly as well. Be aware of all other vehicles around them. They can't go ramming into people they feel "hurt their feelings" or some other none sense.. I
Indeed it looks like there will never be full agreement on "Do
loud pipes save lives?" but there is no refuting human biology and how the process works. Perhaps as I stated earlier in the thread, the entire question is wrong. "Do louder exhausts
create awareness of a biker in the vicinity?" More accurately reflecting what the exhausts actually do in live traffic. I think yes.