With the air tank I can prob hold 10 seconds on a blast then take 20 seconds or so to recover(air pressure and hearing). I don't really see any possible reason to hold it for 10 seconds though 3-5 sec is way more than enough. Usually I can get two short 1 second blasts before the compressor kicks on for a few seconds to refill the tank.
I don't think anyone would ever really need a bigger tank than that just to run a horn. It does good and the whole setup fits under the hood of my metro. If you want realistic sound run 100psi but for super deafening loud run 150psi
I do think it is funny when I get stopped at a train crossing and my horn is louder than the train's. The conductor usually looks at me like I am nuts for putting something like that in a metro
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