Aftermarket horns provide a louder, and often more pleasant sound than stock horns. Stock horns typically have an output of 97 dB. The decibel scale is logarithmic and therefore the sound pressure doubles for every increase of 3.3 points, i.e. a horn with 118 dB produces approximately seven times the sound preasure as a stock horn. Hella Supertone Horn Kit. This horn is best on open interstates where you want to warn a truck that he is about to run into you.