Quoted from Dave's post above.

"If the new horn only draws a bit more power....you might be OK without a relay.  Does the stock horn list a power rating on it?"

Yes. The rating on my 2013 S40 horn is:  12V    3A    105 Decibels

The 2 horns that I purchased from Amazon are rated at 100 Decibels  and stamped on the horn is: 12V 1.5A. I am sure I could get away with out a relay, but since I already have the relay and fuse holder I went ahead and installed them.

Since I installed the horns with Rubber Vibration Isolators I had to run a ground wire from the battery to the horns.

I am not certain if 2 x 100 Decibel Horns will make 200 Decibels?
I will find out tomorrow.......

Kenny G

Kenny G wrote on 08/17/16 at 20:42:45:


I am certain that 2 x 100 does not make 200 when it comes to sound.  The db scale is arranged so that every 10db increase is a doubling of loudness to the human ear.  When you go from 100 db t 110 db, the sound intensity is doubled.!


I tried to GOOGLE this question about 2 horns being twice as loud as 1....and I couldn't find anything.  I believe the reason is that the 2 horns will never have the pressure waves synchronized - so the intensity of the loudness will change as the pressure waves comes in and out of phase.

So the result is that 2 horns of equal power are only twice as loud if they are synchronized so that the pressure waves are in phase and the horns create a simultaneously larger pressure wave.  Most "dual" horns are made intentionally with different frequencies, this allows the horns to come in and out of phase, and the pressure waves change from being in and out of phase continually....and when they are in phase the combination makes the pressure waves stronger and at other times tends to cancel each other.  This pulsing effect does makes the sound more noticeable, and the pulsing may not be audible as it is most likely faster than the ear/brain can process (the same way you can't see the 60 cycle pulse that occurs in florescent bulbs or a cathode ray TV screen).

So...2 horns are louder than 1 - but I am not sure they are twice as loud (and it is maybe impossible for the human ear to be an accurate measure of the "loudness" of a sound from the "fullness" of a sound).

The horn on my Pontiac Vibe was pathetic, and I installed the Hella Supertone Horns.  They are listed as 118db, and they are very loud, and part of that is because they are big...they are almost 5" in diameter.  I don't know if they are just too big to look good on a motorcycle.  I believe it is necessary that loud horns get bigger.....there is only so much air that can be moved by a small horn.  These will require a relay - although I can't find anywhere the power requirement of the horn is listed.

https://www.amazon.com/HELLA-003399801-Supertone-High-Bracket/dp/B000CRZXPI/r...

zipidachimp wrote on 08/13/16 at 12:47:42:


You kidding?  The number of times drivers (both distracted and not distracted) have either started a lane change on top of me or a left turn in front of me can't be counted.  I've been riding since the 80's, retook  the MSF course in '08 and am conscious of staying out of blind spots etc.  I certainly don't overuse my horn; I think we all know how angry and hair-trigger society has turned in to on our roads.  But I'll take having a horn that startles poor drivers vs. a little "beep beep"  when I need it.

That Harley horn cost waay too much but it fits on the stock bracket and wires reach just point the bracket to rear, very simple install
It's loud as hell ! Shiney black plastic blends in with frame nicely .

Sorry posting pics is not my thing
PM your email to me I'll send a pic

Kenny mount relay close to oem horn so you can get oem horn wiring to reach relay , less wiring that way