Nine dollar Amazon knockoff air horn

[2015 Blue RT]

I'm waiting for my 3D bracket to print for it, but have successfully tested it @ 90DB. PDF writeup and the 3D bracket file attached, I'll try & copy & paste the text & pics here.

2015 BMW R1200RT Horn Upgrade

 

OEM horn has 2 wires-

Brown ground to battery

Green +12V to ground module

 

Parts: (Amazon links for convenience)

• An adapter connector to 2x female .250 terminals ($12)

• A waterproof relay ($10). I mounted this under the right fairing cover using an existing screw. Had to drill out the hole to 19/64”.

• A $9 knockoff Nautilus compact air horn.

• I found I needed a 15mm head 10mm x 25 hex bolt along with a hex nut and flange nut. Fairly common hardware.

• My bike used a 6mm bolt to mount the horn, and I used a longer 30mm flange head bolt for it. Again a common hardware item.

• Any inline fuse holder that has at least a 12G wire will work. I made my own using Delphi Metri-pack 630 connectors that are waterproof.

• If you want to direct wire the relay (better all around) vs slicing to the cheap wire leads that come with it, you’ll need 2x of the large and small terminals referenced below. Never hurts to have extra in case you mess one up. This presumes you have the proper crimping tool for these.

• You’ll also need 2x 6mm ring terminals to attach to the battery post and to ground the horn at the mounting bolt, and a pair of .250 female terminals to attach to the horn. These can be found at parts or hardware stores.

• At least 10 feet of ¼” diameter nylon (NOT cheap vinyl that melts) split loom or some braided nylon sleeving. I used both since it was what was on hand. Nylon split loom has a gray stripe on it.

• Splices if going that route and heat shrink tubing.

 

 

Issues:

1. The mounting for this sucks. I’m not talking about the bracket (yet). The opening is slightly over 15mm, and the 8mm bolt supplies just spins in it. I enlarged the slot where the bolt goes and used a 15mm head 10mm bolt. I locked this in place with a common 10mm nut, and then mounted the horn to my custom bracket with a 10mm flange nut.

 

2. a. (Bracket) There’s a nice heavy steel custom bracket you can buy for around $22. It is supposed to work for a wethead, specifically a 2015 RT. It’s not linked because it didn’t work. See pics below. What I did was make my own via 3D printing. I enlarged the mount hole to 10mm, and moved the horn to the rear. Got it right on the 2^nd try.

2. b. This bracket comes with an 8x60mm bolt. Why? The bolt holding my horn in place was 6mm. I used a flange head bolt that was longer then stock, probably like 25 or 30mm.

 

Testing:

Using a free decibel meter app, I put my phone about 2 feet in front of my bike on a stool that was about a foot off the ground. I got a steady 90DB in my closed garage.

 

Wiring: All wiring used was automotive grade, not parts store wire that melts easily. When needed, it was wrapped either in nylon slit loom or braided nylon sleeving.

Relay-

87- To horn + side

30- Battery + side via 30A (suggested) inline fuse. I used a 20A fuse and it didn’t blow when I tested it for several seconds. I used some automotive grade red 12G wire for this.

85- To horn connector – side (OEM brown wire) I spliced in some automotive grade 20G brown wire to the connector adapter.

86- To horn connector + side (OEM green wire) I spliced in some 18G lime green wire to the connector adapter.

 

Either splice wires to existing leads, or use the following terminals to direct wire your wires:

Delphi Terminals Required: Five 1/4"

• 16-14 Gauge Terminals PN: 12066614 

• 12-10 Gauge Terminals PN: 12033997 

Horn-

Positive terminal- to relay #87

Negative terminal- to frame ground

 

 

 

Horn Bracket2.stl Horn_upgrade_with_pics_0423.pdf

[2015 Blue RT]

Note- final 3D bracket is thicker than the one shown (prototype), 8mm vs 6mm. It's now a flush fit on the flat part on top of the horn, which helps to stabilize it.

[lkraus]

FWIW, sound level readings with a phone app may be unreliable.  Using different phones to measure the same sound can produce different results because the microphones have different responses and limitations. The highest my older Galaxy S7 would read was 93dB, the current S10 tops out at 88dB.

[szurszewski]

7 hours ago, lkraus said:

FWIW, sound level readings with a phone app may be unreliable.  Using different phones to measure the same sound can produce different results because the microphones have different responses and limitations. The highest my older Galaxy S7 would read was 93dB, the current S10 tops out at 88dB.

 

It would be interesting to know, regardless of "true" db level, what the relative level of this horn is compared to the stock horn as measured by the same phone/same app under the same conditions. 

 

In any case, a nice and thorough write-up. 

[2015 Blue RT]

I didn't think to test the old horn, and the connector is now out of the way to try & do so. IMO, it's noticeably louder, of course being in a closed garage makes it seem louder I'm sure.

 

Day 1 commute with the 3D bracket and so far so good. 

[Paul De]

I put a similar China knock off Soundbomb on my 2008 Honda Civic after the horn on it rusted out. It is pretty loud, prolly a little louder than the OEM Waterhead horn. The big difference is tonal quality.  You get a different sounding horn that gets the cager to wake up because they think they are going to have a very expensive accident with an Italian sports car, instead of the meep meep come and squish me sound.

 

As a side note. If you don’t want to pony up for a Denali Soundbomb, the Stebel Nautilus is a very nice horn. You get the genuine Italian sports car sound and saves about $15 VS the Soundbomb. It is just as loud as the Soundbomb and is well made.  I’ve had the Nautilus on both my Oilhead and Waterhead for many years with no issues.

[Randyjaco]

Can you share the dimensions of your final 3-d bracket? I can't open that stl file.

[2015 Blue RT]

1 hour ago, Randyjaco said:

Can you share the dimensions of your final 3-d bracket? I can't open that stl file.

JPG from Tinkercad attached. I also uploaded it to Thingiverse here.

[Randyjaco]

Thank you.

I opted for a simpler version out of a piece of 11 gauge stainless I had sitting in the shop. It seems to work well and fits the stock horn mount hole 

I am still waiting on the relay and connectors to complete the job.

[Randyjaco]

Finally, got everything installed and buttoned up. I got a 10 dB increase in sound output. In other words I doubled my sound output. The RT sounds like an 18 wheeler   

I am a happy camper! 

 

Thanks, Blue, for your excellent write-up and help

Randy

[2015 Blue RT]

You're welcome, I'm glad my info helped another.

[2015 Blue RT]

Thought I'd pop in and give an update after nearly a year in use. I try & test the horn daily on my rural commute. I've only needed to actually use it twice, and in every instance it has worked w/ no issues. I see the original part is no longer available though.  The closest thing I saw was around $37.

[frogdor]

Another horn option are Fiaam Freeway Blasters. There is a high tone and a low tone version and really need to be installed as a pair. They are quite compact; I fitted a pair to my Honda VFR way back in 2005 and they are still going strong. They are about $12 a piece on Amazon.