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Old 03-28-12, 05:23 PM   #1
Winfried
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Question Battery-powered horn that sounds like car horn (pattern, dB)?

Hello

I know about the AirZound, the (Mini)Megahorn, and the Thunder Horn, but I'd rather a horn that sounds like a car horn and plays at the same volume.

The Wolo Twin Power 200 / 118 Decibels-520/630 HZ is just what I'm looking for, but it runs on a 12v battery.

Ideally, it should be easy to remove from the bike so I can take it with me when I need to park it outside.

Is there really no company that makes a bicycle horn that runs on regular batteries (AA or 9V) and plays a sound similar in pattern/dB to a car horn?

Thank you.
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Old 03-28-12, 05:53 PM   #2
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I mean, something that sounds just like this, without the huge box + cables:

http://www.youtube.com/watch?v=_6APeUHUOcA
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Old 03-28-12, 06:32 PM   #3
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Probably not going to find it. Car horns draw several amps at 12 volts. That's a lot of power. Sound is logarithmic; getting a little more sound takes a lot more energy.

The bottom line is that to provide that kind of sound levels, a standard single car horn draws 6 amps at 12 volts, which is 72 watts. You aren't going to be able to get the same level of sound with less power input than that. Lower voltage, more amps. 6 amps is already very challenging for most batteries that are fairly light.

Add to that, cars actually have TWO horns, so double that.

What you really need is a source of a big whack of power for a short period of time. It would be neat to figure out a way to have a brake that made noise on demand, since brakes are dissipating a heck of a lot of energy quickly.
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Old 03-29-12, 09:31 AM   #4
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You might consider using a 12v battery from a cordless drill for the power source and then work on a quick release mount for the horn.
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Old 03-29-12, 10:07 AM   #5
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Originally Posted by ItsJustMe View Post
Probably not going to find it. Car horns draw several amps at 12 volts. That's a lot of power. Sound is logarithmic; getting a little more sound takes a lot more energy.

The bottom line is that to provide that kind of sound levels, a standard single car horn draws 6 amps at 12 volts, which is 72 watts. You aren't going to be able to get the same level of sound with less power input than that. Lower voltage, more amps. 6 amps is already very challenging for most batteries that are fairly light.

Add to that, cars actually have TWO horns, so double that.

What you really need is a source of a big whack of power for a short period of time. It would be neat to figure out a way to have a brake that made noise on demand, since brakes are dissipating a heck of a lot of energy quickly.
Could you somehow charge a capacitor with your brakes then use that for a power surge?
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Old 03-29-12, 10:43 AM   #6
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Could you somehow charge a capacitor with your brakes then use that for a power surge?
Sure. First, you need a big enough generator to act as a brake and to be able to generate 100 watts at 12 volts (typical generator hub is 6 watts at 6 volts I think). That'll probably weigh about 5 pounds.

You need 6 amps for 1 second? That's 6 coulombs of energy you need to store. At 12 volts, that's half a farad of capacitance. Since the horn will actually stop working when it gets down to 9 volts or so, and the voltage on a capacitor is proportional to the remaining charge, you need 4x as much as that, or 2 farads.

2 farads of capacitors that are fast enough to be capable of delivering 12 volts at 6 amps will be about the size of a lunchbox and will weigh another 4 or 5 pounds.

So yeah, you could do it. It would be very complex and would weigh probably about twice what a lead acid cell would, and would add a lot to the spinning mass.

EDIT: actually after doing some research I think this would be about 10x heavier and at least 20x more size to give you a 1 second burst, versus a lead acid cell which would give you 20 minutes of horn sounding per charge and take up a fraction of the space.


I was thinking more along the lines of a mechanical horn. You've already got a lot of mechanical energy, and you want to produce mechanical energy. Converting to electrical energy along the way is inefficient and a lot of junk to carry around the other 99.9% of the time.

Something like a horn diaphragm that could be linked directly to a corrugated disc on the wheel.

In the end any such thing would be ridiculously complicated and I doubt would be much (if any) lighter than a small 12V gel cell and a car horn.

Here's a battery that would be more than enough:
http://www.batteryspace.com/sealedle...12v23ahs1.aspx
It weighs 2 pounds and would fit nicely on top of a rack. Combined with the car horn, maybe 3 pounds. It has enough power to honk a horn for about 20 minutes continuously per charge. $25 for the whole deal, very simple. A cordless drill battery would also be a good option, and might be a little lighter.
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Old 03-30-12, 04:39 AM   #7
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Thanks everyone for the education + ideas. Unfortunately, I don't the skills to build my own solution on either a drill battery or a lead battery.

Maybe I'm wrong, but I think there's a business opportunity here :-)
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Old 03-30-12, 06:18 PM   #8
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Actually, it struck me while riding my bike yesterday: If the MegaHorn/ThunderHorn can blast 105dB with a 9v battery, why can't the same kind of horn play something that sounds more like a car horn instead?

The reason I prefer that sound is that car/truck drivers are used to it, while the MegaHorn and the ThunderHorn play tones that sound like nothing they're used to (and I don't like the AirZound because it's too bulky to carry with me.)
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Old 03-30-12, 06:47 PM   #9
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I used to be into R/c helicopters and the Lipo batteries they use are super powerful. 2.2 amp hours at 12.6v fully charged. They also have a discharge capacity of 45c+ and thus can put out 60-80amps if needed. Very light, much lighter than a lead acid battery. You do need to ensure they don't go below 20% charge so one with a low voltage cutoff like they use in transmitters would work well.
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Old 03-30-12, 07:31 PM   #10
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I know next to nothing about audio, but I think lower frequencies require more power to produce the same sound pressure level. If so that is why all the high decibel horns that run on small batteries are really high pitched.
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Old 03-30-12, 08:08 PM   #11
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There is an issue, from my own experience, that seems to eat into the original premise of Winfried, which may tie with what ItsJustMe is mentioning. To radiate effectively within the frequencies that are characteristic for car horns, the radiator needs to be attached rigidly to a stiff mount. Possibly even the resonance frequencies of that mount need to be tweaked. This does not mesh with the desire to be able to take the device off the bike and carry away. Of course you can go with something ineffective but then the power source needs to be even bigger.
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Old 03-31-12, 07:57 AM   #12
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I used to be into R/c helicopters and the Lipo batteries they use are super powerful.
Thanks for the tip. I'll throw that idea to people who are into that sort of thing and see what they think. Looks like a nice week-end project :-)

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To radiate effectively within the frequencies that are characteristic for car horns, the radiator needs to be attached rigidly to a stiff mount. Possibly even the resonance frequencies of that mount need to be tweaked. This does not mesh with the desire to be able to take the device off the bike and carry away.
Good to know. That would explain why I failed finding a compact, loud bike horn that sounds closer to a car horn.

Alternatively, as seen in Paris this very afternoon...


It probably takes a bit getting used to not to sound the horn without meaning to by sitting too hard on the mattress pump that now stands at the base of the seat.
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Old 03-31-12, 08:55 AM   #13
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I have a moped horn on my bike, powered from 5 NiMH AAs, but it is attached permanently to the bike's rack. In my surroundings, it has worked very well reducing, multiple times, the chance of an accident and enhancing my stature in road negotiations.
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Old 03-31-12, 09:41 AM   #14
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If you look up car horns on wikipedia, you'll find an explanation of how the horn part of it is critical to really conducting the audio energy to the air. The vibrating surface by itself is not very efficient in this regard, the horn is required to really get a large volume of air moving, rather than just super-compressing air in a small volume and turning a lot of the energy into waste heat. Sometimes there's just no substitute for something that's large and substantial.
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Old 03-31-12, 10:00 AM   #15
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I have a moped horn on my bike, powered from 5 NiMH AAs, but it is attached permanently to the bike's rack.
I'll add this to the list of ideas.

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The vibrating surface by itself is not very efficient in this regard, the horn is required to really get a large volume of air moving, rather than just super-compressing air in a small volume and turning a lot of the energy into waste heat.
That explains why the AirZound sounds loud but not at all like a car horn.
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Old 04-02-12, 08:21 AM   #16
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Seems like a simple handpump is enough to power a couple of loud horns:

"Painfully loud bike horn w/ hand pump"
http://www.youtube.com/watch?v=VFcFs6qQY1Q

Has anyone tried it?
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Old 04-02-12, 09:15 AM   #17
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Seems like a simple handpump is enough to power a couple of loud horns
There is the Dealextreme Horn. I even got it, but have not got around yet to mount it, so cannot tell about the experience.
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Old 04-02-12, 11:16 AM   #18
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I think anything you have to actually pump is an immediate failure. Even when just pressing the button on the AirZound, I don't always have time to hit the button. At least when it's just a button I can still keep my hands on the bars while pressing. If I had to take a hand off to pump something I would never use it.
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Old 04-02-12, 12:18 PM   #19
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I think anything you have to actually pump is an immediate failure. Even when just pressing the button on the AirZound, I don't always have time to hit the button. At least when it's just a button I can still keep my hands on the bars while pressing. If I had to take a hand off to pump something I would never use it.
True, but there is room on a bike for more than one signal. E.g. I thought about installing the particularly loud signal for encounters with trucks. Also, one can be innovative. I was thinking about mounting the DX horn in such a way that I could stomp onto the pump with my foot.
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Old 04-09-12, 03:43 AM   #20
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I was thinking about mounting the DX horn in such a way that I could stomp onto the pump with my foot.
Good idea :-) Anybody's feeling like building a prototype?

In the meantime, I ordered the Megahorn. I'll report back about its effectiveness as compared to the AirZound.
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Old 04-09-12, 07:01 AM   #21
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I would like a better solution then the air zound aswell. It's good on paper but alittle jinky out in the field.
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Old 04-16-12, 02:48 AM   #22
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Just got back from Amsterdam: The ding-dong is pretty effective with pedestrians :-)

I don't have the tech skills to tell, but I'm surprised there's no battery-powered horn that can play two tones, at two different volumes: One regular volume ding-dong to warn pedestrians, and one 100dB for cars (if it can't play car horns, I'll settle for the annoying Megahorn tune).

And it should be compact and easy to remove from the bike: The AirZound is a bit big to fit in a backgpack, not to mention there's no lock to prevent pushing the button while it's in the bag ;-)

There's an opportunity right there for an engineer.
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Old 04-16-12, 03:15 AM   #23
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Could you somehow charge a capacitor with your brakes then use that for a power surge?
This is a Darwin Award waiting to happen.
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Old 04-16-12, 07:19 AM   #24
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This is a Darwin Award waiting to happen.
In what way, because it's likely not to work when you need the horn, or the brakes are not likely to be as effective when trying to regenerate power rather than just dumping energy as heat as normal brakes do?

I can see either of these being a good argument against the idea.
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Old 07-05-12, 03:36 PM   #25
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Good idea :-) Anybody's feeling like building a prototype?

In the meantime, I ordered the Megahorn. I'll report back about its effectiveness as compared to the AirZound.
This type of horn is already in use and was designed and made by TrafficDroid of London, his youtube and twitter alias is Sonofthewind. His current model, I believe is the DroidHorn 3.0 however 4.0 may be in the manufacturing stage!

Search for Droid Horn and you will find him.
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