# How do car horns work? **URL:** \ **Category:** Factual Questions\ **Created:** [October 15, 2004, 8:12pm UTC](https://boards.straightdope.com/t/how-do-car-horns-work/269445 "2004-10-15T20:12:23Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![McDeath\_the\_Mad](https://avatars.discourse-cdn.com/v4/letter/m/a3d4f5/32.png) [@McDeath\_the\_Mad](https://boards.straightdope.com/u/McDeath_the_Mad)\ **Post date:** [October 15, 2004, 8:12pm UTC](https://boards.straightdope.com/t/how-do-car-horns-work/269445/1 "2004-10-15T20:12:23Z")
This came up during our weekly Friday lunch at the pub. How do car horns work? You need electrical for them to work (dead battery = no horn). I’m pretty sure they use air, but where does it come from? They don’t have reservoirs, or do they? Thanks MtM ---
**Author:** ![FatBaldGuy](https://avatars.discourse-cdn.com/v4/letter/f/ecd19e/32.png) [@FatBaldGuy](https://boards.straightdope.com/u/FatBaldGuy)\ **Post date:** [October 15, 2004, 8:29pm UTC](https://boards.straightdope.com/t/how-do-car-horns-work/269445/2 "2004-10-15T20:29:15Z")
Depends on the type of horn. Many tractor-trailer rigs use air horns, which are quite loud, but most car horns are simply speakers attached to a tone generator if I’m not mistaken. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [October 15, 2004, 9:02pm UTC](https://boards.straightdope.com/t/how-do-car-horns-work/269445/3 "2004-10-15T21:02:47Z")
> [@Fat Bald Guy](#): > > Depends on the type of horn. Many tractor-trailer rigs use air horns, which are quite loud, but most car horns are simply speakers attached to a tone generator if I’m not mistaken. Agree–to amplify, I once installed air horns on my car. It is a horn that uses forced air, and includes an air compressor to force the air. I don’t know how the actual tone is produced, though. Regular car horns don’t require any forced air. ---
**Author:** ![Cervaise](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cervaise/32/16693_2.png) [@Cervaise](https://boards.straightdope.com/u/Cervaise)\ **Post date:** [October 15, 2004, 9:15pm UTC](https://boards.straightdope.com/t/how-do-car-horns-work/269445/4 "2004-10-15T21:15:08Z")
So there’s no practical technical reason why the trucks and SUVs get the aggressive _BLAT_ and the little passenger cars are stuck with a squirrel and its kazoo? ---
**Author:** ![Elvez](https://avatars.discourse-cdn.com/v4/letter/e/8491ac/32.png) [@Elvez](https://boards.straightdope.com/u/Elvez)\ **Post date:** [October 15, 2004, 9:54pm UTC](https://boards.straightdope.com/t/how-do-car-horns-work/269445/5 "2004-10-15T21:54:29Z")
A friend of mine got a horn that played the opening to Dixie, like the General Lee had in Dukes of Hazard. It had a compressor that forced air through 5 or 6 different horns (that looked just like the kind with a rubber bulb on the end that you might put on your bike), and each horn played a different note. Some little mechanism in there directed the air from the compressor to each horn in the note succession of the song. Worked pretty well for a while, but then one or two of the horns crapped out and it just played the other ones: “Honk! \_\_\_\_\_ honk honk \_\_\_\_\_ honk honk honk \_\_\_\_ \_\_\_\_\_ honk.” ---
**Author:** ![Chairman\_Pow](https://avatars.discourse-cdn.com/v4/letter/c/838e76/32.png) [@Chairman\_Pow](https://boards.straightdope.com/u/Chairman_Pow)\ **Post date:** [October 15, 2004, 10:09pm UTC](https://boards.straightdope.com/t/how-do-car-horns-work/269445/6 "2004-10-15T22:09:36Z")
> [@Cervaise](#): > > So there’s no practical technical reason why the trucks and SUVs get the aggressive _BLAT_ and the little passenger cars are stuck with a squirrel and its kazoo? Big car gets big sound. It’s pretty funny to hear a car alarm going off that’s just about drained the battery. Tho’ not funny enough to make up for four hours of the thing going off in the first place. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [October 15, 2004, 10:42pm UTC](https://boards.straightdope.com/t/how-do-car-horns-work/269445/7 "2004-10-15T22:42:26Z")
Related thread [How does a car’s horn and an ambulances siren work?](http://boards.straightdope.com/sdmb/showthread.php?t=175939&highlight=horn) ---
**Author:** ![rjung](https://avatars.discourse-cdn.com/v4/letter/r/45deac/32.png) [@rjung](https://boards.straightdope.com/u/rjung)\ **Post date:** [October 15, 2004, 11:37pm UTC](https://boards.straightdope.com/t/how-do-car-horns-work/269445/8 "2004-10-15T23:37:20Z")
> [@Cervaise](#): > > So there’s no practical technical reason why the trucks and SUVs get the aggressive _BLAT_ and the little passenger cars are stuck with a squirrel and its kazoo? None at all. I’ve seen electric car horn kits that will do the big semi-truck air-horn TOOOOOOT; you can hook one of those to a little ol’ hatchback and surprise folks on your commute, if you’re inclined. ---
**Author:** ![wolf\_meister](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolf_meister/32/15202_2.png) [@wolf\_meister](https://boards.straightdope.com/u/wolf_meister)\ **Post date:** [October 16, 2004, 12:17am UTC](https://boards.straightdope.com/t/how-do-car-horns-work/269445/9 "2004-10-16T00:17:38Z")
Just thought I’d add my 2¢ about a special type of car horn - the AHH - OOO - GAHH horn !!! I took one apart and found that it is driven by an electric motor. On the motor shaft is a disk with a few bumps on it. This in turn spins underneath a fixed membrane that has MANY bumps in it. Result? A very raucous mechanical grinding that sounds like … well I’m sure you’ve all heard it. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [October 16, 2004, 3:17am UTC](https://boards.straightdope.com/t/how-do-car-horns-work/269445/10 "2004-10-16T03:17:33Z")
> [@Cervaise](#): > > So there’s no practical technical reason why the trucks and SUVs get the aggressive _BLAT_ and the little passenger cars are stuck with a squirrel and its kazoo? Dunno. I put an air horn on my motorcycle once but the electrical system couldn’t deliver enough amps to power it unless I was going at least 50. At low speeds I could tell that the compressor was spinning but no sound. Similar might be true of very small cars with underpowered alternators. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [October 16, 2004, 3:44am UTC](https://boards.straightdope.com/t/how-do-car-horns-work/269445/11 "2004-10-16T03:44:52Z")
Fiat Spyders of the 70’s used two air horns with an electric compressor. They worked great. I suspect the one that didn’t work well on the motorcycle was a poor design, or perhaps designed to be used with an automobile battery rather than a motorcycle battery. ---
**Author:** ![hammerbach](https://avatars.discourse-cdn.com/v4/letter/h/73ab20/32.png) [@hammerbach](https://boards.straightdope.com/u/hammerbach)\ **Post date:** [October 16, 2004, 5:48am UTC](https://boards.straightdope.com/t/how-do-car-horns-work/269445/12 "2004-10-16T05:48:38Z")
Imagine a diaphragm with and electromagnet pointed at its face. A switch is carefully arranged such that when the diapragm moves toward the magnet, the switch opens, turning off the electromagnet. The diaphragm, not longer attracted by the magnet, relaxes and drops away from the magnet, closing the switch and re-energizing the magnet. Repeat as necessary. Easy, eh?