# So my friend has a 120dB horn on his car. How loud is that? **URL:** \ **Category:** Factual Questions\ **Created:** [August 30, 2003, 4:34pm UTC](https://boards.straightdope.com/t/so-my-friend-has-a-120db-horn-on-his-car-how-loud-is-that/198652 "2003-08-30T16:34:21Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Sqube](https://avatars.discourse-cdn.com/v4/letter/s/aca169/32.png) [@Sqube](https://boards.straightdope.com/u/Sqube)\ **Post date:** [August 30, 2003, 4:34pm UTC](https://boards.straightdope.com/t/so-my-friend-has-a-120db-horn-on-his-car-how-loud-is-that/198652/1 "2003-08-30T16:34:21Z")
Well… yeah. The question pretty much speaks for itself. I’m under the impression that it’s louder than normal, but I don’t really know the extent of it. Can anybody tell me? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 30, 2003, 4:42pm UTC](https://boards.straightdope.com/t/so-my-friend-has-a-120db-horn-on-his-car-how-loud-is-that/198652/2 "2003-08-30T16:42:54Z")
It’s loud. But a quick Google search turns up even louder ones at 130 dB. Typically they run around 90 dB or so. ---
**Author:** ![SpaceDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spacedog/32/9932_2.png) [@SpaceDog](https://boards.straightdope.com/u/SpaceDog)\ **Post date:** [August 30, 2003, 4:49pm UTC](https://boards.straightdope.com/t/so-my-friend-has-a-120db-horn-on-his-car-how-loud-is-that/198652/3 "2003-08-30T16:49:25Z")
Pretty damn loud – this link has some example levels [http://www.glenbrook.k12.il.us/gbssci/phys/Class/sound/u11l2b.html](http://www.glenbrook.k12.il.us/gbssci/phys/Class/sound/u11l2b.html) At first I though that you wouldn’t get a horn that loud, but some consideration and some checking turn out that you can and thinking of the other things people do to their cars I’m surprised I doubted it. SD ---
**Author:** ![Chris\_Luongo](https://avatars.discourse-cdn.com/v4/letter/c/7cd45c/32.png) [@Chris\_Luongo](https://boards.straightdope.com/u/Chris_Luongo)\ **Post date:** [September 1, 2003, 1:10am UTC](https://boards.straightdope.com/t/so-my-friend-has-a-120db-horn-on-his-car-how-loud-is-that/198652/4 "2003-09-01T01:10:31Z")
Car nut and car-alarm installer here. I highly doubt they’re rating those horns by any strict standard. How far away is the sound meter----six inches? one foot? one millimeter? And where is the horn mounted in the car’s engine compartment----are other components in a place where they can impede the sound? I was in Pep Boys yesterday looking at replacement horns for the dead ones in my car. They were selling original-equipment horns rated at 125 dB, and for $1 more, an extra-loud model at 132 dB. But I smell tomfoolery-----when I looked through the clear packaging, both horns sported the _exact_ same part number! So I put in some used Cadillac horns instead; they have a nice sound. Also, for what it’s worth, many car alarm sirens have stickers on them claiming 120 dB. ---
**Author:** ![antechinus](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@antechinus](https://boards.straightdope.com/u/antechinus)\ **Post date:** [September 1, 2003, 3:07am UTC](https://boards.straightdope.com/t/so-my-friend-has-a-120db-horn-on-his-car-how-loud-is-that/198652/5 "2003-09-01T03:07:19Z")
You could ask your friend to beep it for you. 🙂 ---
**Author:** ![mrsam](https://avatars.discourse-cdn.com/v4/letter/m/b5ac83/32.png) [@mrsam](https://boards.straightdope.com/u/mrsam)\ **Post date:** [September 1, 2003, 4:36am UTC](https://boards.straightdope.com/t/so-my-friend-has-a-120db-horn-on-his-car-how-loud-is-that/198652/6 "2003-09-01T04:36:12Z")
Since the dB scale is logarithmic, given **Q.E.D.'s** figure of 90dB for a normal horn, it would be 1000 times louder than your average horn. But personally, I’m with **antechinus.** Get your friend to beep it for you. 🙂 ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [September 2, 2003, 4:16pm UTC](https://boards.straightdope.com/t/so-my-friend-has-a-120db-horn-on-his-car-how-loud-is-that/198652/7 "2003-09-02T16:16:38Z")
Hehe… Is that 120 dB of “meep!” or 120 dB of “WHONNNK!” I think Chris has the right idea - those mid-70s Caddy horns (four tones, rather than the usual one or two) had a good strong tone that cut through just about anything and said “MOVE IT! Something BIG is coming at you!” ---
**Author:** ![Rocketeer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rocketeer/32/4437_2.png) [@Rocketeer](https://boards.straightdope.com/u/Rocketeer)\ **Post date:** [September 2, 2003, 6:15pm UTC](https://boards.straightdope.com/t/so-my-friend-has-a-120db-horn-on-his-car-how-loud-is-that/198652/8 "2003-09-02T18:15:31Z")
My pocket ref book says that a car horn at five meters is 100 dB; 120 dB is described as “Thunder, diesel engine room (Incidentally , my lovely wife arranged for me to tour the engine room of one of the Alaska state ferries, big ocean-going boats; it was god-damned LOUD), nearby riveter.” Also, car horns sound much more authoritative when you have two horns in unison, tuned maybe a third apart. ---
**Author:** ![Rocketeer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rocketeer/32/4437_2.png) [@Rocketeer](https://boards.straightdope.com/u/Rocketeer)\ **Post date:** [September 2, 2003, 6:23pm UTC](https://boards.straightdope.com/t/so-my-friend-has-a-120db-horn-on-his-car-how-loud-is-that/198652/9 "2003-09-02T18:23:01Z")
My pocket ref book says that a car horn at five meters is 100 dB; 120 dB is described as “Thunder, diesel engine room (Incidentally , my lovely wife arranged for me to tour the engine room of one of the Alaska state ferries, big ocean-going boats; it was god-damned LOUD), nearby riveter.” Also, car horns sound much more authoritative when you have two horns in unison, tuned maybe a third apart. ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [September 2, 2003, 8:57pm UTC](https://boards.straightdope.com/t/so-my-friend-has-a-120db-horn-on-his-car-how-loud-is-that/198652/10 "2003-09-02T20:57:44Z")
Yeah, but rule of thumb is that when you halve the distance, the SPL increases by 6 dB, pretty close. So the 100 dB car horn at 5 meters is a ~113 dB horn at 1 meter. Obviously, a point source like a horn sounds louder the closer you are to it, so tucked into any noise measurement is some distance measurement\*. [This place](http://www.brown.edu/Research/EnvStudies_Theses/summit/Briefing_Papers/Respectful_Society/noise.html) says a typical car horn is 115 dB at 3 ft (darn close to **Rocketeer** ’s cite); other places seen to peg it anywhere between 110 dB and 120 dB (without the distance). One meter is kind of a standard measuring distance, so often a “120 dB” figure given with no distance implies one meter. However, given that marketing forces are at work here, I would be hesitant to assume that’s the way the horn’s being measured. But hey, 120 dB ain’t _that_ much louder than 115 dB. Additionally, there’s a couple perception issues involved. First, the human ear is more sensitive to certain frequencies than to others, so a 120 dB noise at one frequency can _seem_ much louder than a 120 dB noise at another. Often, noise will be cited using “A-weighted” dB, which increases or reduces the “actual” dB based on the perceived loudness of the noise frequency. Second, there’s something of a noise quality issue, where certain noises are more jarring (and likely to be noticed) than others. \*Anecdote: I occasionally use a dB meter at work. This meter is calibrated with a 140 dB noise source that fits directly over the tip of the microphone. Thus, the source is 140 dB…at 1/2 inch (or whatever) distance. If you hold the source in your hand and turn it on, it makes about the same noise as someone whispering a couple feet away.