# Is it Possible to "Create" Silence? **URL:** \ **Category:** Factual Questions\ **Created:** [September 14, 2008, 12:13pm UTC](https://boards.straightdope.com/t/is-it-possible-to-create-silence/463549 "2008-09-14T12:13:34Z")\ **Posts on this page:** 8\ **Page:** 2
**Author:** ![jjimm](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@jjimm](https://boards.straightdope.com/u/jjimm)\ **Post date:** [September 15, 2008, 10:45am UTC](https://boards.straightdope.com/t/is-it-possible-to-create-silence/463549/21 "2008-09-15T10:45:34Z")
On a related subject, I’ve always wondered how radio stations broadcast silence. How do they overwrite white noise with, essentially, nothing at all? ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [September 15, 2008, 11:38am UTC](https://boards.straightdope.com/t/is-it-possible-to-create-silence/463549/22 "2008-09-15T11:38:09Z")
> [@jjimm](#): > > On a related subject, I’ve always wondered how radio stations broadcast silence. How do they overwrite white noise with, essentially, nothing at all? White noise on a non-station frequency is the result of your stereo amplifier amplifying nothing (well, the random bits of RF that hit the receiving antenna at the right frequency). That’s why communications radios have squelching circuitry – to cut off that white noise when there’s no transmitted signal. The transmitted signal, then, is just a carrier frequency; the “real” frequency is a result of either modulating the amplitude (AM) or the frequency (FM) of the carrier. If you modulate to an inaudible frequency, then you hear silence. Short version: the transmitted signal is stronger than the white noise. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [September 15, 2008, 11:55am UTC](https://boards.straightdope.com/t/is-it-possible-to-create-silence/463549/23 "2008-09-15T11:55:11Z")
> [@](#): > > I suggest reading the short story “Silence Please” from Arthur C. Clarke’s collection “Tales From The White Hart”. A cautionary tale about an acoustic silencer, written in the 1950s. Clarke’s device in that story works the same way modern “sound cancelling” headphones work – by creating an “anti-acoustic” wave to cancel the existing sound wave. Since these devices work without any of the ill effects Clarke has in his story, I conclude that Clarke either missed or else suppressed for the sake of the story some salient facts. BTW, **HalfManHalfWit** , you _can_ “create darkness” by making an interference pattern, or by adjusting one arm of an interfrometer to completely cancel. With light, making the two waves coherent is not trivial, and is sometimes impossible, but sound waves are MUCH more forgiving. Making an intereference pattern using ultrasound is a piece of cake – you can use two separate transmitters, whereas in optics you have to use two coupled sources or a single split one. All that said, I’ve got no personal experience with human-hearing-range sound cancelling headphones, so I’m not aware of their capabilities and limitations, bt people who use them tell me they work great. ---
**Author:** ![BMalion](https://avatars.discourse-cdn.com/v4/letter/b/e274bd/32.png) [@BMalion](https://boards.straightdope.com/u/BMalion)\ **Post date:** [September 15, 2008, 12:26pm UTC](https://boards.straightdope.com/t/is-it-possible-to-create-silence/463549/24 "2008-09-15T12:26:11Z")
If we could just get hold of some vibranium… ---
**Author:** ![Shoeless](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/shoeless/32/7099_2.png) [@Shoeless](https://boards.straightdope.com/u/Shoeless)\ **Post date:** [September 15, 2008, 5:39pm UTC](https://boards.straightdope.com/t/is-it-possible-to-create-silence/463549/25 "2008-09-15T17:39:13Z")
> [@MLS](#): > > If you ever find one, PLEASE tell me – I want it! Especially if you can make a really portable one. I want one that goes to eleven. ---
**Author:** ![Kolga](https://avatars.discourse-cdn.com/v4/letter/k/e56c9b/32.png) [@Kolga](https://boards.straightdope.com/u/Kolga)\ **Post date:** [September 15, 2008, 9:34pm UTC](https://boards.straightdope.com/t/is-it-possible-to-create-silence/463549/26 "2008-09-15T21:34:52Z")
Wasn’t this a plot in an episode of Profiler? Some lady who had seen her grandfather die in a woodworking accident kept hearing him scream, and kidnapped a scientist to make her a silence-creating or sound-deadening apparatus, not realizing that the scream was in her head? Ah yes, found it: [Shattered Silence](http://www.episodeworld.com/episode/10011). ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [September 15, 2008, 11:10pm UTC](https://boards.straightdope.com/t/is-it-possible-to-create-silence/463549/27 "2008-09-15T23:10:05Z")
Noise cancelling headphones work based on an extremely simple principle: a microphone just outside the earphone and an amplifier which inverts the signal so that the earphone generates a signal which cancels the original sound. There is no “predicting” or anything of the sort and it does not care whether the sound comes from 3 or 300 feet away. It is really very simple. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [September 15, 2008, 11:31pm UTC](https://boards.straightdope.com/t/is-it-possible-to-create-silence/463549/28 "2008-09-15T23:31:26Z")
> [@CalMeacham](#): > > BTW, **HalfManHalfWit** , you _can_ “create darkness” by making an interference pattern, or by adjusting one arm of an interfrometer to completely cancel. With light, making the two waves coherent is not trivial, and is sometimes impossible, but sound waves are MUCH more forgiving. Making an intereference pattern using ultrasound is a piece of cake – you can use two separate transmitters, whereas in optics you have to use two coupled sources or a single split one. Well, yes, with any superposing theory you can find a way to cancel out waves, but you can’t create a general-purpose ‘darkness’ or ‘silence’ source; there’s no ‘dark bulb’ in the same way as there is no ‘quietspeaker’. [Previous page](https://boards.straightdope.com/t/is-it-possible-to-create-silence/463549.md?page=1)