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July 28 Information
Hearing Distance in humans.
Where would I find out, how far away a 'wanted' sound can be heard by a normal human?
(Context is that when reading about Dutch cycling rules I came across some requirement that cycle bells apparently had to be heard 25m away. I'm assuming that this would be for normal hearing under typical conditions.)
"In a normal three-dimensional setting, with a point source and point receptor, the intensity of sound waves will be attenuated according to the
inverse square of the distance from the source." Measure the decibel level of the bell and using the above law calculate the distance where the decibel level is not discernible to humans.
196.213.35.146 (
talk)
13:37, 28 July 2016 (UTC)reply
Yes, but the inverse square law just implies that the attenuation obeys the format I = k * (1/d2) where I is intensity and d is the distance from the source. The problem is that k, the constant, is itself a complex function, and will be dependent on both the wavelength of the specific sound (lower frequency sounds travel farther, see for example
infrasound) and the medium itself (i.e. the air properties such as density, temperature, pressure, and humidity, all of which change a lot). While bringing up the inverse square law makes it sound simple, the devil is in the details, and the details (the "k" factor here) are quite devilish. --
Jayron3218:26, 28 July 2016 (UTC)reply
Clicking on my link would have clarified that I meant five
kilometers. The more appropriate symbols would have been '5 km'. From our kilometre article: "k (pronounced /keɪ/) is occasionally used in some English-speaking countries as an alternative for the word kilometre in colloquial writing and speech." For example, I often hear runners saying "I ran five kay yesterday".
SemanticMantis (
talk)
18:34, 28 July 2016 (UTC)reply
John Tyndall, in "The Science of Sound", devotes chapter 7 to things that affect the propagation of sound through the atmosphere. The motivation seems to have been fog horns and shipping safety. This was in 1875, and understanding has probably advanced some since then.--
Wikimedes (
talk)
21:01, 28 July 2016 (UTC)reply
On the subject of foghorns. They were noticeably audible because of the long duration. They made the air vacillate. Bit like what the
Alphorn does, and on which one doesn't try to play the
Trumpet voluntary as the sound just would not carry so well. So perceivably (subjectively) they were more perceptible . The
Buncefield fire explosion in Hemel Hempstead was heard as far a way as Holland but that was probably due to an early morning atmospheric condition (an inversion) which tunnels the sound. It woke me up and I live miles and miles away. So I don't see how we can really answer the OP's question because if one sets up a long duration sign wave sound source it can travel for miles and mile depending on the atmospheric conditions.--
Aspro (
talk)
22:08, 28 July 2016 (UTC)reply
Somewhat related, a former prof of mine has extensively studied the propagation of elephant calls under different atmospheric conditions. Although it's about elephants some of the basic ideas are general. Interesting stuff; an article on it is
here.
Shock Brigade Harvester Boris (
talk)
03:22, 29 July 2016 (UTC)reply
I refrained from mentioning that, as the OP's question was about human hearing. But I'm surprised why you
DrChrissy did not also mention that elephants can also communicate long distances, by apparently just picking up the telephone and making
trunk calls? --
Aspro (
talk)
12:58, 31 July 2016 (UTC)reply
I put this batbox up only a few months ago so I'm surprised to already be hearing activity inside as instructions state it may take years for bats to settle. So I'm not sure if what's inside is a bat - I haven't seen anything leave or enter. I recorded the sound made.
https://vid(dot)me/xeHw
Sounds like a bat to me. Compare e.g. this recording
[2] It's not exactly the same, but similar, search youtube for more examples. I'm not sure what specific type of box you used by most bat boxes are designed to be not attractive to e.g. birds, non-flying rodents, and other things that might like a box. It MAY take years, but I think you got lucky and had bats move in more quickly. Keep an eye out near dusk and hope to catch them leaving :D
SemanticMantis (
talk)
18:29, 28 July 2016 (UTC)reply
I have often wondered if the microphones built into smart phones have a high enough frequency response to pick up bats. If so, they would only need an app with a software 'heterodyne' to make the ultra sounds audible. Any kick-starters out there (?) as a dedicated bat heterodyne detector can cost over a £100. With one of those one can identify one's bat.
Bat Detectors. Mind you, if the critter is weareing a a yellow cape, a green mask, a red jerking and tights, it is probably a Robin.--
Aspro (
talk)
21:23, 28 July 2016 (UTC)reply
"Holy mis-identification Asproman!" Another piece of technology you could use is a camera trap, sometimes called trail cameras. DrChrissy(talk)21:33, 28 July 2016 (UTC)reply
Lol. Images would indeed help for ID, and so would ultrasonic information. For clarity, many bat vocalizations are outside normal human hearing range, but they do plenty of chattering vocalization in the
human hearing range too. Also WHAAO
trail cameras and
camera traps (which are different articles that perhaps should be merged, if anyone is feeling bold).
SemanticMantis (
talk)
21:45, 28 July 2016 (UTC)reply
It would (in a perfect world) be advantageous to place a web cam in the box from the out set. One can't (as you will already know) do it after they start roosting, unless one has a license permitting one to handle bats and make adjustments to their habitat. Trail cameras however, are a bit tooo slow for the amateur -me thinks. They have an in built delay which needs some knowhow to adjust. This is because if they fired immediately, all one will see is the snout of a badger or something. So a (typically) ten second delay is built in with the hope that the whole critter is in view buy the time the exposure is taken. I haven't came across one suitable for bats yet. I can't even see bats on my night scope (admittedly it is a cheap one and not a class III military spec). The image is clear but the response is too slow to for the fast moving bats to register. Maybe better to use use a infra red video camera at dusk whilst there is still some light. And anyway, if one could get a image on a Trail cam it would be so blurred that even an expert would not be able-to identify it. Lots of bats look the same. Finally, It would be interesting to know the circumstances of how the OP came by the bat box to start with. He is right that they don't usually get inhabited so quickly. The reason - I think- is that freshly cut wood releases terpenoids and esters, which to a bat, in confide confined space, must be pretty suffocating until the wood has seasoned (about two years minimum). So did the OP by chance get his hands on a old matured box?--
Aspro (
talk)
23:06, 28 July 2016 (UTC)reply
All sources I find about the latter gravitate around sci-fi or cracks who developed anti-gravity-like devices. Hasn't the possibility being seriously considered?
Hofhof (
talk)
21:58, 28 July 2016 (UTC)reply
Depends, what do you mean by "antigravitational waves"? As it passes, every
gravitational wave will stretch some of space and compresses other parts of space, depending on its orientation. One can also imagine a new gravitational wave that compresses the things the first wave stretched (and vice versa), but that is just a differently polarized gravitational wave. So a gravitational wave with the opposite effects of the first wave is just a different kind of gravitational wave. Is that what you mean, or were you imagining something else by "antigravitational"?
Dragons flight (
talk)
22:17, 28 July 2016 (UTC)reply
One thing I was thinking on was what you describe. The other would simply be matter that repels matter, unless of attracting it. --
Hofhof (
talk)
22:24, 28 July 2016 (UTC)reply
Matter that gravitationaly repels other matter is not theoretically prohibited by either general relativity or quantum mechanics, but there is no known form of matter with this property. The existence of gravitational waves doesn't change that, since their existence was derived from GR to begin with. The article you're looking for is
negative mass.
Someguy1221 (
talk)
22:37, 28 July 2016 (UTC)reply
I think that gravitationally repulsive matter is forbidden by field theory (even classically) because it's a perturbation of the vacuum with lower energy than the vacuum itself, and that means the vacuum is unstable. In general relativity, you get weird pathologies (notably closed timelike curves) if you permit locally negative energy density. Probably the deeper theory of gravity that general relativity approximates is fundamentally inconsistent with negative energy. --
BenRG (
talk)
06:09, 30 July 2016 (UTC)reply
Existence of gravitational waves, if confirmed, would raise questions like 1) what is their supporting medium such as an
"aether", or have they none other than a mathematical consistency of simultaneous differential equations such as
Maxwell's for electromagnetic waves; 2) do they have all the degrees of freedom that we expect in waves (amplitude, frequency, phase); and 3) are there non-linear effects (comparable to dispersion in optics or to diodes, transistors and logic gates in electronics) that we might exploit? A rich source of speculation is that sound waves have already demonstrated ability to manipulate small objects - see
Acoustic tweezers - including
levitating a few kilograms. However by the rules against speculation on this desk, we should confine the references we give to the
First observation of gravitational waves.
AllBestFaith (
talk)
10:45, 29 July 2016 (UTC)reply
The existence you propose would allow for regionally suppressing gravity, but not "negative" gravity - repelling things. Just like noise-cancelling headphones car eliminate noise but not create negative noise. --
Q Chris (
talk)
11:50, 29 July 2016 (UTC)reply
Has anyone ever seen anti-sound waves or anti-waves on the sea or anti-light waves or have any idea what any of them would be supposed to be? I guess I could have done with something emitting anti-heat waves recently like Arnold Schwarzenegger as Mr Freeze in a Batman movie ;-)
Dmcq (
talk)
12:29, 29 July 2016 (UTC)reply
First, isn't the hypothetical graviton its own anti-particle? Second, I am not aware of anti-electromagnetic waves. While every particle is thought to have an anti-particle unless it is its own anti-particle, not every wave has an anti-wave. Third, negative gravity would require, not negative gravity waves, but negative mass, and I think that does pose technical challenges.
Robert McClenon (
talk)
12:48, 29 July 2016 (UTC)reply
Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the
current reference desk pages.
July 28 Information
Hearing Distance in humans.
Where would I find out, how far away a 'wanted' sound can be heard by a normal human?
(Context is that when reading about Dutch cycling rules I came across some requirement that cycle bells apparently had to be heard 25m away. I'm assuming that this would be for normal hearing under typical conditions.)
"In a normal three-dimensional setting, with a point source and point receptor, the intensity of sound waves will be attenuated according to the
inverse square of the distance from the source." Measure the decibel level of the bell and using the above law calculate the distance where the decibel level is not discernible to humans.
196.213.35.146 (
talk)
13:37, 28 July 2016 (UTC)reply
Yes, but the inverse square law just implies that the attenuation obeys the format I = k * (1/d2) where I is intensity and d is the distance from the source. The problem is that k, the constant, is itself a complex function, and will be dependent on both the wavelength of the specific sound (lower frequency sounds travel farther, see for example
infrasound) and the medium itself (i.e. the air properties such as density, temperature, pressure, and humidity, all of which change a lot). While bringing up the inverse square law makes it sound simple, the devil is in the details, and the details (the "k" factor here) are quite devilish. --
Jayron3218:26, 28 July 2016 (UTC)reply
Clicking on my link would have clarified that I meant five
kilometers. The more appropriate symbols would have been '5 km'. From our kilometre article: "k (pronounced /keɪ/) is occasionally used in some English-speaking countries as an alternative for the word kilometre in colloquial writing and speech." For example, I often hear runners saying "I ran five kay yesterday".
SemanticMantis (
talk)
18:34, 28 July 2016 (UTC)reply
John Tyndall, in "The Science of Sound", devotes chapter 7 to things that affect the propagation of sound through the atmosphere. The motivation seems to have been fog horns and shipping safety. This was in 1875, and understanding has probably advanced some since then.--
Wikimedes (
talk)
21:01, 28 July 2016 (UTC)reply
On the subject of foghorns. They were noticeably audible because of the long duration. They made the air vacillate. Bit like what the
Alphorn does, and on which one doesn't try to play the
Trumpet voluntary as the sound just would not carry so well. So perceivably (subjectively) they were more perceptible . The
Buncefield fire explosion in Hemel Hempstead was heard as far a way as Holland but that was probably due to an early morning atmospheric condition (an inversion) which tunnels the sound. It woke me up and I live miles and miles away. So I don't see how we can really answer the OP's question because if one sets up a long duration sign wave sound source it can travel for miles and mile depending on the atmospheric conditions.--
Aspro (
talk)
22:08, 28 July 2016 (UTC)reply
Somewhat related, a former prof of mine has extensively studied the propagation of elephant calls under different atmospheric conditions. Although it's about elephants some of the basic ideas are general. Interesting stuff; an article on it is
here.
Shock Brigade Harvester Boris (
talk)
03:22, 29 July 2016 (UTC)reply
I refrained from mentioning that, as the OP's question was about human hearing. But I'm surprised why you
DrChrissy did not also mention that elephants can also communicate long distances, by apparently just picking up the telephone and making
trunk calls? --
Aspro (
talk)
12:58, 31 July 2016 (UTC)reply
I put this batbox up only a few months ago so I'm surprised to already be hearing activity inside as instructions state it may take years for bats to settle. So I'm not sure if what's inside is a bat - I haven't seen anything leave or enter. I recorded the sound made.
https://vid(dot)me/xeHw
Sounds like a bat to me. Compare e.g. this recording
[2] It's not exactly the same, but similar, search youtube for more examples. I'm not sure what specific type of box you used by most bat boxes are designed to be not attractive to e.g. birds, non-flying rodents, and other things that might like a box. It MAY take years, but I think you got lucky and had bats move in more quickly. Keep an eye out near dusk and hope to catch them leaving :D
SemanticMantis (
talk)
18:29, 28 July 2016 (UTC)reply
I have often wondered if the microphones built into smart phones have a high enough frequency response to pick up bats. If so, they would only need an app with a software 'heterodyne' to make the ultra sounds audible. Any kick-starters out there (?) as a dedicated bat heterodyne detector can cost over a £100. With one of those one can identify one's bat.
Bat Detectors. Mind you, if the critter is weareing a a yellow cape, a green mask, a red jerking and tights, it is probably a Robin.--
Aspro (
talk)
21:23, 28 July 2016 (UTC)reply
"Holy mis-identification Asproman!" Another piece of technology you could use is a camera trap, sometimes called trail cameras. DrChrissy(talk)21:33, 28 July 2016 (UTC)reply
Lol. Images would indeed help for ID, and so would ultrasonic information. For clarity, many bat vocalizations are outside normal human hearing range, but they do plenty of chattering vocalization in the
human hearing range too. Also WHAAO
trail cameras and
camera traps (which are different articles that perhaps should be merged, if anyone is feeling bold).
SemanticMantis (
talk)
21:45, 28 July 2016 (UTC)reply
It would (in a perfect world) be advantageous to place a web cam in the box from the out set. One can't (as you will already know) do it after they start roosting, unless one has a license permitting one to handle bats and make adjustments to their habitat. Trail cameras however, are a bit tooo slow for the amateur -me thinks. They have an in built delay which needs some knowhow to adjust. This is because if they fired immediately, all one will see is the snout of a badger or something. So a (typically) ten second delay is built in with the hope that the whole critter is in view buy the time the exposure is taken. I haven't came across one suitable for bats yet. I can't even see bats on my night scope (admittedly it is a cheap one and not a class III military spec). The image is clear but the response is too slow to for the fast moving bats to register. Maybe better to use use a infra red video camera at dusk whilst there is still some light. And anyway, if one could get a image on a Trail cam it would be so blurred that even an expert would not be able-to identify it. Lots of bats look the same. Finally, It would be interesting to know the circumstances of how the OP came by the bat box to start with. He is right that they don't usually get inhabited so quickly. The reason - I think- is that freshly cut wood releases terpenoids and esters, which to a bat, in confide confined space, must be pretty suffocating until the wood has seasoned (about two years minimum). So did the OP by chance get his hands on a old matured box?--
Aspro (
talk)
23:06, 28 July 2016 (UTC)reply
All sources I find about the latter gravitate around sci-fi or cracks who developed anti-gravity-like devices. Hasn't the possibility being seriously considered?
Hofhof (
talk)
21:58, 28 July 2016 (UTC)reply
Depends, what do you mean by "antigravitational waves"? As it passes, every
gravitational wave will stretch some of space and compresses other parts of space, depending on its orientation. One can also imagine a new gravitational wave that compresses the things the first wave stretched (and vice versa), but that is just a differently polarized gravitational wave. So a gravitational wave with the opposite effects of the first wave is just a different kind of gravitational wave. Is that what you mean, or were you imagining something else by "antigravitational"?
Dragons flight (
talk)
22:17, 28 July 2016 (UTC)reply
One thing I was thinking on was what you describe. The other would simply be matter that repels matter, unless of attracting it. --
Hofhof (
talk)
22:24, 28 July 2016 (UTC)reply
Matter that gravitationaly repels other matter is not theoretically prohibited by either general relativity or quantum mechanics, but there is no known form of matter with this property. The existence of gravitational waves doesn't change that, since their existence was derived from GR to begin with. The article you're looking for is
negative mass.
Someguy1221 (
talk)
22:37, 28 July 2016 (UTC)reply
I think that gravitationally repulsive matter is forbidden by field theory (even classically) because it's a perturbation of the vacuum with lower energy than the vacuum itself, and that means the vacuum is unstable. In general relativity, you get weird pathologies (notably closed timelike curves) if you permit locally negative energy density. Probably the deeper theory of gravity that general relativity approximates is fundamentally inconsistent with negative energy. --
BenRG (
talk)
06:09, 30 July 2016 (UTC)reply
Existence of gravitational waves, if confirmed, would raise questions like 1) what is their supporting medium such as an
"aether", or have they none other than a mathematical consistency of simultaneous differential equations such as
Maxwell's for electromagnetic waves; 2) do they have all the degrees of freedom that we expect in waves (amplitude, frequency, phase); and 3) are there non-linear effects (comparable to dispersion in optics or to diodes, transistors and logic gates in electronics) that we might exploit? A rich source of speculation is that sound waves have already demonstrated ability to manipulate small objects - see
Acoustic tweezers - including
levitating a few kilograms. However by the rules against speculation on this desk, we should confine the references we give to the
First observation of gravitational waves.
AllBestFaith (
talk)
10:45, 29 July 2016 (UTC)reply
The existence you propose would allow for regionally suppressing gravity, but not "negative" gravity - repelling things. Just like noise-cancelling headphones car eliminate noise but not create negative noise. --
Q Chris (
talk)
11:50, 29 July 2016 (UTC)reply
Has anyone ever seen anti-sound waves or anti-waves on the sea or anti-light waves or have any idea what any of them would be supposed to be? I guess I could have done with something emitting anti-heat waves recently like Arnold Schwarzenegger as Mr Freeze in a Batman movie ;-)
Dmcq (
talk)
12:29, 29 July 2016 (UTC)reply
First, isn't the hypothetical graviton its own anti-particle? Second, I am not aware of anti-electromagnetic waves. While every particle is thought to have an anti-particle unless it is its own anti-particle, not every wave has an anti-wave. Third, negative gravity would require, not negative gravity waves, but negative mass, and I think that does pose technical challenges.
Robert McClenon (
talk)
12:48, 29 July 2016 (UTC)reply