______________________________________________________________________________ | File Name : GEO180.ASC | Online Date : 05/22/95 | | Contributed by : Jerry Decker | Dir Category : KEELY | | From : KeelyNet BBS | DataLine : (214) 324-3501 | | A FREE Alternative Sciences BBS sponsored by Vanguard Sciences | | KeelyNet * PO BOX 870716 * Mesquite, Texas * USA * 75187 | | Voice/FAX : (214) 324-8741 InterNet - keelynet@ix.netcom.com | | WWW sites - http://www.eskimo.com/~billb & http://www.protree.com | |----------------------------------------------------------------------------| The following are messages relating to phasing and where the energy goes. ------------------------------------------------------------------------------ From: Visor@globalcom.net Subject: To phase or not to phase? Date: Sat, 06 May 95 22:59:26 PDT Organization: GlobalCom Lines: 11 This is a simple question that was asked to me by a scientist working on a problem dealing with geology. I gave a quick answer but thought it might be fun to see what other would say. "If two waves, sound or EM are combined out of phase with a net sum of 0, what happens to the energy in the waves?" ------------------------------------------------------------------------------ From: kplotkin@access5.digex.net (Kenneth Plotkin) Subject: Re: To phase or not to phase? Date: 7 May 1995 00:17:19 -0400 Organization: Express Access Online Communications, Greenbelt, MD USA Lines: 25 In article , wrote: [snip] >" If two waves, sound or EM are combined out of phase with a net sum >of 0, what happens to the energy in the waves?" That was asked here not too long ago. The only way that two waves could add up to zero everywhere would be if their sources were coincident. In that case, for coincident out-of-phase sources, the energy is zero to begin with. (Think of one-dimensional acoustic waves in a tube with a piston at the end. Or a piston at either end. Zero sum means zero pressure on the piston(s), hence zero work.) Local cancellation increases the energy elsewhere. Think of a lens coating, where the reflection from the coating is out of phase with the reflection from the lens itself. The net reflection is reduced, hence increasing the light transmitted through the lens. Arthur C. Clarke wrote a delightful short story (forget the title, but I believe it's in his "Tales From the White Hart" collection) about the consequences of sound cancellation where the net energy was not all preserved as sound. Ken Plotkin ------------------------------------------------------------------------------ Subject: Re: To phase or not to phase? Date: Tue, 9 May 1995 05:11:02 GMT Organization: Monash University Lines: 47 In article <3oh5bu$sc1@quiknet3.quiknet.com> Steve Rickman writes: >From: Steve Rickman >Subject: Re: To phase or not to phase? >Date: 7 May 1995 00:47:39 GMT >> >> >> This is a simple question that was asked to me by a scientist working >> on a problem dealing with geology. I gave a quick answer but thought >> it might be fun to see what other would say. >> >> " If two waves, sound or EM are combined out of phase with a net sum >> of 0, what happens to the energy in the waves?" >> >> >Boy, this comes up a lot. >You cannot get perfect cancellation *everywhere* of two waves unless >the sources are identical in directivity and content, 180 degrees >out of phase and superimposed in space. The last condition is the >key. If these otherwise perfectly cancelling sources are not in the >same location, then there will be regions of cancellation and regions >of reinforcement. If you integrate the energy density over the >entire field then the result will be just twice what it would be >if only one of the sources were radiating. Energy density, however, >will be "lumpy," varying from point to point throughout the field. >So can we actually superimpose the sources in space? Well, how do >you do that? Suppose we're talking about sound and you want to put >two speakers in exactly the same location. Since you can't physically >do that, you choose the next best thing and drive one speaker with >two perfectly cancelling electrical signals. Net result? The speaker >cone does not move! >But now at least we can see what happens to the energy. The amplifiers >generating the two perfectly cancelling signals are forced to absorb >it, turning it into heat. >Well, that's a lot of hand-waving. If you want to direct your >scientist (?) to a good introduction to this subject, refer him to >"Active Noise Control," in IEEE Signal Processing Magazine, >October, 1993. >Steve What about 2 pulses one the inversion duringf overlap the energy is is diminsihing to zero (perfect overlap) and then increases again. So where does the energy go during this period? ------------------------------------------------------------------------------ From: acampane@postbox.acs.ohio-state.edu (Angelo Campanella) Subject: Re: To phase or not to phase? Date: Tue, 9 May 1995 05:37:00 GMT Organization: The Ohio State University Lines: 31 In article Visor@globalcom.net writes: >From: Visor@globalcom.net >Subject: To phase or not to phase? >Date: Sat, 06 May 95 22:59:26 PDT >This is a simple question that was asked to me by a scientist working on a problem dealing with geology. I gave a quick answer but thought it might be fun to see what other would say. >"If two waves, sound or EM are combined out of phase with a net sum of 0, what happens to the energy in the waves?" The energy is reflected to be elsewhere. For istance, it could be sent back from whence it came. Just in front of a mirror, the energy flow is the same away from and towards the mirror. In the case of standing waves, where the pressure is zero (from opposite pressure waves cancelling), the velocity is at is maximum; a transformation from potential energy to kinetic energy. So that the "cancellation" is only in one (of many possible) energy form. Ang. /\/\/\/\/\/\/\ Sound Technology /\/\/\/\/\/\/\/\/ ------------------------------------------------------------------------------ From: andy@moose.mv.com (Andy Borsa) Subject: Re: To phase or not to phase? Sender: usenet@mv.mv.com (System Administrator) Organization: RF Design Consultant Date: Wed, 10 May 1995 21:36:47 GMT Lines: 13 In article , jrw@dio.dod.gov.au (Jerry Williamson) says: > >consider that the average apmlitude of a sine wave is zero, it is only the >insternaious apmlitude that causes the effects that can be measured. So if >you add zero to zero you get .... zero. think about that one for a bit. > > jerry Actually, the median over 1 cycle is 0. The heating power (RMS) is (0.7071 x peak)^2/R. If that weren't true then we'd have no need for all those power transmission lines. Andy Borsa -- !!!The universe is discretely analog!!! ------------------------------------------------------------------------------ From: Steve Rickman Subject: Re: To phase or not to phase? Date: 7 May 1995 00:47:39 GMT Organization: Quiknet Information Services Lines: 39 > > > This is a simple question that was asked to me by a scientist working > on a problem dealing with geology. I gave a quick answer but thought > it might be fun to see what other would say. > > " If two waves, sound or EM are combined out of phase with a net sum > of 0, what happens to the energy in the waves?" > > Boy, this comes up a lot. You cannot get perfect cancellation *everywhere* of two waves unless the sources are identical in directivity and content, 180 degrees out of phase and superimposed in space. The last condition is the key. If these otherwise perfectly cancelling sources are not in the same location, then there will be regions of cancellation and regions of reinforcement. If you integrate the energy density over the entire field then the result will be just twice what it would be if only one of the sources were radiating. Energy density, however, will be "lumpy," varying from point to point throughout the field. So can we actually superimpose the sources in space? Well, how do you do that? Suppose we're talking about sound and you want to put two speakers in exactly the same location. Since you can't physically do that, you choose the next best thing and drive one speaker with two perfectly cancelling electrical signals. Net result? The speaker cone does not move! But now at least we can see what happens to the energy. The amplifiers generating the two perfectly cancelling signals are forced to absorb it, turning it into heat. Well, that's a lot of hand-waving. If you want to direct your scientist (?) to a good introduction to this subject, refer him to "Active Noise Control," in IEEE Signal Processing Magazine, October, 1993. Steve ------------------------------------------------------------------------------ From: IANM@staff.monash.edu.au Subject: Re: To phase or not to phase? Date: Tue, 9 May 1995 05:11:02 GMT Organization: Monash University Lines: 47 In article <3oh5bu$sc1@quiknet3.quiknet.com> Steve Rickman writes: >From: Steve Rickman >Subject: Re: To phase or not to phase? >Date: 7 May 1995 00:47:39 GMT >> >> >> This is a simple question that was asked to me by a scientist working >> on a problem dealing with geology. I gave a quick answer but thought >> it might be fun to see what other would say. >> >> " If two waves, sound or EM are combined out of phase with a net sum >> of 0, what happens to the energy in the waves?" >> >> >Boy, this comes up a lot. >You cannot get perfect cancellation *everywhere* of two waves unless >the sources are identical in directivity and content, 180 degrees >out of phase and superimposed in space. The last condition is the >key. If these otherwise perfectly cancelling sources are not in the >same location, then there will be regions of cancellation and regions >of reinforcement. If you integrate the energy density over the >entire field then the result will be just twice what it would be >if only one of the sources were radiating. Energy density, however, >will be "lumpy," varying from point to point throughout the field. >So can we actually superimpose the sources in space? Well, how do >you do that? Suppose we're talking about sound and you want to put >two speakers in exactly the same location. Since you can't physically >do that, you choose the next best thing and drive one speaker with >two perfectly cancelling electrical signals. Net result? The speaker >cone does not move! >But now at least we can see what happens to the energy. The amplifiers >generating the two perfectly cancelling signals are forced to absorb >it, turning it into heat. >Well, that's a lot of hand-waving. If you want to direct your >scientist (?) to a good introduction to this subject, refer him to >"Active Noise Control," in IEEE Signal Processing Magazine, >October, 1993. >Steve What about 2 pulses one the inversion duringf overlap the energy is is diminsihing to zero (perfect overlap) and then increases again. So where does the energy go during this period? ------------------------------------------------------------------------------