Dear all, Just read a paper and I am not sure what 'spherical isotroic noise' is? How can I simulate it in array processing? Should I treat it as a white noise in the near field of an array? Thanks, L. N.
spherical isotropic noise?
Started by ●December 15, 2006
Reply by ●December 15, 20062006-12-15
linsnail2@yahoo.com writes:> Dear all, > > Just read a paper and I am not sure what 'spherical isotroic noise' is? > How can I simulate it in array processing? Should I treat it as a white > noise in the near field of an array? > > Thanks, > > L. N.I think you mean "spherical isotropic noise," which upon Googling was found in this paper: http://axiom.anu.edu.au/~williams/papers/P111.pdf -- % Randy Yates % "Ticket to the moon, flight leaves here today %% Fuquay-Varina, NC % from Satellite 2" %%% 919-577-9882 % 'Ticket To The Moon' %%%% <yates@ieee.org> % *Time*, Electric Light Orchestra http://home.earthlink.net/~yatescr
Reply by ●December 16, 20062006-12-16
Dear Prof. Yates, Thanks a lot. L.N. Randy Yates wrote:> linsnail2@yahoo.com writes: > > > Dear all, > > > > Just read a paper and I am not sure what 'spherical isotroic noise' is? > > How can I simulate it in array processing? Should I treat it as a white > > noise in the near field of an array? > > > > Thanks, > > > > L. N. > > I think you mean "spherical isotropic noise," which upon Googling > was found in this paper: > > http://axiom.anu.edu.au/~williams/papers/P111.pdf > -- > % Randy Yates % "Ticket to the moon, flight leaves here today > %% Fuquay-Varina, NC % from Satellite 2" > %%% 919-577-9882 % 'Ticket To The Moon' > %%%% <yates@ieee.org> % *Time*, Electric Light Orchestra > http://home.earthlink.net/~yatescr
Reply by ●December 16, 20062006-12-16
linsnail2@yahoo.com writes:> Dear Prof. Yates, > > Thanks a lot.Bless you, my child, but I'm not a professor, and you can call me Randy. --Randy> > L.N. > > > Randy Yates wrote: >> linsnail2@yahoo.com writes: >> >> > Dear all, >> > >> > Just read a paper and I am not sure what 'spherical isotroic noise' is? >> > How can I simulate it in array processing? Should I treat it as a white >> > noise in the near field of an array? >> > >> > Thanks, >> > >> > L. N. >> >> I think you mean "spherical isotropic noise," which upon Googling >> was found in this paper: >> >> http://axiom.anu.edu.au/~williams/papers/P111.pdf >> -- >> % Randy Yates % "Ticket to the moon, flight leaves here today >> %% Fuquay-Varina, NC % from Satellite 2" >> %%% 919-577-9882 % 'Ticket To The Moon' >> %%%% <yates@ieee.org> % *Time*, Electric Light Orchestra >> http://home.earthlink.net/~yatescr >-- % Randy Yates % "Ticket to the moon, flight leaves here today %% Fuquay-Varina, NC % from Satellite 2" %%% 919-577-9882 % 'Ticket To The Moon' %%%% <yates@ieee.org> % *Time*, Electric Light Orchestra http://home.earthlink.net/~yatescr
Reply by ●December 17, 20062006-12-17
On Dec 15, 7:29=A0pm, linsna...@yahoo.com wrote:> Dear all, > > Just read a paper and I am not sure what 'spherical isotroic noise' is? > How can I simulate it in array processing? Should I treat it as a white > noise in the near field of an array? >In the RF world, an "ideal isotropic radiator" is an imaginary antenna that radiates electromagnetic waves equally in all directions, with the wavefront therefore being in the shape of a perfect sphere. In reality, we don't have isotropic radiators, as any antenna has some directivity. However, it's useful to compare any antenna to the isotropic case, using dBi (decibels over isotropic), as we then have a standard. The same would apply to the world of sound or noise: http://en.wikipedia.org/wiki/Isotropic Slick
Reply by ●December 19, 20062006-12-19
radio913@aol.com wrote:>> > In reality, we don't have isotropic radiators, as any antenna has > some directivity. However, it's useful to compare any antenna to > the isotropic case, using dBi (decibels over isotropic), as we then > have a standard. > > The same would apply to the world of sound or noise: >Well certainly for E-M, the minimum order (in terms of a multipole expansion) for a radiator is a dipole. However, for sound (which is longitudinal instead of transverse) can be created by a monopole source. Hence a true isotropic radiator for sound can exist. Clay
Reply by ●December 19, 20062006-12-19
On Dec 18, 8:21=A0pm, "Clay" <phys...@bellsouth.net> wrote:> radio...@aol.com wrote: > > > In reality, we don't have isotropic radiators, as any antenna has > > some directivity. =A0However, it's useful to compare any antenna to > > the isotropic case, using dBi (decibels over isotropic), as we then > > have a standard. > > > =A0 =A0 =A0The same would apply to the world of sound or noise:Well cer=tainly for E-M, the minimum order (in terms of a multipole> expansion) for a radiator is a dipole. However, for sound (which is > longitudinal instead of transverse) can be created by a monopole > source. Hence a true isotropic radiator for sound can exist. >Where have you seen/heard a true isotropic radiator for sound? Every source of sound i have heard was obviously directional. The fact that you cannot build one doesn't diminish the usefulness of the mathematical concept as a reference to compare to. S
Reply by ●December 19, 20062006-12-19
radio913@aol.com wrote:> > On Dec 18, 8:21�pm, "Clay" <phys...@bellsouth.net> wrote: >> radio...@aol.com wrote: >> >>> In reality, we don't have isotropic radiators, as any antenna has >>> some directivity. �However, it's useful to compare any antenna to >>> the isotropic case, using dBi (decibels over isotropic), as we then >>> have a standard. >>> � � �The same would apply to the world of sound or noise:Well certainly for E-M, the minimum order (in terms of a multipole >> expansion) for a radiator is a dipole. However, for sound (which is >> longitudinal instead of transverse) can be created by a monopole >> source. Hence a true isotropic radiator for sound can exist. >> > > Where have you seen/heard a true isotropic radiator for sound?In the laboratory. Imagine a liquid-filled balloon in which the internal volume is forced to change according to a schedule that moves the surface sinusoidally. Being a radially symmetric structure, it is of course isotropic. The device served to show that a spherical cluster of dynamic loudspeakers surrounded by a diffuser (felt) behaved substantially the same way.> Every source of sound i have heard was obviously directional.Limited experience? How about eight folded horns -- two stacked clusters of four back to back -- hanging in space? A bit directional, perhaps, but not obviously so.> The fact that you cannot build one doesn't diminish the > usefulness of the mathematical concept as a reference to compare to.Indeed! Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●December 19, 20062006-12-19
Jerry Avins wrote:> radio913@aol.com wrote: > > > > On Dec 18, 8:21?pm, "Clay" <phys...@bellsouth.net> wrote: > >> radio...@aol.com wrote: > >> > >>> In reality, we don't have isotropic radiators, as any antenna has > >>> some directivity. ?However, it's useful to compare any antenna to > >>> the isotropic case, using dBi (decibels over isotropic), as we then > >>> have a standard. > >>> ? ? ?The same would apply to the world of sound or noise:Well certain=ly for E-M, the minimum order (in terms of a multipole> >> expansion) for a radiator is a dipole. However, for sound (which is > >> longitudinal instead of transverse) can be created by a monopole > >> source. Hence a true isotropic radiator for sound can exist. > >> > > > > Where have you seen/heard a true isotropic radiator for sound? > > In the laboratory. Imagine a liquid-filled balloon in which the internal > volume is forced to change according to a schedule that moves the > surface sinusoidally. Being a radially symmetric structure, it is of > course isotropic. The device served to show that a spherical cluster of > dynamic loudspeakers surrounded by a diffuser (felt) behaved > substantially the same way.How did you suspend the balloon? Or was it mounted on a pole or shaft of some sort? It would be difficult if not impossible to have a truly isotropic sound radiator. You could consider a suspended firecracker as being roughly isotropic, as it radiates sound in all directions roughly equally.> > > Every source of sound i have heard was obviously directional. > > Limited experience? How about eight folded horns -- two stacked clusters > of four back to back -- hanging in space? A bit directional, perhaps, > but not obviously so.It would be far from a true isotropic sound source, especially in the near field, but the further away, it would approximate it. But why would you ever need an isotropic speaker of any sort? Unless you were in a spinning sphere, outside the pull of gravity, and your audience was covering the whole inner surface. And even then, you would lose any stereo imaging.> > > The fact that you cannot build one doesn't diminish the > > usefulness of the mathematical concept as a reference to compare to. > > Indeed! > > Jerry > -- > Engineering is the art of making what you want from things you can get. > =AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF==AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF= =AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF
Reply by ●December 19, 20062006-12-19
radio913@aol.com wrote:> Jerry Avins wrote: >> radio913@aol.com wrote: >>> On Dec 18, 8:21?pm, "Clay" <phys...@bellsouth.net> wrote: >>>> radio...@aol.com wrote: >>>> >>>>> In reality, we don't have isotropic radiators, as any antenna has >>>>> some directivity. ?However, it's useful to compare any antenna to >>>>> the isotropic case, using dBi (decibels over isotropic), as we then >>>>> have a standard. >>>>> ? ? ?The same would apply to the world of sound or noise:Well certainly for E-M, the minimum order (in terms of a multipole >>>> expansion) for a radiator is a dipole. However, for sound (which is >>>> longitudinal instead of transverse) can be created by a monopole >>>> source. Hence a true isotropic radiator for sound can exist. >>>> >>> Where have you seen/heard a true isotropic radiator for sound? >> In the laboratory. Imagine a liquid-filled balloon in which the internal >> volume is forced to change according to a schedule that moves the >> surface sinusoidally. Being a radially symmetric structure, it is of >> course isotropic. The device served to show that a spherical cluster of >> dynamic loudspeakers surrounded by a diffuser (felt) behaved >> substantially the same way. > > How did you suspend the balloon? Or was it mounted on > a pole or shaft of some sort? It would be difficult if not impossible > to have a truly isotropic sound radiator.The balloon was suspended from the tube that moved the fluid. It's diameter was a very small fraction of a wavelength of the test frequency, so both reflection and diffraction were negligible.> You could consider a suspended firecracker as being > roughly isotropic, as it radiates sound in all directions roughly > equally.Provided the thread it hung from is thin enough, which is probable.>>> Every source of sound i have heard was obviously directional. >> Limited experience? How about eight folded horns -- two stacked clusters >> of four back to back -- hanging in space? A bit directional, perhaps, >> but not obviously so. > > It would be far from a true isotropic sound source, > especially > in the near field, but the further away, it would approximate it. > > But why would you ever need an isotropic speaker of > any sort? Unless you were in a spinning sphere, outside the > pull of gravity, and your audience was covering the whole inner > surface. And even then, you would lose any stereo imaging.Why does stereo get lost? As to why one is wanted; a reference of some sort? ... Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
