On Thu, May 24, 2012 at 08:51:15PM +0100, Augustine Leudar wrote: > - thanks for the replies , but just to clarify my question specifically > relates to the phase inversion (fig8 etc) - not any other aspect of the mic > design, W omni signal etc
The way to explain this depends on if you're using omni mics or directional ones. I'll assume the latter for now - if that is not correct then you need to do more than just take the difference anyway and things become a bit more complitcated. Consider a cardiod mic: max response in front and zero in the back. That is in fact the sum of an omni and a fig-of-8. In the front the two add, in the back the fig-of-8 is in antiphase and the two cancel, assuming they have the same sensitivity. If not you get a subcaridiod or a hypercardiod. Now consider two such mics, very close together and pointing in opposite directions. That means that the fig-of-8 parts of the two mics are in antiphase w.r.t. each other. If you add the signals from the two mics, the fig-of-8 parts cancel out and you get an omnidirectional mic. But if you subract the signals (that is inverting one of them and then taking the sum), the omni parts cancel and the fig-of-8 parts are added in phase. The result is a fig-of-8 mic, which is what you need for the Ambisonic components X, Y and Z. Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
