Kirchhoff's law of thermal radiation rarefied material such as air, or transparent material, through which observations can be made. The interface is not a material body and can neither emit nor absorb. It is a mathematical surface belonging jointly to the two media that touch it. It is the site of refraction of radiation that penetrates it and of reflection of radiation that does not. As such it obeys the Helmholtz reciprocity principle. The opaque body is considered to have a material interior that absorbs all and scatters or transmits none of the radiation that reaches it through refraction at the interface. In this sense
A/B Sound System eliminate the comb-filtering effect.” An A/B system is used in the Avon Theatre at the Stratford Festival in Canada. Stratford Festival sound designer William Fallon said, "I've found that it has also helped in creating separation and clarity in large production numbers, by being able to send half the cast down one path and the other half down another, either based on parts, blocking, leads vs ensemble, etc." A/B Sound System An A/B Sound System is a type of Sound reinforcement system or Public address system. Unlike a more typical sound reinforcement system, an A/B Sound System provides two electrically