On Fri, Jun 24, 2011 at 01:58:47PM +0200, Philipp Überbacher wrote: > I found a bit of explanation of wave propagation in one of my books, but > it seems to differ slightly. It basically takes energy and heat into > account and says (simplified) that there are basically two states, one > without motion but increased pressure and heat, one with maximum motion > and little pressure/heat, and everything in between. I guess this > corresponds to P() and V() in your explanation? Can't say without seeing your book. P() and V() certainly are not 'two states', they are two components of a single state. You can create any combination of P and V at a given point. But for a _single source_ they are related, and you could map them to voltage and current, with the quotient being the acoustic impedance (as in Ohm's law). Again, for the P and V fields generated by a single source at suffient distance, or a plane wave, P and V are in phase. Their maxima occur at the same points at any time. It's very common misconception that the energy in a wave 'alternates' between potential energy (at a P maximum) and kinetic energy (at a V maximum) as it does for e.g. a pendulum. Even the Wikipedia article on acoustic waves gets this wrong. In fact the power is proportional to the product of P and V (as it is to the product of voltage and current). If the two were 90 degrees out of phase the average power would be zero. > I guess this sort of analysis or model is used for more complex systems > like ambisonics as well? Yes. In ambisonics the P/V ratio, divided by its expected value for a plane wave (i.e. the acoustic impedance), is called 'rV'. A good decoder is designed to generate rV = 1 for low frequencies. It's done by adding an antiphase signal in a direction opposite to the intended source. This increases the vector sum of V, and decreases the sum of P, so they can be made to match again. Ciao, -- FA _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
