Click here to purchase the entire book in PDF format. Wave Addition and Subtraction Go throw a rock in the water on a really calm lake. The result will be a bunch of high and low water levels that expand out from the point where the rock landed. The highs are slightly above the water level that existed before the rock hit, the lows are lower. This is analogous to the high and low pressures that are coming out of a clarinet, being respectively higher and lower than the equilibrium pressure that existed before the clarinet was brought into the room. Now go and do the same thing out on the ocean as the waves are rolling past. The ripples that you create will cause the bigger wave to rise and fall on a small scale. This is essentially the same as what was happening on the calm lake, but now, the level of equilibrium is changing. How do we find the final water level? We simply add the two levels together, making sure to pay attention to whether we should be adding a positive value (higher water level) or negative value (lower water level.) Let's go outdoors and put two small omnidirectional (that is, they radiate sound equally in all directions) loudspeakers, about 34.4 cm apart. Let's also take a sine wave generator set to produce a 500 Hz sine wave and send it to both speakers simultaneously. What happens?