Click here to purchase the entire book in PDF format. Electrical Equivalents Here's where things get really interesting if you're like me and you're curious about how things are the same instead of how they're different... An acoustical resistor (like the water in the swimming pool) just causes you to lose energy. This is just like a resistor in an electrical circuit which converts current into heat. An acoustical reactor (the plate on the spring) causes you to work harder when you're moving slowly (think about pushing the plate away and then stopping...). The faster you move (the higher the frequency) the less you have to work (because you don't have to hold the spring in a compression for very long). This is the same as a capacitor. The lower the frequency, the harder it is to get signal through it. Once you get the mechanical reactor (the heavy plate) moving, you don't have to do anything. It keeps going in that direction. The faster you try to move it back and forth (the higher the frequency) the harder you have to work to overcome inertia. This the same as an electrical inductor which allows DC (0 Hz) though but doesn't allow high frequencies through it. Since these three things, an acoustical resistor, an acoustical reactor and a mechanical reactor all have electrical equivalents, we can draw an `` acoustical circuit'' using electrical analogies. We'll get into this in a later section.