20. Explain the difference between compression and rarefraction relating to what we call sound? 21. What does it mean when we say the microphones "area of rejection"?

20. Sound travels as longitudinal waves, meaning the particles of the medium (like air) vibrate back and forth in the same direction the wave is traveling. **Compression** refers to the regions of a sound wave where the particles are squeezed together. The air pressure is higher in these regions. **Rarefaction**, on the other hand, refers to the regions where the particles are spread apart. The air pressure is lower in these regions. Think of it like a slinky: when you push a pulse through a slinky, the coils bunch up in some areas (compression) and spread out in others (rarefaction). This alternating pattern of compression and rarefaction is what propagates as a sound wave.<br /><br />21. A microphone's "area of rejection," sometimes called its "null" or "off-axis rejection," refers to the directions from which the microphone is least sensitive to sound. Essentially, it's the area where the microphone "rejects" or minimizes the pickup of sound. This is important because it allows the microphone to focus on sounds coming from a specific direction (its "on-axis" response) while minimizing unwanted sounds from other sources. Different microphone designs have different rejection patterns, which are often described as cardioid, supercardioid, hypercardioid, figure-8, or omnidirectional. These patterns visually represent the microphone's sensitivity to sounds from different angles.<br />