When designing a speaker system, be it a single unpowered tower speaker or a lithium ion portable speaker system, a firm grasp of some basic acoustical principals is essential in designing an effective system. Sound can actually take many different forms, three of which are radiating waves, standing waves, and pressurization of the listening area.
Radiating waves are what we most often think of when we visualize sound waves, and can be seen as a series of high and low pressure areas radiating from the source of sound. These are the types of sound waves we want to excite as they are very linear and have low distortion.
Standing waves are often the cause of unwanted hotspots and distortion in a listening area, standing waves are stationary waves caused by interference from reflections of a sound wave producing nodes (small pressure differences and low volume) and antinodes (large pressure differences and high volume). As standing waves are produced by interference with a reflected sound wave, these waves are generally avoided when possible.
Pressurization of a listening area happens at either really large wavelengths (deep notes) or in small listening areas (headphones, between the driver and ear). When the wavelength of a given frequency becomes larger than the listening area, there is no room left for a wave to be formed to travel across the listening area, and instead the entire listening area becomes pressurized or depressurized. An example of this is room or cabin gain, in which the deeper notes are seemingly "amplified". Room and cabin gain begin when the wavelength exceeds the size of the room, and can be highly dependent on the rooms ability to hold pressure for the duration of the wave.
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