1 Introduction

Modern phones, tablets and laptops are expected to produce loud, clear, bass-capable sound from speakers that are physically tiny — sometimes barely larger than a coin. That's a challenging problem because sound output is closely tied to how much a speaker cone can physically move and how much electrical power its coil can handle. A small speaker used in many industrial and personal electronics end-equipment is inherently limited on both the above factors compared to a large one. The most direct way to make a small speaker sound bigger is to push more electrical power through it, but pushing too much will damage the speaker.

There are two distinct, and different, ways a small speaker gets damaged:

1. It gets pushed too far: The cone (the moving surface that actually creates sound) is only designed to travel a limited distance in either direction. If it is pushed further, then the cone can strike the frame, tear the suspension, or permanently deform. This kind of damage is usually sudden and mechanical, similar to over-extending a spring past its natural range of motion.
2. It overheats The coil of wire that drives the cone (the "voice coil") heats up whenever current flows through it, exactly like the heating element in a toaster. Sustained loud volume means sustained current, which means sustained heat. Enough heat will melt the insulation on the wire or the glue holding the coil together, and the speaker fails.

Simply limiting the maximum volume low enough to avoid both types of failure works, but it prevents the speaker from playing loud content even when the speaker isn't close to the danger zone. The job of the smart amp is to replace this conservative fixed limit with a smart, dynamic adjustment, so the speaker can be driven right up to its safe limit whenever conditions allow and pulled back only when it is actually needed.