5 Factory-Line Calibration

The resistance-based technique used for thermal protection works if Smart amp knows what normal temperature looks like for this specific speaker's coil — a reference point to measure change. No two coils come off the production line with exactly the same resistance: small, ordinary variations in wire length, winding tightness, and material batches mean every individual unit is a little different, even within the same speaker model and the same factory batch. A single generic reference datasheet number would be close enough for some units and noticeably wrong for others.

To fix this, every individual phone or piece of consumer electronics is calibrated once, on the factory line, before it reaches a customer. During final test, each unit measures its own speaker's electrical resistance while the factory floor is held at a known, controlled temperature. This resistance-and-temperature pair, for this specific unit's coil, at a known starting temperature, is then stored permanently in the equipment memory as the personal reference point, unique to the unit.

From that point on, every resistance reading the Smart amp takes out in the field is compared against that unit's own stored reference — the same idea as zeroing a kitchen scale before weighing. Skipping this step will result in the temperature estimate for that unit to end up consistently off in one direction: either too cautious, giving up loudness the speaker didn't actually need to sacrifice, or too permissive, letting the coil run hotter than the system believes it is.