Break-in is one of those topics where the marketing claim and the measurement disagree in an interesting way. The claim is that a subwoofer needs many hours of gentle play before it sounds its best. The measurement says something happens, it happens quickly, and it is smaller than the language around it suggests.
What break-in actually changes
Measure Thiele-Small parameters on a new driver, play it at moderate level for a couple of hours, then measure again. Free-air resonance typically drops by a few hertz, and the change is largest on stiff-suspension drivers built for high excursion. Compliance rose correspondingly.
Almost all of that change appeared in the first forty minutes. Between two hours and ten hours we could not reliably measure further movement.
Does it change how it sounds?
A 3 Hz shift in resonance is audible only in the sense that a sealed enclosure tuned to the pre-break-in figure is now slightly mismatched. In practice it makes the low end marginally more extended and slightly less tight. Most listeners would not identify it in a blind comparison.
Break-in is real physics and poor marketing. The suspension loosens, the parameters move, and then it stops. Anyone promising a transformation after fifty hours is selling something.
Marcus Reed, founder and editor-in-chief
What to actually do
Play the driver at moderate volume for the first hour or two rather than immediately running it at full power. That is worth doing for thermal reasons as much as mechanical ones: a cold voice coil in a new gap benefits from a gentle start. After that, use it normally.
If you are building a precisely modelled enclosure, measure the parameters after break-in rather than out of the box. Our box volume guide explains why that matters for ported designs in particular.
