What does the sweep actually do for headphones?
Two things. For new headphones, the sweep exercises the driver across its full mechanical range — every part of the diaphragm, every voice coil position, every suspension travel — which is the 'burn-in' process some manufacturers recommend for the first 20–40 hours of use. For used headphones, the low end of the sweep agitates dust and debris trapped in the earcup mesh, and the sweep helps you identify if any frequency region has gone weak or distorted.
Does headphone burn-in really make a difference?
It depends. Dynamic drivers, especially ones with stiff diaphragms, often loosen up slightly in the first 20–50 hours and gain a small amount of bass extension. Planar magnetic and electrostatic drivers do not change measurably. Most of the 'burn-in' effect people report is actually their brain adapting to the sound signature. That said, running a full-range sweep at moderate volume cannot hurt and is the standard ritual.
How loud should I play it?
Moderate — about 50–60% of your normal listening volume. The point of the sweep is to exercise the driver, not blast it. Sustained tones near the extremes (below 30 Hz, above 15 kHz) at high volume can stress the voice coil more than music ever would. If anything rattles, distorts, or smells warm during the sweep, stop immediately.
Is this safe for my ears?
Yes if you do not wear the headphones during the sweep. Place them on your desk or a stand, set volume to moderate, and let it run. Sweep tones near the top of human hearing (12–18 kHz) are uncomfortable and tiring at close range, even at modest levels, so this is a 'set it and walk away' tool. If you want to listen, listen at arm's length and only briefly.
Will it unmuffle muffled over-ear headphones?
Sometimes. If the muffled sound is from dust on the inner mesh or grille, the sweep will agitate it loose. If it is from worn earpads (the foam has compressed and changed the acoustic seal), no signal can fix that — replace the pads. If it is from a driver that has actually failed, distortion is the giveaway, and you need a repair.
Should I run this on Bluetooth headphones?
Yes, with the caveat that Bluetooth audio is compressed and some codecs roll off above 16 kHz, so the very top of the sweep may not actually reach the driver at full level. Wired headphones get the full sweep. AirPods Max, Sony XM5, Bose QC Ultra all work fine for this purpose because their internal DSP handles the full range.