Why aftermarket cables measure identical (and when they don't)

A headphone cable's job is to carry a small electrical signal a meter or two. Its electrical properties (resistance, capacitance, inductance) are so far below audibility thresholds at headphone impedances and audio frequencies that replacing one competent cable with another changes the signal by thousandths of a dB. Measurements confirm this: swap cables on a measurement rig and the curves overlay within the rig's own repeatability.

This is not a claim that all cables are identical as products. Cables legitimately differ in ergonomics (weight, microphonics, memory), durability, connector quality, and looks, all fine reasons to buy one. And a genuinely broken or miswired cable absolutely changes the sound: intermittent contacts, a cracked conductor raising resistance enough to alter response on low-impedance IEMs, or channel imbalance from a bad solder joint.

The exception worth knowing: very high resistance in series with a low-impedance, impedance-swinging IEM acts like a high output impedance and can shift tonality slightly. That is an argument for a non-defective cable of sane gauge, not for expensive wire. Blind listening tests on functioning cables have consistently failed to distinguish them.

Sighted impressions of cable 'improvements' are real experiences: expectation, level differences, and unit variation between listening sessions are powerful. That is a reason for skepticism about sighted impressions generally, which is exactly why this site leans on measurements, labeled incentives, and disclosed methodology.