Thirty seconds to certainty: left, right, center, a full sweep, and a bass check. If all five behave, your audio works - if one fails, you know exactly where to look.
A channel is silent or weak: OS balance, cable, or blocked grille. Bass buzzes: debris or rattle - the speaker cleaner handles dust and water. Sweep sounds uneven: map it precisely with the full sweep generator, and check whether the top end is your ears rather than the gear.
The diagnostic tools: Headphone Test · Balance Test · Fix My Speaker · Sweep Generator · Hearing Age Test · Mic Test
Run the four checks in order: Left plays a tone only in the left channel, Right only in the right, Both should image dead center, the sweep should glide smoothly from low to high without dropouts, and the bass tone should sound clean, not buzzy. Thirty seconds, and you know whether the problem is your device, your speakers, or a specific channel.
In order: the physical volume/mute on the device and in the OS, the output device selection (Bluetooth devices love to steal the output silently), the browser tab mute (right-click the tab), and the cable or pairing. If another site or app plays sound, the fault is per-app; if nothing does, it is system-level.
Check OS balance settings first (they drift after some updates), then the cable - wiggle it at the plug while a tone plays; crackling means a broken conductor. On earbuds, a blocked earwax filter is the top cause. Only after those, suspect the driver. The full diagnosis path is on the headphone test page.
Gaps in the sweep mean frequencies your gear (or ears, at the top end) cannot reproduce - normal for small speakers below 100 Hz. Buzzing on the bass tone means something is rattling: a hair on the driver, loose grille, or resonating furniture. Clean the grille and isolate the speaker, then retest.