There is certainly a range of quality in audio gear, but it's a complicated thing. Some things that are reasonably easy to notice with a stereo system: 1) Dyn

There is certainly a range of quality in audio gear, but it's a complicated thing. Some things that are reasonably easy to notice with a stereo system: 1) Dynamic range: how loud does it get, how quiet does it get? Does it sound good when its loud? does it sound good when it's soft? Small/inefficient speakers will struggle at high volumes, resulting in high distortion. That's measurable and often not hard to hear. Big speakers with the powerful amps needed to drive them which sound good at high volume often suffer from audible hiss at lower volume, short distance listening, due to inadequate power supply noise rejection relative to the gain. Big speakers also will generally have further-spaced drivers, and that bigger geometry can have a noticeable effect on spacial coherency, especially at short distances. (Ideally you want your speakers to be a point source, not different frequencies coming from different angles) 2) Flatness in frequency response: this is easy to measure with equipment, but also quite easy to hear by playing a sine wave that slowly sweeps the audible range. If the amplitude of the wave in the signal is consistent, there shouldn't be a ton of variation in volume of the reproduction. It can be heavily effected by the room they're in, usually in the bass & mid-bass range where the wavelengths are similar to room dimensions, but some speakers will be much more consistent than others across the rest. 3) Dispersion characteristics: when you move your ears around relative to the speakers, does the frequency response change dramatically? Some speakers don't sound very good in the high frequencies once your ears go a few degrees off axis from the source. This stuff gets a lot more obvious when doing A/B comparisons. You're right that you can't really tell how good a system is just by listening to a random song and judging it's sound quality like you can with video on a TV, and I think that stems from an inherent difference between hearing and vision. The sound you hear is ALWAYS heavily effected by the space its in, reflections and sympathetic vibrations, the angle you hear it from, and so on. Source material varies wildly in quality and recording/mastering technique. It's much harder to perceive "wrongness" in audio because it's so varied to begin with.