Things to listen for

In mono, you should concern yourself with spectrum, timbre and transparency.

Rate the speaker in terms of the breadth and apparent smoothness of the bandwidth. Are there any peaks or dips that are apparent across multiple selections. How are the extreme highs (above 7 kHz.) and extreme lows (below 100 Hz.)? How smooth is the bass? How punchy (not necessarily good!)?.

How boxy is the sound? This can be re-expressed as: does the sound seem to reside within the speaker enclosure and be leaking out through the drivers? Or does it seem to co-exist as a point in open space in the same position as the speaker? (I think the latter is generally better.)

How transparent is the sound? Can you hear low level details, reverberance and ambience, even in the presence of high level signals? Can you resolve harmony vocal parts? Can you hear into the instrumental sounds, can you “wrap” your perception around the sounds?

Do acoustic instruments sound natural? Does ear candy sound good? Is the reverb spacious? Is the ambience convincing?

In stereo, first, listen to your three pink noise excerpts. Now, your room is involved, and the results will depend on the quality of the speakers, of the room, and the symmetry of the room/setup. Single pink noise to two speakers should be a narrow, discrete phantom image midway between the two speakers. The narrower it is, the better the match between speakers, generally speaking.

Two uncorrelated pink noise signals should obviously come from each of the two speakers, with no phantom image and a significant sense of spaciousness.

The single pink noise signal with one channel out of polarity should sound ideally like it is coming from behind you. Most likely, it sounds confusing, a little hard to localize, and slightly disturbing.

Images of music recordings with reverberance should have apparent depth.

The loudspeakers should tend to disappear, and the image or soundfield should spread across the front of the room. Wide dispersion speakers will tend to have a broader, more spacious image. Narrow dispersion speakers will tend to have a narrower, less spacious image, usually held between the speakers. I personally think wider is better. In fact, neither is more “accurate” in a literal sense.

Depending on the recording technique used, the sound ambience and reverberance should “envelop” or wrap around the listener to at least some extent.

The soundfield should be natural, entertaining and comfortable. Phantom images should be clear and reasonably unambiguous, depending on the recording technique and the instrument(s) involved.