The monitor or loudspeaker has a unique position in the signal chain. What comes out of it, or rather, what you perceive comes out of it, is subject to more variables than any other part of the audio path. The output of a processor can be measured or even predicted with a good degree of accuracy, and so electrical specifications are good descriptors of its performance in – and its contribution to – a real-world signal chain. Even a microphone, though it is mechanical and often subject to much imaginative terminology, will only reproduce sound pressure at its position, and according to its own particular acoustic, mechanical, and electrical performance.
A loudspeaker output, while it too can be subject to calculated or measured objective scrutiny, cannot normally be perceived in practice without introducing a host of external variables. The output of a loudspeaker only exists externally.
Even discounting the room, the way any one person perceives an acoustic sound source is subject to a lot of variables. From variations in the Head Related Transfer Function (normally used to describe differences in perception between ears for the purposes of source localisation) and auditory filters to more basic ‘internal’ variations in preferences between listeners. The latter is not simply down to taste but could include finding a balance between requirements such as long-term listening comfort, dialogue intelligibility, simulation of other environments or listening conditions, and more.
The performance of a loudspeaker really does rely on the ears of the beholder.
Because of this, a particular loudspeaker can become a benchmark ‘voicing’ for a system, for a particular job, and for a particular person or group of people – a reference point that is useful for relative judgement. Producers, for example, will often take their preferred near-field monitors with them as such a reference point. Of course, a room is a variable that cannot be transported, but for practical purposes, using a reference monitor, at least, reduces the potential error and has a degree of ‘confidence’ associated with it.
The physical size, shape, materials, and cost of a loudspeaker also have a big effect on its performance, and these are considerations that have to be taken into account. The best comparison for imperfect loudspeakers may well be subjective.