You wrote:
«I am more fascinated by your obsession with the hypothetical question related to these two particular loudspeakers...»
The reason why I chose these particular speakers was to make a practical case to apply audio science on gear that people know reasonably well. The case method is well known in situations where skill acquisition is a goal.
I am surprised you don’t think it’s intriguing to discuss the speakers’ attributes in order to put together a weight of the evidence case for a majority to prefer the one over the other. What’s the point of audio science if not to apply it to practical cases?
I also think the Salón vs M2 case is interesting because their frequency responses are similar, but people who took part in the audio society blind test describe their sound as quite different. Personally, I have only heard the M2
It would be great if ASR promoted a language - based on science - to discuss why people tend to prefer one speaker over the other even if the speakers appear similar frequency response wise.
As long as volume is kept reasonable and listening distance is not too long, most - in this case very likely the only - differences in sound are caused by linear distortions - which means frequency response.
If they sound different, those differences are also present in the measurements. But the problem is how to analyze and interpret the measurements to give useful and repetitive and accurate information about the sound from a loudspeaker. Clearly, looking at on-axis alone is not enough. You need the complete radiation pattern. You also need to study what happens in time - a speaker is not necessarily minimum phase. And diffraction and secondary sound sources can play a significant role in a loudspeakers sound. All these are linear phenomenon, and can be seen as part of frequency response.
For very strange or defective creations, it is easy to spot the defect - the frequency response (on-axis) is not flat. But for good speakers, the differences are not so obvious.
A simple in-room measurement can tell a lot of differences between the speakers, and especially if you get to listen, look at the measurements, and then listen again, you can learn and find things. The first you will notice is that it is not obvious what to look for, and the measurements often look quite similar, while sound is perceived very different.
Frequency response on-axis and the suggested additional graphs are useful for the casual buyer to see if a speaker performs reasonably accurate, kind of a does-it-work verification, but it will not tell the full story about how it sounds. It is also dubious whether the casual byer can get much good information from reading those charts, even this simplifed presentation requires expert knowledge to interpret.