@amir_asr Well, measurements show why it is not perfect. For measurements to fail, would have been if it didn’t show that!
I was following a scope readout by a tube amp designer recently who was acknowledging a "non-perfect" sign wave existed in the last design iteration. The top left corner of the sign wave was lively, less than perfect in terms of uniformity, yet reportedly sounded really good, alive and well, when the amp circuit was left as-is. Letting it be or hammering it into submission was the next case study to tune and listen more. This is where things get to be a LOT more interesting to me.
This designer mentioned when taming those little sign wave spikes (aka flare), now making it a more uninformed and perfect sign wave, all of the sudden the amp sounded "dead", no longer alive or enjoyable any more, bleh. After several tests, the designer then made a conscious decision to let it be, since it sounded much better in its original untamed state after extensive listening tests. This is what many of us mean by "listen first and then measure". Putting more emphasis on listening and what sounds best as a means to an end, rather than making graph lines flat.
Some of the popular mid woofer speaker drivers I’ve used from Scanspeak are this way, measuring less than perfect, yet they are alive and musical as-is when left alone - "less tamed" if that’s a description that resonates with a few members here. With tests showing a bit of less-than-perfect jagged flare on the graphs in the upper midrange frequency range on the last drivers I used - most electrical engineers would beat it back into submission with an overly controlling crossover. Some look at this flare as noise, distortion, needing correction. That’s one point of view, not all.
Once again, in my own self made speakers later discovered leaving the drivers as it was designed resulted in a captivating and engaging sound - left in less than perfect form. Sometimes what is perfect to an electrical measurement engineer is not always perfect music to others ears. Most of the audio systems I enjoy listening to do not measure perfectly at all - fwiw. The absolute best measuring dac I’ve ever owned was one of the worst to listen to. Sounding "dead", or boring being a great description.
Unfortunately a debate that won’t be solved on this tread it seems.