How Sound Works in Rooms (from YouTube)

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Pretty basic stuff. The color pattern showing sound reinforcement/cancelation is a good illustration. Almost everyone notices this with lumpy bass. But it happens across the spectrum. That is what makes this Audio 101. In the more advanced classes we go into the physics of wavelength and why different approaches and techniques are used for different frequency ranges.
Thanks for the post. I am in the learning process of all of this now. I'm starting with a miniDSP product, I've had the mic for two months! I'm hoping that and REW will be easy to follow to make some of the corrections I need to make for a challenging room. After that I plan on doing some room treatments. No matter how much I learn I hope I will never be like some who think they know so much and try to lord it over everyone.
Wow that is very important.
But the final sentence opens a whole can of worms: the use of diffusers and absorbers "make the sound more natural."   But there is nothing 'natural' about the best symphony hall (which itself is far from perfect), or studio, and we never experience music in such an environment.
BTW, The person who made the video has others. Haven't looked yet but sure to be interesting. Glad I helped someone...
Acoustic is a more "deep" subject than meet the eye ...Or more than rolled the waves ....

Why a ionizer(non ozone one) for example can modify the sound in a room?

There is a scientific explanation for sure but not in audio threads.... 😁