How do you prevent beaming from a trumpet?
Or destructive interferences from the soundboard of a piano or the top of a violin or guitar (time delays)?
Does a vibrating string interfere with itself along its length when heard from some perpendicular location (time delay again) ?
If you play instruments in a room, don't they "suffer" similar FR issues as would a speaker playing their anechoically recorded tones?
Aren't we used to all these chaotic effects and largely ignore/process them accordingly on the fly?
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As for the panel sending resonances back toward the speaker cables, there's a 100:1 (or so) step-up transformer between the amp and the stators in an ESL, so, resonant perturbations (if there) would be reduced by 1/100th going back toward the amp.
Beaming in a trumpet is a function of the bell taper (something I am pretty intimately familiar with).
At the source, e.g. piano or guitar, the interference pattern is part of "the sound" of the instrument. Generation and playback are two different things.
A vibrating string is used as an example to show wave modes/nulls in most introductory physics classes. Wave propagation along the string is a different than the cohesive wavefront most speakers (try to) produce. I wasn't going to dig too deep, at least for now (need to get back to work, test finished).
We ignore them to a certain extent, but comb filter effects and so forth are what muck up the image of a lot of systems, especially if the back wave is not damped. The effect of killing those reflections can provide a dramatic improvement in the sound stage and image. I can ignore a lot of things but prefer to fix what I can.