Girl, you ask a lot of good questions.
I'll try and take them as you gave them.
Great informative video! The data presented makes it superior to other folks info audio videos.
Several of the questions asked at the YouTube page are relevant.
The one I thought of also, where one is playing a monaural record.. Does the fact I am using stereo speakers mean much? (for comb filtering. My thought is the DISTANCE between the speakers, being several feet instead of just inches, makes the comb filtering problem 'go away'.) but I do not know if this is true.
I answered that question earlier today. The distance can push the cancellation much lower in range, but the longer wavelengths could all couple with each other. It all depends on the distance that they are apart and from you and if there is a difference in those distances.
Here is what I replied tot he poster on Youtube.
Whether you drop out a channel or not could depend on the speaker placement and distance that they are from each other compared to you. And the number of recordings made that way are limited. Go with what works best (or sounds best) for you and your application.
So the question about playing monaural source material... What does that do? is a good question. And is there SOME FREQUENCY at which the actual typical distance between stereo pair of speakers IS going to create the comb filter problem playing monaural source???
Lower wavelengths will couple as the distances (time delay of one speaker compared to another) are not that different. But a little time delay difference up top will knock them right out. But so can a wall reflection.
The second question, which seems to have more confusion, and 'alternate theory' kind of commenting is about LINE ARRAY. Seems some folks posting think a line array does the same thing. But from the actual video, it seems he is saying no. a line array (or a ribbon tweeter) is different.
Yeah, with a line array instead of two sources you have a lot of sources. So there are many very slight time delay differences. With a line array I can move the microphone up a few inches at a time and will see +/-2db ripples across the top end. As the mic is moved up or down you still have +/-2db ripples, but the peaks and dips will move around and swap places. The effect is actually still much less than room related reflections.
And finally my question about what about a multi driver system, with say a five way design. (Like Infinity IRS)
Anyway, in general, HOW FAR APART do drivers need to be, for what frequency range...
Something to keep in mind in that regard is the length or distance of a wavelength. See this chart: http://www.soundoctor.com/freq.htm
And then compare that to how far the drivers are apart. Then you have to consider the time arrival differential verses wavelength to know how much phase rotation is occurring and if there will be cancellation.
Clearly the tweeter range, two suck. And with the demo the tweeters are a few inches apart.
So my general question boils down to what is the relationship of DISTANCE to frequency response matters to the comb filter problem... Which adds in the mono. dual mids all into one question.
One other thing that was interesting... How moving the mic changed the frequency of the suckout... amazing...
Again compare wavelengths verses distance differential. That website with the chart will really help.
And sharp questions...