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Author Topic: Rule of Thumb for Allowable Source Separation  (Read 296 times)

Frank Koenig

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Rule of Thumb for Allowable Source Separation
« on: September 13, 2019, 05:06:00 pm »

Nothing new here, just a distillation of my other off-topic post on this subject.
https://forums.prosoundweb.com/index.php/topic,171973.40.html

We have two identical sources (which could model two disparate sources near crossover frequency, such as tops and subs) that we wish to combine. We'll allow 6 dB amplitude variation in the coverage area and hence Wavelength / 3 distance difference. For 90 deg coverage (45 deg half-angle) the maximum source separation is Wavelength * sqrt(2) / 3 or just under 1/2 wavelength. For 60 deg coverage (30 deg half-angle) the maximum source separation is Wavelength * 2 / 3.

90 deg ---> 1/2 Wavelength
60 deg ---> 2/3 Wavelength

I was thinking a little, too, about flown tops with centered,  ground-stacked subs. The situation might not be as bad as it first appears. The coverage volume (where the sources add constructively) is, in the far field, the volume outside a (complete, double-ended) cone that is the object of revolution of a triangle about the line connecting the subs and tops. If the tops are high in the air compared with their horizontal separation from the subs the intersection of this "anti-cone" with the ground sweeps out to the sides of the tops widening the coverage area. I suppose a picture would help.
 
I know the modeling programs many of you use show all this implicitly, but I like simple heuristics that I can "take home" to help my intuitive understanding. Along the same lines, I put up those little R codes to encourage folks likewise to code-it-up-and-plot-it when they're trying to understand some problem. The little programs I write clearly don't replace full-on, commercially available simulations but serve to help my understanding. One could do much of this in Excel, for example, but I prefer a normal programming language. (Speaking of which, the forum helpfully interpreted the letter i enclosed in square brackets as the markup for italics. Next time I post code I'll make it an attachment.)

--Frank
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Rule of Thumb for Allowable Source Separation
« on: September 13, 2019, 05:06:00 pm »


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