RichardHOS
Second Unit
- Joined
- Mar 11, 2003
- Messages
- 454
Really have no idea why this thought came up... probably because it's late and my brain is beginning to short circuit.
Anyway, I understand the physical basis of comb filtering. I also understand that for line arrays there typically seems to be a concerted effort to keep the center to center distances of the drivers within a certain percentage of the wavelength of the upper end of their desired response, say 25%. Not sure if a -30dB or -40dB down target is used before comb filtering begins, or if the target is right at the crossover frequency.
In any case, this is the question that at the moment I can't seem to answer for myself... why use the center to center distance at all? I know that for the wavelengths involved the driver will act like a point source due to its size, but in reality it isn't a point source. It has a distributed radiating area, and part of that area is adjacent to part of the next driver's area.
To illustrate better my question, imagine for a moment that the drivers were square. A single driver would still model and behave like a point source, but a line of them would have distributed radiating area of a nearly continuous surface from top to bottom of the line. I wouldn't expect comb filtering in the vertical direction in that case anymore than I would for large planar drivers with continuous diaphragms, except for very, very high frequencies.
So a line of round drivers isn't quite as continuous as a line of square drivers, but it's less broken than a string of point source radiators with center to center separation.
I suppose, what I'm really curious about, is whether someone has taken measurements of the vertical comb filtering of a line array at high frequencies and compared those results to what is predicted by a simplistic point source model.
Oh, and if comb filtering was really a concern for the XO point and drivers chosen, would a double column of drivers with one staggered such that the drivers overlapped ~20% in both the vertical and horizontal directions yield the behavior of essentially a continuous diaphragm? Higher driver cost, I suppose, but since when has a line array been about the simple and cheap way of doing something?
OK, time for bed. :b
Anyway, I understand the physical basis of comb filtering. I also understand that for line arrays there typically seems to be a concerted effort to keep the center to center distances of the drivers within a certain percentage of the wavelength of the upper end of their desired response, say 25%. Not sure if a -30dB or -40dB down target is used before comb filtering begins, or if the target is right at the crossover frequency.
In any case, this is the question that at the moment I can't seem to answer for myself... why use the center to center distance at all? I know that for the wavelengths involved the driver will act like a point source due to its size, but in reality it isn't a point source. It has a distributed radiating area, and part of that area is adjacent to part of the next driver's area.
To illustrate better my question, imagine for a moment that the drivers were square. A single driver would still model and behave like a point source, but a line of them would have distributed radiating area of a nearly continuous surface from top to bottom of the line. I wouldn't expect comb filtering in the vertical direction in that case anymore than I would for large planar drivers with continuous diaphragms, except for very, very high frequencies.
So a line of round drivers isn't quite as continuous as a line of square drivers, but it's less broken than a string of point source radiators with center to center separation.
I suppose, what I'm really curious about, is whether someone has taken measurements of the vertical comb filtering of a line array at high frequencies and compared those results to what is predicted by a simplistic point source model.
Oh, and if comb filtering was really a concern for the XO point and drivers chosen, would a double column of drivers with one staggered such that the drivers overlapped ~20% in both the vertical and horizontal directions yield the behavior of essentially a continuous diaphragm? Higher driver cost, I suppose, but since when has a line array been about the simple and cheap way of doing something?
OK, time for bed. :b