There are several schools of thought on this area, so here is one approach
I tend to use the
Dsp type units ie drive rack
etc, for setting up the
system, correcting issues with the speakers themselves, cross over points, alignment delays
etc, basically not addressing room issues at all but the :
system:
If youom look at the user interface
etc for these driverack type units, you can see that they are designed
IMO from this standpoint, you work you way
thru menus, and various parameters for eq and delay
etc, and then it is pretty much a set and forget it.
Feedback issues tend to come down to two main areas, Mains, and Monitors.
In most cases similar to yours,
feedback from mains should not be an issue, as you should be able to correct for placement of speakers and mics. For the most part you are looking at attempting to improve how the
system sounds in the room. There is an old joke of "how do I flatten a room... get a bull dozer" which has a lot of truth in it, but also points out a lot of the confusion.
Again, since you are using this
system in a specific
venue,
IMO the best way to correct for room issues is to use treatment (panels/
drapes etc) to alter the room response.
You then can use eq
etc to try to improve how the
system sounds in the room. This is where the graphic or parametric is useful. So again if you have proper placement of speakers/mics the
FOH sound should in most cases be corrected for
feedback resulting from peaks and valleys with room treatment
etc. There are different approaches to this issue, so different people take different correction measures.
Monitors are a different issue entirely, Here you are typically ringing out for
feedback, have less control over
speaker/mic placement
etc, and eq is typically done each time the
monitor system is used, based on the likelyhood of different mics, placement
etc.
Most people use a Graphic for this, I can be argued that this is a pretty
broad blunt
instrument, as if you were to look at the actual response curves based on frequency
fader alteration, you will see that while the center
point of the "
effect" is at the
fader frequency, this is not a notch filter and the alteration spreads out quite a
bit.
Some people use a parametric for this, since it can be more precise, but it tends to be a
bit more difficult for the non experienced user. Here is where companies like Sabine decided to make
feedback eliminators. Their use is controversial, since improperly used they can dramatically alter the sound of the
system in a negative way. Their advantage is that they detect the frequency with the "excessive" energy and implement more of a notch filter.
I certainly can be argued successfully that a properly rung out
monitor system does not need a
feedback eliminator, and that any automatic
system is a series of compromises, BUT they can be useful in a
system where for instance there can be a lot of variation between mic placement during ringout and performance, or the person running the
system is having diffuculty associating a frequency with the beginning signs of
feedback, and therefore has some difficulty determining exactly which
fader to alter.
So in some cases I use for example the Sabine FBE systems, as a compromise where the automatic feature or more correctly the quick response is usefull, especially if the user clears and resets the filters before the performance. Again a lot of this is personal taste and judgement, and in some cases where the people running the
system might not be all that experienced, might not be able to be highly attentitive to the
system during the performance, or there can be major variation in mic placement during the performance, an auto
feedback eliminator can be useful.
In the main the
feedback eliminator mainly determines the offending frequency and attempts to correct it. that is the good news, and the bad news and where there needs be be a lot of caution is that since it is automatic, it certainly can be fooled with a set of frequencies that are infact part of the program , which it then attempts to correct, with the result of negatively impacting the overall sound of the
system.
so in a long winded way, Graphics are a good way to go for monitors,
Feedback eliminators CAN save the day on some occasions, Driverack type units work best for
system setup, and if you are working in a specific
venue with the
system on a fixed basis, using physical room correction can make a major difference and is usually very worth while.
I have on many occasions had the challenge of turn this airplane hanger or gym in to a reasonable sounding
venue. No amount of electronic correction is going to save the day, but
reflection panels, absorption panels and
drapes can produce some amazing improvements. Again in a long winded way, with
feedback or simply how the
system sounds in the
venue, it is very worth while looking at placement and treatment solutions, in many cases first when you are doing an install
If you for instance look at a graphic on the mains on an install and the settings are obviously dramatic and severe, USUALLY it is an attempt to correct something that really should have physical correction.
Hope this helps
Sharyn