During the show, I would agree that in many cases an RTA is the best tool-but what are you actually doing with that tool? Are you making any "system level" adjustments based on what is on the RTA?
I would be scared to do that during a show.
The dual transfer function (when used properly-most people DO NOT use it properly), is much more immune to "other sounds". An RTA will respond to any sound, a truck going by for example, that is not part of the actual sound coming out of the loudspeakers.
If the ONLY thing you are interested is the phase response-then yes, an mic will show you the differences.
HOWEVER- you should ALSO be concerned with the AMPLITUDE response of the two speakers are you are looking at.
So you need a flat response mic in order to show that.
Pretty much any "measurement mic"-including the Behringer, should be just fine at any freq you are trying to "align the phase".
I would assume you are not trying to "align the phase" at 12KHz-because that is a waste of time. If you move the mic a little bit , it will be all over the place.
But at lower freq (which is what I am assuming you are talking about), a cheap measurement mic will work just fine and give you the information you are looking for.
The tool you use depends on what job you are doing. I don't see many people taking the BK4007s out to bar gigs or any case where it is likely to be damaged.
No, usually not. But just like in the studio you can't have a 100% correct prediction of how things will sum together while you are eq-ing them channel by channel. So even if none of the instruments had any kind of 100-300hz ring or mud, that doesn't mean that in the overall mix some unexpected things might show up there. So if any kind of a "ring" shows up in the lowmids during the show, the SMAART RTA (especially with the slow spectrograph) tends to be usefull for things like this.
I am able to detect the problematic frequency by ear, relatively precise. But when you take a look at the nice big RTA it really helps you to put some things into better perspective. Helping you to touch up some of the channel eq-s a bit more or even the main mix eq if you want to generally rebalance the mix a bit.
Together with that, in case of a monitor feedback i usually know which monitor it came from since i keep looking at the stage and tracking what is the band doing. But if you had the smaart spectrograph turned on. You take a look at it and find a nice red line from a few seconds ago.
Then you can open the monitor EQ and eliminate a few dB from the problematic frequency.
2. Talking about the dual transfer function i will research a bit more about it and them possibly ask some quiestions.
3. Of course not, with the yamaha system that i run in a local club quiet much every weekend, the top boxes do combfilter but i know that it's not possible to solve that with a phase response graph since it would only work for one spot.
However i was going to try aligning the subs with the top boxes in the crossover area. (80-120hz)
I run the system crossed over at 110hz with a 24dB/octave BW cut.
4. True. The mic i need is mostly for "bar" gigs.
EDIT: What did you mean with "i should also be concerned with the amplitude response of the speakers that i'm looking at ?
If i'm aligning a dual 18 with the 2x15+1.5 top box, the levels that the sub is going to be running at compared to the top box is going to be my choice based on the type of music i'm mixing?