correct TA is very difficult to achieve especially if your playing 3 - way ...
like foo said, TA to zero first, from there i believe you try to play with the gain or level sensitivity ....
if it can be balance that way, there is no further use of TA ...
for so called center imaging, sometimes playing with the gain would be more than sufficient ...
in my previous setup, gain sensitivity was set first, then TA and finally EQ ...
since i go for tube, all 3 has been discarded .... because Tube provides full tonality and also ambience ... although some might argue no imaging..
however, i am trying to be a purist, i.e. let the music be what it is, bearing in mind that not all CDs or Songs were recorded to give out it source in the middle....
it would be a wrong move to use a wrong CD or track e.g. that focuses on ambience when one is looking for center imaging.... best is to use IASCA test tracks i guess... cheerio!!
