I've been working on sweeping my system frequencies, measuring how close my system comes to 75db for a wide range of frequencies put out by the Avia DVD measured by a R.S. SPL meter. I have read a handy guide on the THX webiste on how to conduct a low frequency sweep and can see its value for setting crossover on the sub and finding where any low freq anomalies lie in my room or speaker positions etc. My question/problem is in mid to high frequencies. First, I know that high freq >10kHz aren't as readable so the SPL meter isn't as reliable at this. The mid ranges in between I can measure but what can I really do about it? There is no crossover to set, or phase switch and outside volume control I can't do much. Furthermore I can't find much information on conducting a freq sweep of the mid ranges, THX seems to say nothing about it (unless I'm just looking in the wrong places). Does anyone find measuring/charting their system's freq response useful? Did you get noticeable gains with an equalizer? Is there anything else beside go out and buy new speakers or an EQ you can do about fluctuations in freq response?