Moved into a new house setup the speakers and run some tones to test the response and setup the sub. the sub gave a very smooth response but the mains produced a massive nearly 20dB peak @ 80Hz follwed by quite a large null. (the 20dB was without any correction on the RS spl meter) The mains are X-overed at 80Hz, even setting the x-over to 120Hz still produces the peak. Turning the sub off does nothing so it's not that combining with the mains. Surprisingly moving the speakers also has very little effect, maybe knocking off 3-4 dB of the peak. Any ideas or is my only option equalization?