I have 4 15s with two amplifiers. 2 subs to each amp. When all 4 subs are active at the same time they have less power than just one pair. I had setup a bass knob to one amp to kick in the 2nd pair of subs when I want heavy bass that’s when I noticed the moment the 2 pair gets any power it cuts the bass in half of the first pair already in use. I have a 4 gauge wire ran to a distributor block then 8 gauge split from that to both amps which are 2500watt power acoustic razors and the subs are 2 15in Pyle Power 2000w subs and 2 15in Hifonic Brutus 1200w subs. Any advice or idea to why this is happening?