Running the LPF on both the HU and amp

I've read some conflicting opinions on this but I can't turn off the LPF in my HU but I also have the LPF on my amplifier turned on...basically just as a backup. The only reason I created this thread is I have heard some people say that it is good to have double protection but I'll have to assume they are referring to midbass, as the software max setting for my HU sub out is 120 Hz, nothing out of the ballpark.

Was digging around on Crutchfield with some free time and saw their sub tuning section and they specifically mentioned to only run one filter or the other but not both. The easy test will be to go outside on lunch break and turn the amplifier filter off but I was curious about forum opinions on the subject.

 

this is a new one to me. on my hu I can set it to several lpf outputs (could only turn the sub output off, not lpf), I think I had it set to 120 or so but that was after fiddling with it while my amp lpf was on as well. I forget what I tuned the amps lpf to but I ended up breaking my amp (it got stuck in protection mode, too lazy plus low funds to go have it checked), but imo what caused my burn out was that I had two 350w subs hooked up to a 540w rms amp ... which was not really a good idea (that maternal need to want more kicked it bad ).
On your break turn the lpf on the amp off and see if there's any change. Curious about this. Not sure why there would be a lpf setting on the hu when it's not recommended to use both.

 

Yeah the main point in the article seemed to be related to distortion:

Note: Do not use the low-pass filters, crossovers, or bass boosts on the receiver and the amplifier at the same time — use one or the other, but not both. The reason is that something called phase distortion generates around each filter or boost's crossover frequency, muddying up the sound.

I'll give it a try over lunch break...I've wanted to try flipping the polarity to the sub anyway as I've read in a few places that it's worth while to reverse the polarity just to see if one sounds better than the other.

 

that makes sense. on my hu (pioneer), it's got a bunch of subwoofer settings which I guess allow for better tuning, but makes it more confusing enough, while the amp I was using had options for tuning the lpf also. man ... what ever happened to plug and play lol.