I've seen most of the extremely knowledgable people on this forum say to set the low pass freq. somewhere between 80-90 hz on an amp going to a subwoofer. I'm just wondering why that is (I have no doubt you are 100% right considering the understanding of car audio you guys have displayed). I am a lot more concerned about sound quality than loud bass so I guess what I'm asking is why setting it to that low of a LPF is the best choice? Would it not be better to set it higher to 100 hz or even 125 hz so that bass notes in that freq. range are also handled by the subwoofer which can reproduce those notes more efficiently than my full range speakers?
My other question is about bass boost. I have a Alpine mrd605 powering a 10" Type-R and when I turn the bass boost above 0db gain even by one db the speaker itself actually seems to get softer but more of a muddy tone. The power is sufficient without the bass boost on for my needs but I'm trying to learn more about car audio in general. Also the bass boost says it boosts the signal X db at 45 hz. If it only increases the sound level at that particular frequency how does increase the overall sound of the full range of bass?
Your bass boost is basically a 1 band parametric equilizer centered at 45 Hz. The further away from 45 Hz you get, the less is will effect output. As for the LP crossover frequency, I like setting it low because sound below approx. 80Hz is unlocalizable, meaning you can't tell that its coming from the trunk. This is important for setting up a sound stage. Also, if you set the filter it too high, you'll start to hear the bottom of low male vocals come out of your sub.