How Do I Adjust A Subwoofer For Best Sound?

Lots of good information here, but I’ll add what I can to see if we can confuse you some more.

As @273 said, it won’t be a set it once and be done thing. You can get it close, but as you listen to different music, you might need to tweak it now and then, eventually you get it where it sounds good on almost any type of music you listen to.

First, a crossover is a circuit that sends low frequencies to the speakers that can handle that, and high frequencies to speakers that handle those. The crossover dial on your unit should actually be labeled low pass filter. It sets the frequency at where the subwoofer starts to quit working. I say starts to quit because it is not a switch, it is a slope, and the number represents where the slope starts. Some manufactures like shallow slopes, some manufactures like steeper slopes, and more advanced electronics allow you to adjust the slope. This one does not.

The reason for the filter is the same as you don’t want too many cooks in the kitchen. You don’t want the subwoofer and the speakers trying to reproduce the same frequencies or it starts to muddy the sound. That’s why others have said to listen to music and figure out where, your speakers start to get kind of shy in the bass. 80 Hz is really a very good starting point. 6 1/2 inch speakers are usually pretty good down to somewhere between 70 and 100. A lot depends on the speakers enclosure (your door cavities), and a lot depends on the room, (the vehicles interior). Whereas the speakers have a slope in the other direction, they don’t just stop working like a cliff, the response “rolls off”.

The Crossover (or Low pass filter) will set the point at where the subwoofer starts taking over reproducing lower frequencies. (It allows the low freq to pass the filter to the subs amp and speaker)

First, in your case, listen to the system without the subwoofer. Since the subwoofer is driven off the rear output of your system, whenever you adjust the front/rear fader control, it will affect the balance of bass to higher frequencies. I prefer a little more forward presentation because I go to see music with the musicians in front of me, and add just enough rear to make it sound a little more full. Some people like more in the rear (like our old-school cars when we had decent 6X9s in the back and crap up front). Figure out what you like first. Once you figure that out, this would be the one control that you probably don’t want to change too often, or take note of your settings so you can return. (you might be able to use this to your advantage later-if something is a little too bass heavy, you have the option to either adjust the Bass control on the head unit OR give a little Fader to the front)

Your door speakers will definitely cover the range of female voice frequencies. They will cover all but the very lowest range of male voices, James Earl Jones being the exception. That point is generally between about 80 and 100 Hz. That’s the point that human hearing is able to pinpoint where a sound is coming from, below that we are less sensitive to direction. You don’t want the subwoofer contributing to directional cues, so you won't want to be to the higher end of the scale. Localization AND cooks in the kitchen- both bad.

At this point, it’s helpful to have somebody help you. Starting with subwoofer Volume at MIN, Crossover @ 80, and Phase at 0. Listen to a good recording of the type of music you will mostly listen to. If this is a vehicle that has air conditioning and you will usually have the windows up, then listen with the windows up and the AC running. Have your helper bring the woofer level Volume up from its lowest setting. Stop when you get a good balance between enough bass, yet not overbearing. Again, some back-and-forth might be necessary.
Now have your helper quickly spin the phase from 0 to 180. Do you notice more bass at 0 or 180? It will probably be somewhat subtle because this will affect the area where the sub and speakers overlap (they are both reproducing the same frequencies. If there’s more bass at zero, the “ideal” setting will between 0 and 90. If there’s more at 180, then ideal will be on the higher side.

If there was enough added bass, you may want to tweak the bass volume setting again. Get that leveled again, and see if you can discern a difference as someone moves the Phase within the 90° range you previously determined. It starts to get more and more subtle, but you are looking for the spot where it “just blends” or sounds “right”.

If this is a windows down vehicle, this is all mostly moot, because all the wind noise is going to mask most of these settings. Set it all with the engine running, but know that you are going to probably add a lot of bass later, but once you get the system to overcome the wind noise, stop the truck leaving the system playing at the volume and bass level you had, and make sure the system and or sub isn't all distorted sounding. If everything is distorted, bring it down to where it sounds clean, if just the bass is distorted, lower it level to the clean point, and that's about the limit of where you want to run it.

As said, over the next few days or even weeks, you might find yourself doing minor tweaks as you listen to different music and/or sources.

I think I speak for anyone here- Feel free to PM if I (or we) can offer any additional info.