Originally Posted by
EarmarkMarine
Razzman,
The crossover frequency selection will be unique to each system. Usually you go a little higher with a small woofer, free-air woofer or woofer that is in a less than optimum application. You'll get an increase in overall output by widening the bandwidth which causes you to gain down the sub. And that results in improved tonal construction, particularly at higher volumes.
Here's one way to proceed. Set your high and lowpass crossovers at 120 Hz. With your tower speakers off, turn up your coaming coaxials to just under clipping (no harshness or significant distortion). With your sub down, incrementally increase the sub's gain until it is a linear extension of the fullrange coaxials. If it sounds boomy, remote or detached then back it down some until the sub sounds like its seemlessly spliced with the mids rather than sounding like an independent source. At this point you'll have good tonal construction with balanced output. If you want more bass emphasis then use your bass tone control. At least it presents a subtle octave-to-octave rise versus the ubrupt edge of a steep crossover slope. Listen to it for awhile this way and get used to it. It may not be for everbody but it is a good reference point.
From this point if you want to increase the sub's gain, the elevated output will raise the frequency of the lowpass -3dB intersection relative to the highpass. So as you increase the sub's gain you'll also simultaneously lower the lowpass frequency to eliminate the broad overlap of the high and lowpass crossover filters. Hopefully your amplifier has independent high and lowpass controls that you're able to stagger the filters. This will allow you to maintain a more uniform phase and amplitude response through the crossover region.
In an open-field environment , even with larger and more powerful subs, we rarely use a lowpass point below 90 Hz. Its very different from a vehicle.
For tuning purposes, use only good recordings without heavy bass emphasis. You don't necessarily want to use your favorite material. Use a variety for contrast. Stay away from downloads, burnt CDs or anything that may have built-in EQ. Have all tone controls flat with the bass EQ on the amplifier defeated.
I know its a protracted answer but there's no perfect frequency. This is a proven technique that has converted many nasty systems to pretty good sounding systems. Plus its a very subjective perception ranging from purists to bassheads.
I hope this helps. Its only a snapshot in the system tuning process.
David
Earmark Marine