Another Sub Q: Is my sub mismatched with speakers?

Maybe...What sub do you have??

Some brands of subs have a crossover device where the device is suppose to cut off the bass signal to the main speakers, so only the sub plays those low frequencies?? That may explain the 50hz lowest setting. Or it might be an HT sub where the HT receiver should be adjusted.

The lowest setting on my sub(s) is 22Hz.

What do your ears tell you ? Is the bass slow and heavy, bloated and one note or is it quick, clean and authorative or slightly soft and rounded ? Chances are that regardless of what you are hearing now, it can be improved with some work.

Much of where a sub is crossed over will have to do with the actual in-room frequency response of the main speakers, the rate of slope used in the crossover itself, the design of the sub ( sealed, vented, etc... ) and the distance that one places the sub(s) from the mains.

The bottom line is to experiment with your set-up and see where you end up at. Most of the time, it is best to try and situate the sub near the mains if at all possible. This might not produce the greatest level of output or the deepest bass possible, but the ability to "blend" with the mains in a more natural manner will be increased. When properly adjusted, one should not be able to tell that there is a sub running in the system. The only thing that a sub should give you is the potential for greater low frequency extension at higher levels. That is, when the recording calls for such. If your "sub" is playing along with every song and its' contribution to the music is very noticeable on a regular basis, the chances are, you are using it more as a "woofer" than a "SUB-woofer". Sean
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Find the point where your speakers start to roll off their bass, maybe the point where they are down 3db. and cross over at a point above this. Some overlap between the mains and sub will sound best, find this by listening. Subs work best for music if they are near the mains and I have found that is somewere between the mains in most cases but not all cases. Get a cheap rat shack spl meter (nice to have anyway) and a must for hometheater.

beside, all the points above, dont forget that many speakers claim to reproduce music in low Hz, but they dont sound as good as quailty sub,, the best is to do comparision and hear, even cross at 125 Hz , may sound more solid and richer bass

Are you using the crossover in the sub? Does your preamp have a crossover built in? If you are running full range to your speakers and full range to the sub, you will get some overlap with a crossover at 50hz. Remember that most crossovers are not 1st order, so you will get a gradual roll-off over a 12db to 18db range. The only way to avoid this is to have the system crossed over between the pre and power amps or between the amp and the speakers so the sub won't get too much of the same signal.
Some very high end subs will allow you to adjust for a good blend.