I know its hard to just say yes or no but I been playing around with the freq. and anything higher just has way too mich mid bass that muffles everything else and gets annoying. I have 2 10' fosgates in a bandpass

 

The crossovers in amps are notoriusly inaccurate. Even with seperates it's a guessing game unless you have a frequency counter or other equipment to test the crossover frequency. In addition to that the bandpass box in addition to the vehicles resonant frequency are likely somewhat to blame for increased output in that range. Many bandpass and ported boxes are tuned to peak in the 50-70 Hz range for max spl.

 

I personally wouldn't run mine that low. A 10 has some great range and shouldn't be cut off the same place a 15 would be. I've worked with many a sub and most 10s I find can handle themselves admirably up to 75-95h depending on the application. If your mids pick up that early in the frequency, go for it, but few mids have any sort of flava before 75h. My .02

 

10's definitely sound nice up to around 80hz. I do prefer 12's and up to hover around 50hz. Keeps that kick drum sounding good

 

You guys are talking about the sound characteristics of cheap subs in sealed boxes, possibly sealed boxes that bring out that cahracteristic. A quality sub in a sealed box will play the full bass range. Some will easilly and accurately play up to several hundred or thousand Hz. The size of the sub is not an ultimate determineing factor for how high it can play. If you doubt me come out to my house and I will try to have at least two different size high quality subs to let you listen. But hopefully by years end I will have a couple more for you to hear.

 

I read somewhere that for subwoofers in a ported box, you should try and keep hz at or below 100h.

I have a 12 Rockford, only 400w, in a ported box, and for me I keep it up around 90 Hz, you just have to play around with the settings on the amp. Like the gain and the bass boost... play with those two until you find something that sounds good, and does not distort -- until you get into the peak volume ranges of your HU.