building basic woofer and inductor/cap calcs

[mk1982]

Hi there !

I'm creating a very basic subwoofer from an 8" paper cone woofer listed here, specs are here:
http://tinyurl.com/2v6qx

i'll be using a small sealed enclosure to so i can use scrap MDF .. website suggests 20L which is about .75ft^3.

my question is regarding my inductor calculations, based on the EXCELLENT well written in the WinISD help file (i can't praise it enough, very readable for newbies ..

i've calculated that for a 9mH inductor I will achieve a low pass crossover at about 140hz which I am only guessing is appropriate for this woofer.

Using the signal generator i found my home speakers to loose SPL at less than 200hz so I think this will be ideal.

I'm also considering using an appropriate capacitor connected to the speaker cables in series as they are happy playing ultra low frequencies which I don't think is very good for them. I don't think the woofers in the 2 way speakers are high passed at all as i can feel them move at very low frequencies (30hz .. and lower

so in series i'll probably connect a 100uF capacitor.

so currently should look like
ch1: 100uF capacitor for 100hz HP --> 2 way bookshelf
ch2: 100uF capacitor for 100hz HP --> 2 way bookshelf
ch3: 9mH inductor for 140hz LP --> 8" sealed paper woofer

i selected 100hz as the HP as the filter simulation in WinISD suggested i'll get a dip in SPL if I use a HP at 140hz ..

well i'd LOVE some feedback on my ideas ..

Hope this woofer creates SOME bass but if the 6" woofers on the speakers can't really produce audible frequencies below 100hz i don't see why the 8" will be any different and this really worries me.

Even the tiny little driver (probably 5" or less) in my computers speakers subwoofer produces a lot more bass than the bookshelf speakers .. maybe the bookshelf speakers ARE high passed so i can only feel the lower frequencies (30hz and under) when i really turn up the volume. perhaps some signal is still getting through ???

well it's a long post so ---- thanks HEAPS !!!!