cross over frequency....help!!!

[Dannyball]

Hi everyone. I have just built myself a subwoofer and had a 40watt armstrong amp bridged to 160watts. I have the sub plugged into the 5.1 sound card built into my motherboard in my PC. Only prob is that the cross over frequency is set to high so i've got funny sounds coming through the sub as well as bass. My qestion is: are there any software out there i can use to change the cross over output? I do have a separate 5.1 decoder but the cross over on that is fixed at 140hz so i have the same prob with that.

After christmas i will have enough money to get a new decoder so what would you recomend for round about £150?

Thanks for anyhelp on both questions

[ERICSPEEd]

We need more info on your soundcard.
though I doubt the frequency can be altered via software.

You could try augmenting a passive crossover with the sub to increase the high-end roll off (I would attempt to do so at the same frequency as the "cards" crossover.

[Dannyball]

Its a ASUS K8VSE delux motherboard and the sound codec is ADI AD1980 SoundMax AC '97. How can i make a passive crossover (what do i need? Is it easy to do?) The crossover just now is set to 140Hz.

[ERICSPEEd]

Well lets assume the crossover is a first-order type, 6dB roll off per octave. That would mean that it's only 6dB down at 280Hz, so some midrange frequencies are getting through.
As far as the difficulty factor it's not all the hard. You would simply (term used loosely) add an inductor in series the the sub (ie: wire an inductor coil of the proper size on the positive lead to the sub).

I'll post later to required size inductor for 140Hz high pass (@ 6dB, which is what a single coil will give you - the total - if I'm correct in assuming the current high pass slope, would result in a 12dB per octave slope). To acheive a 12dB slope (exculding the present crossover built into the mobo) you would need to use a coil in conjuction with a capacitor.

Gotta love ASUS though - great for overclocking!

[ERICSPEEd]

Is your K8VSE the Deluxe version?
If so...
ASUS K8VSE Deluxe

downloadable stuff here...
http://www.asus.com/support/download...%20SE%20Deluxe

I couldn't find anything on adjusting the crossover (because I didn't download the manual), and I hate their site (poor navigation).

Anywho... good luck, but again i doubt it can be altered and the I wouldn't fuss with the codecs.

Just try and augment the crossover passively. Like i mention above I'll try and get you the proper size coil in a future post.

[Dannyball]

Ok great. Thanks very much for your help

[ERICSPEEd]

Hello, do you have the T/S specs for the woofer? That would help choose the proper size coil.
My guess is it would be around 4.5 or 9mH (I could be way off - so I'll double check with the specs if you have them).
All I really need is the impedence of the driver.

And the coil would be wired in line on the positive lead after the amplifier.
Shouldn't cost you more than 8 to 10 pounds.

[Dannyball]

All i really know is that it is a 100Waatt sub with 8ohm impedance. I'll research i bit more into it tho and get back to you.

[ERICSPEEd]

That should mean a 9mH coil would give you 6dB roll-off at 140 hz. That should give you a combined roll-off of 12dB or more depending on the cut-off the mobo's integrated soundcard provides.

[Bill Fitzpatrick]

Don't forget the Zobel.