Low Pass filter for sub?

[cathode_ray]

I need a simple low pass filter/volume for a sub. I can solder if I can's buy economically. B&W 602's are good to about 48hz, gone by 40hz. If I could get down a bit more it would facilitate some of the mixing I do. No thump,thump stuff, I want clean "Smooth" low-end extension...
I have a pair of Bozak 12" and a pair of JBL K145's to experiment with. 'spect the Bozak(s) would be more suitable in optimally sized box.

comments/suggestion welcome!

[richie00boy]

I believe your main speakers are vented, so you will need a 4th-order filter to suit, on your sub. Search for Sallen-Key filters, it's pretty straightforward.

[AndrewT]

Hi,
Richie is probably right, but the roll-off characteristic will almost certainly not be a clean Butterworth or other usable Q value.

I suggest you make an active crossover and put the new frequency at about 100Hz, maybe even a bit higher going towards 120Hz or even 150Hz.

Now feed the new crossover to the main amp and to the amp that will drive your sub.

I have a sub crossed at 150Hz at the moment and it is off about 3feet to the right of the right speaker. I never hear any signal coming from the sub. It always appears to come from near the central position. It seems to me that the harmonics of the bass signals are locating the image for me.

How do others find a sub works with high crossover frequencies?
Either centralised between the mains or offset or even under your seat!

[richie00boy]

I have to disagree a little. You will be able to get a 4th-order slope that is a good enough match to the B&W speakers. I would also not cross as high as 150Hz, unless the sub was inbetween the main speakers. It becomes a lot more room and position dependent once you go higher than about 90Hz, also some sub drive units aren't good above 300Hz or so.

It seems you have been lucky Andrew and everything has worked out, but it might not for some people, IMO.

I also reckon that if you crossed at 100Hz with the B&W speakers you would have a very boomy response, I think you need to aim for around 60Hz as a start.

[cathode_ray]

My idea was(is) to take a line from the preamp and feed a low pass to sub only. This would greatly simplify things(And not send entire signal through additional curcuit). I understand the "slope" is important in blending the 2.

I never felt very deprived before (maybe don't know what I'm missing?!) but I play bass guitar and when scrutinizing recordings the bottom string just isn't there so... test tones revealed the B&W 602 start to disappear @ 45-50 hz so picking up there would seem appropriate.

Thanks everyone for the useful responses(ideas).

[richie00boy]

Your idea is right, a pre-out is the best way as long as it follows the level of the volume control.

[FastEddy]

FYI: same kind of question w/ one type solution = stereo to mono sub woofer with low pass: http://www.diyaudio.com/forums/showt...99#post1191899

[Cal Weldon]

If you don't want to solder, here are a couple options from CSS. I have the B1 and am very happy. Not DIY but...

http://www.reckhorn.com/index.php?ln=en&prod=f1

http://www.reckhorn.com/index.php?ln=en&prod=b1

[Marsh]

Something like this?

http://www.bkelec.com/MODULES/asbf.htm

[FastEddy]

Marsh: Excellent choice. This could even be a future "mod project". The open chassis = plenty of elbow room for tweaks ...