Need subsonic filter

[buzztiger]

Hi ! I have built my subwoofer from an old SVS driver that i upgraded. I use a DIY 400 Watt amp to power it. However i hear noises when i feed it with frequency below 16Hz. I think its bottoming out. I need a subsonic filter to protect my driver. I came across a subsonic filter here http://sound.westhost.com/project99.htm . This is not suitable. I was then looking at Linkwitz Riley high pass filter. But it has confused me. The active filter posted at this site http://www.subwoofer-builder.com/active-filter.htm differs from http://www.linkwitzlab.com/filters.htm#3 so i don't know which one to build.


Pls help. Has anyone else made a simple subsonic filter ?

[collo]

Hi there Buzztiger,

the active filter on my site is based on the circuits at the Linkwitz site.

I just added together all the elements listed on his site to get the full circuit.

The design uses the hipass section of linkwitz's 24 dB/octave crossover. (section3 on the linkwitz page)
To the front of this is added the buffer stage (section1 on the linkwitz page)
At the end, the line driver stage is added (which is an amalgum of sections 10 and 11 on the linkwitz page)

Adding these elements together gives a filter that doesn't load down the line that is driving it, and is happy to drive whatever load you place on it. In addition, the +/- 6dB adjustment might just save you needing a cleanbox.

All the explanations on the linkwitz site apply to this circuit as well.

regards
Collo

[buzztiger]

Wow answered by Collo himself ! Thank you so much for your reply.

I don't think i need the +-6dB gain on the line driver because i thought of having a potentiometer to control the volume of the subwoofer after this subsonic filter . Can i just substitute the line driver with the circuit shown in section 11 of Linkwitz website ? There's 2 circuits there A and B, should i be using B ? Thanks.

[collo]

That should be OK.

I would go for option B, since that is closest to what I built, so I know it works.

Your circuit would be.....

[buzztiger]

Thanks. Just bought all the parts for the filter. I wanted to use a regulated power supply for this circuit but I only have 9-0-9 auxiliary out from my transformer in the amp. So i only have +12V and -12V dc. This means that i can't use any of the voltage regulator chips. Would using unregulated power for this circuit affect the sound quality ?

[collo]

I think 12v would be OK. You could use 12 volt regulators if you wanted.
Some good reference info in this power supply article at Elliot Sound Products

[buzztiger]

The problem is that the voltage regulators require that the voltage input to them be a min of 14V before it regulates the voltage to 12V.

[collo]

hmm, I see..

You could always try it unregulated.
If it's noisy, you could add an external plugpack supply

[buzztiger]

I think i will just do that.

[collo]

Sounds good. Let us know how it turns out....