Singular as subwoofer: low pass filter design (Singular)

by Giovanni, Ravenna, Friday, March 16, 2007, 13:47 (3967 days ago)

The project is to use a dedicated Tripath based amp for a Singular with Fostex FW208N woofer. The singular will be used as subwoofer in the range of 35hz~200hz.

The idea is to modify the low pass filter present at the output of the Tripath amp to get a frequency cut at 200hz.

The low pass filter in the T-amp is a second order 107kHz LC filter with a L=10uH and C=0.22uF. The T-amp has too a Zobel RC filter with R=6.2ohm/2W and
C=0.22uF.

Using some calculators on line I got a 2nd order 200hz LC filter with L=9mH and C=70uF. I couldn't calculate the Zobel filter because there is not the "Le" (bobbin inductance?) in Fostex datasheet.

I've to confess I don't understand much about filters, can you help?

P.S.
T-amps work better with copper foil coils used in Xovers.

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Singular as subwoofer: low pass filter design

by Bert @, Friday, March 16, 2007, 15:07 (3967 days ago) @ Giovanni

Hi Giovanni,

I've to confess I don't understand much about filters, can you help?

Why don't you create that filter in front of the T-amp? This way the amp is not bothered with the impedance behaviour of the driver, any filter likes to see a flat impedance to work optimally...

Ciao,

Bert

--
BD-Design - Only the Best!

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Singular as subwoofer: low pass filter design

by Giovanni, Ravenna, Friday, March 16, 2007, 15:18 (3967 days ago) @ Bert

"In front" means before the amp? (anyway the t-amp would need the LP filter to recover audio from the switching signal).

Any circuit for a suitable filter for this driver?

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Here is a link to give you an idea...

by Bert @, Friday, March 16, 2007, 15:31 (3967 days ago) @ Giovanni

Here is a link to give you an idea...

by Giovanni, Ravenna, Friday, March 16, 2007, 17:29 (3967 days ago) @ Bert

Thanks for the link.

But I've no fun if I don't try new things.

For a line level LP filter I have another option: I have two DACs and an EMU1212M inside the PC, with a huge DSP and 2 separate digital outputs. So I could do filtering inside the PC and send different digitally filtered signals to the 2 dacs.

The problem is that I have still to learn how to syncronize the two dacs to a common clock.

The other option to use the amp output filter as LPF is funny because there are no components to add, only to mod. I think nobody tried this, that's why it is attractive :grin:

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Knock yourself out...

by Bert @, Friday, March 16, 2007, 18:03 (3966 days ago) @ Giovanni

Hi Giovanni,

The other option to use the amp output filter as LPF is funny because
there are no components to add, only to mod. I think nobody tried this,
that's why it is attractive :grin:

Then you have to play around with that and try to have the Fostex driver's impedance flat from about 1 octave below the crossover frequency and up...

This way the filter works as it should but still, you might want to cross sooner to EQ a rising response if present.

Enjoy!

Bert

--
BD-Design - Only the Best!

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