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matjans 1st June 2004 10:42 AM

xover question; will this work?
hey guys,

finally finished my desktop-speakers for use with my laptop. THey're using visaton frs-8 drivers (dirt cheap and not that bad) and go down to about 100 hz so i decided i needed a small sub. Finished that too; picked up a second hand vifa pl18w009-8 (yay!) pretty cheap and put it in a 15 liter vented box.

And now, the xover. I decided on an active linkwitz/riley filter at about 110-120 hz and came up with this:

top and bottom blocks are highpass filters for stereo speakers, mid block starts off with a summing amplifier. last two opamps are the lowpass filter. In front of the summing amp are 2 100k resistors. First opamp in the top and bottom block use 100k to ground on the inputs.

Assuming that i can work out the correct values for the filters with rod elliott's l/r calculator (yay for rod!), is the rest of this schematic correct? In other words; will this work?

what kind of signal-level loss can i expect after the lowpass section? I presume that with the highpass section signal loss isn;t that bad.

Ouroboros 1st June 2004 11:22 AM

The schematic shows all op-amps connected as unity-gain buffers, so within the pass-band of each of the filter paths, the gain wil be close to unity.

Centauri 1st June 2004 11:40 AM

Depending on the power amp used for the sub, you may need a little more gain in the low pass section. You could easily achieve this around IC4. Looks fine otherwise.


moamps 1st June 2004 11:52 AM

Use inverted opamp topology for summing amp.(+in connected to ground).

Ouroboros 1st June 2004 11:59 AM

Good point.

For the inverting summer, R3=R9=R10 for unity gain from each input. R10 will now need to go between pin 5 and pin 2 of the op-amp.

Don't forget this will invert the phase of the LP section, so you'll have to swap over the connection to the woofer.

matjans 1st June 2004 12:01 PM

moamps: why inverted?

moamps 1st June 2004 12:21 PM

Inverted topology is used for correct summing function without influences in channels crosstalk.


matjans 1st June 2004 12:29 PM

ah, right on. nice link!

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