Variable center frequency filter

[12 Cents]

I was wondering if the precision of standard stereo pots is sufficient. Linkwitz writes IIRC, that pots should not be used in his active filters. However, I tried to simulate, and with the second resistor (the one at Opamp IN+) in an LR2 LP having only 2/3rd of the first resistor value, the outputs are 8° out of phase and a bump of <1dB is noticed in the LP + HP sum output. Any opinions?

[richie00boy]

If you're after the ultimate performance they aren't great and the higher the filter order the worse the problem is. That said, I've built 2nd- and 4th-order filters with common Alps pots and they have all been fine.

[metal]

Helo 12 cents

I got no options, ehat do you think ..the notch filter has a variable center frequency, that is 79Hz to 140Hz, and there should be a phase difference. btw, I can sya this is not the best way to enforce bass in deed. I talked to russ yester day, and he told me there are better ways, using a 2nd or 4th order bandpass filter, and summing its out put signal with the original one, but that should be carefully designed to avoid phase lags between the original signal and the bandpassed bass signals.

[metal]

Hello richie00boy

Can you share the filter circuit you are using for your subs.

BTW, I was looking for a filter circuit the enforces bass without using any subs, I always see those huge stereos which have only two woofers and two tweeters, they got a button by which you can increase the bass, that is, bass boost button. Any circuits suggestion here please.

[12 Cents]

Thanks richie.

metal, ...bass boost... do you want to equalize a driver or just gain some "kick bass"?

[metal]

Originally posted by 12 Cents
Thanks richie.

metal, ...bass boost... do you want to equalize a driver or just gain some "kick bass"?

Hey 12 cents

you got it, gain some "kick bass"

Can you suggest some thing brilliant...

Thanks

[richie00boy]

The filter circuit is basically the same as what you have drawn up with a some small component value differences.

If you want to make a loudness (bass boost) circuit be aware that it will stress your speakers much more. If you want lots of bass a sub or big speakers is the only way to go really.

[metal]

Hello

I did simulated the bass boost circuit yesterday night using circuit maker, in deed, results were just amazing, the bass was boosted 4 times, just changing the 330 to 220 simply did that, also the group delay thingy was acceptable, and most important was that the circuit doesn't affect other signals at all.

If you can, will you post your schematic with values to be able to comapre that.

Regarding the speaker stress, I know that, but I don't want to increase the system cost, you know, some guys are not aware of the quality as they are to cost for me, I orefer the bi-amplified systems, so, I am really aware about that

Thanks

[jackinnj]

just parenthetically (as it is out of current production) Zetex made a continuously variable bandpass filter for audio -- the Zetex ZTX36FL01 -- it had a mixer so that you could tune the frequency and maintain "Q" (which was set by one resistor) -- too bad it's past tense --

[theChris]

there are a few things that can be done. simply put, real bass boost is not possible. this would be something like a linkwitz transform where extra power is put to the speaker at very low frequencies. this would extend the response down to 20hz, but would require more power and more excursion. that'd be bad.

next thing that can be done is to increase the bass at useable frequencies -- basically boost the harmonics. if you compress the music this will work better. but sound quality will suffer. still it may be justified if the "clean" levels are too soft.

Another more advanced method is to use DSP to add harmonics to the music that, when played, fool the ear into hearing lower fundamental that are not actually being played.


As for the sallen key filters:
with a gain of 1, the circuit is resistively normalized -- if the resistors are equal value then the capacitors can be used to easily set the Q and Fc of the filter.

my preference is for a gain of 2. then the circuit is capacitively normalized -- if the capacitors are equal value the resistors can be used to easily set the Q and Fc of the filter.

i'll post the analysis later