subwoofer filter

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#23
Originally posted by Optical what is wrong with
having that last 0.1uF cap before the phase section? i dont understand
the problem with having more rolloff before 20Hz?
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I am something of an organ fanatic who would like to reproduce all the notes, the lowest of which has a 16 hz fundamental. This is why I quoted -4.5 dB at 16 hz. If you accept a 1 dB drop as barely tolerable in a piece of electronics, the rolloff is already too high starting around 35-40 hz. If other units in the signal chain have similar rolloffs, the situtation gets even worse. I think you should only have rolloff where you want it (in subsonic filters) or where you can not avoid it (in microphones and loudspeakers).

Using larger coupling capacitors, or rearranging the filter chain so that you may eliminate some of them, will easily make the rolloff negligible. This may require parts with a larger lead spacing, however, and was one reason I wrote that the design did not seem ready for a PCB.

Hmmm. Could you replace that 0.1uF capacitor with a more neutral resistor?
 
#24
I use a HP filter in series with a LP filter for my sub project.

This, together with som EQ filters gives me full control of the signal and even gives me the option of helping the SUB in the low end below 40 hz.

If you don't want the EQ, you can change the Q of the HP filter to give some more gain at 20 hz. This could be enough to help the system response to be flat to 20 hz

\Jens
 
#31
This is a bit off topic.

The subwoofer crossover I mentioned earlier includes a muting switch that also quiets the subwoofer channel at power up and power down. The circuit seemed to have enough interesting twists that I decided to submit it as a design idea to EDN magazine.

I just received an email from them that they intend to publish it.:up:

The royalty check should pay for the extra PCB spins.🙂
 
#32
No need to concern yourself with EQ induced "phase distortion." Subwoofers, rooms, and analog IIR filters are all minimum phase systems. A roll-off of the amplitude response in a subwoofer stipulates a complementary phase shift. Using electronic EQ to restore the amplitude response to flat will also correct the phase response, not distort it. Similarly, any room induced peaks and nulls (in the modal response dominated bass region) are minimum phase phenomenon, and electronic EQ can again correct not only the amplitude response but also the phase response.

EQ has received a bad rap over the years... mostly due to poor use on the consumer end and not because of any fundamental problems when using it correctly.
 
#33
well i rebuilt my cct with better pots, and added the input stage too, that 'gainer' section is a bit odd, not quite what i was expecting, i cant really here any change in resonant frequency..
but all up it is sounding really good, the 4th order filter is perfect!

does seem a bit like the bass is lagging, what could be causing this do you think? -most likely the room or something.. :xeye:
 
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