Hmm, the XO's don't sum flat. Bad news. Must be an inappropriate Q.
For a given slope, there must be an ideal Q (like 12dB/oct is .5, 24dB/oct is dual .71). What Q gives a flat response for 24dB/oct with only one filter?
There must be active XO filters using a single opamp that can do more than 12dB/octave...
For a given slope, there must be an ideal Q (like 12dB/oct is .5, 24dB/oct is dual .71). What Q gives a flat response for 24dB/oct with only one filter?
There must be active XO filters using a single opamp that can do more than 12dB/octave...
Hi
Q is only defined for a 2nd order polynominal expression.
LR filters are formed by cascading of 2nd order Sallen-Key filters, and are of even order LR2,LR4,L6, etc each stage with it's own Q. Luckily, crossover filters of higher order than LR4 are probably not useful, because of an increasing peak in group delay around f0.
Q is only defined for a 2nd order polynominal expression.
LR filters are formed by cascading of 2nd order Sallen-Key filters, and are of even order LR2,LR4,L6, etc each stage with it's own Q. Luckily, crossover filters of higher order than LR4 are probably not useful, because of an increasing peak in group delay around f0.
For the record...
At burning amp this october, I had the chance to talk with Mr. Linkwitz. He said he could not recall ever seeing a fourth order filter around one opamp. So it sounds like it isn't a trivial task - and probably doesn't have much to gain. I am going to continue developing a multi-channel line level ASP for my three (or four) way speakers, I'll just have to accept a couple extra opamps.
At burning amp this october, I had the chance to talk with Mr. Linkwitz. He said he could not recall ever seeing a fourth order filter around one opamp. So it sounds like it isn't a trivial task - and probably doesn't have much to gain. I am going to continue developing a multi-channel line level ASP for my three (or four) way speakers, I'll just have to accept a couple extra opamps.
That is right. He is a great master in electronic filters.
But that is only referring to electronic filters.
A single opamp usually gives a second order filter (Third order is fine but you will have some insertion loss which may or may not be an issue). If your driver has a 1st order roll-off, dipole roll-off is also 6dB/oct, so using a single opamp with second order can achieve 4th order. Your second order usually need to have a high Q in order to come up with a LR4.
Regards,
Bill
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