Low freq. from small drivers? Is it possible

And to Eldartford:

I was too quick to jump on you in my last post, got my hackles up I suppose. I don't like to think of myself as a pontificator, but I do sometimes get a bit hardheaded when it comes to trying to get people to see what I'm saying. My apologies, and I agree with your assessment that we are only differing in how we name the elements. I think of the series and parallel forms as being equivalent, since the equations are the same, but I must admit that my calling it a "woofer" inductor could raise some eyebrows.

Peace,
Karl

It's more than 40 years since EE101, and although, as an aerospace systems engineer (not an EE) I worked with a lot of fancy circuits since then I never actually designed a crossover network except at home for audio. I went to the only reference that I have handy at home to read up on series networks, Dickason's Cookbook, but I drew a blank. He says that the parallel configuration is "definitely preferable" and therefore does not discuss series further.

I have always been a "contrarian", so if everyone else is using parallel configuration I would probably look at series, as you have done. However, when you take the contrarian path you must be prepared to strike out a lot. But the grand slam HR makes it worth while. Your bases are loaded.

Peace
Ed

Eldartford,

My apologies again for yesterday's outbreaks, it was a pretty rough day and I'm not the best at being calm anyway. A good night's rest helps a lot.

To try to explain what I was after:

In the parallel case, you have two separate filters, LR and CR, which both have Butterworth responses by default (maximally flat, Q=0.7). You can change L or C, and it will change the corner frequency but not the Q of the filter, and it does not affect the other filter at all. On the other hand, it does affect the voltage sum of the two drivers, which affects the summed frequency response.

In the series case, you have the equivalent of an LCR loop, which is a resonant circuit. (It's not the simplest form of LCR, but it's a loop nonetheless.) Now if you stick to Butterworth values for L and C, you have an equivalence to the parallel case, and everything works the same. However, in an LCR loop, the resonant frequency is singular and is determined by the product of L and C. In addition, the loop has a resonant Q which is determined by the ratio between L and C. What this means is that you can double one, and halve the other, and end up with the same resonant frequency but a different Q. So it doesn't behave the same as a parallel except in the case where you use standard Butterworth values. Also in contrast to the parallel network, the series network by its very nature maintains a constant voltage sum across the drivers, which maintains flat frequency response despite the variations in the components.

Of course, there are a lot of assumptions built into all of this, such as equal resistive drivers, equal amplitude and phase response, constant voltage source, etc., none of which are really achieved in the real world. That is why I view the series as being superior to the parallel, because it automatically minimizes the effects of at least some of these "non-perfect" conditions.

Best Regards,
Karl

Here is a link which has a downloadable .doc file (as a .zip) by John Kreskovsky, which is an excellent primer on series crossovers. Note that the damping which I referred to as "Q" is called "zeta" here.

http://www.geocities.com/kreskovs/Series-1.html

Best Regards,
Karl

Karls...Thanks, I guess :-)

How many continuing education credits do I get for this?. Will there be a final exam?