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RE: Mixed crossover???

Posted by Paul Joppa (P) on November 5, 2015 at 21:19:08

In Reply to: RE: Mixed crossover??? posted by TomWh on November 5, 2015 at 15:11:36:

OK, one more try :^)

For a first order ribbon tweeter crossover you start from the actual impedance of the tweeter in the vicinity of the crossover, assuming this to be fairly flat and free of reactive impedances. Then, given that resistance and the target crossover frequency, you can calculate the capacitor. In fact, given any two of those numbers, the third can be calculated. For example, if you have 1600Hz with 10.3uF, then the resistance you assumed must be 9.66 ohms. That seems an odd value to have chosen, but I have no data on the ribbon impedance.

The woofers are more tricky. For simple home-based calculations it is usual to first put a Zobel series RC network across the woofer to make it a constant resistive impedance, then put the calculated network in front of the [driver plus Zobel]. For commercial manufacture you could then use a computer optimization program to adjust the values for a simplified network, for example replacing the crossover cap plus Zobel with a single cap. It's not exact, but in combination with the driver's response you might easily get a good fit with the desired acoustic crossover function.

Finally, you said "I am still confused let's say I wanted a 1st order on tweeter and a 2nd on woofer let's say at 1500hz. All the books and calculators are done with the same slope/order for woofer and tweeter. So if you use 1st order on tweeter it will be 1st order on woofer. So could you say use the values from calculator for a 2 way 2nd order crossover then just remove the grounded inductor on the tweeter." No, the capacitor for a second order filter will depend on the Q of the filter, and will not in general be the same as the capacitor for a first order high pass filter. For second order filters, the Q determines the type of response - Butterworth, Linkwitz/Riley, Bessel, etc. You can instead use the low-pass portion of a second order design on the woofer, and the high-pass portion of a first order design on the tweeter.

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