Crossover question

[Grahamt]

When designing a crossover, how do you know what impedance to use?

For example:

Say I have an 8 Ohm nominal woofer and an 8 Ohm nominal tweeter of identical efficiencies. Also, lets pretend I want to crossover at 2000 Hz.

At 2000 Hz, in my enclosure, the woofer's impedance is 10 Ohms and the tweeter's impedance is 14 Ohms.

So when using the crossover formulas, which impedance would I use? The nominal or the specific at the crossover frequency or is it something else entirely?

This is all hypothetical. I am just trying to learn more about speaker design. I have read The Cookbook and other books, and searched, but have never found this answer.

Thanks in advance,
Graham

[BillFitzmaurice]

The stated impedance of all drivers is an averaged figure within their nominal passbands. The actual impedance varies with frequency. Crossover component values are usually chosen according to the nominal impedance, though extreme deviation from the nominal at the crossover frequency could require addressing that circumstance. At the most sophisticated levels of crossover design the final component values are derived via extensive testing on the finished speaker until the desired response attributes are realized; the process can take hundreds of hours to complete.

[Grahamt]

Thanks Bill, exactly what I was looking for.

[richie00boy]

To add to that, impedance-compensation networks are often used to flatten out the impedance curve of drive units, making them easier to design the crossover for. Such a network is usually a resistor and capacitor in series, in parallel with the drive unit.

[rabbitz]

Originally posted by Grahamt
When designing a crossover, how do you know what impedance to use?

So when using the crossover formulas, which impedance would I use? The nominal or the specific at the crossover frequency or is it something else entirely?

Hi Grahamt

Go for the impedance at the crossover frequency and not the nominal. You'll get heaps closer this way and is a good starting point.

[Grahamt]

Thanks for the replies guys.