terryforsythe
Major Contributor
Also, much depends on the actual impedance of the low pass filter connected to the woofer. My speakers are 3-way and were crossed over around 220Hz or so, with a 3rd order filter. The resistance of the inductors is fairly high, together 1.6 ohms.That probably is a good rule of thumb. In the examples I provided, when using a low output impedance amplifier, with a passive crossover the DF is 3.50 and is 70.17 without. The passive crossover setup has a DF well below 20 and the all active setup has a DF well above 20, and thus should reflect a visible change in the transient signals.
If you take a 2-way speaker with a higher crossover frequency, perhaps 1st or 2nd order, the resistance likely will be lower. Thus, the negative impact of the crossover on the damping factor will be less. Using my examples of an amplifier output impedance of 0.02 ohms, a speaker cable resistance of 0.04 ohms and a 4.15 ohm driver, the total DCR of the filter inductors can be as high as 0.15 ohms (ignoring core losses) while still achieving a damping factor over 20. Again, this is just an estimate as the actual impedance is frequency dependent.