The Coil is not intelligent, it has no way of knowing what is connected to it, whether is be two speakers or 8 speakers or 16 speakers. It simply sees the combined impedance.
However, each driver may have different impedance characteristics; different impedance at different frequencies. For example if one has an Fs resonance of 30hz and the other has a resonance of 50hz, when one is at it Peak impedance, the other is going to be at its lowest impedance.
A lot of factors come into play. But in the end, the coil will see the combined impedance of the two drivers as a single entity, and will react accordingly.
So, barring all the complications that come into play, yes, both speakers will have the same Crossover Roll-Off.
At least in my opinion.
Steve/bluewizard
so, if the two drivers are different, impedance variations of one driver might be compensated by the other driver
which also makes the opposite true, impedance variation of one driver will affect rolloff of the other driver
Those impedance variation are always going to be there. There is a peak in impedance at the resonance frequency, a deep dip on either side, and a gradual rise in impedance as the frequencies go higher. There is no way around that.
Rather, you want the functional impedance at the crossover frequency, which will be the blend of the two at that specific frequency.
This is one of the flaws of all passive crossover design, they are design at one assumed nominal impedance, but in reality speaker drivers are more complex impedance loads. There is just no way around that.
The idea situation is if the two drivers are the same, or at least from the same series of speakers. However, two randomly combined speakers will have slightly unpredictable results.
Regardless, what the coil sees will be a combination of the impedance of the two speakers. The best you can do is to get some sense of the individual driver's impedance at the crossover, and do the best you can with that knowledge.
As others have indicated, this would not be an ideal first choice combination. Rather it would have to have some purpose in the final design. No one would make this choice unless they were forced by circumstance to use two such dissimilar drivers.
The only way to predict how the drivers will combine is to either find a full spec sheet on them or to calculate the frequency and impedance plots using some type of software.
But yes, the combination, depending on impedance fluctuation, could work for you, could work against you, or both for and against at different frequencies.
Steve/bluewizard
Rather, you want the functional impedance at the crossover frequency, which will be the blend of the two at that specific frequency.
This is one of the flaws of all passive crossover design, they are design at one assumed nominal impedance, but in reality speaker drivers are more complex impedance loads. There is just no way around that.
The idea situation is if the two drivers are the same, or at least from the same series of speakers. However, two randomly combined speakers will have slightly unpredictable results.
Regardless, what the coil sees will be a combination of the impedance of the two speakers. The best you can do is to get some sense of the individual driver's impedance at the crossover, and do the best you can with that knowledge.
As others have indicated, this would not be an ideal first choice combination. Rather it would have to have some purpose in the final design. No one would make this choice unless they were forced by circumstance to use two such dissimilar drivers.
The only way to predict how the drivers will combine is to either find a full spec sheet on them or to calculate the frequency and impedance plots using some type of software.
But yes, the combination, depending on impedance fluctuation, could work for you, could work against you, or both for and against at different frequencies.
Steve/bluewizard
yeah
btw, its related to a mid/tweeter xo in a synergy horn project for bass guitar
so no, its not a choice I would do in any other case either
but still, its interesting that the low Fs ressonance might be 'flattened' by another driver with a lower Fs
and also, one driver's rising impedance could be 'flattened' by another driver with no rise, or different rise
but phase is a strange thing
and I have learned that even a speaker for a bass guitar is in no way simpler than hifi
stick to basics, it's always safer
yeah, I know (that I don't know)
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