Adding a resistor in a parallel wiring system

I see, I wonder whether it can be wired backwards. I'll test them tomorrow when I get them thanks

No, you definitely don't want to wire them backwards. That will LOWER the impedance seen by the amp, by 2x or 3x or 4x depending on the connections. So the 1.6 ohm combination of the four drivers would be seen by the amp as well under an ohm. See this paragraph in their FAQ.

Good luck. Regards,
-- Al

I see. Thanks. I think the increased damping factor as a result of the zeros could help. I'll add the resistor to see how it goes thanks!

Hi Al,

Thanks for all your inputs and help. The zeros are installed yesterday and they are great. To take care of the 8 ohm vs 4 ohm problem, I think I've found the ultimate solution. The 3 ohm resistor would reduce 50 watts of power (directly only to this speaker) to reduce to about 16 watts, which is not what I want. If all the other 8 ohm drives receives 25 watts, I want this 4 ohm to receive 25 watts also. Therefore, I will install a 1.5 ohm resistor which increases the power transfer to about 25-27.5 watt given the error tolerance of 5% on the resistor, which is reasonably close.

The new damping factor for this drive will be 2.5 and with the zero's 4x setting, this damping factor should go up to 10 or so, which is again, reasonably acceptable.

Is my analysis correct?

Thanks,
Ryan

Hi Ryan,

Glad the Zeros are working out well. I did some calculations and I agree with most of your analysis about the 1.5 ohm resistor. I calculate that if 25 watts is going into each of the 8 ohm drivers, 26.45 watts will go into the 4 ohm driver, if it has a 1.5 ohm resistor in series with it. 26.45 watts vs. 25 watts is a difference of about 0.24 db, essentially negligible.

This is all an approximation, of course, because it assumes that the driver impedances are accurate and are purely resistive. But it all seems to add up to a reasonable approach.

The damping factor seen by the 4 ohm driver, though, will not be multiplied by the impedance transformation ratio of the Zero. It will be approximately 4/1.5 = 2.67. The damping factor of the amplifier, as seen at the secondary (output) side of the Zero, will correspond to the amplifier's damping factor multiplied by the 4x impedance transformation ratio, which (especially if you are using a solid state amp) will almost certainly be high enough to be neglected relative to the damping limitations imposed by the resistor. But since the resistor is on the output side of the Zero, the driver will "see" its resistance directly, not through the Zero's transformation ratio.

Putting it another way, damping factor equals speaker impedance divided by the output impedance of the source providing the signal to it. The output impedance seen "looking back" into the output side of the Zero will be the amplifier's output impedance divided by 4, which except for a few unusual cases mainly involving tube amps will be very small in comparison with the 1.5 ohm impedance of the resistor. Therefore the impedance seen looking back from the driver will be 1.5 ohms in series with (i.e., added to) a very small impedance, resulting in a damping factor very close to 4/1.5.

In saying this, I'm also neglecting whatever damping effects may result from interactions between the drivers themselves. Again, those should be negligible given that their impedances are shunted by the extremely low impedance that will exist at the output of the Zero.

Regards,
-- Al