Adding a resistor in a parallel wiring system

Doing that won't affect the damping factor of the other three drivers. But perhaps you don't even have to add the resistor. Three nominally 8 ohm drivers in parallel with a nominally 4 ohm driver results in a nominal overall impedance of about 1.6 ohms. If you step that up 4x with the Zero, and probably also 3x or possibly even 2x, your amp should be happy (in terms of the load impedance it sees; I'm assuming the amp can supply sufficient power for your application).

Keep in mind, though, that without the resistor the 4 ohm driver would receive twice as much power as each of the others, while with a 4 ohm resistor the 4 ohm driver would receive half as much power as each of the others.

Regards,
-- Al

As I interpret the information provided at zeroimpedance.com, if the Zero is being used to increase the load impedance seen by the amplifier (as opposed to decreasing it) there is one and only one pair of output wires on the Zero that can be connected to the speaker drivers. The choice of 2x, 3x, or 4x impedance multiplication is made based on which pair of input wires on the Zero is connected to the amplifier. So it appears that you would not be able to connect the 4 ohm driver (plus any resistor you may place in series with it) to the Zero any differently than the 8 ohm drivers.

Regards,
-- Al

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

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

Clever thoughts, Jim (Jea48).

However, as you'll realize placing drivers or speakers in series will not produce good results unless the impedances of the drivers or speakers vary as a function of frequency in a similar manner. Which ideally means that they should be identical models. Otherwise the voltages applied to the series combination will divide up between the two drivers or speakers differently at different frequencies.

For that reason I suspect that placing an 8 ohm driver in series with a 4 ohm driver boosted to 8 ohms with a Zero is unlikely to produce good results. Also, we don't know how similar the three 8 ohm drivers are to each other.

Best regards,
-- Al