The problem with parallel is that, even based on nominal impedance, you are looking a 2.4 ohms; much lower than that probably at minimum impedances; and what if minimums of the two speaker coincide?
Greenhorn question: Beware!
Is a 4 ohm exciter speaker and a 6 ohm woofer box, wired in series (total 10 ohm) connected to an 8 ohm output amp OK?
- ...
- 14 posts total
I agree with Larry that in this case a parallel configuration would provide too heavy a load for most amps. And while a series connection won’t be a problem for the amp, it is likely to result in poor sonics. The main reason for that is that since in a series configuration the voltage provided by the amp at any instant of time will divide up between the two speakers in proportion to their impedances, the variations of each of their impedances as a function of frequency will have unintended effects on the frequency response of the other speaker. Therefore a series connection is only likely to be suitable if the two speakers are identical models. In that situation, putting aside whatever small differences might exist between their impedance characteristics due to component tolerances, each speaker will see half of the amp’s output voltage, at all frequencies. Also, regarding Roberjerman’s point about damping, I used to think that also, but while it seems counter-intuitive, that is not an issue. See this paper, which I must credit A’gon member Kijanki for calling to my attention here some years ago. Regards, -- Al |
"Avoid using a series connection! Damping of both speakers by the amp is degraded!" This is a misconception. Unfortunately it was printed in a JBL white paper on car audio, so the myth has persisted. And on the surface it seems to make sense. If you were connecting a resistor in series with a speaker, the effective electrical damping (Qes) WOULD be degraded. The BL would stay the same while Re (effective resistance) would increase, and the net result would be a corresponding decrease in Qes. This is the same thing as saying the damping is decreased. But when using series connection of two woofers, you are connecting a powered voice coil in series with a powered voice coil. The motor strengths (BL) add, just as the voice coil resistances and inductances add. If the two woofers are identical (not the case when one of the motors is an exciter), then the effective Qes (electrical Q, or electrical damping) is unchanged. Obviously when the two motors in series are different, the effective Qes will not be the same as either one of them, but the resistor analogy still does not apply. Consider this thought experiment: The first half of your woofer’s voice coil is in series with the second half of your woofer’s voice coil. Do they ruin one another’s damping factor? Of course not. And the reason is, they are both inside the field of an electric motor (the same one in this case), so both of halves of your voice coil bring a commensurate increase in motor strength (BL). This can be extrapolated to two voice coils within the fields of two separate motors, as when two woofers are wired in series. I manufacture a subwoofer system that has woofers connected in series. If the damping factors were ruined by this configuration, the system would be unbearably boomy. You can take a look at Robert Greene’s April 2015 review of the Swarm and see whether he found the system to be boomy. Duke |
Al brings up an excellent point - one I hadn't thought about. However, he's totally correct. Another thing -- the crossovers inside the speakers are engineered based on the expected impedance of the following driver (i.e. low-pass coil circuit for a single woofer). If you tack on a second speaker in series, the impedance in that frequency area will rise and cause the crossover frequency to move drastically. This will cause the frequency response of the first speaker to have all these bumps or holes - making a very imbalanced sound. That being said, the first entire speaker will also affect the crossover in the second speaker, therefore causing the same problems in that second speaker. |
"Another thing -- the crossovers inside the speakers are engineered based on the expected impedance of the following driver (i.e. low-pass coil circuit for a single woofer). If you tack on a second speaker in series, the impedance in that frequency area will rise and cause the crossover frequency to move drastically. This will cause the frequency response of the first speaker to have all these bumps or holes - making a very imbalanced sound. That being said, the first entire speaker will also affect the crossover in the second speaker, therefore causing the same problems in that second speaker." It’s not that bad. I’ve done it many times. Doing a crossover section for identical drivers wired in series is no different from using a single driver. The crossover component values will differ, (inductance and resistance values will be doubled, and capacitance values halved), but that’s pretty much it. You might want to take the modified radiation pattern into account, if you haven’t already, but that’s an acoustic consideration, not an electrical one. I've received three Golden Ear awards and one Product of the Year award from The Absolute Sound. In each case, ALL of the drivers were wired in series with another identical driver. So thus far I've had pretty good luck with drivers wired in series. Duke |
- 14 posts total