Running 4 speakers from a 2-channel amp

Re connecting speakers in series:

1)To the extent that the speakers which are connected in series do not have identical impedance vs. frequency characteristics, frequency response irregularities will be introduced into each speaker. That is because the voltage applied by the amplifier across the series connected speaker string will divide up between the speakers differently at different frequencies, if the speaker impedances have different proportions to each other at different frequencies. Avoiding that effect will typically mean that the speakers should be identical models.

2)Even if the series connected speakers are identical models, bass damping will be degraded. That is because the source impedance driving each speaker will be the sum of the impedance of the other speaker and the power amp's output impedance, instead of just the power amp's output impedance.

Regards,
-- Al

The highs and mids will all be traveling through the other speakers low frequency choke.

With much respect, HifiTime, I don't think that is true. I believe that at any given frequency the signal will follow the same path or paths through each speaker that it would follow if the speaker were connected to the amp by itself.

High frequencies, for instance, will be blocked by a choke in series with the woofer just as they would be if the speaker were connected directly to the amp. They will follow a path through the high-pass part of the crossover, and the high frequency driver, and from there continue to the other speaker.

An unrelated further thought, about having more than one speaker per channel: If each channel is being reproduced by two speakers, and the two speakers are producing comparable volumes at the listener's ears but are located at significantly different distances from the listener's ears, what are called comb filtering effects will occur, which will degrade the sound. That occurs when the same sound arrives at the listener's ears at multiple arrival times. How significant that effect will be is obviously dependent on many variables, including the listener, but I would expect it to be significant for many listeners under many circumstances. And it applies whether the speakers are connected in parallel or in series. Something to consider.

Regards,
-- Al

Hmm, actually HifiTime's statement about highs passing through the woofer crossover is more correct than I initially thought.

If speaker A is series connected to speaker B, the high frequency energy that manages to get through the inductor that is in series with the woofer of speaker A will not be shunted to ground via a cap, it will be shunted to speaker B through the cap. Where some fraction of that shunted signal will be reproduced in its full glory by the mid or high frequency driver of speaker B, complete with whatever distortions, phase effects, etc., were imposed on it by that inductor and capacitor in the woofer section of speaker A.

Figure 5 of the article HifiTime linked to in his previous post is helpful in visualizing this.

In any event, all three of us are in agreement on the bottom line -- for any of several reasons series connection is not a recipe for quality sound.

Regards,
-- Al

Jim -- Thanks for the update. Enjoy!

Kijanki -- That's an interesting thought, which I hadn't previously seen stated.

A series connection, whether of two woofers within an enclosure, or of two series connected speakers, would have to be done such that the plus (or red) terminal of one woofer or speaker is connected to the minus (or black) terminal of the other woofer (or speaker). Otherwise the two drivers would operate out of phase and cancel acoustically.

Given that arrangement, the voltages corresponding to the back-emf of each driver would add together, resulting in double the voltage assuming the drivers are identical. And the papers you referenced appear to say that the doubled voltage compensates for the doubled total impedance, resulting in the same current and hence the same dissipation of energy from each woofer (or speaker) that would occur with a single woofer (or speaker) connected to the same amplifier.

That seems to make sense. Thanks!

In any event, we (you, me, Rodman, HifiTime) are all in agreement that for other reasons series connection of speakers, especially if they are not identical, is a no-no.

Best regards,
-- Al