Running 4 speakers from a 2-channel amp

Find a used David Hafler DH-200, DH-220 or DH-500. All can drive a two Ohm load with ease, utilizing MOS-FETs for output devices(not prone to thermal runaway). An operating 200 or 220 should be fairly inexpensive, and appear often on eBay. ie: (http://cgi.ebay.com/Hafler-Dh-200-Amplifier-Clean-Cheap-No-Reserve-1-Wow_W0QQitemZ390151415488QQcmdZViewItemQQptZVintage_Electronics_R2?hash=item5ad6d626c0) You can find the manual for the DH-220 here: (http://www.hafler.com/techsupport/pdf/DH-220_amp_man.pdf)

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

Besides what Almarg mentioned about running speakers in series,the highs and mids will suffer too.The highs and mids will all be traveling through the other speakers low frequency choke and other parts of the crossover that otherwise would never,and was never meant to by the speakers designers.

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

re: Series connection- Anytime components are added to a signal path, the signal is degraded. Introducing the reactance(and Back EMF) of the drivers of the systems to the signal path WILL CERTAINLY cause distortions. Whether they bother the listener or not will depend on how discerning they are. Further- raising the impedance that the output of a typical solid state amp sees, above 8 Ohms, can cut it's power significantly.