You can, indeed, hook two different speakers to a single channel of amplification either in series or in parallel.

Neither of these is likely to yield good sound reproduction. Connecting the two speakers in parallel would be better, though. Speakers are voltage driven devices and in parallel they should see the same voltage across their input terminals.
Separate leads from amp to each speaker would be a good idea. One danger of this is that the listed speaker impedance for most speaker is an approximation, as the speaker includes reactive (energy storing) elements that make the impedance frequency dependent. An 8 ohm speaker may dip to 3 ohms at certain frequencies and be as high as 70 at others. Trying to drive the combined curves may make life very interesting for the amplifier.


Hooking them in series is worse, because the changing (with frequency) impedances mean that the two speakers will share the available voltage/current/power unequally and neither will have a proper frequency response. In addition, if one speaker has capacitive reactance and the other has inductive reactance, at a particular frequency these will cancel, leading to an extremely low series impedance and the possibility of amplifier instability or overcurrent limiting. Most speaker do have inductive reactance but electrostatics (Dayton Wright, Martin Logan, Infinity Servo-Stat, Apogee among others) are generally a capacitive load.


Steve