Sensitivity question

Good question,

my instincts are: only in a small space, i.e. 10 x 12.... like an office, den, ..., but not enough power/enough volume for a large space where the listening position is likely to be further away.

Combining with a self-powered sub or two subs combined could work in a larger space.

You need to get the bass load off the amp, so it only needs power for upper bass/mids/highs which need much less power than low bass.

That means line out of the amp to the sub(s), then line minus low bass from the sub(s) back to the amp. Now, amp receives no low bass, doesn’t need power for that, AND the small speakers do not have to make low bass, thus they probably will sound better.

small space, I would probably use one in-expensive sub, just to get the load off the amp and add just enough bass so the main speakers do not sound small. Unaware of sub until you turn it off.

larger space, a stereo pair of self-powered subs, better quality, front firing, located adjacent to the mains. Very low bass may start mono, but the overtones quickly become directional.

8 ohm speaker rated at 88dB will produce 88dB/W at 1m distance.  At 2m it will drop to 82dB/W, but room reflections add 3dB and second speaker adds another 3dB, resulting in 88dB at 1W.  At 23W they will produce 102dB - should be loud enough.

Sensitivity is specified at 1W or 2.83Vrms.  It is the same with 8ohm speaker, but specifying 4ohm speaker at 2.83V (2W) shows better (by 3dB) sensitivity in specs.

Speaker's nominal impedance is specified usually at 1kHz, but might vary a lot at different frequencies.  As you stated lower impedance speaker is a little harder to drive, but the same goes for speakers that have impedance dip at certain frequencies.  My amplifier is specified for >2ohm speakers, while my 6ohm speakers' minimum impedance is 3.6ohm - so I'm OK.

You seem to be mixing concepts. "hard to drive" is usually reserved for speakers with very low impedences in certain frequency bands that need very high current. Not the same as sensitivity

Low sensitivity needs more watts of power, but isn’t necessarily hard to drive.

High impedence means less amps required and generally requires less current for the same watts.

Now if you’re looking for a speaker to pair with an SET at low wattage, the only thing you really need to look at is sensitivity. Then check that it isn’t one of the "problem" speakers that has impedence dips. 4 ohm or even 3 ohm is fine for most amps (the amp manufacturer will warn you if it is designed for 8 ohm only). Infinity speakers, especially the Kappa’s are known to have very low impedence dips and thus require huge currents and are very "hard to drive’. Lesser amps tend to fry.

If you're trying to match to a 23 wpc amp, you might look for 90 and above but 88 may work.  Do you listen loud?  Check that the 88 is not a "problem" load.  

Jerry