3 way vs. 2 way

You need at least 3 ways to have sufficient displacement for bass reproduction without compromising speaker directivity at higher frequencies.

Drivers like Mangers and full-range units with whizzer cones count as 2-ways, where the cross-over between the two is mechanical instead of electrical.

A horn couples the air in the throat to the air at the mouth so linear displacement is the same at both ends; in effect providing MUCH more surface area. A full-range whizzer-coned driver in a back-loaded horn is a 3-way.

A 2-way stand-mounted monitor plus a sub-woofer is a 3-way with independant placement for the bass-unit.

This is orthagonal to what the best compromises are once you limit price - more lower quality drivers, reduced output limits, missing the last two octaves (your brain does a reasonable job filling in the fundamental from harmonics)...

I think that absent the lowest octave, my Merlin VSM-MXe provide the coherency of two-ways, with the bass extension, dynamics, and loudness (105db peaks) of most three-ways, down 3db at 33Hz. Of course this is done with bass EQ (BAM), but from 40 Hz up this is my favourite speaker, and the bass is satisfying for 95% of the music I would ever listen to. A different approach to dealing with the tradeoff and compromises required when choosing to go 2-way or 3-way.

In theory, there is no way that 2 drivers can cover a frequency range of 20Hz to 25000Hz as well as three drivers can. This of course assumes that everything else is equal such as, driver quality, proper crossover design, prober box design, etc.

If you build your own speakers, three ways also give you much more flexability to balance your sound to suit your particular taste. For example, I have adjustable L-pads on my mids and tweets so that I can bring the mids or highs up or down to achieve the sound that I desire. My woofs cover 20-500 Hz, my mids cover 500-5000Hz, and my tweets cover 5000-25000Hz

HG

Soda14a6v, I agree with you that not only in theory, but in practice, you can't have 20Hz response from from a good sounding two-way. But I think we start to accept serious compromises and complexities and power requirements when we seek 20Hz response. I think for most applications, and most rooms, good response down to 40Hz or so provides the best set of compromises (and possible with 2-ways), especially when value is taken into consideration - in most cases the low,low bass (16-30Hz) comes at a serious sonic cost to the rest of the spectrum IMHO, and is not suitable for most domestic rooms.