One way way

First there is a one way approach, when one full-range speaker is used. Or almost full-range, since there is no such thing....its all compromises in audio.
The advantage of this arrangement is no crossover, which is a big plus, no loss of power, no phase shifts, sound is coherent coming from one voice coil.
     The disadvantages are limited frequency response on both or one end of frequency range, limited power handling, may require complicated and large enclosures to extend lower end.
Full-range speakers were historicaly first used on open baffle. Later in closed enclosures. Many variants of enclosures exist, their goal is  to extend low frequencies. Some are more effective than others.

backloaded horns

   

         

more backoaded horns

transmission line

                                                                                        

Another approach to one way speaker is the use of multiple fullrange drivers, like in line array or omni-directional speaker on next two pictures. There are some advantages, like increased power handling, pinpoint imaging for line array, spacious sound with large sweet spot for omni-directional speaker, but there are disadvantages too, like the comb effect in line array or too much early room reflections in omni-directional speaker. It all comes to personal preference.

  

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Two way way

 These are the most common speakers. They come in two categories. First category is when midwoofer is paired with suitable tweeter. These vary from small bookshelf speakers up to big floorstanding speakers.  Second category has  full-range speaker accompanied with subwoofer.
     First category comes in numerous designes and configurations. Perhaps this is the most common form of the speaker.
The advantage of this speaker arrangement is that by using two speakers one can get much better extension on both ends of frequency range, specialized speakers for smaller frequency range have usualy flatter frequency response, decreased distortion and increased power handling.
    The disagvantage of this speaker arrangement is introduction of passive crossover, although biamplification with active crossover can be done too, there is still a crossover with its limitations and compromises. Another issue is the use of two speakers as two point sources for sound, which leads to phase shifts, differences in horizontal vs vertical frequency response and so on. This can be partly avoided by the use of coaxial drivers.
All the enclosure types in order to extend low frequency range as mention in one way speaker systems apply here as well.

   

  

D'Apolito

coaxial

another coaxial, Tannoy

with horn tweeter











line array, Dali

 

 

 

 

omnidirectional top

 

fully omnidirectional








Second and quite different approach to two way speakers is the use of full-range speaker supported with subwoofer. In this arrangement we have all the advantages of full-range speaker, no crossover in the most critical region of frequency spectra, plus a good bass extension. Various combinations of speaker enclosures can be used.

if you are very brave with waf or live alone, you can construct this industrial looking two way system with full-range accompanied with subwoofer done as horn with compression driver, bravooo...

Three way way

 In three way speaker designers are solving some issues of two way speakers, for instance if you choose midwoofer, and you want excelent midrange performance, you have to sacrifice the bass, if you insist on excelent bass extension, you sacrifice the midrange, than you have to go lower with frequency for tweeter, which bring another issues, like tweeter's power handling, directivity, plus you get crossover point to a very sensitive area. So the solution might be three way speaker. Audiophiles like them, you select best midrange, mate it with best tweeter of similar efficiency, put these into small box on top of the big box with best woofer/subwoofer. Than you spent countless hours tweeking the crossover, after you spent fortune on crossover parts. Life's not easy, but live we must. Anyway, you can get pretty decent results here, but you will almost always hear the crossover.  Power handling is great if that's what you want. 

 

 

Four way and up...

Nautilus

Jadis

Alon Phalanx

                                       Audio Artistry

Legacy

TAD Pioneer