2-way design vs. 3-way design means ?

this ’speakerchoices’ link has cool diagrams that give you clues, you can sort by any column, put in limits ...

https://speakerchoices.com/index.html

number of drivers does not tell you the whole story, here’s

a 2 way with 3 drivers

https://amphion.fi/products/helium520/#specifications

a 3 way with 5 drivers

https://www.aperionaudio.com/products/verus-v8t-tower-speaker

the crossover which divides the frequencies, and sends only some frequencies to specific drivers is the determinant regarding 2 way, 3 way,

sometimes a single diaphragm will work with two horns like this

https://products.electrovoice.com/binary/847A%20EDS.pdf

thus a 3 way crossover becomes a 4 way speaker

 

Tekton V12 is a 4 way with 25 drivers

https://tektondesign.com/product/full-range-speakers/flagship/1812-model-v12/#color

also, you used the word bookshelf, caution, there are very few speakers designed shallow enough to fit a shelf (11-1/2" deep max let’s say), and many have rear vent(s)/port(s) which won’t work in a bookcase.

My Office AR-2ax are 3 way, and true bookcase size, no ports, wire terminals recessed within the 11-1/2 depth, even the rear mounted level controls for the mid and tweeter are recessed. Compact 3 way Bookshelf with 10" woofer. AR-2ax grilles were not designed for easy frequent removal.

 

KLH Model 5’s, re-introduced, compact stand mounted 3 way, also 10" woofer, are 13" deep, too deep for a bookshelf, they have a single rear mounted level control

 

 

JBL L100’s have easily removable grilles and front mounted level controls, a much easier arrangement for adjusting them in place while playing. 12" woofer, too deep for a bookcase

 

https://forum.audiogon.com/users/elliottbnewcombjr
 

Excellence and thank you for the effort for us all here on Audiogon! Thoroughly done. 

Then there’s the 2 1/2 way …

A 2 way speaker has a bigger physical demand put upon the 2 drivers of a  tweeter/mid bass. Think about this...those 2 drivers have to make ALL the sounds!

The load is reduced when you divide the frequency and add a speaker to handle just the mid-range and a speaker for just the deep sub bass. The mid-base driver isn't jumping around as much trying to reproduce everything when the load has been greatly reduced by adding a dedicated mid-range and a sub-bass driver.

The same reason why a subwoofer is designed to handle ONLY the deep bass. With the addition of a high pass filter the mid-bass driver can breath easier and has much less movement to the cone surface. Less distortion is the goal.

4 way speaker... is a tweeter/midrange/midbass then add a subwoofer.  

 

Whether a design is two way or three way won't tell you a whole lot about its capabilities.  Some people even swear by a single driver design (although I have yet to hear any of the exotic examples of them).  As most audiophiles will tell you, listening to a speaker in YOUR room with YOUR components is the only true way to see if a speaker is to your liking.  There are subjective measurements like tonal accuracy and dispersion patterns, but only your ears will tell you what works well in your setup.  I personally love the three and four way designs by Tekton Design because the concentric tweeter arrangement handles different frequencies within the mid and upper mids.  I own the double impacts and impact monitors.