what do the model letters stand for?

[jeh]

cbm, cmt, htm, etc.

[curtis]

I think it is like this....

Compact Bookshelf Monitor
Compact Mini Tower
Home Theater Monitor

[Quinn]

And I think the number is the millimeter measurement of the driver(s). 170mm= ~6.5 inches. Two of the drivers in the 340. 4" is ~100mm times 2= 200.

[davef]

Both Quinn and Curtis got it right....