The main goals of any monitor or main PA speaker is to have a flat frequency response, high efficiency (plays louder with less power) and reliability.
Probably about 80% of all speaker/monitor/amplifier companies out there use Eminence speakers in their cabinets.
Eminence speakers have been around for over 40 years, handle more power then most and are very efficient (louder), not to mention are inexpensive and have decent frequency response.
Typically a company (Yamaha for example) specs out exactly what they want a speaker to do (power handling, frequency response etc.), they find that Eminence can meet all of the afore mentioned criteria and have them make as many units as they need with the final portion of the assembly being the attachment of the company brand sticker (Yamaha in this example) to the back of the magnet.
...Just to name a few that have Eminence speakers inside -SWR, some Peavey, Carvin, Bag End, Yamaha, Yorkville, some Marshall, Ampeg, Genz Benz, Klipsch, SWR, some EAW and on and on.
Basically there is not too much difference in overall tone and power handling from a typical Yamaha 12"/horn monitor to a Carvin cabinet of the same type, of course the price difference between these two is not too extreme however in some cases the price difference is vast,
for example when comparing a Yamaha cab to an EAW cab of the same type you'll find a large price difference but in reality both use plywood with speakers made by the same company-when you realize they are selling for different prices its easier to go for the cheaper item without feeling like the price difference reflects the difference in quality.