Minimum recommended amplification requirements and amplifier matching

If a speaker manufacturer has the following specs; do they mean the recommended power in 8 ohms or 6 ohms?

Neither. I'd imagine the particular speaker manufacturer is providing a spec for minimum amplification because they are wanting to avoid clipping, which occurs more easily when lower powered amps are driven hard (played loud).  

Thanks @gdhal 

So, if I buy an amp for my 6 ohms speakers with recommended minimum power of 50wpc and if the amp has a power of 50wpc in 4 ohms and 25 wpc in 8 ohms. Am I meeting the "technical" recommendation?

I know what matters is whatever sounds good to us regardless of the specs (as long as you do not know want concert levels in your room) but I am just trying to learn the technical aspect of it.

@cleo  Have you asked the speaker designer/ manufacturer/ importer/ dealer?  I'm sure they will answer your questions with more specificity and accuracy.

You're welcome, celo.

IMO there is a little more to it than the numbers you've mentioned. For instance, how loud do you typically listen? The efficiency of the speaker would also play a role as to an accurate answer to your question. The fact that the wattage output capability is doubled when the impedance is halved is usually a sign of a high quality and power (current) capable device. The idea though is simply to avoid clipping. In general, if you're not listening at loud levels you would be fine.

So, is there a speaker made today that is 16 ohms, 90db+ in sensitivity that is not a horn type that would be considered a high end home speaker below $10,000? 
I haven't been able to find any.

ozzy