Speaker power ratings

I have a couple of stupid questions regarding power ratings of speakers.

My understanding is that the power rating of a speaker is the maximum continuous power that can be applied to the speaker before possible damage can ensue.

Is there any correlation between power rating and speaker efficiency?

Is there any concern with using a low power amp with a high power speaker?
For instance--My little 20 watt Subway Blues has a 50 watt 10 inch Eminence. Sometimes depending on the situation I use an additional extension speaker--a Thiele cab with a 300 watt 12 inch EV. Does this pose any issues at all for my amp?

For instance--My little 20 watt Subway Blues has a 50 watt 10 inch Eminence. Sometimes depending on the situation I use an additional extension speaker--a Thiele cab with a 300 watt 12 inch EV. Does this pose any issues at all for my amp?

This does pose no risk to your amp at all. As recommended by amp guru Gerald Weber, your amp should drive one or more speakers with a combined power rating of twice the power rating of your amp. Your 20 Watt Subway Blues driving a 50 Watt speaker fulfills that requirement, as does your amp driving a 300W Thiele cab. And if both cabs are hooked up, assuming both have the same impedance (likely 8Ω), they each provide half of the power delivered by your amp. To dive into the how and why becomes a bit too technical for this post, but if you want to know, drop me a note.

As recommended by amp guru Gerald Weber, your amp should drive one or more speakers with a combined power rating of twice the power rating of your amp.

Thanks for your response.
Should that read "at least twice the power rating of your amp"?

Should that read "at least twice the power rating of your amp"?

Yup.