How do I get a good match between speakers and amps?
So you're shopping for a speaker cabinet, or a new amplifier head, and you're worried about matching wattages. Should you put a higher-wattage head with lower-wattage cabinets? The opposite? Or should you be trying to "match" the numbers as closely as possible?
It’s a common perception that “too much” wattage from a solid-state amp is bad for the speakers, but it’s actually more common for the opposite to be true. Having more wattage than you “need” to properly drive a speaker cabinet is much better than “starving” a cab by asking an amp to make volume that it’s simply not capable of.
It’s kind of like putting a too large motor into a small car vs. a too small motor into a large one; as long as you drive the first car conservatively, you’re going to be just fine. Meanwhile, the Civic motor in the Escalade is probably going to self destruct the first time you floor it on the ramp to enter the freeway!
As an example, let’s take a look at the EA Doubler amp (rated at about 625w) and the EA Wizzy cabinets (rated at 250w).
That 250w rating is an RMS (continuous) rating, meaning that you can send 250 watts of sonic content through it all day long without any concerns. However, the amp can also handle “peaks” of probably twice that wattage; and in bass, particularly, you’ll get peaks that will exceed that level. As long as they are momentary peaks, they don’t cause a problem.
So, assuming that the Wizzy cab in the above example is a 4ohm model, you'll be pushing the full 625w through it - but only when you have the controls at their maximum. You're more than likely to get more than enough volume out of that rig with the master volume not even set halfway, and at that level, you're more than safe, and the amp has plenty of headroom. Even if the Wizzy is an 8ohm model, you'll still have roughly 310w or so, which is plenty to make the cabinet "bloom" nicely without getting destructive or risking "blowing it up." (more on ohm ratings)
OTOH, if you try to power a cabinet rated at 1000w with a 150w amp head, you’re going to have to push that amp as hard as it can go just to create a useful level of volume. And when it hits its power ceiling, things get really ugly – a solid-state amp doesn’t distort in a “pretty” way like a tube amp does – it can go into a “square wave” distortion, (commonly called "clipping"), which is EXTREMELY damaging to speaker cones and will fry them pretty quickly, subsequently releasing their magic smoke. I had this happen to my beloved SWR Goliath 2x10 cab when the young bassist for our band's opening act tried to run it at gig levels with a seriously under-powered Hartke head, and with the knobs all dimed. He did pay to re-cone the speaker drivers, but it made for an interesting scramble when it was time for us to play!
So, in my opinion and experience, it’s safer for most players to have the wattage in reserve (commonly referred to as “headroom”) so that the amp can produce the peaks, which the speaker should capably handle.
Again, just don’t get silly about it, because yes -- if you run the amp at 11, bad things will likely happen. Remember that with a certain amount of power comes the requisite level of responsibility.