I have read a lot of threads recently in which folks are using the electrical power rating of speakers as a guideline for matching cabs to heads. To my way of thinking, not only do you need headroom on your amplifier, but also on your speakers to avoid losses due to power compression- (see this Loudspeaker FAQ for description). To quote their excellent FAQ: Power Compression The Watts that are not turned into sound get transformed into heat. This heat increases the electrical resistance of the speaker, making it harder for the amplifier to drive. The harder you drive the speaker, the more heat is generated. To return to the motoring analogy: This is the "aerodynamics of the speaker": The faster you drive, the more wind resistance there is. Thus, even more power is required to make up for this. The lower the power compression figure is, the better. Unfortunately, I have not seen any drivers quote a spec for power compression (I'm not really sure how that is measured). A friend who seems knowledgeable about such things once told me that for a specific driver rated at 600w RMS, there was no real change in volume in driving it at 300w vs 600w due to changes in speaker specs caused by power compression. Can anyone shed light on this topic? This sort of thing wasn't much of a problem 'in the old days' when we had 100w amps and 200w speakers, but now drivers can withstand a kilowatt and folks are making 'watts' their primary shopping consideration.