Dynamic Headroom
Last (for the purposes of this discussion), but not least (by any means), is the ability of your receiver/amplifier to output power at a significantly higher level for short periods to accommodate musical peaks or extreme sound effects in films. This specification is very important in home theater applications, where extreme changes in volume and loudness occur during the course of a film. This specification is expressed as Dynamic Headroom.
Once again, Dynamic Headroom is measured in Decibels. If a receiver/amplifier has the ability to double is power output for a brief period to accommodate the conditions described above, it would have a Dynamic Headroom of 3db.
Conclusion
So, when shopping for an receiver/amplifier, be wary of wattage output specifications and also take stock of other factors such as Total Harmonic Distortion (THD), Signal-To-Noise Ratio (S/N), and Dynamic Headroom.
In conclusion, your amplifier or receiver, although the centerpiece your audio or home theater system, other components such as Loudspeakers, Input devices (CD, Turntable, Cassette, DVD, etc...) are also links in the chain. However, you can have the best components available, but if your receiver or amplifier isn't up to the task, your listening experience will definitely suffer.
This has been a very brief overview of some of the factors to take into consideration when buying a Receiver/Amplifier. Don't base your buying decisions from a single specification, such as a Watts-Per-Channel rating. A single spec, taken out of context with other factors, does not give you an accurate picture of the receiver/amplifiers true capabilities. There are many other factors to take into consideration, and never buy any receiver/amplifier without giving a good listen for yourself. Make sure the dealer allows a 30-day satisfaction period or other accommodation for return/exchange if you are not happy with the performance of the unit.
For an additional perspective on this subject, check out two articles by Gary Altunian, About.com Guide For Stereos: What is the Relationship between Loudness and Amplifier Power? and Amplifier Power and Speaker Efficiency.
