Audio specs are some of the most misused numbers in the world. There isn't really any enforced standardization in how manufacturers measure and report the numbers behind their audio power specs (watts). For example, two manufacturers may both claim that their systems put out 50 watts per channel (a decent amount). Neither manufacturer is lying when it states this specification - but one system may be much more powerful than the other.
How is this possible? Well, the simple answer is that there are different ways of measuring the same thing (watts, in this case). Brand X's watts may not equal Brand Y's. Here's an explanation:
- Watts: The most basic measurement of an audio system - the number that gives you some idea of how loud the system is - is the power rating in watts. All else being equal, a system with a higher wattage rating should be able to play more loudly. Wattage is measured in watts per channel (or speaker).
- THD: Audio-system wattage is measured at a certain level of distortion (noise introduced by the audio amplifier system) called THD (total harmonic distortion). As audio systems are pushed closer to their limits (in terms of volume), they tend to produce greater amounts of distortion. Manufacturers can make a system seem more powerful "on paper" by measuring watts at a higher THD. Look for receivers that meet your wattage requirement when measured at low THDs, like .02 percent, rather than higher ones like 0.2 percent or even 1.0 percent.
- Full-bandwidth power ratings: Another gray area in power ratings is the frequency range at which watts are measured. The human ear can hear audio signals between 20 and 20,000 kHz. It's best if the system's power is measured across this entire range. Some manufacturers provide wattage ratings at only one frequency (such as 1000 kHz), which can create an artificially high power rating. Try to find specifications that cover the full 20-to-20,000-kHz range to make true comparisons.
- Ohms: The number of watts a system can produce is also affected by the impedance (or resistance) of the speaker being driven. Manufacturers generally measure impedance at 8 Ohms, but sometimes you'll see wattage measured at lower impedances, such as 4 or 2 Ohms. It's good that a receiver can drive speakers with such low impedances (not all can), but the wattage measured at 4 Ohms is higher, so it shouldn't be compared directly to wattage measured at 8 Ohms.
- Power handling: This rating (also measured in watts) relates to the speakers in an audio system, not the amplifiers. This is simply a measure of how many watts the speakers can take before they start to shred themselves into confetti.
The bottom line here is to make sure that you're comparing apples to apples as you look at audio systems - either built into an HDTV, or in a separate home theater receiver system. Two manufacturers may have 50-watt systems, but one may be measured at a limited bandwidth, at a high THD, and on a lower-Ohm impedance - and may be significantly less powerful than the other.
