Also for details on additional Home Theater Receiver functions to consider, such as: Multi-zone Audio, iPod, Networking, and Video Connectivity, check out Before You Buy a Home Theater Receiver - Part Two.
A Home Theater Receiver combines the functions of three components1. A tuner for AM/FM; in some cases, HD (High Definition Radio), XM or Sirius Satellite Radio, and/or Internet Radio.
2. A Preamp that controls which audio/video source is selected (Blu-ray Disc Player, DVD player, VCR, CD player, iPod, etc...), processes the incoming stereo/surround sound signals, and distributes audio to the channels and subwoofer output. Video from components (such as a DVD player) are routed to a TV.
3. A built-in Multi-channel amplifier (5.1, 6.1, or 7.1 channels) that sends the surround sound signals and power to the speakers.
Power Ratings (WPC) - Watts Ain't EverythingADs in the newspaper for an AV receiver, always lists the Watts-Per-Channel rating. One receiver has 50 Watts-Per-Channel (WPC), another one has 75, and still another has 100. The more watts the better right? Not Necessarily.
Most people think that more watts means more volume. An amplifier with 100 WPC is twice as loud as 50 WPC right? Not exactly. Read the following reference article for full details...
Decibels (db) - Sound Level PerformanceSound level is measured in Decibels (db). Our ears detect changes in volume in a non-linear fashion. A db is a logarithmic scale of loudness. A difference of 1 db is the minimum perceptible change in volume, 3 db is a moderate change, and 6 db is doubling of volume.
For a Receiver to be twice as loud as another, you need 10 times more wattage output. A Receiver with 100 WPC is capable of twice the volume level of a 10 WPC amp. A receiver with 100 WPC needs to be 1,000 WPC to be twice as loud.
Distortion (THD) - If It Doesn't Sound Good - The Watts Don't MatterA Receiver that has excessive noise or distortion at loud volume levels can be unlistenable. You are better off with a receiver of about 50 WPC with a low distortion level than a more powerful amplifier with high distortion levels.
A Receiver that has a distortion rating of 10% at full output is unlistenable. A receiver that has a .01% distortion level at full output level would be excellent at all listening levels. Distortion specs are expressed by the term THD (Total Harmonic Distortion).
Signal-To-Noise Ratio (S/N) - Separating The Sound From The Background NoiseAnother factor is Signal-To-Noise Ratio (S/N), which is ratio of sound to background noise. The larger the ratio, the more the desirable sounds (music, voice, effects) are separated from acoustical effects and background noise. In amplifier specifications S/N ratios are expressed in decibels. A S/N ratio of 70db is much more desirable that a S/N ratio of 50db.
Continuous Power (RMS) - Does The Receiver Deliver Over The Long Haul?An additional factor is the ability of a receiver to output its full power continuously. In other words, just because your receiver/amplifier may be listed as being able to output 100WPC, doesn't mean it can do so for any significant length of time. Always make sure that, when you check for Specifications, that the WPC output is measure in RMS terms. This means that the listed power output is sustained output at a specific volume level.
Dynamic Headroom - Is Extra Power There When You Really Need It?Another factor is the ability of a receiver to output power at a significantly higher level for short periods to accommodate musical peaks or extreme sound effects in films. This spec is important in home theater, where extreme changes in volume occur during the course of a film.
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.
The Bottom Line - Take All Factors Into Consideration When Buying a ReceiverDon'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 an accurate picture of the receiver's true capabilities. There are other factors to take into consideration, such as, sound quality, ease of use, and flexible connectivity with other components. Never buy a receiver without giving a listen for yourself. Make sure the dealer allows a 30-day return/exchange if you are not happy.
For more on buying a Home Theater Receiver, check out Before You Buy a Home Theater Receiver - Part Two, as well as our About.com Video Presentation: Advanced Functions to Consider When Buying a Home Theater Receiver.