Today's home theater continues the tradition, although now it's an A/V (audio/video) receiver that has become the workhorse; providing not just the power to drive the audio, but also the means for transferring video from those devices connected to a TV or projection system. But due to the advent of iPods and portable speakers and sound bars, the advantages of an A/V receiver has been downgraded in people's minds. That's a shame, because an A/V receiver offers much to a person's home theater for creating the type of atmosphere that a movie theater does so well.
Audio/Video receivers still abound, as do the variability of their prices. But there are a few things about them that are worth considering because these things can not be changed.
The audio power of an A/V receiver is expressed as wattage; 50 watts being less than 100, 100 less than 150, etc. Since a basic speaker setup begins with stereo (i.e., two speakers, one at each side of the TV), the wattage of the receiver shouldn't exceed that which the speakers are rated at. But in order to properly assess this (including what wattage is noted for additional speakers, such as the center and surrounds which make up a 5 speaker system, it's also important to consider RMS, because this describes the average amount of power output of the speakers over a long time. This information can be found in the specifications, something that should always be looked at prior to making a receiver purchase.
An A/V receiver quite correctly has inputs for both audio as well as video. As these inputs are hard-installed, they can not be updated as the receiver's software can be. So if you have a 3D capable Blu-ray player, the HDMI input on the receiver must be able to accept a 3D signal -- if it can't then the output from the receiver going into the 3D TV will be 2D. Audio inputs have become fairly standardized over the last few years; there will be an optical input, a coaxial and (legacy) RCA stereo inputs. More important will be the number of inputs, both video and audio, since this is fixed and unchangeable. So if you wanted to use a HDMI input from a Blu-ray player, for example, that only transferred audio for listening to music, there would have to be enough HDMI inputs to cover this besides those needed for the Blu-ray player's video as well as any other video devices (i.e., cable box, etc.). In addition, the new HDMI standard for 4K can’t be added in later to the receiver; for the receiver to be able to “video switch” a 4K video signal, it must be 4K compatible right out of the box.
One of the major additions to A/V receivers has been the ability to join a home network. This was facilitated through an Ethernet cable connection, and enabled the receiver to play music being stored on the home computer. A short time later, wireless capabilities were added to the receiver. This made it unnecessary to connect cabling, since the receiver could join the home network via WiFi. And a short time after that, Internet options and "Smart TV" like capabilities were being built in, for example, the receiver being able to receive Internet radio stations and connect to music playback services such as Pandora and I Heart Radio. It wasn't long before it became obvious that smartphone apps could be created to connect wirelessly to the receiver and provide remote control as well.
Stereo consists of 2 speakers, but a surround sound system bumps that number up considerably as well as adding a powered subwoofer for enhancing the bass response. The most conventional surround setup, made popular by the advent of DVDs is called 5.1, where there is a left and right speaker, a center speaker and two surrounds (L/R). Plus that subwoofer. But there wasn't any reason that the number of discrete audio channels couldn't be increased, and so added to 5:1, we now see 7.1, 9.1 or even 11.1 (or 7.2, etc. where dual subs are brought into play). Obviously the more speakers added into the home theater, the more physical space must be available for lacing them. But other than through psycho-acoustic trickery to fool the ear that speakers facing you from the front are actually producing sound from the sides or read, the only way to add more audio channels for your ears to listen to is to add more speakers. Of course a 7.1 system can be downgraded in use, should there not be enough speakers, but what's vital to consider is that the number of audio channels the receiver can present is locked in when it's made. So if you want a 7.2 system now or at some future date, and have a 5.1 receiver, the only way to bump up the number of audio channels to 9 is to go out and buy an new A/V receiver.
Flat panel TVs, be that HDTVs or the new 4K Ultra HD TVs, have spoiled us into thinking that the less space home theater components take up, the better. But nothing could be farther from the truth when it comes to a surround audio system: you want to have as many speakers as you can so that the audio can be as enveloping and all-encompassing as is possible. For that, you'll need an A/V receiver. Be sure to get a good one.