Good PA speakers are essential to a good sounding karaoke system. The best player, mixer, and amp are redundant if they play through poor speakers. You may get great sounding music from your home stereo speakers or surround sound but the live vocals of karaoke are an entirely different story. I'm not suggesting that you go crazy and stack 15" woofer 2-ways on top of 18" subs like your local DJ but you do need quality PA speakers.
Full Range SpeakersFull range speakers are those that can produce a full range of sound from deep bass to high treble. In PA speakers these come in the form of 2-way or 3-way configurations. Some will have a woofer (bass) plus a tweeter horn (highs) and others may also incorporate a mid range driver. A pair of quality 12" or 15" woofer 2-way full range speakers are all you need. If you're a person who enjoys richer bass in their music then you will want to opt for the 15" woofer speakers.
Active vs Passive SpeakersActive (also referred to as powered) speakers have a built in amplifier and only need the signal from a mixer which can be supplied with a light gauge shielded XLR cable. These speakers eliminate the need for amp/speaker power matching. The down side to active speakers is that they are much more expensive than passive speakers (although they do save the cost of buying an amplifier), they are heavier than passive speakers, and each one needs to be plugged into an electrical outlet. Passive speakers are powered by an external amplifier via heavy duty speaker cables. The power output of the amplifier must be matched to the power handling capability of these speakers. This is explained in more detail at the Karaoke Amplifiers and Mixers page. These are generally much lighter than powered speakers and they don't need to be plugged into an electrical outlet. Active speakers are my recommendation for a home karaoke system. The reasons include the fact that you do not need to worry about matching them to an amplifier... not requiring an amplifier in your setup saves space.... adding more power to your system is as simple as adding more or bigger active speakers... and the weight is not an issue because you will not be hauling them around. If you want to get into the technical aspects of PA speakers there is plenty of this information to be found online. But after you're done doing all of that you will end up buying speakers just like the ones below. :) These are speakers that I have used personally or that have been highly recommended to me by other professional karaoke hosts and home users.
Active (Powered) Speakers
Article by Richard Wise. Follow me on