A karaoke amplifier is a powered amplifier designed specifically for the needs of the avid karaoke equipment owner. Many are designed for the karaoke DJ while a few are more designed for home use. They typically are designed to make hooking up and taking down a karaoke rig easy and provide numerous extra features over a typical public address system power amplifier.
These features typically include features that any DJ would appreciate. For example, many of the karaoke amplifiers are considered hybrid amplifiers because they have features normally associated with pre-amps.
One of these features is multiple inputs so you can send audio signals from multiple sources. This eliminates the need for a mixer if you have two audio sources, such as the karaoke source and an iPod for filler music. Many of these units also include a radio tuner.
A typical karaoke amplifier has enough power to run four or more speakers efficiently. For a good karaoke setup, you will need 2 main speakers, at least one subwoofer and at least one monitor speaker. The main speaker and subwoofer work together to get all of the sound out to the audience.
The monitor speaker is there so the singer can hear themselves. The quality amplifiers for karaoke and other DJ applications have a crossover built in meaning the low frequencies for the subwoofer only go to the subwoofer, keeping them from the rest of the mix. The best way to run the speakers is to run the the mains and monitors on the same channel, as high frequencies do not need as much power.
Be sure to match your amplifier to your speakers and vice versa. You want to make sure the speakers can handle more power than the amplifier can put out, but not by too much. For instance, if your amplifier can put out three hundred watts, then speakers that are rated to handle four hundred and fifty watts would be perfect.
If the amplifier is able to put out eight hundred watts, then an individual speaker must be able to handle one-thousand. However, when running that many watts, you will likely be running multiple speakers. In this case, you add the wattage of each together to determine how much they can handle. With eight hundred watts, you could run two five hundred watt (or even four hundred and fifty) speakers, or four two to three hundred watt speakers.
The flip side of this is buying a subwoofer that is rated for fifteen hundred watts and only running it off of a three hundred watt amplifier. You will likely burn out the amplifier and never get a good sound from the speaker because it needs more power than it is getting just to properly produce sound.