If you are going to use unpowered speakers, it is best that you use them together with a power amp. However, you need to know that you don’t just use any amplifier. Make sure that the amplifier matches your speakers in such a way that the impedance (ohms) of the speaker and the power (watts) are rightfully matched. To match the ohms is easy because the speaker will only be 4 or 8 ohms. The complicated part is matching the power. Basically, the PA must be as powerful as the combination of the whole instrument amplifiers. For example, to avoid having problem with a 400W speaker, you should use a 100W amp. When you choose a power amplifier, see to it that you look for the one that specifically fit your requirements. Some of the famous power amps in the market are Crown Live Power Amplifiers and QSC Live Power Amplifiers.