6. What Watts?
How much power should you have?
The answer, unfortunately, is as much as you need. Your choice of amp is inevitably bound up with your choice of speakers, and your decisions about the whole system are heavily dependent on how you are going to use it.
If youre investing in a permanent system for a room, hall, or arena, then you should consider the size of the room, its acoustic qualities, and the way it is used. A church will not require the same size PA as a rock and roll venue for instance. Generally, the best advice is to invest in a bit more than you need, so that you always have some capacity spare, and the sound quality remains excellent, even at the highest volumes youll be using.
If youre taking your system on the road, you may have to compromise. Base your choices on the largest and smallest venues you think you will play, and strike a balance somewhere between power, size and portability. Again, go for as much power as you can afford, for the same reasons of quality and spare capacity - you may just get that really big gig one day! It may be wise to consider two or more smaller amps and speaker sets which can be combined when you need them your back will thank you on the smaller gigs!
As far as specific amplifier power is concerned, it is generally recommended that the power amp has a slightly higher rating than the speakers it will drive - with the caveat that you should not operate it at its peak for any length of time. Note that you can damage your speakers just as easily by delivering too little power as too much, because the amp has to work too hard to drive them. The critical sign of trouble is clipping - you can hear the sound beginning to break up. It is an indication that either the amp is overloaded, or the speaker coils are under stress. You either have a bad match, or the amp is turned up too high. The trouble is, that clipping is caused in particular by distortion in the high frequency ranges, creating a disproportionate loading on the drivers that handle these signals. The sensitive coils can burn out if they are subjected to too much signal.
To be sure of a safe set up, pay close attention to the RMS ratings. Also take into account the nature of the equipment you will be attaching to the system - you have to be sure that your power amp can handle the strong signals generated by modern audio equipment. As a rule of thumb, you can reckon that the amp should be 30% more powerful than the speakers it is driving, and that the whole system should be around 50% more powerful than your expected maximum requirement. Provided that you dont over-crank the amp, you should then be able to create rich, warm sounds at low and high volumes, in all sorts of spaces.