To get the best out of your speakers, tweeters and subs, there are some fundamental truths that you need to know.
Big Numbers
The people who make and sell loudspeakers know that you are impressed by big numbers. Well, you ARE aren't you? Wouldn't you rather have a 150 Watt speaker than a 60 Watt?
But wait, which would you want if I offered you a 60 Watt RMS rated speaker or a 150 Watt PMP? If you just decided on 150 Watt Peak Music Power, you lost. The 60 Watt RMS speaker is more powerful. In fact it's roughly equivalent to 180 Watt Peak Music Power.
That's not quite a fair comparison but it's near enough. RMS and PMP are different measurements. It's a bit like having a bicycle tyre than is supposed to be pumped up to 40 PSI (pounds per square inch) pressure with a maximum rating of 90 PSI (the pressure at which it will burst). You wouldn't want to ride your bicycle with the tyres at 90 PSI because
- They'd be as hard as stone
- They'd burst the first time you hit a stone
So think of PMP as the absolute peak that the speaker will tolerate for a fraction of a second before it burns out or blows its cone through your windscreen. RMS, on the other hand, is the continuous rating at which power the speaker should last for a long time.
RMS = "Root Mean Squared". It's a mathematical term and, since I've never been good at maths, I won't attempt to explain it. Just consider it as the typical continuous power level that the speaker can handle. the PMP is usually about two or three times the RMS figure, although it varies slightly because a strongly made speaker might tolerate a large power peak without damage, even though its RMS power rating is quite low. Manufacturers love to quote big numbers but, wherever possible, I've tried to find out the true "RMS" rating.
Frequency Range
The human ear can hear sounds from roughly 10Hz to 20kHz. In my case, my old ears can't hear anything higher than about 12kHz. So all those nice cymbal clashes sound a bit dull to me. Don't laugh. You'll be old one day. You'll also be deafer than I am if you play your music too loudly. Be sensible. If it's loud enough to hurt or give you a headache, it's damaging your hearing. Too loud or too often and the damage becomes permanent. It's not kool to be a fool.
The frequencies that a speaker can handle depend mostly on its physical size. A woofer fed with high notes sounds muffled. A tweeter fed with bass notes sounds tinny. To make sure that each speaker has to handle only the range of frequencies for which it's designed, we use a filter unit called a "crossover". This is simply a bunch of coils and capacitors which prevent bass notes from getting to the tweeter and mid-range unit and prevent high notes from getting to the subwoofer. The mid range only receives the middle range of frequencies.
Different speakers have various ranges over which they are most efficient so it's important to match the crossover to the speakers that you use. If you buy a ready-made speaker stack, the manufacturer will have done the matching for you (hopefully!) If you buy individual speaker units and put them in your own cabinet, then you'll need a crossover to suit. Look at the overlap in frequency range of the speakers and decide where you need the crossover points to be. Some amplifiers have the "crossover" filter built-in. For example, an amplifier designed to drive a Sub will have a "low pass" filter which prevents high frequencies from damaging the Sub.
The efficiency of a loudspeaker depends on its size and rated power. A speaker rated at 100 Watts RMS will be less efficient than a speaker rated at 50 Watts RMS and that brings us to the next subject which is amplifiers....
