GAIN11

The Art & Science of Audio & Video

Setting up Crossovers

How do you determine where to set the crossover frequencies in a multi-cabinet system?

The obvious answer here is to refer to the manufacturers specifications. So we will assume these aren’t available. Where this gets tricky is when you’re dealing with cabinets that are bi-ampable and have a passive crossover as well. For now though let’s assume we’re dealing with a standard three way system consisting of a subwoofer, mid and high cabinets. Now to do this correctly would require far more explanation than I can provide here. So the method we will discuss will be nothing more than a means of finding a starting point to get your system up and running so that you can fine tune it properly. To do this you will need a tone generator with selectable frequency output and a RTA. The easiest way to do this is with a tone generator plugged directly into your amplifiers. Pick a cabinet, say the subwoofer for instance. Plug your tone generator into the amplifier for that particular cabinet and increase the frequency until the amplitude drops by 3dB. This will tell you where the subwoofer begins to “roll off”. Now what this won’t tell you is the rate at which it rolls off. This starts to get pretty in depth because you will then need to know the rate the signal’s amplitude drops expressed in “dB” per octave to accurately determine a good crossover frequency. Now you move to the midrange cabinet and do the same thing. The only difference is you will need to know where the midrange rolls off on the “low” end and on the “high” end. Let’s say for our example that the subwoofer started rolling off at 450Hz and the midrange begins to roll off at 550Hz. Logic would say let’s split the difference and dial in our crossover. In reality you would not want to set the crossover point for both cabinets at 500Hz. Remember the point at which a speaker, cabinet or driver begins to roll off does not mean it stops there. It will continue to produce frequencies beyond that only in reduced amplitude. At some point the output of these two or more cabinets will sum together increasing the amplitude of a given portion of the frequency range around the crossover point. So by spacing our crossover points at say 475Hz and 525Hz we will hopefully create a flat and more natural frequency response. No matter what even when dealing with manufacturer specs. Always use your ears as the final test. No speaker or equipment manufacturer can determine what environment you will be using their product in amongst the many other variables. So don’t be afraid to experiment with your crossover settings to achieve the best possible performance in your particular application. A WORD OF CAUTION!!! It’s always wise to experiment at low volumes for the protection of your equipment and the most valuable piece of gear we all own, our EARS!

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February 27, 2008 - Posted by | FAQ's | , , , , , , ,

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