How Not To Set Up A Crossover

How Not To Set Up A Crossover

This week I am working with a modern black-box theater to configure and optimize their installed system. I haven’t gotten to any of the “fun” stuff yet because we’re still untangling the mess left by the original installers. Allow me to elaborate on that statement:

Usually when a subwoofer is not working, someone’s blown up either the amplifier or the sub itself. Not so in this case. An examination of the DSP revealed this little gem:

Here we can see that the L/R feeds from the console are passed through an input processing block and then a crossover, where the highs are sent to the mains, and the lows are mono-summed to the sub. A pretty standard configuration, although an unusual choice seeing as the house console (a gorgeous APB Dynasonics ProDesk 4) was installed with the dedicated Mono bus labeled as “Subwoofer,” which actually was going nowhere. But hey, nothing wrong with running a fully crossed over system. Here’s the configuration of the three DSP blocks shown above:

The L/R feed is high passed at 100 Hz as soon as it comes in, then crossed over at 200 Hz to the sub, which is then low-passed again at 150 Hz.

So the passband on the subwoofer information is 100 Hz – 150 Hz, causing the client to think it was broken.

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