Do I need a crossover for my PA?

Do I need a crossover for my PA? Crossover Effects – How a crossover affects your sub.

Just a quick post – someone on Guitar/amp help tips and fixes Facebook group was asking about whether a sub woofer was required for use with vocals. My first reaction was that there was no need at all – I’ve always used sub only for kick and bass guitar, but he’d found that it helped his vocals at one gig. It’s always best to challenge your assumptions so I did a little test while I was eating my cornflakes this morning.

What’s a crossover, why does a sub need one?

Most subs can produce signals up to a few kHz. if they aren’t controlled. If you don’t use a crossover, the sub will let through all the mid frequency signals, competing with the tops and your band will sound like mush. The efficiency of the system is compromised and your tops still end up trying to produce the bass signals. You might as well sing into a bass amp. More later…

How can we test the crossover?

This is an audio track that has been filtered with a steep EQ treble cut, as you would expect in a good sub crossover. The track plays a few seconds of full range audio then a few seconds of sub-filtered audio.

Crossover simulation Technical details

Do I need a crossover for my PA?These crossovers are all 24dB/octave but three cutoff points were tested:

  • 80Hz crossover (typical for use with 15in sub)
  • 100Hz (pretty high, even for a 15in)
  • 200Hz (If you’re setting it this high, you’re doing something funny)

Tracks are Barry White’s “My first, My last, My Everything”, U2 ft Johnny Cash “Wanderer” and AX7’s cover of Pantera’s “Walk”.


Crossover Simulation Results

Here are the results of the test – you’ll need headphones with a good bass response to hear anything at all in the filtered sections.

Even Bazza’s vocals are pretty much in audible through the sub-filtered audio. You can see the graph opposite. Do I need a crossover for my PA? Graph

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