Our recently acquired subwoofers are designed to go in-line to powered mains.

There are two options - straight pass through and high pass.

The manual recommends high pass. It's clear the sentiment is "the subwoofer will chop the bass out of the mains and handle the bass itself".

But why would you do this? What downside can there be to letting the mains still do the same job they did, and just boosting the bass with the sub?

2 Answers 2


Without precise time alignment, trying to provide bass from multiple sources could lead to interference patterns which would cause the low end sound to be way too loud in some parts of the room and almost nonexistent in others. Even if that weren't a problem, high passing the signal before sending it to the mains means that the mains have more power bandwidth available for the mids and highs.

You can always try it both ways and see if you have a preference in your particular environment. Personally I would high pass it and not even try it the other way.


As you move forward in the future with PA upgrades, you might consider a speaker management system that would include a crossover and delay for time alignment. Then you would actively cross over the FOH sends in the speaker manager and have separate connections to the tops and subs and then the high pass option on the subs will be obselete. I wouldn't go this route unless or until you have a snake with enough returns to handle it. Without the snake, it's very convenient to just run one cable to each side's sub and then run each high passed cable from the sub to the top.

  • Thanks - the power bandwidth thing makes some sense. Bass interference patterns are a different kettle of fish: the same argument applies to "should I have one subwoofer or two?", doesn't it? Would you argue "one, of course"? Dec 7, 2015 at 11:57
  • You've got it exactly, the question of one sub or two is not so easy to answer. If you're working on a home system or a small room, you should be able to get away with one sub, which is generally preferred, as you say. Two subs may be necessary for several reasons, and then you get into placement questions. There's more information here: music.stackexchange.com/questions/39327/… Dec 7, 2015 at 12:56
  • I have a "strange" situation. My bandmate purchased two. (They were on special, doh!). I'm like "gnnnh... dude, um... will we have dead spots to deal with?" But it's kinda hard to prove or be ungrateful for someone who brings extra gear! Dec 7, 2015 at 13:20
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    Read the linked question. A lot of times two subs is the best compromise. I wouldn't get too down on your bandmate. If you only have one and you can't place it in the middle, it can make the sound more lopsided than having two spaced out, so having two isn't so bad. If you can put them together in the middle of the stage, that's the best - especially if you can time-align them with the tops. There's lots to learn and it's not easy but with research, practice, and a little experimentation you can make almost any system sound its best. Dec 7, 2015 at 13:22
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    Sorry - I forgot to mention I already read and upvoted the other :) Thanks for that. Looks like we'll be experimenting with "top-on-pole-on-sub" on each side and see how it goes! Dec 7, 2015 at 13:24

That's for use where the "receiver" isn't already separating the bass out and sending one signal to the speaker amps and another to the "sub out". Instead there's just a patch point (out, in) and you plug in the device to modify the signal in any manner you desire.

  • But the question is why would I want to separate the bass out and not sent the whole spectrum to the mains? Dec 7, 2015 at 22:08

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