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[Jason Gabrieli]

Full disclosure: I know this is probably a stupid question. The fact that I have not been able to easily find a definitive answer using Google and the search function on here is frustrating me, so I bring you:

As we know, many powered subwoofers have both a right and left input. I have never given a second thought to running a signal to only one of those inputs, especially when using more than one sub. However, it came up in conversation with a friend tonight that he’s “sure” that running signal to both right and left inputs on a sub would somehow increase output.  That seems like it would not be the case, but does anyone who has a better understanding of the circuitry that goes on behind the panel actually have the answer?

[Scott Holtzman]

Full disclosure: I know this is probably a stupid question. The fact that I have not been able to easily find a definitive answer using Google and the search function on here is frustrating me, so I bring you:

As we know, many powered subwoofers have both a right and left input. I have never given a second thought to running a signal to only one of those inputs, especially when using more than one sub. However, it came up in conversation with a friend tonight that he’s “sure” that running signal to both right and left inputs on a sub would somehow increase output.  That seems like it would not be the case, but does anyone who has a better understanding of the circuitry that goes on behind the panel actually have the answer?

It depends.  If you have one sub and two mains, then yes, there could be LF information in one channel not present in the other.   I will say the LF energy is non-directional so it should be panned equally in both channels (standard mastering).

As far as "what goes on behind the panel", that should not be black art.  The inputs are not labeled L&R (except on home subs) they are labeled 1&2 and as such are summed like all inputs to a single output device, a two channel mixer for all intents and purposes.  Does this make sense?

With a mono mix it doesn't matter.

[Chris Grimshaw]

If you use an XLR Y-splitter to feed both inputs, you'll get 6dB more signal into the powered sub's amplifier section.

That's the same as pushing the desk fader up by 6dB, or turning the input gain on the sub up by 6dB.

... All of which means you're 6dB closer to the limiters.

Chris

[Ivan Beaver]

I would argue that very few PROFESSIONAL powered subs have left and right inputs.

That is more of a home sub type of thing.

But to answer your question, for signals that are common to both the left and right channels (not all are), you will get a 6dB gain in summation.  It is simple voltage addition.

But for signals that are less than equal, you could have 0 to 6dB gain.

So, once again, it depends.

The total maximum output will not change any, that has nothing to do with the input, but rather the limitation of the output of the amplifier.  If you are running your sub to where it is "out of gas" on a single input, then adding another input will only result in more distortion or compression/limiting.

[Luke Geis]

An easy way to look at is this.

1. The speaker only has so much output to give regardless of what you send to it. If the subs max input signal ( before clipping ) is +20dbu, then it will not matter how you get to that level, once there it will be clipping and have all the output the sub has to give.

2. If you double up on the inputs and they are the same signal, you will see an increase of +6db at the input and a reflected increase in output from the sub. This DOES NOT change the output capability of the sub/speaker, once you hit the max input of the unit you have met bullet point number 1's criterion.

3. It will change the required drive level by reducing it -6db. Simply put, the addition in gain you get by sending the same input into two of the speaker's inputs allows -6db less drive level to get the same relative output as only having 1 input being used.

I find doing things such as this is only good for creating a balance without having to alter gain structures elsewhere in your chain, or if for instance, the speaker's max input is greater than your mixers output capability. Some mixers are only capable of +18dbu output levels before they are clipping. Some speakers can have +21db or more for their input before they clip ( the input ). If by some slim chance you need more drive level to get the desired output from the speaker, doubling the input can help. Outside of simplifying the system's balance or cheating a couple of db for additional headroom earlier in the chain, it has no appreciable benefit. 

[ProSoundWeb Community]