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[Debbie Dunkley]

I run my Danley system mono subs but I've never worried too much about the small powered system -  I usually run the subs in stereo. One each side of the stage with tops above - makes set up and wiring fast. My stereo settings are very subtle - panning is not far from center on any channel - but I use it mainly to separate instruments slightly. I have done things this way for many years. Sometimes I couple the subs when I can.
However, I'm going to start using mono in the subs to see if I can hear much difference in these smaller places....
My question is this: Is the result the same whether I  1) send L & R from the mixer to a sub Ch1 and Ch2 and allow the sub to sum the inputs OR 2) send a combined L & R to sum mono before it hits the sub inputs. ??

[Bob Stone]

Assuming the overall sub level stays the same and the mono-summing circuit/algorithm is the same, then shouldn't make a difference.

I have found if I send stereo to the sub and let it mono sum, rather than just sending it a single mono signal, the output level does increase with the sum of those signals. In other words, have one signal at say -10db going to the sub, plug a second signal at -10db going to the sub, and you pick up ~3db.

[Debbie Dunkley]

Assuming the overall sub level stays the same and the mono-summing circuit/algorithm is the same, then shouldn't make a difference.

I have found if I send stereo to the sub and let it mono sum, rather than just sending it a single mono signal, the output level does increase with the sum of those signals. In other words, have one signal at say -10db going to the sub, plug a second signal at -10db going to the sub, and you pick up ~3db.

Thanks Bob - the potential increase in level did occur to me. This is not  my goal but I'd need to keep in mind when I set the levels.

[Helge A Bentsen]

Should be the same. Expect a 6dB level increase when you sum down two channels.
I like to do this in the system DSP so it can be quickly reconfigured if I have guest mixers.

[Bob Stone]

Should be the same. Expect a 6dB level increase when you sum down two channels.
I like to do this in the system DSP so it can be quickly reconfigured if I have guest mixers.

Shouldn't it just be 3db?

[Frank Koenig]

Shouldn't it just be 3db?

When two signals of the same average power are summed the resulting signal is between 3 and 6 dB greater. In one extreme, if the signals are perfectly correlated (the same signal), the voltage, current, sound pressure or volume velocity sum (coherently) to result in a 6 dB increase. If the signals are uncorrelated the power sums to result in a 3 dB increase. If there is partial correlation, say the channels of a stereo program where there is considerable overlap, the result is somewhere in between.

This is the basis of signal averaging where adding multiple segments of a signal in such a way that the desired part is correlated and the noise is uncorrelated results in an increase of signal-to-noise of sqrt(N) where N is the number of segments.

--Frank

[John Schalk]

When two signals of the same average power are summed the resulting signal is between 3 and 6 dB greater. In one extreme, if the signals are perfectly correlated (the same signal), the voltage, current, sound pressure or volume velocity sum (coherently) to result in a 6 dB increase. If the signals are uncorrelated the power sums to result in a 3 dB increase. If there is partial correlation, say the channels of a stereo program where there is considerable overlap, the result is somewhere in between.

Thanks for this explanation.  I had noticed this result recently when sending L+R to a single matrix output.  I was expecting more level and thinking it would be +6dB, but it was closer to +3dB using recorded music as the signal. 

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