Stereo sub out to mono, is it safe?

Erikt raises a good point about the possibility of using an adapter containing a pair of resistors to do the summing. That can be thought of as a passive mixer. It would sometimes, but not always, be a viable (and less expensive) alternative to an active mixer in situations where directly shorting the two outputs together with a y-adapter would not work well.

It would eliminate the possibility of the particular distortion effect that I had mentioned, as well as whatever slight possibility of eventual damage might exist with the y-adapter approach. However, if the sub outputs of the amp are not separately buffered from the main signal path, while a mono signal would not be heard from the main speakers there would probably be a significant reduction in channel separation. A properly chosen active mixer would eliminate that possibility. Also, the high impedance of the summing resistors may or may not be sonically optimal for driving the sub, as powered subs often have relatively low input impedances compared to the line-level inputs of other components.

Regards,
-- Al

Well, now that answers of "no" and "yes" have both been presented, I'll offer a third answer, which is "maybe" :-)

First, I assume that the sub outputs of the integrated amp are signals that are separately buffered and different than the signals that drive the power amp section of the integrated. That would certainly be the case if the sub outputs are low pass filtered by the amp, but may or may not be the case otherwise. If those outputs are not separately buffered from the main signal path, then connecting them together with a y-adapter would result in mono from the main speakers.

Second, assuming the sub outputs are separately buffered from the main signal path, how well shorting them together would work depends on the design of the circuits that drive them, especially their output impedance.

If at any instant of time the bass content of both channels is the same, as would be the case for example if a bass drum were recorded dead center, then both outputs would be putting out the same signal, and everything would be cool. Although in that situation, as Elizabeth indicated, the results would be just as good if only one channel were connected.

Now imagine that the bass drum, or a low frequency note from some other instrument, was recorded off to one side, so that its sound is mostly in just one channel. And imagine that nothing else is playing at that instant. One output will be trying to generate a signal corresponding to that note, while the other output will be trying to put out zero volts. What that means is that for the duration of that note the output circuit for the channel in which the note is present will have to drive a load impedance equal to the output impedance of the other channel, which may be 50 or 100 ohms or so, rather than the tens of thousands of ohms it is designed to drive.

The sonic consequences of that may or may not be good, depending on the specific design. And although it is probably very unlikely, I would not absolutely rule out the possibility that damage could eventually occur, as a result of accumulated stresses caused by the larger than normal current flow that will be drawn by the low load impedance. I would be most concerned about that possibility if the output impedance of the sub outputs is very low, say a few tens of ohms or less.

The bottom line, as I see it: It will work OK in some but not all cases. I would ask the manufacturer of the amp. If an answer can't be obtained, it would PROBABLY be OK to try it and see how it sounds.

Another alternative, btw, would be to use a mixer to combine the channels.

Regards,
-- Al

Phasecorrect, I'm not sure whose answer(s) you are referring to as "bizarre," but the original question was not which channels bass "can operate in," or whether a sub "acknowledges left or right." The question was would it be safe (or could it cause damage or other problems) to combine the left and right channel sub outputs of an integrated amplifier by shorting them together with a y-adapter.

Geared4me, the suggestion by Bifwynne is an excellent one. A line-level mixer having reasonably high input impedance, and that provides RCA connectors, would eliminate all of the possible issues that have been discussed.

Regards,
-- Al

Phasecorrect, thanks for the follow-up.

To be sure that my first post above is clear to everyone, I will summarize it without the techno-stuff:

1)There is a reasonably good chance that the y-adapter approach will work well.

2)Depending on the specific design, there is a possibility that the y-adapter approach will result in mono being heard through the main speakers.

3)Depending on the specific design, there is a possibility that the y-adapter approach will result in a perceivable increase in distortion (or other perceivable sonic degradation) on deep bass notes produced by instruments that are positioned off to one side.

4)Depending on the specific design, there is a VERY SLIGHT possibility that the y-adapter approach could over the long term result in damage.

5)Using a properly chosen mixer instead of a y-adapter would eliminate all of these adverse possibilities.

6)Hopefully the manufacturer will provide further information that will narrow down these possibilities.

Regards,
-- Al

Thanks, Loomis. I've answered in your other thread.

Best regards,
-- Al