Stereo sub out to mono, is it safe?

My new integrated amp has L/R sub output and my sub only has a mono input. Is it safe to use a Y adapter to sum the L/R output to the mono input or will this cause a short? Thanks for your insight.
Generally the idea of one sub would be to use the right output only.
The owners manual would be the definitive place to check.
However it is never a good idea to sum outputs.
You can split them usually without any problem. But not add them together.
So the answer is NO, you cannot add them together.

Generally the low frequesncy output is pretty much the same in both channels (except maybe 'trick' recordings.)
So no loss to connect to only one side.
The answer is yes; I have no idea what Elizabeth is talking about. Why is it wrong to convert a stereo signal to mono? I started with a stereo cartridge feeding a mono pre amp;for that matter what do you think a mono switch on a pre amp does except sum the channels?
If the sub outs are not buffered and high pass filtered, and are merely connected in parallel with the main L/R outs, then when you connect the sub outs to a y adapter you will also mix the main L/R channels and make the whole system mono.
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.

-- Al
Thank you for the responses. The amplifier is an ATC SIA2-150,new version,and I should receive it on friday. I can't find the manual online so I thought one of you might know. I will contact ATC and see what they have to say.
I also do not agree to the "use one side" theory. I have quite a few recordings where the bass may be on one side or the other or even switching from right to left etc. This is on a 2 channel system of course.
When I asked Krell if I could do it VIA a "Y" connector they said go ahead. I never ended up doing it though for the same reason I note above.
Good luck, JD
I would check with the factory. I haven't a clue, but if you check my threads, you will see that I had a custom summing buffer made to mix the channels into mono for my single sub woofer. If you learn that you also need the type of device I have, give Tom Tutay a call. I believe his number is listed in one of my threads.
Some bizarre answers...the short answer yes...bass can operate in either channel or both channels...although in theory...a sub is mono in the sense it is only speaker functioning at a specific crossover point and it doesn't acknowledge left or right...
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.

-- Al
Don't you need a 'summing' adapter for this application?

I don't think this is the same as 'splitting' a single output which a vanilla flavored "Y" adapter would do.

But 'summing' two signals into one would take a different "Y" configuration.

The quickest example I could find was the one on Antimodes website: thirty years of audio I have never had an issue combining channels to form mono from a pre out...adding a mixer seems complicated and does utilizing only one pre out channel...just my findings...
Thank you Al. Appreciate your comment. Phasecorrect, I respectfully suggest you read my threads on the subject. Tom Tutay's buffer solved several problems: (1) asymetrical loading (i.e., output to amp was XLR; output to Paradigm control box or the sub was SE); (2) combined output impedance presented to my linestage was lower than factory recommended, the buffer increased impedance; and (3) the device summed L/R channels without shorting the linestage.
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.

-- Al worries...this is audio and there are more ways to skin a cat...and I believe we all have good intentions...I just try to inform others of thje pitfalls I have encountered...this situation isn't one of those...99 percent of the time it will work...happy listening....
Too technical....I like music...all the best
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.

-- Al
Al, having made a significant investment in my system, I generally rely on the tech experts at ARC to advise me on what works and what does not. OTOH, I learned about Tom Tutay from A'gon Forum members.

The bottom line is that my solution was factory approved and works. In fact, my system even sounds better because I'm properly loading my pre. I'm sorry that some other folks may find our advice "too technical," but sometimes doing the right thing means learning a little bit about electronic, asking for the proper advice from the people who know YOUR equipment, and remediating a problem in a safe, factory approved fashion.

I know you agree with me and have said so above. My recommendation to the OP is to call the factory and ask for their advice since it's their equipment. If a custome buffer or some other sort of gear is needed, Tom Tutay is a go-to guy whi is well respected by many knowledgeable A'gon members.

That's all I have to say because otherwise I'm just repeating myself.

So . . . I thank you for your technical and experienced based advice, given here and in many other threads.

But if the OP or others want to play their systems with a one channel sub, or short out their amps, or damage their equipment -- I'm sorry for them.
Thank you for all of the input! I will be looking into the solution suggested by Bifwynne.
Well, before tha manufacturer could get back to me the amp arrived and had a problem right out of the box so it is going back to the distributor. I will keep all of this info for the future and hopefully it will help the next person who is wondering. Thanks everyone
I had the same issue.I just got a new Music Hall a70.2 integrated amp and Martin Logan Vista speakers.My MH integrated has pre outs that the manual says can be use to hook up a sub.I had a old paradigm sub that only has one line level input.So I used a y adapter to combine both Right Left into the sub.It worked but made my main speakers mono.So I just use the right preout into the sub.This sounds decent but not perfect.I am waiting on a new HSU sub with right left inputs to do it right.So for me using the y adapter made my new integrated mono.
lord almarg:
your explanation, as always makes a lot of sense. in your expert view, would there be an issue with simply connecting one channel of the amp to the sub input as elizabeth suggests?
Thanks, Loomis. I've answered in your other thread.

Best regards,
-- Al