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.
128x128geared4me
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
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 below...so it doesn't acknowledge left or right...