Axiom Home Page Forums General Discussion Home Theater Re: question asked about the L+R inputs on subs

I cannot find the topic now but It was asked if you need to hook up the Left and Right with a Y adapter when connecting to a sub. Or which one to hook a single RCA to. Aslo, if there are any differences.


I mentioned one or the other, but some subs give more db's. I thought I read it in my B&W sub manual and have now found the source.

Connect the "Sub Out" of your Receiver / Preamp Processor using an RCA cable into a Y-cable into the "L" and "R" inputs of your subwoofer. Note: Unless otherwise stated by the manufacturer, be sure to utilize both inputs of the sub as many subs sum the "L" + "R" inputs to yield a 6 dB gain from the input voltage of the processor.

http://www.audioholics.com/tweaks/speaker-setup-guidelines/crawling-for-bass-subwoofer-placement

also as a great guide to home theatres

http://www.hometheatershack.com/forums/g...ater-101-a.html

I've got my sub hooked up via a Y-cable as well.

Also, thanks for the second link. A link to a bunch of links about anything HT is always handy to have saved off. Heck, I clicked a random link, and it was THX 7.1 speaker placement. I only have space in my HT for 5.1, but I was surpised that they put the "6th and 7th" speakers side by side in the rear. I've seen most people put them in rear separated from each other.... Interesting...

Hi Joey,

No, there's no reason to use a Y cable to hook up your EP500 to the mono LFE feed from your AV receiver. Virtually all subwoofers will sum the L and R low-level inputs anyway. Traditionally, if a subwoofer has separate Left and Right channel line-level (low-level) inputs, the Left input is designated as the single connection to use.

Using a Y-cable will not increase the signal level to the subwoofer, despite the curious advice from the B&W manual.

If you check your EP500's rear panel, there is one RCA line-level input jack and a second RCA line-level output jack. There are also duplicate XLR balanced input and output connectors.

If you operate a second subwoofer, use the same type of line level output--RCA or XLR--as you use for the input.

Regards,

I have always just used one cable to my line-in on my sub, as Alan mentions. Your not gaining any performance by using both.

The reason for the lack of gain in performance when you use a Y-splitter is a passive device such as a Y splitter doesn't magically give you twice the original signal. It does the opposite, since total input = total output on the splitter. When the sub sums the two inputs, you get the same signal that came into the single end of the splitter.

Now you got me thinking.

The voltage (V) on each leg of the Y will be the same. So the voltage to the left will be V and the voltage to the right will be V.

So if the sub sums the left and the right, the voltage at the output of the summer will be 2V if the right and left are in phase and zero if they are 180 degrees out of phase.

Yes, it isn't a major advantage(contrary to the implication in the B&W manual)to get a Y-adaptor and feed both the L & R inputs. The 6dB increase mentioned does occur, but this is only an increase in the voltage supplied to the output section of the sub amplifier, and doesn't mean that the maximum output capability of the sub has been increased by 6dB, or by any amount. The same voltage increase can be had by turning the sub output on the receiver higher, and most receivers are capable of supplying more than enough voltage to keep the sub amp "awake".

Some of this seems to be contrary to common sense, but the technology is clear. First, when a Y-adaptor is used the voltage on each output of the Y isn't cut in half, but is the same as the input voltage. A discussion and proof of this can be studied here . Then, merely rejoining the two wires wouldn't of course double the beginning voltage(wires are passive elements and there aren't any miracles in audio), but the two voltages are fed into a summing circuit in the sub amplifier. This results in a doubling of the voltage, which is a 6dB increase(voltage doubled is 6dB, rather than 3dB when power is doubled, using the formula 20xlog[V2/V1]). An illustration and proof of the technology of a summing amplifier can be studied here . So, this is true but not a big deal, and using one input is fine.

That's assuming the resistance of each leg of the splitter is identical. Which I think is a safe assumption.

I wonder if B&W recommends the Y for improved normal mode noise rejection.