Another Subwoofer Cable Topic

Sorry folks, I cannot find a reasonable answer to this quandary and not many people are willing to answer it properly.

Powered subwoofers seem to enjoy having a left and right RCA input, despite the driver being 100% mono. Practically all manuals say the same thing, choose one of the RCA inputs (usually Right) and everything will be fine.  I have not found this to be true.

Somewhere, in the annals of the internet(s) I had found an audio discussion where someone explained it. On a basic level, the mono driver requires 2 incoming volts to properly drive. One single RCA output delivers 1 volt of signal. Using that one input will cause the driver to activate and make bass, this is true.  But using both RCA inputs doubles the voltage and the driver functions much better.

In my floor standing system I have two subwoofers that both use NHT monoblock amps. They both have left/right input RCAs. When I connected a SINGLE connection to the block, I had to crank the volume to the maximum to get any reasonable bass out of the subwoofers.  At that time I bought a splitter so that the single LFE out on the receiver (I have left and right LFE outputs, hence two subs) could split into two to cover both left/right inputs and suddenly there was more bass than could possibly be endured and I had to crank the volume way down. So, that seems to prove the theory that using one single RCA input is not correct.

So, on to my quandary.

In my office reference system I have a powered sub that currently connects via two RCA.  The sound quality is pleasant and enjoyable. I wouldn't mind tightening the bass down a bit more. To that end I want to switch to actual Subwoofer cables, that have been specifically tuned to amplify bass. The question is, should I buy two subwoofer cables or buy one cable and two splitters?  Yes, buying two cables is more expensive.  However, ANYTIME you split a signal, there *WILL* be signal quality loss.  That's just the way it is. The more point to point the connection is, the better the signal flow. So...has anyone actually tested whether two sub cables works better or the same as a single sub cable split?



Sub cables do not matter (if not electrically compromised.) Unless you like "investing" money.

I just run decent stereo patch all the way



A subwoofer amplifies the signal that is put into it.  If the low frequencies on both channels are the same, there is no reason the let the sub see both channels.  It will have the same output no matter which channel is put into it.

Very rarely, the sub frequency tracks for left and right may be different and then it is good to have both (if you have one sub).  But to tell the truth, I've never heard a song when I had one channel hooked to the sub and said "oops, the sub missed that".

I think the issues you are trying to solve have nothing to do with cables.


There is a left and right bass signal. Period. If you don't use the LFE you won't get the full signal by using only one RCA. That is the same thing a LOT of people can't seem to understand. The signal is NOT MONO the results is MONO in nature because it's omni present below 60-80hz. The Complete signal from the source usually has even more than just a left, and right track they can have a signal that is surmised (3rd channel not TRACK) also. Guys that play BASS will chime in and tell you they don't record MONO bass tracks for playback. 

DBA misinformation is the problem.. Just because is sounds better doesn't mean it's playing the whole bass track especially if only the left or right signal was used.

Yes if the signal being sent to the plate amps is through junk RCAs that can cause a signal loss too and you will have to crank it to get any bass out of it or increase the signal. Either way more is better.

Better BASS resulted from a better signal to the sub plate amps.

Another thing LFE bass is modified. It has a step baffle to increase the signal, that is what you experienced. not all LFE signals are the same and some can be modified vs onboard options..


I think you misunderstood.  I am not trying to take one bass signal and split it into two.

The engineer who makes subwoofers see fit to install a Left and Right RCA input.  Why, if the driver is mono? There is no stereo input into the driver.  It's a positive/negative wire.

Again, I have connected a single RCA to just ONE RCA input and got terrible bass output, until I used a splitter to attach to BOTH RCA inputs in the AMP that powers a single subwoofer.

My question is really why does that happen and why do manuals always say to use one when clearly that isn't the best setup for performance.

On my other system, the receiver has a LEFT LFE and a RIGHT LFE mono output.  When dealing with Surround Sound, you can program a separate left and right bass response.


Again, I clearly confused folks or folks aren't reading my entire post.

My questions has nothing to do with LFE.  It was mentioned because I have two different setups and each is connected differently.

One powered sub has two RCA inputs.  White/Red - Left/Right. Manual says, connect only to ONE INPUT, usually the Right/Red. I have discovered this to be wrong and do not understand why they continue with that instruction when you get more volume in your bass by choosing to connect to both RCA inputs.

My question is whether to use single point-to-point connections or use splitters.

@guakus My answer was meant to address your question.  Sorry I didn't word it better.  

Here ae my thoughts:  I've used subwoofers with 2 inputs and instructions on which one to use if only one signal provided.  This has to be in the design since many people use 2 subs, one for each channel.  I have never had a problem with a sub unable to perform well with only one input.  As I said above, it just amplifies what is supplied to it.

So if your sub is performing poorly with one input, I'd contact the manufacturer.


OP I understand what you said, and I explained WHY. You just proved it. If you look at most of the plate amp wiring the signals are combined in the plate to a mono signal. The difference (as you found out) is the signal strength is doubled if you plug into both L/R. 

There is a difference though. The signal is NOT a complete bass track. PERIOD.
You did not understand ME!. You are playing 1/2 the bass signal IF you only use the LEFT or the RIGHT RCA wire coming out of the head set.  With an LFE signal from a head set (most stereo preamps don't, HT preamps do), BOTH left and right make a LFE signal with a step baffle. It is NOT what is recorded.. DO YOU UNDERSTAND. It is hocus pocus sound effects...

It will play louder for sure, it's just not playing all the music or the way it was mixed.

I use Bass columns and subs. The columns play from 300hz and down to 80hz. If I play the left and right columns they image a THIRD phantom speaker, just like a stereo. WHY? The signal is STEREO not MONO. LFE doesn't work there does it?

You want to make sure you get only 1/2 the information there but deliver it to BOTH left and right inputs. Split the signal you'll be like 1/2 of the DBA crowd. It will smooth out the bass that's there though. :-)

There are a lot of sub makers. 20% are good at it.. 80% have great paint. :-)

NOW decouple your subs and the rest of the speakers. Wait till you hear that difference. :-) Go to Servos subs. Bigger :-) go with Columns. :-) :-) :-)

Have fun.


Where is the other signal going? In this configuration, the signal path is being provided by a powered speaker. That speaker has left/right outputs.  They aren't specifically for bass; they're just RCA outputs.  Therefore, they would produce full range.  The speakers are the same manufacturer. So they say just run one RCA down to the sub via one RCA.  However, I am using both.

So, is it that I am doubling down on the same signal and marring bass? Again, why do they put two inputs if you aren't meant to use two?


Sorry, I am on Prednisone and it makes things a bit cloudy. :(

Columns are something I can aspire to in my main system, but not in the office. It's powered bookshelf speakers with a single powered sub. I wanted to upgrade the cable for the sub, but was trying to figure out if I should use two cables or one cable that is split.  I still don't understand why it has two inputs if you aren't meant to use both.

Somewhere, in the annals of the internet(s) I had found an audio discussion where someone explained it. On a basic level, the mono driver requires 2 incoming volts to properly drive. One single RCA output delivers 1 volt of signal. Using that one input will cause the driver to activate and make bass, this is true.  But using both RCA inputs doubles the voltage and the driver functions much better.


That's not how this works. Line level signal output varies from 0 to some number, like 1 or 2 volts, all the time.  That's how analog signals work. It isn't a fixed voltage.

On the receiving end, the sub amp is a voltage amplifier.  That is, whatever input you feed them they multiply it by some amount, minus any loss in a volume pot, to produce the final output.  Subwoofers usually have too much gain to adjust for being fed from 1 or 2 inputs.  If you use 2 lines, at best, you reduce the chance of noise. If 1 line has enough output and there's no noise you have no problem.


Then why was I not getting reasonable volume until I used both inputs on my main system?

Well, it is possible you don’t have enough gain in the sub, or in your pre/processor but that’s rare.

It is true that you get 2x the voltage, but it's not true that you get 1V with 1 and 2V with two lines.  The standard is usually 2V on line level, but remember that's peak, not an absolute.  That is, no output, no volts.


The connection in this case is one shielded/grounded cable out of one of the Receiver's LFE channel to NHT  monoblock amps.  One is the MA-1A and the other is the Sw2p amp. Both behaved the same. Connecting to one RCA,  I had to crank the volume knob to its max to get audible bass, and not very loud. Connecting a splitter in order to use both RCA inputs on the amp resulted in overwhelming volume and the volume, of course, had to be turned way down, to maybe 10 or 11 o'clock to get extremely loud bass.

I haven't had such problems on the office sub, but I also haven't tried.  Although, I did run a test against using just any old RCA interconnect vs using a higher quality interconnect and heard an extreme loss of bass on the ordinary cable. *shrug* That's a different post for a different day. ;)

Rel work more direct line level ,direct from the amplifiers audio output signal.

From what I understand is if you have a sub out on your AV amp or pre amp you need only one run going to the life on sub. If you run separate  pre and amplifier then two runs are required  from left and right.  As far as splitting one run to two I don't know.  If it increases the output  and sounds like bass then do it.

Apologies if not reading your question correctly; I'm using two subs.  My IA has left and right sub RCA outputs. Each sub has L and R RCA inputs.  I'm simply running the L IA output to the L input on one sub and the R IA output to the R input on the other sub.  My sub RCA cables are Audioquest BlackLab.

No problem with volume or realistic bass, only challenge was getting cross-over and level just right for the room and intended effect.

IA = McIntosh MA352

Subs = Martin Logan Dynamo 400s

I’m pasting this for you to read it will answer your questions 



Using a Y adapter on most, but not all, subwoofers will increase the sound level from 3 to 6 db.

Aperion Audio Subwoofer Y Cable
"Why, oh why do you need a subwoofer Y cable? Most AV receivers come with a single sub output while most powered subwoofers come equipped with left & right inputs. By using a subwoofer Y cable for both the left and right subwoofer input, you can increase the bass output of your subwoofer by about 3dB."

HDMI cable for home theater and high-performace audio video cables.
"Attach this cable to an existing subwoofer cable to split the signal into two inputs. 
Instantly improves your home theater or home audio experience.
Many subwoofers have increased clarity and bass response when both inputs are fed with a mono signal."

Wye Y Cable
"Typically, powered subwoofers will come equipped with either a single RCA connector, or double RCA connectors. However, both connections typically only require a mono (single) connection. Therefore, if you have both right and left inputs, a single cable connected to the "left" input will probably work just fine. However, you can get anywhere from a 3dB to 10 dB gain from your subwoofer by plugging into both stereo inputs. To plug into both inputs with a single cable, simply purchase our Y adapter Cable along with your subwoofer cable."

This is the science behind it:

There are two formulas used to find the db ratio between sound levels.

The first is used ONLY FOR POWER (watts): 10 . log (P2/P1). This formula is used when comparing Sound Intensity, measured in watts.

The second is used ONLY FOR VOLTAGES (and SPL levels): 20 . log (V2/V1). This formula is for voltage relationships and Sound Pressure Levels.  

Using a Y adapter will add two correlated signals. When you sum two equal correlated audio signals (i.e., mono sources from sub output on the receiver/preamp), you will get twice the signal level (A1 + A2 = 2A1, since A1=A2).

Therefore , since V2 = 2 V1 and the log (2) = 0.30103, it follows

20 . log (2V1/V1) = 20 . log (2) = 6dB gain in voltage.

For power, it will be 

10. log (2P1/P1) = 10 . log (2) = 3dB increase in power.

These are a few advantages (some real and some claimed) to using a Y adapter:

  • If you leave one of the RCA inputs open, dirt may get in there.
  • Using a Y adapter may add a few dbs to the subwoofers's output.
  • Some claim that the subwoofer works better at lower levels with the Y-cable.
  • The auto-off mode of some older subwoofers (e.g, Velodyne CH-12) may not come on at lower levels without the use of a Y-cable.
  • Some older subwoofers may actually need a Y cable because the left channel L may not default to mono signal.
  • Another benefit of using a Y-cable at the sub input jacks may be for reducing the amount of Radio Frequency (RF) and Electomagnetic (EM) interference, because you are not leaving the other input open and active. Subwoofers can be affected by annoying buzzes and hums.

Conclusion: Since Y adapters cost a few dollars and there is no significant risk involved, I would recommend using a Y adapter (2 male, 1 female) at the subwoofer's RCA input jacks. Make sure you use a good quality Y adapter that is shielded. Otherwise, you may hear hum and noises. 


Ok, now that I have a baseline on what's going on, what are your thoughts on this idea.

I want to get Synergistic Research's Reference Subwoofer cable. Since it is single RCA end-to-end, and they don't make a Y-Splitter, what if I use that cable on the manufacturer's recommended RCA input, and use the Synergisitic Foundation RCA cable I am currently using on the other RCA input.  That way I am satisfying the voltage but are using the stronger cable for signal? 

@guakus  Unfortunately I’m not expensive cables believer 

im using simple quality build from Amazon Mediabridge 

Mediabridge™ Ultra Series RCA Y-Adapter (8 Feet) - 1-Male to 2-Male for Digital Audio or Subwoofer - Dual Shielded with RCA to RCA Gold-Plated Connectors - Black - (Part# CYA-1M2M-8B)

Post removed 

I’m using mostly balance XLR on all my SVS subs 

and Mediabridge RCA Y splitter on my old subs for 



I am a believer, and I did do one test on my subwoofer which helped seal the deal for getting better cables for it.  Keep in mind this is purely rhetorical and only impacted this setup, so other people might have a different result.

When I was spec-ing out my subwoofer cable, I was reading up on what was "assumed" made a good subwoofer cable. It seemed the most expensive had a conductor that was a solid core of copper plated in silver.  Well, I just happened to have some old Audioquest Component (R,G,B) cables that had that EXACT same conductor.  A solid copper core plated in silver. At the time I was using some very old Audioquest Ruby X3's on the subwoofer.  I connected the RGB component cables and.....lost almost all my bass. I cranked it to full 250 watts and the bass was still weak and flabby. However, according to most people, it shouldn't matter because a conductor is a conductor and shouldn't limit or stop the signal.  IN other words, it not supposed to be "tuned."

Now, with that said, Component cables are setup to propagate a 75 OHM, high speed video signal and not audio. It was also a single conductor, end-to-end.  The Ruby X3 has three solid copper conductors per cable and was designed to propagate all signals from 20hz to 20Khz.

So, it clearly means that one cannot just connect any RCA ended cable to a subwoofer and expect good bass.

Ergo, I became a believer that it is possible to create a cable through careful conductor choices and geometry choices that would propagate a low frequency signal better than another cable. :)