XLR vs RCA to Sub (Phase Issue)

Chronic

Standard Member
Joined
Dec 6, 2011
Messages
138
Reaction score
1
Points
39
Age
40
Hi there,

When I run an XLR (via passive XLR splitter or direct) from a pre-amp/DAC (M-DAC) to a powered sub (XLR to RCA cable), it is much quieter than if I use the RCA outs on the M-DAC. This means I have to crank the sub's gain very high and feel it's not working optimally, it's not a weak sub either (BK XLS400). If I'm using the XLR splitter (SZ-SS1) the sub sound is very low and improves when pressing one of the phase switches. Similarly, if I plug the M-DAC directly into the sub (XLR to RCA stereo) the sound is very low, until I unplug one of the channels and then the sound is fine.

That is my main query, the reasoning behind wanting to use XLR is I find using the XLR outs on the M-DAC sound better through the studio monitors; the RCAs produce more high frequency hiss/noise, albeit which is only audible right next to the speakers and inaudible when playing music. The M-DAC is also a good 3-5 metres from the speakers/sub.

A logical option could be to use the XLRs to the speakers and the RCAs to the sub which does work, however this isn't recommend by the manufacturer as apparently it unbalances the XLR outputs on the M-DAC.

Thanks for any advice on this. :)
 
Last edited:
XLR should only be connected balanced to balanced. If one or other is unbalanced then XLR loses it edge. XLR is a far better connection for long distances over RCA. If you have a choice of XLR or RCA from the balanced unit to the non balanced then RCA should be used.
 
XLR should only be connected balanced to balanced. If one or other is unbalanced then XLR loses it edge. XLR is a far better connection for long distances over RCA. If you have a choice of XLR or RCA from the balanced unit to the non balanced then RCA should be used.
Yes I use balanced to balanced for DAC to studio monitors as it sounds best. I'd also like to connect a subwoofer which has an unbalanced RCA input, so I use an XLR splitter then have to use balanced to unbalanced cable as the sub has no XLR input. It sounds fine but requires significantly more gain compared to RCA to RCA connection.
 
Just to help my understanding of the issue, are you saying that even when using XLR outputs of the M-DAC and an XLR to RCA cable to directly feed the sub (i.e. studio monitors not connected), the sub volume is very low? If so, and your studio monitors have an RCA input, remove the sub and connect the monitors to the M-DAC in the same way (i.e. M-DAC XLR > XLR to RCA cable > monitors). Now, do you need to turn the monitors' volume controls up significantly to get decent volume? Do the monitors sound as if they are connected out of phase?

Is it possible that one of your XLR to RCA cables has different internal connections to the other - hence the phase issue?
 
A logical option could be to use the XLRs to the speakers and the RCAs to the sub which does work, however this isn't recommend by the manufacturer as apparently it unbalances the XLR outputs on the M-DAC.

For one thing that they claim it has this affect make me seriously question their balanced output buffer (or lack of) design, but then there are quite a few DACs around that lack adequate output buffering in order to keep the test results better.

Secondly, I cannot imagine this would be any worse than using a splitter on one channel of the XLR to split off the hot signal into another cable to the sub.
 
Saying the volume on the sub is low doesn’t really mean much, the sub and your active monitors amps probably have different gain structures. Also, the monitors being fed XLR means the signal is 6dB hotter to them than the split-off signal going to the BK, because it’s leveraging only a single phase. And so that will have to be compensated for too.

What sort of position do you need on the gain dial for the sub? I mean ultimately this is exactly why there’s a gain dial on it, unless it’s humming and buzzing it’s tit’s off, no problem.
 
XLR to RCA can either be done using a Balun, where you will not lose 6dB, or by not connecting a wire, which has multiple adverse effects, including the one you've mentioned. My recommendation is either buy a balun (an entry level balun works out to about £25), or use an RCA lead. The RCA lead will work out cheaper, and it has no audible deterioration over XLR with a subwoofer not supporting balanced connectivity.
 
Saying the volume on the sub is low doesn’t really mean much, the sub and your active monitors amps probably have different gain structures. Also, the monitors being fed XLR means the signal is 6dB hotter to them than the split-off signal going to the BK, because it’s leveraging only a single phase. And so that will have to be compensated for too.

What sort of position do you need on the gain dial for the sub? I mean ultimately this is exactly why there’s a gain dial on it, unless it’s humming and buzzing it’s tit’s off, no problem.

Thanks, this makes sense. The gain is around 80% and you're right it's not really a problem. When the phase switch on the XLR switch box wasn't selected it was very quiet, where even 100% gain wouldn't be adequate.

XLR to RCA can either be done using a Balun, where you will not lose 6dB, or by not connecting a wire, which has multiple adverse effects, including the one you've mentioned. My recommendation is either buy a balun (an entry level balun works out to about £25), or use an RCA lead. The RCA lead will work out cheaper, and it has no audible deterioration over XLR with a subwoofer not supporting balanced connectivity.

I would use an RCA but I find the studio monitors have less interference noise with the XLR connection, perhaps as my speakers are 5m of cable running from the DAC. If I use the RCA outputs on the DAC (to sub) at the same time as the XLR outs (to speakers), it unbalances the XLR signal according to the man who made it. So I use the XLR outs on the DAC, into an XLR splitter, with 'Thru' to powered speakers, then one of the outputs running to the sub. The balun looks like a good solution if I really needa boost, thanks.
 
What monitors are you using? Some of them have outputs and allow you to adjust phase. I.e feed the sub from the speakers.
 
I would use an RCA but I find the studio monitors have less interference noise with the XLR connection, perhaps as my speakers are 5m of cable running from the DAC. If I use the RCA outputs on the DAC (to sub) at the same time as the XLR outs (to speakers), it unbalances the XLR signal according to the man who made it. So I use the XLR outs on the DAC, into an XLR splitter, with 'Thru' to powered speakers, then one of the outputs running to the sub. The balun looks like a good solution if I really need a boost, thanks.
The XLR signal is "unbalanced" through the splitter too. A balanced signal is one with two wires having the same impedance to each other and ground. Details: Balanced line - Wikipedia.
 
The XLR signal is "unbalanced" through the splitter too. A balanced signal is one with two wires having the same impedance to each other and ground. Details: Balanced line - Wikipedia.
If I'm using the 'Thru' output on the splitter to active speakers with XLR inputs, would that not mean the signal is still balanced? The manufacturer of the splitter says the thru is unchanged, so I presume this is the same as just linking two XLR cables. The A/B outputs are a 'copied signal' and will be used converting to RCA one way or another so will be unbalanced.

I found that using the Thru on the splitter gives the full signal but either of the A/B outputs are quieter, so the original issue is the XLR splitter which is giving a lower signal on it's outputs.
 
Last edited:
If I'm using the 'Thru' output on the splitter to active speakers with XLR inputs, would that not mean the signal is still balanced? The manufacturer of the splitter says the thru is unchanged, so I presume this is the same as just linking two XLR cables. The A/B outputs are a 'copied signal' and will be used converting to RCA one way or another so will be unbalanced.

I found that using the Thru on the splitter gives the full signal but either of the A/B outputs are quieter, so the original issue is the XLR splitter which is giving a lower signal on it's outputs.
Thru will still be balanced, signal unchaged. The A/B outputs are the ‘Y’ splitter outputs.

There’s several issues here:
1) as I said previously the sub and monitors will likely have different gain structures
2) then there’s the fact that the sub is only using one phase so compared to the monitors the signal is 6dB quieter.
3) what I didn’t mention before, is the input impedances are going to be different, and as the sub and the monitor appear in parallel to the source this I believe means it’s not a 50/50 voltage split to each (There’s a lot of math here and a quick google…err beyond what I can be bothered to work out!!)

This all means it’s probably an unequal voltage split, the sub then discards half the voltage it does get by only leveraging 1 phase, and for further salt in the wound the amp gain could well be less! So no wonder it’s much quieter than the monitors.

Use both sets of outputs from the DAC. And if the DAC has unbuffered outputs (only reason I can think they would say the XLR’s become unbalanced when using both) - then buy a competently engineered DAC with twin outputs.
 
3) what I didn’t mention before, is the input impedances are going to be different, and as the sub and the monitor appear in parallel to the source this I believe means it’s not a 50/50 voltage split to each (There’s a lot of math here and a quick google…err beyond what I can be bothered to work out!!)

Assuming the resistance of the interconnects is low relative to the input impedance of each device, the voltage will effectively be a 50/50 split as the voltage across each input will effectively be the same even if different current flow through each due to the voltage drop across the interconnects being insignificant.

OTOH if the interconnect resistance is not low enough on one or both interconnects such as to cause a significant voltage in the context of the overall network and combined with an insufficienly high input impedance, then it may not be a 50/50 split.

I expect even with a 10M interconnect to the sub and a typical 10K+ if not much higher input impedance on each input, then effectively this would end up with near enough 50/50.

Also while the 6dB loss of the due to half of a balanced output seems significant, likely full scale on the RCA input is at least 6dB lower than that of a balanced input which typically operate at higher differential voltage anyway.

What is unknown is how the output circuits of the DAC are organized in terms of the internal split and drive to the two output types along with their output impedance (which I would hope is around 100R or less) and that is the specific bit I am deeply suspicious of in this scenario. (I have not looked at any specs of the equipment involved, but I am aware that some DAC designs have taken some really nasty shortcuts with output stage designs in pursuit of better measurements).

I am quite familiar with doing nasty things with balanced connections due to in the past working in studios and running my own studio and some of the hackery inflicted on instruments via patch bays would make the average hifi person utterly cringe - level issues such as described by OP were never a problem despite some of the hideous things we did :)
 
Last edited:
The DAC is the audiolab M-DAC, the guy who designed it says that:

"Using Balanced and unbalanced outputs at the same time is not a great idea as this unbalances the balanced outputs due to the extra loading of the RCA cable on one phase of the balanced output stage."

I wonder if the klark teknik DS50 which has 4 'Thru' outputs would help. The current splitter's Thru goes to powered speakers via XLR, then XLR to RCA cables go to a sub and also to an amp which drives TV sound system, the gain on the sub is high and the volume on the M-DAC when watching TV is also high. They're workable as not at maximum, I just think the DS50 or perhaps an active XLR splitter could be better and give more head room.
 
A transformer-based XLR - XLR splitter will retain balanced connectivity, but of course halve the voltage. An XLR to RCA cable (as per your first post) will not be balanced, and will likely halve the level too.
 

The latest video from AVForums

Is 4K Blu-ray Worth It?
Subscribe to our YouTube channel
Back
Top Bottom