Cons of using main XLR/Balanced outs for subwoofer?

I run my two subs out of the single-ended (rca) outputs from my buffer, and feed my main amps from the balanced outputs. To the subs, I run longer rca cables into Jensen PI-RX transformers and then very short XLR cables from the transformers to the subs. Looking at the Jensen graphs and spec sheets, it appears the SUB-RX transformers would have been a slightly more optimum solution to use with the subs....but not by much, and not by enough to worry about. I actually purchased the PI-RX transformers for a different situation involving a single-ended tubed preamp into SS mono amplifiers that had only balanced (XLR) inputs. You do need to be careful with impedances in those full-range situations since having too high an output impedance into the transformers can roll off the high frequencies.

Within very generous tolerances, humans are insensitive to phase shifts. He also points out that in a normal room sound is reflected many times from objects at multiple distances resulting in enormous amounts of phase shifts that dwarf the far smaller phase shifts in amplifiers (a lot of this read like Duke's take on this)

This is entirely correct; you can't sense phase at all if you're talking about a single frequency like a sine wave.


But leaving sound stage information aside (which might be messed with due to reflections) phase shift over a spectrum is perceived as a **coloration**, for example a rolloff above the audio band can be heard as a darkness in the highs if the rolloff is close enough to the audio band. In the bass its a similar phenomena, if rolling off prematurely (above 2Hz) even though your speakers are flat to 20 Hz it will be perceived as a lack of impact.


Because speakers are mechanical devices, a rolloff in them does not cause this problem.


I first became aware of how profoundly this was true a long time ago when trying to find out why an MFA Magus preamp sounded bright in the phono section. A dealer of mine wanted to sell the preamp instead of a competitor's but the brightness made it as bad as poor digitial of the day. I investigated the circuit and found that at 50KHz the circuit went from the RIAA equalization curve to flat. I removed the components responsible and the brightness was eliminated, with no sense of darkness- LPs sounded just fine after that. Now you'd think that at 50KHz there wouldn't be an issue, but phase shift can extend down to about 10th the frequency where this was happening (5KHz) so its easy to see how this was heard as a brightness. This principle is easy to demonstrate. 


I can put this another way: there is a **reason** that Jensen feels they needed to go so low (1Hz) with their subwoofer transformers. Jensen transformers are extremely well designed, are high quality, and the designer is held in high regard in home and professional audio. Anecdotally, I've tried using regular full range audio transformers made by Jensen for subwoofers and while they work OK, you can easily hear that something isn't right about the bottom octave- which is fixed using the Jensen subwoofer transformer. Preventing phase shift is is also why Stuart Hegeman of Harmon Kardon Citation fame insisted on wide bandwidth in his designs.


Since you already have the transformers I would go ahead and use them. But I would also get the subwoofer transformers and then audition them side by side- see what you think.

Apologies for not asking clear questions or understanding your brief answers, which prompted me to learn what a phase shift in a transformer means. I found a Floyd Toole article (Audibility of Phase Distortion) which reports studies showing that "Within very generous tolerances, humans are insensitive to phase shifts. He also points out that in a normal room sound is reflected many times from objects at multiple distances resulting in enormous amounts of phase shifts that dwarf the far smaller phase shifts in amplifiers (a lot of this read like Duke's take on this). Rowland tells me transformer bandwidth in this very low bass is not important for their solid state amp's line outputs. I did read that a possible exception to this is in valve amps that use a high level of negative feedback, which may be relevant to your fine Atma-sphere products. I thank you for spurring me to learn more. Decided to use my older Jensen 2 ch transformer.

Duke always says the ear is very forgiving of small timing errors in the low frequencies such that the speakers + room = a minimum phase system. So I am unclear how a phase shift in the low (< 20Hz) bass is consequential. OTOH he also notes that the ear has exaggerated sensitivity to frequency response errors (non-flat curve below 20Hz) in the bass region, so maybe that is what you are trying to tell me.

Duke is right; phase shift is different from delay, and 'yes' in that order :)

I am now way beyond my knowledge base and hearing the voice of common sense confusion- which could be just confusion, nothing more. You indicate that transformer roll-off will cause phase-shift up to about 100Hz and this is important to avoid. The frequency response of the Rowland's outputs is 5Hz-70kHz -3dB @ 8 ohms, so seems appropriate to output into the Jensen transformer (the SUB-1RR) with flatter F-R response. But immediately downstream from that transformer could be either a Dayton SA1000 amp which doesn't appear to have flat rating below 18 Hz ( its specs are hard for me to understand) or the first sub in a DBA chain (unlikely to have flat rating to less than 20 Hz for my system). Furthermore, setting up a "swarm" DBA usually involves intentionally producing a mix of different arrival times from the subs by adjusting position, phase, polarity, closing ports, etc. Duke always says the ear is very forgiving of small timing errors in the low frequencies such that the speakers + room = a minimum phase system. So I am unclear how a phase shift in the low (< 20Hz) bass is consequential. OTOH he also notes that the ear has exaggerated sensitivity to frequency response errors (non-flat curve below 20Hz) in the bass region, so maybe that is what you are trying to tell me. FWIW, Rowland recommended the 2 channel Jensen transformer for running subs off the balanced outputs in my Concerto (but that was 14 years ago). I again want to say I will be running my Salk mains (+/-3dB at 33 Hz) full range, no high pass crossover. I appreciate your efforts to understand my options.

@milarep Yes to both questions.
The 1Hz response will insure that you have no phase shift at all at 20Hz or even 16Hz. Phase shift in the bass will cause a lack of impact. The transformer rolling off at 10Hz will exhibit phase shift up to about 100Hz.

2 followup questions to your helpful response. The straight Rowland to Revel connection would be balanced. Are you thinking the balanced to single-ended interface inside the Revel might not provide ground isolation like the transformer so hum could show up downstream in the daisy chain? Second, any significance to fact my Jensen PC-2XR is rated flat to 10Hz vs the flat to 1Hz of the SUB-1RR?
Thanks 

I'd use the Jensen transformers if I were you.
The problem you can run into is that of ground loops when interfacing single-ended and balanced equipment. The transformers sort that out by providing ground isolation. They won't rob you of any impact as they go down to nearly 1 Hz.

Plan to use my Rowland Concerto integrated amp to drive my Salk Song3 mains full range and preamp output to a chain of 4 active subs in a Distributed Bass Array. Would like to do the Audiokinesis Swarm eventually but right now have to use existing subs from home theater system. The Rowland is fully balanced from inputs to outputs, with  2 sets of balanced XLR outputs, no unbalanced outputs. First option: balanced output A to a Jensen Transformer Iso-Max PC-2XR (2 Ch XLR in/RCA out), then RCA into L/R inputs of sub #1, then daisy chain to rest of subs somehow using either dual or mono RCA connections. Option 2: Rowland balanced out to balanced inputs of a Revel Performa3 B110 sub, then begin daisy chain using mono RCA output.  Already have the Revel sub and Jensen Transformer model, rather not have to buy the Jensen SUB-1RR unless that is truly better. The Revel sub also has mono XLR out but looks like XLR inputs are only found on hi-end/cost subs or pro gear, so likely just sticking to low cost good DBA subs with RCA inputs like the SVS-1000 Pro (already have a pair). Option 1 could use the summing circuit within any sub like the SB-1000 Pro to start the chain. Option 2 uses the Revel (maybe better circuitry?) and means I don't have to use the Jensen with its extra cost and cabling. Would really appreciate input on these options or others from Ralph @atmasphere and anyone else on XLR/RCA issues with multiple subs. Thanks

Question/clarification...since the ISO-Max transformer has a single ended input and a single ended output, are you using something like this Neutrik adapter to go from preamp balanced out to transformer rca input?

No.

The Jensen ISO-MAX can be supplied how you need it- for example with a balanced input (that is how mine are set up) and a single-ended output. That is specified when you order it.

@atmasphere

Ralph said "So if you have a balanced output on the preamp and a single-ended input for the sub, the ISO-MAX Jensen box is the elegant solution". 

Question/clarification...since the ISO-Max transformer has a single ended input and a single ended output, are you using something like this Neutrik adapter to go from preamp balanced out to transformer rca input?

Neutrik NA2FPMM 3 Pin XLR Female to RCA Plug Adapter (parts-express.com)

@rauliruegas
"If you can connect a decent amplifier maybe coming from one of your friends instead the Dayton and se what happens.¨
The think with the Dayton is that it is also a sub x over preamp, but i will check out if its possible to bypass it amp section (1000 w class AB) and yes borrow another Bryston or something good to try. Yes 5 subs , two Vandersteen 2wq with their highpass filters at 80 hz and 3 passive B&W,s that are moved by the dayton 1000 sub amp. The mains are the Gradient Revolution, and yes very easy load for them with the help of the subs.
Yes , i will contact Bryston and see what they have to say.
Saludos Raul!

Thanks Ralph @atmasphere , so it seems like there is a good chance for improvement since you said before ¨If the RCA outputs are in parallel with the balanced outputs on your preamp then what you describe makes sense. If it were me I'd be using the Jensen ISO MAX¨
   I will check it out, Thanks a lot!

@cardani  : 5 subs, so your Vandersteen and your main amp are really happy hadling the mid/high frequency ranges, good.

If you can connect a decent amplifier maybe coming from one of your friends instead the Dayton and se what happens.

Bryston know perfectly its products and I insist that contact them directly along that other amp tests..

R.

two of these op-amps are to buffer the signal to the tape output and level control, the remaining four for the two balanced outputs. These integrated circuits are specified as delivering high output with low noise. "
Could we deduct something from these facts?

@c

Yes. The tape outs and volume control have nothing to do with this. From the statement I would also deduce that the RCAs are in parallel with the balanced outputs, so if you load both even though the preamp is perfectly capable of driving the load, you will probably notice an artifact and more noise could easily be it.

Thanks @atmasphere and @rauliruegas for the advice. It in not that I get hum, is just that with the dayton sub amp I get minimal white noise at around 120 hz and what i think is a higher noise floor. My bryston preamp only has one balanced and one rca outs, and i use the balanced ones first a Vandersteen m5hp high pass filters which cut at 80 hz and then to my bryston amp , susequently a cable that goes from the amp outputs to to the  two Vandersteen 2wq subs. The unbalanced output of the preamp goes directly to the Dayton sub amp and then to three 10 inch B&W passive subs.  So yes , a total of five subs.
Ralph, I will try the advice you gave to @rlb61 as i think we have a very similar case. I just want to make sure that by adding the use of the unbalanced  pre outputs to Dayton i am not degrading the signal in any way as pointed above ¨Unless the preamp has entirely separate circuitry driving the RCA and XLR outputs, when driving both you will have a lower impedance load on one of the XLR signal pins (pin 2 or 3) than you do on the other. The preamp may make less voltage on the pin that has the lower impedance load, but at any rate the total impedance to ground will be lower on that side even if the output voltage is unaffected.
This will in turn reduce the Common Mode Rejection Ratio (CMRR) that is available to the main amplifier, which will raise the noise floor and possibly also the distortion¨. ´on the other hand @rauliruegas picked up some info from Bryston ¨two of these op-amps are to buffer the signal to the tape output and level control, the remaining four for the two balanced outputs. These integrated circuits are specified as delivering high output with low noise. "
Could we deduct something from these facts? Thanks in advance for your help.

Dear @rlb61  : You own very good two-way speakers with a " little " trouble and this is that crossover at 2khz so the woofer runs frequencies from around 35hz to over 2khz and no matters what that facts says that the IMD and THD distortion levels are higher than desired to listen MUSIC.

I know that you are not really happy with your JL sub:

"""   I’ve concluded that a subwoofer is not necessary in every application where a 2 way speaker is used  .. """

by the contrary the conclusion is the other way around: with a two way speaker design subs always are need it.

I know too that your room is not to big but this does not avoid the sub use or integration.

The first premise to add subwoofer to any system is that must be a pair of self powered subwoofers and never only one unit, this is not the way to go. You need a pair of subs and if you follow the information in the link I posted you will be way satisfied with.

Now, adding a pair of subs running in stereo way is not plug and play we need time and patience and if you have it then you will have success.

Your Pulsar will shines as never before and you will have all the frequency ranges at the higher quality level performance you can imagine: really good an accurated bass range handled by dedicated woofers and dedicated amplifiers and the same in the mid/high ranges where your main amps will performs better than ever when are not running low frequencies that diminish its overall quality performance and headroom, now you will have pristine and addictive Pulsar MUSIC sound reproduction. Remember, you need two subs.

As I said in other post: is up to you.

R.

Will that configuration really make a big difference?

@rlb61 Did you notice a difference in the mains between not having the sub hooked up and all, and having it connected but its volume turned all the way down? If there is no difference then your RCA output is buffered from the balanced out and the ISO MAX isn't needed. If there is a difference then this is the solution.

@atmasphere Ralph ... I have two main outs - one is balanced and one is single ended. The balanced goes to my power amp directly. The single ended goes to the sub directly. If I used the ISO-MAX, then it would appear I'd just go from the single ended output into the ISO-MAX and then go single ended into the sub. Will that configuration really make a big difference? Thanks.

Dear @zdw11 @cardani  :  I can see that both of you are running your main speakers/subs to listen MUSIC ( at least do not posted for HT. ).

Now in the Ohm speakers the sub is part of the speaker ( I don't know forsure all the subs controls to operation. ).

If we want to listen in specific MUSIC through our room/system and want to add subwoofers the rigth way to do it is that those pair of true self powered subwoofers crossover ( should be. ) around 80hz-90hz but this crossover frequency is not only for the low-pass subs but we need and should be that the main speakers been too crossing around that frequency with the high-pass filter and in this waythat room/system will takes a true advantages to add subs to listen MUSIC because in that way the main speakers will be handling frequencies from 80-90hz and up and the IMD and THD distortion levels that existed in those passive speakers goes really lower in benefit of higher sound reproduction quality level and at the same time that room/system will handled with accuracy the low bass range and even can goes lower in that range.

Due that I don't know of the overall Ohm speaker operation then I could be wrong with but with the other gentleman that's the rigth way to integrates subwoofers to MUSIC soun reproduction as our main system use.

Here a link about:

https://forum.audiogon.com/discussions/do-you-think-you-need-a-subwoofer/post?postid=310058#310058


Of course that one thing is what " should be " and the other what we like/want so in this specific subject everything is up to you and this post is only an opinion and nothing more.

R.

You would run dual balanced outputs, one set to your main power amp. The other set would go to the ISO MAX units (left and right channels). Only at that point would you use RCA connections, between the ISO MAX units and your sub. So the ISO MAX units would be right by your sub so you could run a longer balanced line connection from the preamp to the ISO MAX. If you don't have dual outputs on the preamp, you would use some form of a Y adapter to make it happen. 

@atmasphere Ralph, please explain the hookup with the ISO-MAX. I’m running the balanced main output from my preamp into the power amp. I’m running simultaneously the single ended main output into my sub. So, if I used the ISO-MAX for the sub, how would that be hooked up if you don’t recommend using the single ended output at all? Thanks.

Dear @cardani : " Two of these op-amps are to buffer the signal to the tape output and level control, the remaining four for the two balanced outputs. These integrated circuits are specified as delivering high output with low noise. "

that comes from the design in your Bryston. So the problem could comes from that Dayton unit.

Now you said: " higher noise floor ". Could you detected around wich frequency of that " noise floor " ?

In my system I run my two subs from the balanced preamp outputs and the main amplifiers running with the unbalanced outputs and both performs with no single trouble/noise or the like but with very high quality level performance.

Even that your Bryston is not a today model it’s and has very good design as everything Bryston puts in the market, seems to me that noise floor level is not developed by a " failure " in the unit design because outputs are buffered.

If that noise floor is really high then that ISO MAX can helps. In the other side you can always contact directly to Bryston asking for advise in that issue.
:  https://bryston.com/#contact-form

R.

@cardani  If the RCA outputs are in parallel with the balanced outputs on your preamp then what you describe makes sense. If it were me I'd be using the Jensen ISO MAX subwoofer transformers to do the conversion and not use the RCA outputs of the preamp at all.

Dear @zdw11 :  as @imhififan  posted go a head no problem at all and you don't need to make any added mods.

Btw, did you try it? if not then do it and you will be the best judge about. Don't worry you can't damage nothing with that set up.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.

@atmasphere Hi Ralph , i have the same question as mitch2 , in my case my preamp is Bryston Bp25 and take balanced output to the amp and the single ended to a Dayton 1000 subwofer amp (for a Swarm sub configuration).  I,ve noticed that I get a higher noise floor when I turn on the sub amp. I understand my Bryston pre is not true balanced.  Do you think the jensen transformer will help in my case? Thanks in advance

How about the case where the balanced out provides the signal for the main amplifiers and the single-ended out provides the signal to a pair of subwoofers?  Both of these signals come out of a buffered, unity gain preamp.

@zdw11 @imhififan  has it right. Nice setup!

Is there any harm in using the main XLR output to send signal to the subwoofers, and using the 1, or 2 RCA output to send signal to the main drivers?

Go for it, McIntosh C220 has separate buffer on each output.

@atmasphere is this true even using different outputs? Main(XLR) vs zone 1(RCA) vs zone 2 (RCA).

I will not be using the Main Balanced AND Main unbalanced outputs.
Instead, using Main Balanced out and a separate zone1/2 RCA out.

Not sure if this was well described in my post.
I appreciate your help.

@zdw11  Unless the preamp has entirely separate circuitry driving the RCA and XLR outputs, when driving both you will have a lower impedance load on one of the XLR signal pins (pin 2 or 3) than you do on the other. The preamp may make less voltage on the pin that has the lower impedance load, but at any rate the total impedance to ground will be lower on that side even if the output voltage is unaffected.

This will in turn reduce the Common Mode Rejection Ratio (CMRR) that is available to the main amplifier, which will raise the noise floor and possibly also the distortion. 

You won't hurt anything. But I think you'll find it simply sounds better using the ISO-MAX devices- that is exactly what they are for.

FWIW we were the first anywhere to make a balanced preamp for home use. One of the problems we encountered early on was subwoofers with single-ended inputs. Because our gear supports the balanced standard a.k.a. AES48, if someone tried to connect the subs in the manner you describe a buzz and humm would result. Balanced and single-ended operations are mutually incompatible; its either one or the other and never both. So if you have a balanced output on the preamp and a single-ended input for the subs, that ISO-MAX Jensen box is the elegant solution. They only started making them in the last 20 years or so.

Yes. You'll unbalance the signal going to your main amps.

@atmasphere Can you explain why using the unbalanced RCA out for power amp and Balanced out for each subwoofer will cause a problem?

I also have the option of just using the RCA main and RCA 1,2 outs for each the drivers and the subs.
I thought it would be marginally advantageous to use the Balanced out for the subs since the run is >10ft.

Is there any harm in using the main XLR output to send signal to the subwoofers, and using the 1, or 2 RCA output to send signal to the main drivers?

Yes. You'll unbalance the signal going to your main amps.

The solution is to use a set of specialized subwoofer transformers made by Jensen, which are optimized for subwoofer operation (and so go down to 1Hz to prevent phase shift or any hint of a low frequency rolloff). They can be used to convert from balanced to single-ended. I use a set in my system for this purpose- MP-1 preamp has dual balanced outputs so one set goes to the main amplifier and the other set to the Jensen ISO-MAX boxes. From there I run a very short set of RCA connections that are only about a foot long to the subwoofer amplifier. Link below:


https://www.jensen-transformers.com/product/sub-1rr/