Home Theater Forum and Systems banner

1 - 20 of 30 Posts

·
Premium Member
Joined
·
15,054 Posts
Discussion Starter #1 (Edited)
Its been discussed many times in different posts and it seems there is some confusion on the subject.

This post will help make this much clearer and hopefully with the input of others clear up the does and don'ts of proper connection to pro audio gear.
I do not want to make this sound confusing so I will spell this out in plain English without all the mumbo-jumbo.

Home consumer audio gear uses unbalanced analog audio connections that is designed for short distances and low cost. These connections are usually "rca" and have a shield and a single positive for the signal.
In the graph below you will see the signal (a sine wave in this case) and the shield connected to ground which means it has no signal on it.


A line level audio signal can be looked at as a low voltage signal and unbalanced audio signals are usually between 200mv and 1volt depending on weather it is a fixed or adjustable level.
Given this "lower" voltage signal, long distant runs are susceptible to interference and thus is only good for short runs of usually less than 20ft (50ft can be done if the cable is of better quality).

The problem with using home audio gear with professional audio gear is that the pro gear uses balanced input and output signals. Amps in particular either use a 1/4" Tip Ring Sleeve (TRS) connector
or an XLR connector

The audio signal used in these connectors is at a higher voltage ussually 1.5v and as seen in the graph below has twice the signal as an unbalanced signal.


There are two alternating signals -1.5v & +1.5v and the shield. The advantage of this connection is that when used for long distances the noise (interference) is not only canceled out by the alternating voltages but because its a higher signal voltage it can travel much longer distances without interference (as far as 1000ft) without a booster. The primary factor that allows longer connections with balanced lines has more to do with impedance than voltage. A balanced line has a low impedance (200 to 600 Ohms) while an unbalanced line typically has a 10k impedance or so.

Now here is the problem, when we try to use pro audio gear with balanced inputs connecting to the home audio equipment with unbalanced outputs you usually get incompatibility problems. These problems consisting of noise (usually 60Hz hum) or the signal coming into the pro gear being to low causing the noise floor to be raised when you boost the signal too much making the background hiss or hum to be amplified to the point that it becomes unusable sometimes referred to as signal to noise ratio.
On some amps or other pro gear you may have the ability to "short" the two connectors on the 1/4" TRS to make it a TS unbalanced input. The misconception of this option is that the voltage signal is also boosted but this is not normally the case and is still lower than what a balanced signal should have meaning that the amp at MAX on the level controls will not output the full amount of power it can. If your running this configuration and your amp levels are at MAX to achieve the levels you want I suspect that you have this problem as pro amps should not need to be run more than 75% of its max level control.

The fix to this issue is to use a line balancing transformer like the Samson S-Convert costing around $50


This properly takes the unbalanced signal and converts it to a balanced signal and raises the voltage. Adapters can be bought or made to go from XLR to 1/4" TRS as well as seen on the S-Convert there is only XLR outputs.

There are also several companies that make consumer grade high quality external amps that have proper unbalanced inputs so looking at that rout if your planning on getting an external amp can be a good option. The big plus to using some of the pro gear is that the price seems to be much lower per watts and can be found for under $300 new for two channel amps offering well over 200watts X2 like the Berhinger EP lineup.


Please feel free to comment in this thread and add more info.
 

·
Premium Member
Joined
·
3,374 Posts
Re: Unbalanced vs Balanced audio signals, and the difference

Great info Tony....:T
 

·
Registered
Joined
·
3,068 Posts
Re: Unbalanced vs Balanced audio signals, and the difference

Tony

Great info and should make an interesting thread. Be good to get other people's opinions on this too.

cheers

Graham
 

·
Registered
Joined
·
452 Posts
Good explanation Tony.
The primary factor that allows longer connections with balanced lines has more to do with impedance than voltage. A balanced line has a low impedance (200 to 600 Ohms) while an unbalanced line typically has a 10k impedance or so.

To make an analogy, connecting a 110 volt light bulb (low impedance load) across a 110 volt line (low impedance source) will not make the voltage drop much at all. It will stay pretty close to what it was before the light bulb terminated it. On the other hand, connect that light bulb across a 1.5 volt battery cell (high impedance) and the cell voltage will fall significantly. Most induced noise in balanced lines is of of high impedance in nature, and is "loaded down" by the low impedance at the termination, whereas the original signal voltage comes from a low impedance source and is not loaded much at all. This isn't the only factor involved in balanced systems leading to reduced noise. Since most noise is what called "common mode", having the same polarity on both lines, a balanced receiver (transformer, amplifier, or the like) rejects this and only looks at differences as you mentioned in your explanation. The desired signal is a difference signal (two opposite polarities) and gets passed on.

The shield serves to limit the amount of noise getting to the signal conductors to begin with and helps that much more.

Glad you jumped into this topic. It's really important for folks who work with audio to understand.
 

·
Premium Member
Joined
·
15,054 Posts
Discussion Starter #5
Thanks Bob for the added information :T I will add that info to the above post.
This topic seems to generate allot of confusion and I'm hoping to help clear some of it up.
 

·
Banned
Joined
·
4,015 Posts
Excellent post Tony and it is a subject that I have always thought about but never really looked into it, but I do have a basic understanding of it :T
 

·
Registered
Joined
·
2,604 Posts
Hi Tony, great writeup... one thing I've been confused on... you mention the advantage of balanced for longer runs... does this apply to the low freqs associated with a sub cable? For instnace, if someone has a powered sub at the back of a room when the AVR is in the front, call it a 25ft cable run, is it important to go to a balanced cable (assuming both the avr and sub have XLR connections)... and what would be the audible deficiencies using an (unbalanced) RCA line in this case, simply low/no output, or would distortion products be evident?
 

·
Premium Member
Joined
·
15,054 Posts
Discussion Starter #8
Greg, if you are using a sub with balanced inputs and your AVR has balanced outputs then it is advisable to use them however 25' is not a long run if your rca unbalanced cable is of good quality (assuming the sub has an rca input) and as long as you dont hear any interference at the sub then dont worry about it.
 

·
Registered
Joined
·
2,604 Posts
Thanks Tony... so balanced always preferable to unbalanced?
As for interference, you mean as if the cable were picking up extraneous signals such as radio stations, cell phones, etc? Or simply distortion?
 

·
Premium Member
Joined
·
15,054 Posts
Discussion Starter #10
You should not get distortion but hum or radio interference is a possibility. Balanced is the better way if you have it but for a signal like a sub unbalanced will work just fine.
 

·
Registered
Joined
·
44 Posts
So if you use a pro amp like the QSC GX5 which has rca input jacks it would be ok.
What if you use a Behringer DCX2496 with XLR's to the QSC GX5? Home reciever-DCX2496-GX5 would that work or should the Samson be between the reciever an dthe DCX2496?

Thanks
Bop
 

·
Premium Member
Joined
·
15,054 Posts
Discussion Starter #12
So if you use a pro amp like the QSC GX5 which has rca input jacks it would be ok.
Yes that is just fine.
What if you use a Behringer DCX2496 with XLR's to the QSC GX5? Home reciever-DCX2496-GX5 would that work or should the Samson be between the reciever an dthe DCX2496?

Thanks
Bop
If the DCX only has XLR or TRS inputs you must use the S_Convert and then use the balanced outputs of the DCX to the balanced inputs on the QSC.
 

·
Registered
Joined
·
44 Posts
Ok thats what I thought.
Thank you very much that is exactly what I was looking for coming to this part of the forum.

This is the best HT forum on the net!

Bop :clap:
 

·
Registered
Joined
·
58 Posts
Hi tony,

I have an Arcam AV888 which has balanced output's and my Front amps are Bryston which has balanced input's my front three cable runs are 7 metres long, i asked the question to Arcam as to what cable to use XLR or RCA they said RCA would be better as the XLR board is not true Balanced and the RCA boards have a shorter internal signal path.

So would it be better for me to go with RCA ?

thankyou for any help.
 

·
Premium Member
Joined
·
15,054 Posts
Discussion Starter #15
I would be inclined to believe what Arcam has said to you as I am sure they know what they are talking about. In the end I highly doubt that you or I would be able to hear an audible difference between using either balanced or unbalanced signal path. Given you have the choice why not just try it and see if you can hear a difference. The key thing is the distance you are running the cables 7mtrs is quite long and I suspect going balanced would be a safer bet. If your Bryston amps dont have true unbalanced inputs then as I said above you should use the balanced inputs and outputs.
 

·
Registered
Joined
·
58 Posts
Well they are Balanced at the moment and i would need to solder on the RCA connectors, but buy what you say and what sound i have in my room at the mo i don't want to effect it so as they say here in the UK "If it aint broke don't fix it" :D

Thanks for your input Tony
 

·
Registered
Joined
·
123 Posts
Good post and no doubt helpful to everyone.

The XLR (professional) system is primarily concerned with noise and distance of transmission. It is quite common to have microphone / instrument signal runs of more than 100 feet.

The XLR is significantly better at dealing with noise for many reasons. Noise is simply anything that isn't part of the original signal. It can come from a myriad of sources. 60 cycle hum is not so much a noise issue usually. It is typically a grounding problem.

One of the factors is the higher voltage. Consumer output is usually 1 volt peak to peak. (From high point on curve to low point on curve) Pro equipment is 3 volts peak to peak. A critical factor in noise issues is signal to noise ratio. In this example if there is 50 millivolts of noise on the lines the signal to noise ratio is much better on the 3 volt system. It will be 3 times better meaning that you will not hear the noise as much because relative to the signal it will be smaller.

The two line balanced system, as explained by others, works to cancel noise due to the opposite waves. These cables also have very good shielding which is a metal wrapper or wire around the outside that carries a ground.

Impedance is also important as mentioned. Impedance matching is important in certain scenarios but a rule of thumb that usually works is that you want the input of a device (not speakers) to have a high impedance. This is like connecting a garden hose to sprinkler. If the sprinkler has small holes (high impedance) then it will spray strong and far and maintain pressure in the hose. A bunch of big holes will result in no spray and the hose will have little pressure. So you want your signal to have good pressure in the hose and little holes in the sprinkler.

Regarding a run to a subwoofer, typically it is a short run, the normal av cables are shielded, and the noise you might pick up is all filtered out by the built in crossover of a sub. The only way I would use XLR is if I had to connect XLR equipment together.
 

·
Super Moderator
Joined
·
9,190 Posts

Great article, don’t know how I missed it when it was first posted. Especially love the great pictures!

I’ll add just a couple of things. One, longer unbalanced cable runs should not be an issue if good-quality cables are used. For unbalanced connections of any length, the shield is what makes or breaks noise rejection properties, so it must be substantial and robust. A good cable should have a robust shield; otherwise it does not qualify as a good cable, IMO. In most cases, if adding a long cable introduces noise that wasn’t there before, I’d say the problem is the cable.

Second, while it might be necessary when using a pro amp with an AVR, there is no immediate need for the Samson S-convert when using a pro-audio processor like the Behringer DCX in the signal chain. The processor will work fine with an unbalanced input. Some people will float the home vs. pro gear “level matching” argument, but you have to keep in mind that in most cases the home equipment is going to have a quieter noise floor than the pro equipment. Artificially boost up an AVR’s output signal with a device like the S-Convert, and you’ll raise its noise floor to a higher level than that of the pro processor long before anything resembling a "proper level match" has been accomplished. Not good.

Regards,
Wayne
 

·
Registered
Joined
·
123 Posts
Wayne makes some good points. I have never seen nor had a problem in mixing consumer devices with pro devices in a home setting. Maybe the word "unbalanced" scares people but it is just an electrical description for the system. It means nothing in terms of performance.

The mantra "If it ain't broke don't fix it." applies here as well. Hook it all up and if it sound good then great.
 
1 - 20 of 30 Posts
Top