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-   -   Understanding Unbalanced vs Balanced audio signals, and the difference (https://www.hometheatershack.com/forums/av-home-theater/25984-understanding-unbalanced-vs-balanced-audio-signals-difference.html)

tonyvdb 02-18-10 01:27 PM

Understanding Unbalanced vs Balanced audio signals, and the difference
 

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.
http://www.hometheatershack.com/gall...php?n=3551&w=l

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
http://t1.gstatic.com/images?q=tbn:I...5401859285.jpg or an XLR connector http://t1.gstatic.com/images?q=tbn:C.../11/25/xlr.jpg
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.
http://www.hometheatershack.com/gall...php?n=3550&w=l

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
http://i27.photobucket.com/albums/c1...e/P1000024.jpg

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.

tcarcio 02-18-10 02:52 PM

Re: Unbalanced vs Balanced audio signals, and the difference
 

Great info Tony....:T

gperkins_1973 02-18-10 03:04 PM

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

RBTO 02-18-10 05:29 PM

Re: Understanding Unbalanced vs Balanced audio signals, and the difference
 

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.

tonyvdb 02-18-10 06:45 PM

Re: Understanding Unbalanced vs Balanced audio signals, and the difference
 

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.

recruit 02-19-10 01:07 AM

Re: Understanding Unbalanced vs Balanced audio signals, and the difference
 

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

glaufman 02-19-10 09:03 AM

Re: Understanding Unbalanced vs Balanced audio signals, and the difference
 

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?

tonyvdb 02-19-10 09:16 AM

Re: Understanding Unbalanced vs Balanced audio signals, and the difference
 

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.

glaufman 02-19-10 09:59 AM

Re: Understanding Unbalanced vs Balanced audio signals, and the difference
 

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?

tonyvdb 02-19-10 10:10 AM

Re: Understanding Unbalanced vs Balanced audio signals, and the difference
 

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.


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