Jump to content

Is "Balanced" meaningful when talking about speakers?


pete10uk

Recommended Posts

Moderation: This is split off from this thread which was discussing the appropriate connectors to use with some speakers. However, the original post used the term "balanced" inappropriately, which sparked off a discussion on whether speaker connections were balanced or unbalanced.

 

We've tried to split the two discussions off, but inevitably something will end up in the wrong thread!

 

 

 

Mmm that's a contradiction to my thoughts. I would have said that all speakers are unbalanced as they only have 2 connections. But as I know Paul knows his stuff I've had a think about it and in the traditional sence of balanced i.e. mic cable, I have always assumed that the balanced lable is reffering to 2 signals in opposite phase which is then ballanced out to take away any interference, however I suppose that the fact that you have 2 equal larger cores for + & -, could be what the term ballanced is referring to?

 

I suppose thinking on those lines a speaker cable would be balanced having 2 equal larger cores as oppose to a single core and a screen. That's got me thinking, could anyone clarify?

 

Cheers

Link to comment
Share on other sites

  • Replies 32
  • Created
  • Last Reply

Whether a power amp is 'balanced' or not depends on its topology. Most only drive the positive and hold the negative at 0V, but some amps and all bridged amps drive the negative with opposite polarity, so could be said to be balanced.

 

Speakons, EPs or bare wire for speakers really, anything else is a bad fudge of a job.

Jack plugs also short out during insertion, so can upset amps if plugged up while live.

Link to comment
Share on other sites

I suppose thinking on those lines a speaker cable would be balanced having 2 equal larger cores as oppose to a single core and a screen. That's got me thinking, could anyone clarify?

 

I wouldn't really say the outputs of a power amp are balanced, conceptually it feels more like mains electricity transmission except the voltage is lower and frequency is not constant. If you think about it a voice coil is a special kind of linear electric motor.

 

Something like a buttkicker actually *is* a linear motor and is fed by a 1KW audio power amp.

 

Saying that I once applied myself across the terminals of a 1KW power amp accidentally which I won't be doing again any time soon...

Link to comment
Share on other sites

I think the concept of balanced operation goes back to telegraphy really, with a pair of conductors, and no need for screens and grounding. Nowadays we tend to think of balanced and unbalanced as simply descriptions of common problem solvers. An XLR to XLR cable in most cases is a balanced connection, but if you use one to connect a comms system, then it's unbalanced - because the circuit works differently. Hence why I'd think of a loudspeaker connection as balanced - each conductor being electrically identical. Same as a microphone capsule. Two identical conductors to a floating transducer = balanced (at least to me). Add a screen and it's still balanced. The minute you use the screen and one conductor that are different, electrically, this is when I switch to unbalanced.

 

With amps, even if one leg of the connection is connected to ground, the two wires I'd still describe as a balanced connection.

 

I bet the OP didn't expect this! Welcome to the wonderful world of the Blue Room.

 

I suspect you will find the amp is fine. Are you in Eire? If you are in London, I'd have a look on the Thomann.de web site. The spec on that amp are a little vague - you could find the power output quoted is into a lower impedance speaker than yours, so volume could be a little lower - but nothing wrong with it. You can use the suggested jack to speakon jumper, or a speakon to jack cable. They're just a weaker connector both physically and electrically. Jacks are not totally rubbish - people have been using them for years, it's just that speakons are better!

Link to comment
Share on other sites

I think the concept of balanced operation goes back to telegraphy really, with a pair of conductors, and no need for screens and grounding. Nowadays we tend to think of balanced and unbalanced as simply descriptions of common problem solvers. An XLR to XLR cable in most cases is a balanced connection, but if you use one to connect a comms system, then it's unbalanced - because the circuit works differently. Hence why I'd think of a loudspeaker connection as balanced - each conductor being electrically identical. Same as a microphone capsule. Two identical conductors to a floating transducer = balanced (at least to me). Add a screen and it's still balanced. The minute you use the screen and one conductor that are different, electrically, this is when I switch to unbalanced.

 

With amps, even if one leg of the connection is connected to ground, the two wires I'd still describe as a balanced connection.

 

I bet the OP didn't expect this! Welcome to the wonderful world of the Blue Room.

 

I suspect you will find the amp is fine. Are you in Eire? If you are in London, I'd have a look on the Thomann.de web site. The spec on that amp are a little vague - you could find the power output quoted is into a lower impedance speaker than yours, so volume could be a little lower - but nothing wrong with it. You can use the suggested jack to speakon jumper, or a speakon to jack cable. They're just a weaker connector both physically and electrically. Jacks are not totally rubbish - people have been using them for years, it's just that speakons are better!

 

 

Well. I come from a comms heavy background and I have to argue that "balanced" isn't just using two equal wires, it also implies that neither are referenced to earth (or are equally referenced as in phantom power supply). I'm always suspicious of anything that claims to be "balanced" but doesn't involve a transformer.......

 

Oh yes, back to the plot. Jack connectors for speakers and amps should be avoided. Either fit speakons to your amps and cabs or make up some short speakon to bare ends which you can connect to the terminals and leave on the kit, secured with tiewraps or p clips.

Link to comment
Share on other sites

With amps, even if one leg of the connection is connected to ground, the two wires I'd still describe as a balanced connection.

 

I think J Pearce and Oldradiohand have the right of it. "Balanced" generally refers to impedance to ground. In most power amps one side is connected to ground and the other is not, so unbalanced. An amp in bridged mode however has neither side connected to ground, and the 2 wires driven with equal signals of opposite polarity, so balanced.

 

1/4" jacks and plugs are pretty much the worst of all the connectors that have been used for speaker connections. Even XLRs are better.

 

Mac

Link to comment
Share on other sites

My definition of "balanced" would be a 3 wire system (two signal wires plus an earth)with the two signal cables being 180 degrees out of phase with each other. At the receive end of a balanced circuit, one of the signals has its polarity inverted, causing common mode rejection to eliminate any induced noise the cable has picked up along the way.

 

By this definition, no two wire system could be balanced. However, at the voltages output by a typical amplifier, induced noise is not a problem anyway. As others have noted, speaker wiring is more akin to normal AC and can use similar cables.

 

What I will agree with is that, if there's one connector I'd rather not use for an amp output, it'd be a quarter inch jack.

Link to comment
Share on other sites

My definition of "balanced" would be a 3 wire system (two signal wires plus an earth)with the two signal cables being 180 degrees out of phase with each other. At the receive end of a balanced circuit, one of the signals has its polarity inverted, causing common mode rejection to eliminate any induced noise the cable has picked up along the way.

 

By this definition, no two wire system could be balanced. However, at the voltages output by a typical amplifier, induced noise is not a problem anyway. As others have noted, speaker wiring is more akin to normal AC and can use similar cables.

 

What I will agree with is that, if there's one connector I'd rather not use for an amp output, it'd be a quarter inch jack.

 

I have to disagree. If you are using a dynamic mic and therefore do not need phantom power, there is no need for the screen to be connected at the mic - the +ve and -ve going signal connections, which connect to each end of the output transformer wiring, are all that is required for CMR to work. Similarly at the pre-amp, in incoming signal lines are conencted to the inverting and non-inverting inputs of the pre-amp - it's the voltage difference between these inputs that is then amplified to the required level - there is no need for a ground reference.

 

Another example is the Ethernet physical layer - it uses balanced connections with no third wire.

Link to comment
Share on other sites

My definition of "balanced" would be a 3 wire system (two signal wires plus an earth)with the two signal cables being 180 degrees out of phase with each other. At the receive end of a balanced circuit, one of the signals has its polarity inverted, causing common mode rejection to eliminate any induced noise the cable has picked up along the way.

 

By this definition, no two wire system could be balanced. However, at the voltages output by a typical amplifier, induced noise is not a problem anyway. As others have noted, speaker wiring is more akin to normal AC and can use similar cables.

 

What I will agree with is that, if there's one connector I'd rather not use for an amp output, it'd be a quarter inch jack.

 

There used to be a lot of balanced, unscreened two wire audio circuits around! In fact, there still are.....

I try to explain it as the audio signal being the voltage difference between the two wires, any interference being the same voltage on both. A common mode amp or a transformer will therefore pass the voltage difference but reject the interference. It's probably not helpful to think of the two wires being out of phase (gets confusing when you are using working with stereo). Admittedly, if you put a scope on one wire and look at the voltage on the other you'll see the audio signal, swap the wires over and it will appear to be 180 deg out of phase but it's actually a polarity inversion you're seeing caused by the measuring method.

 

 

Link to comment
Share on other sites

My definition of "balanced" would be a 3 wire system (two signal wires plus an earth)with the two signal cables being 180 degrees out of phase with each other.

 

I'd go along with that.

 

I have to disagree. If you are using a dynamic mic and therefore do not need phantom power, there is no need for the screen to be connected at the mic...

 

That's not balanced - that's 'floating', although you can argue it's balanced if you consider the aether as the third wire.

 

There used to be a lot of balanced, unscreened two wire audio circuits around! In fact, there still are...

 

Not balanced but floating.

 

 

...any interference being the same voltage on both...

 

With respect to what?

Link to comment
Share on other sites

Hello big can of worms... (Mods - perhaps this deserves a new thread?)

 

My understanding of balanced relates purely to the two legs having the same impedance to ground. That's why output schemes that involve only the hot signal being driven whilst the cold / phase / call it what you will is just connected via an appropriate resistor to ground are balanced. It works just as effectively even though there aren't identical and opposite signals on each wire. There's no need for a third wire either - many buildings are wired with simple unshielded twisted pair cable without a problem.

Link to comment
Share on other sites

My definition of "balanced" would be a 3 wire system (two signal wires plus an earth)with the two signal cables being 180 degrees out of phase with each other.

 

I'd go along with that.

 

I have to disagree. If you are using a dynamic mic and therefore do not need phantom power, there is no need for the screen to be connected at the mic...

 

That's not balanced - that's 'floating', although you can argue it's balanced if you consider the aether as the third wire.

 

There used to be a lot of balanced, unscreened two wire audio circuits around! In fact, there still are...

 

Not balanced but floating.

 

 

...any interference being the same voltage on both...

 

With respect to what?

 

"floating" isn't necessarily balanced - it just means unreferenced to earth. A battery powered device is floating but it won't necessarily be balanced. Most of the definitions of "balanced" I've come across involve both circuit balance and equal reference to something, usually earth.

 

Common mode rejection isn't the easiest concept to get across - think of an interference field running across your cable, be it electrostatic or magnetic. A pulse of interference field will induce a current on both wires in the same direction - it's easier to think of currents than voltages here. At a common mode input, such as a transformer, the two interference currents will meet and cancel out if they are the same. You get more equal interference pickup in twisted wires so this is a common form of construction. Wiring the opposite twists of star quad together gives you even more even interference pickup which is why they're used in places with large amounts of interference such as TV studios.

Link to comment
Share on other sites

Yes, you can have a functioning balanced circuit with the earth link cut at one end--this is a common way to eliminate earth hum problems in gear with the dreaded Pin 1 problem. However, without the polarity inversion part of things there can be no common mode rejection therefore, to my mind, it's not a true balanced circuit. For the avoidance of doubt, we're all talking about removing the SIGNAL earth at one end, never the mains earth which is a seriously dangerous practice.

 

It's worth saying though that the original question is, to some extent, the wrong question anyway. Levels coming out of a typical amp are such that a little bit of induced noise will barely be noticeable (if at all). Beyond that, the sort of cable used for speakers (in effect mains cable of a suitble gauge isn't twisted anyway so (even if you could do a balanced circuit) CMR would be fairly ineffective.

Link to comment
Share on other sites

However, without the polarity inversion part of things there can be no common mode rejection

But it does still work as a balanced line without the polarity inversion if the impedances to ground are the same. Think of it in mathematical terms:

 

On the hot line we have: signal + noise

On the cold line we have: Ground (nothing) + noise

 

In the receiving circuitry, the cold is inverted and summed with the hot:

 

(signal + noise) - (nothing + noise) = signal

 

The noise is always common mode so is always rejected. Whether the cold leg carries an inverted signal or no signal at all is irrelevant.

Link to comment
Share on other sites

If the polarity inversion takes place, yes. However, in a simple unbalanced two wire circuit (like the speaker cabling that started the thread but also in things like basic Phono/RCA connections as found on consumer gear, no. These rely on screening (with good cables) or good luck (with most of the ones you buy) and offer no CMR.
Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.


×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.