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balanced is inherently flawed

A recent post asking for opinions on balanced vs. single ended got me thinking once again about the inherent flaws in a balanced scheme.

A balanced signal has 2 parts called plus (+) and minus (-) that are equal in voltage but opposite in polarity. Therefore a balanced amp is really 2 single ended amps in one package, one for the + singal and the other for the - signal. So a balanced amp using the same quality parts as a single ended amp will be twice as expensive. Strike one.

That brings us to the "equal but opposite" notion. In order for this to work as planned, all of the + stages and cables connecting them must be exactly equal to all of the - stages all the way through the source, preamp, and power amp. Any deviation from the + stage being the exact mirror image of the - stage will result in an imbalance. Since perfect symmetry cannot be achieved, especially with tubes, distortions are introduced. Strike two.

Some think that balanced has to be better for various reasons that include:

1. If they hook up a balanced device using single ended cables they loose some gain.
2. They think a balanced system can achieve a lower noise floor.
3. They have balanced equipment and it sounds better when they hook it up with balanced cables vs. single ended cables.
4. It's used in recording studios by the pros so it must be better.

These arguments are flawed for the following reasons:

1. More gain does not equal better sound. Of course you need enough gain to drive your speakers to satisfactory levels, but the fact that one connection has higher gain than another has really nothing to do with sound quality.

2. This is the most misunderstood of all. A balanced amp CAN reject noise that is coming in through the interconnects. However, it can do nothing to reject or cancel the random electrical noise that comes from within the devices inside the amp. A balanced amp has no advantage over a single ended one when it comes to the major contributor of noise in the system, that which is generated inside the amp. The rejection of noise from cables relies on the fact that it is generally equal to both the + and - inputs and is therefore cancelled, but since the noise voltages generated by the devices inside the + and - stages in the amp are random and unrelated, they do not cancel and are passed on to the next stage.

Furthermore, since well designed, shielded interconnects of any type are very good at rejecting electrical noise from the outside, balanced has no advantage except in very noisy enviroments or when using very long runs, both of which apply to recording studios, not to typical home systems.

3. Since a truly balanced amp was built from the ground up to operate in a balanced mode, it makes sense that it will sound worse when fed a single ended signal. That doesn't mean that balanced is better, just that that particular amp sounds better when fed a balanced signal.

If you subscribe to the theory that more money can get you better performance, and since a single ended amp has 1/2 as many components as an equivalent balanced amp, it stands to reason that if the designer put as much money and effort into designing a single ended amp, it would sound better.

4. See 2 above.

And this brings us to our last point. ALL sound sources are single ended. Whether from a plucked string, blowing air through a horn, the human voice, or anything else; the resulting increses and decreases in air pressure that we perceive as sound are single ended. There is no "equal but opposite" waves of pressure. This is also true when the signal finally gets to a loudspeaker. There are no "equal but opposite" pressure waves coming from the speaker. It is a single ended device.

In a balanced system these pressure variations are picked up by a microphone and then some where along the line converted to balanced. A phonograph record is encoded single ended as is a digital disc. Your CD player may have a balanced output but the data that is read from the disc is single ended and then converted. In order not to introduce ditortions, this conversion from single ended to balanced has to be done perfectly. And since it can't be, strike three.
herman
inpepinnovations1e75
395 posts
 
Sean, it is a common myth that sound is air "moving" balanced or not. Sound is produced by a vibrating object causing the air pressure in its immediate vicinity to vary according to the frequency and amplitude of the vibrating object. This air pressure variation is propagated as a wave of varying pressure - the air does not move - that would be wind!

To use your cymbals as an example, it is not the movement of the cymbal up and down that causes the sound - a single unstruck cymbal moving does not make a sound - but the vibration of the metal cymbal as it is struck that causes the air pressure to vary as described before. In fact, if we move the 2 cymbals towards each other but stop their movement before they touch, we will move a lot of air but there won't be any sound.

The ear responds to varying pressure, not air flow or movement, after all if the air is moving, where is it going in the ear?
sean
6,229 posts
 
Bob: I understand that sound doesn't move air, the air simply "transports" the energy of the sounds created. Most people don't understand that, so i tried to word it in a way that was easier to follow. It is good that you mentioned this though, because my "simple analogy" could be considered "misinformation" if one were to take it word for word. Thanks for the clarification.

"To use your cymbals as an example, it is not the movement of the cymbal up and down that causes the sound - a single unstruck cymbal moving does not make a sound:

This is incorrect. Anything moving is creating sound because that movement imparts energy into the air. Whether or not that energy / sound is of high enough amplitude or at a frequency that we can hear is another matter.

" but the vibration of the metal cymbal as it is struck that causes the air pressure to vary as described before"

This supports my comments above. The only variance between the unstruck yet moving cymbal and the cymbal that was struck is the intensity of the movement generated and the frequency of excitation. Add the resonant and transient ( rise and fall ) characteristics of the cymbal to this movement and you have a specific sonic trait.

"In fact, if we move the 2 cymbals towards each other but stop their movement before they touch, we will move a lot of air but there won't be any sound."

False. There is sound, but it may not be of high enough amplitude or high enough in frequency for us to easily hear. If you doubt this, take a large yet solid lightweight item and move it back and forth in the air making long and slow excursions. You might not hear anything even though air is moving. Moving the item back and forth at a faster rate ( like "fanning" yourself ) will produce sound that is more audible and centered at a higher frequency. Same thing is taking place in both examples, the only variances are amplitude and frequency.

"The ear responds to varying pressure, not air flow or movement, after all if the air is moving, where is it going in the ear?"

Herman and i discussed this somewhat privately via email. Neither of us will argue this point. Sean
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psychicanimal
1,738 posts
 
Ralph Atmasphere, so my friend Dejan Veselinovic does have a point: under most circumstances single ended system with ground filtration will sound better. Doing a properly balanced setup takes some real $$$.
sean
6,229 posts
 
Filtering of the ground can be beneficial if properly implimented, but it also increases the potential for reduced safety. By placing filter circuitry in the path to ground, you limit current capacity. In the event of component failure or an electrical problem ( severe surge or spike ), the filter circuitry could become damaged, opening the safety path to ground. Obviously, this is not good and i don't think that you'll ever see any design using such an approach obtaining UL approval. That's because something like this could literally be a matter of life or death. No manufacturer with any brains wants to risk something like this.

Having said that, providing the shortest, lowest series resistance path to ground that you can is the next best thing that you can do short of creating the above mentioned safety hazard. As i've mentioned in other posts, having someone that knows what they are doing clean and weatherproof your ground connections can sometimes make a world of difference. Most ground connections that i've seen from the AC mains to Earth were severely corroded, offering very poor conductivity. If conductivity to ground is reduced, any noise / RFI that was shunted to ground elsewhere in the house can now find its' way into your audio system. As such, maintaining your ground connection would not only be safer, it could reduce grain and glare while lowering your noise floor.

By the way, wasn't Dejan the guy that was shilling some specific PLC's that he was associated with over at Audio Circle? Sean
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inpepinnovations1e75
395 posts
 
Sean, of course you are correct in saying that there is sound present when moving an unstruck cymbal and that we just don't hear it.

I am heartened to see that you realise the danger of using analogies. The problem with using "incorrect" analogies is that the model used might then be applied to many other phenomena and even less comprhension ensues.

I am in the training of technical subjects business and I have seen the pitfalls of using incorrect or misleading analogies. A good analogy, however, is an extremely powerful training tool.

Salut, Bob P.
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