Forces always combine linearly. At least, they do in my universe - most of the others in this thread live here in the same universe too. Life must be more complex in your universe, if nonlinearity can spontaneously emerge from linearity when just two forces are involved.45 said:
This is just another miserable tentive...
That sentence was referred to a combiantion of two linear terms which is not what really takes place!!
Again. As there is another non-linear term (with voltage drive) that need to be taken into account, once this is considered than the linear combination can take place. Should write this in chinese?
Perhaps you should post a hypothesis, you know an attempt at an actual speaker/crossover/amplifier system with real components to talk around. You seem very concerned that conventional engineering has nothing to contribute at all to this problem. The propeller heads and their Fourier transforms don't know squat about real music.
You keep saying that nonlinearity can appear from linear forces, then keep saying that this is not what you mean. It would still be wrong if written in Chinese, because apart from the definition of watts they live in the same universe as the rest of us.45 said:
Let's drop this fruitless discussion and get back to negative feedback and its usefulness.
Usefulness?🙁
With more than 12 dB NFB the soundfield collapses and the birds stop singing....🙄
No I keep saying that with current drive the non-linearity can be negleted because is small if certain driver design criteria are met! It is quite different.
I am not concerned dear scott. I keep playing hide ans seek because of some individuals I don't like. Individuals that actually want to teach people without having built anything.
And of course it is conventional engineering it's just that there are different design chioces.
I read this paper a few years ago when I was wanting primarily to reduce the gain of my old Maplin Mosfet amp, the one that is basically the Hitachi application note from the '80's.
I was fascinated by his notion of "stratospheric" NFB. At first I merely increased the feedback a little, expecting dire repercussions, but nothing terrible happened. So I just kept going.... all the way...to 100% negative feedback, at one point I even removed the DC blocking capacitor. It sounded wonderful.
Why was I able to get away with this? Bruno says that the only problem with massive amounts of NFB is how to implement it. Was it possible just because the amplifier is such a simple design?
I was fascinated by his notion of "stratospheric" NFB. At first I merely increased the feedback a little, expecting dire repercussions, but nothing terrible happened. So I just kept going.... all the way...to 100% negative feedback, at one point I even removed the DC blocking capacitor. It sounded wonderful.
Why was I able to get away with this? Bruno says that the only problem with massive amounts of NFB is how to implement it. Was it possible just because the amplifier is such a simple design?
The current, using voltage drive, is unfortunately distorted so even if had a driver with a fairly linear behaviour in terms of suspensions that non linear term cannot be generally neglected. You can see this in the impulse response as inversions appearing along the impulse. If you control the current, the varying voltage applied to it doesn't cause any trouble and in fact the impulse response is cleaner (and faster).
I have not designed any driver but I can tell you that a woofer with low compliance will not work. A woofer where the cone suspension is stiffer than the spider will not work. Foam or similar materials are best for cone suspension and compliance has to be as constant as possible in the range of use.
I don't know him personally but we once met in a thread. Actually, I entered the discussion because he was under (unfair, IMHO) attack! Guess what was the discussion about?😀
"Starting out life as an immensely useful number for counting and dividing things, the number 12 became a number revered by mathematicians and early astronomers. So the skies were divided into 12 portions as were the months of year, reflecting the annual movement of heavenly bodies. Superstitions and religious beliefs were piled on top of respect for the number 12 and was adopted by multiple early civilisations. The sky, divided into 12, has each portion ruled by a personification, a god, a divine being, a teacher, a prophet or a son of the sun. Odin of Norse mythology sat on a chair that overlooked all of creation, and had 12 sons1. The Babylonians had the longest lasting influence upon our calendars, timekeeping, mathematics and religions; all of which emphasize the number 122,3. The Babylonians' most ancient myths defined zodiacs where each portion was ruled by a different god (some good, some evil)4. Pseudoscientific enterprises such as astrology have the number 12 at its core. The ancient Zoroastrians had twelve commanders on the side of light (light being a symbol for the sun)5, and in Judaism and the Hebrew Scripture there are many references to the 12 tribes of Israel, and later on the Greeks imagined 12 Gods on mount Olympus. Mithraists, and then Christians believed that their saviour had 12 disciples. Shi'a Muslims list 12 ruling Imams following Muhammad. Such holy persons are depicted with a bright solar light around their heads such as occurs when any object approaches from the sun and now stands infront of it. Although many ancient religions such as the Gnostics understood things like the twelve disciples of Mithras to be symbolic of the stages of the waning and waxing sun throughout the year, later religions took it literally and believed in an actual 12 disciples - and some still do.
Now we understand what stars, planets and stellar objects are, it makes no sense to retain the mystical, nonsensical connotations of the 'holy', 'perfect', 'divine' or 'special' number 12. If the number is employed in a practical sense to divide time, measurements, or angles, then the chances are it makes awesome mathematical sense to utilize such a factorable number as the number twelve. But if you see it used in a superstitious, religious, magical, paranormal, holy or weird way, then watch out, because you have entered the world of flat-earth delusion. It is, after all, only a number."
The Divine Number 12: 12 Gods, 12 Disciples, 12 Tribes and the Zodiac
Now we understand what stars, planets and stellar objects are, it makes no sense to retain the mystical, nonsensical connotations of the 'holy', 'perfect', 'divine' or 'special' number 12. If the number is employed in a practical sense to divide time, measurements, or angles, then the chances are it makes awesome mathematical sense to utilize such a factorable number as the number twelve. But if you see it used in a superstitious, religious, magical, paranormal, holy or weird way, then watch out, because you have entered the world of flat-earth delusion. It is, after all, only a number."
The Divine Number 12: 12 Gods, 12 Disciples, 12 Tribes and the Zodiac
There's always one deviant in a crowd...and you are "on-topic"! What were you thinking?
Bruno designs, or was designing(?), switching amps for Hypex. His problem was the switching frequency of a few hundred kHz did not allow enough NFB loop gain at 20kHz using a single pole roll-off. As you know, normally, the open loop bandwidth of a linear amp is well above 1MHz, so some 10x higher. And presumably, the switching amps needs a lot of distortion fixing...although I don't know what the OL distortion is compared to a competent linear amp. Maybe someone will tell us. So to get higher loop gain at 20kHz and below, he stacked a load of poles and zeros in the forward gain path to give a Butterworth filter sort of steep roll-off. This is mathematically similar to the roll-off of nested feedback loops as explained by Cherry in the 80s.
Bruno's paper draws a comparison between stacked (or cascaded) poles and zeros and nested differential feedback loops. He uses linear models to derive the equations of both and shows they are very similar. He then draws the sweeping conclusion that there will be no difference in practice. Err...no. Feedback systems do not work like maths equations when the system contains non-linearities and many other practical characteristics not captured by the simple maths.
It is an interesting comparison, though, and something to ponder. We know that in many practical, linear circuits, adding heaps of NFB can make them sound just awful. I made a Maplin clone once...2SJ48/2SK133 were they? Those were the days...paper clips across the pins. The simplicity of the maplin amp will definitely have helped it to not get totally screwed by increasing the feedback. Do you know how much loop gain you achieved?
I am curious to know what effect a Bruno'esque cascade of semi-integrators (I heard he may have used 5 in his amp) has on the music. A wild phase ride not to mention all the extra circuitry to implement it, although he could have done it digitally in theory; but I don't think his amps use DSP as far as I know.
Who knows? 🙂
Last edited:
Perhaps you meant to say "Feedback systems do not work like maths equations when the system contains significant non-linearities and many other practical characteristics not captured by the simple maths."traderbam said:
Do we know that? Or do people assume that, as the alternative explanation is unpalatable to them?
Anyway, you can't have it both ways: criticising Bruno for applying NFB to a non-linear circuit then complainng that NFB also ruins a linear circuit.
- Status
- Not open for further replies.