Ok audio nuts, see what you make of this!

[Kevin P]

I read this somewhere. Post your thoughts. I'll tell you later where I found it.

Eleventh Law of Acoustics:

In a minimum-phase system there is an inextricable link between frequency response, phase response and transient response, as they are all merely transforms of one another. This combined with minimalization of open-loop errors in output amplifiers and correct compensation for non-linear passive crossover network loading can lead to a significant decrease in system resolution lost. However, of course, this all means jack when you listen to Pink Floyd.




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[David Meek]

Well duh - EVERYONE knows this! :roll:


The most important part of that whole pronouncement is:

"of course, this all means jack when you listen to Pink Floyd."

A seminal truth if there ever was one. :B




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[JonMarsh]

Only time for a few quick comments....

We don't know nearly enough about how the ear and brain combination work, or understand what things they're really sensitive too, and what are truly less important.


Let's take one simple example.

I've designed and built true transient perfect loudspeakers, capable of excellent pulse reproduction (on axis), and my personal conclusion and finding was that the compromises and side effects of doing this with dynamic drivers didn't necessarily result in the expected improvements compared with non time correct systems.


In point of fact, the ear is sensitive to a great many things, and excessive group delay between some ranges of frequencies can present clearly audible problems- but avoiding this doesn't require transient perfect loudspeakers- especially when 1st order multiway crossovers produce problems with room power response when tuned correctly for flat axial and time impulse response.

Other factors are also very important-

uniformity of off axis frequency response, especially from 200 Hz through 12 kHz, up to 45 to 60 degrees off axis;

absence of driver cone mode resonsnaces which smear the inner detail in midrange or high freqency ranges

Low Q in HP driver response, and low distortion to expected peak levels

Very low levels of cabinet "talk"- i.e., large wall area's dont' have to vibrate hardle at all to have significant acoustic output.

This is what makes for the difference in philosophy between different designers, in that the place different weightings on the importance of various factors.

Then too, their are nutballs like Charles Hansen, Neil Sinclair, John Curl, the folks at BAT, APN Hawk Audio, and even myself, who staunchly believe that the best sound will only be obtained in a system without conventional global negative feedback loops. Believe me, if you do everything necessary to make an amp measure and work decently with no feedback loop, the sound is pretty dang awesome. Why? Don't know for sure, but after 30 years, I know that's what works.


Best regards,

Jon




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[Kevin P]

Ok, now for the moment you've all been waiting for.

I got that quote from the "fortune" program on my Linux computer. Like most of the quips that this program spits out, it is essentially meaningless. I thought it would spark some interesting discussion.

KJP




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[Lex]

What are the first 10 laws? I think I better learn those first.

Nice post John.

Lex

[dsmith]

Kevin, thanks for confirming my initial assessment - I was afraid I was losing my reading skills (my job involves proofing contracts).

Audiofreaks (not you Jon, of course) can sometimes sound like philosophers debating how many angels can dance on the head of a pin. But when you keep in mind that most of what you hear from your system at any given time is the room's response, it makes you wonder whether those angels really matter so very much. Don't get me wrong, I value accuracy, and my speakers are among the most accurate you can buy. But I wish I had a dollar for every time some audiophool claimed he heard a "huge" difference when he switched power cables, or put his solid state gear on a vibration isolator, or "de-magnitized" his CDs.


dsmith

[Digital Bob]

John,

Oh man! Just this morning I posted a topic on the now dieing DT Forum about why I belived it has withered to it's current state. In it I made reference to some of the truly brilliant people in the industry not having all the answers or "math" to explain every last thing they heard. And saying that if it can't be measured or put in a formula then it's "bunk" is just what DT did for a very long time.

I have been in the industry for a while and have met some amazing people. And I have little tolerance for those that claim to know "the" answer, or are certain that some other answer/approach can't possibly work ever.

So then I come over here and read this post from you where you readily admit to not fully understanding why something occurs but that it does anyway. And THAT folks is why I visit here and not DT Forum.

Keep up the good work,




dB

[JonMarsh]

Thank you Bob.

(P.S., funny thing, you're from where I was born!)

We always want to understand as much as possible about what works and why it works, - this makes it possible to make better products and eventually for less money, too. But then there are often times when there is no substitute for careful experimentation and refinement and just plain old listening.

ThomasW and I have tried out an awful lot of different things over the years, and we tend to value hands on experience and evaluation just as much or more than a so called theoretical explanation. (a hard won perspective for an EE like me) The latter can drift all too easily into marketing hype. Since we're not selling anything, at least we don't have that axe to grind!

So thanks for your vote of confidence and your participation at HTGuide- we'll do our best not to let you down! :LOL:

Best regards,

Jon




Earth First!
_______________________________
We'll screw up the other planets later....

[Victor]

Jon posted,

Then too, their are nutballs like Charles Hansen, Neil Sinclair, John Curl, the folks at BAT, APN Hawk Audio, and even myself, who staunchly believe that the best sound will only be obtained in a system without conventional global negative feedback loops. Believe me, if you do everything necessary to make an amp measure and work decently with no feedback loop, the sound is pretty dang awesome. Why? Don't know for sure, but after 30 years, I know that's what works.

I would have to raise the lonely voice and disagree, with Jon. I do not think that feedback is all that bad. In fact I would go as far as to say that a linear system in an audio sence cannot exist without feedback. I have yet to see a truly ‘feedbackless’ design that works. Well, I think I must define what ‘works’ for me. In a nutshell, - the THD+N down to at least 16 bits is all I ask for.

I know that there are amplifiers (power or line level kind) out there that claim not to have any feedback or very little of it. Little feedback is all that is necessary to produce a successful design and so I shall not discuss it here. However, ‘no feedback’ design approach will be very hard-pressed to produce THD numbers better then 14 bits. The notable exception is the ‘buffer’ type circuits that have no gain. They are useful as line drivers but nothing else.

Another possible approach is a ’current conveyer’. Strictly speaking it has no feedback, however it is very difficult to get it to work and consequently there is only one such IC on the market that I am aware off. Building this topology with discrete devices is possible but will not produce desired results as the device matching will have to have ‘stratospheric’ precision.

Now, let’s come back to design that I have seen that claim to have ‘no global feedback’ Global is the operative word here. This statement gives a perception that there is no feedback at all. This is not so. There is feedback, just it is not global. Here is what is commonly done; - the amplifier circuit is naturally broken into 2 parts. The first part contains gain and it indeed employs a feedback. The 2-nd part is an output driver with no gain and it has no feedback. Hence the design can be seen as lucking Global Feedback. However, as we all see this is really not the case, as the feedback is used where it is needed, - around the gain stage.

The examples of such approach are many, the famous Pass A75 comes to mind as well as many BAT designs and there are others. The penalty paid in this approach is the inferior THD performance by at least an order of magnitude or worst comparing to the same amplifier with global feedback.

So, my position is that there is no way to design a low-noise, high precision amplifier without the feedback. In many ways the feedback is an ‘icing on the cake’. The 'cake' or the amplifier in question must be linear to begin with, before any feedback is applied. So it is entirely doable to design an open loop system with a THD at just below 1%. Applying ‘very little’ feedback would make this system to show a THD of 0.01% without any problems.

Kevin posted,

In a minimum-phase system there is an inextricable link between frequency response, phase response and transient response, as they are all merely transforms of one another. This combined with minimalization of open-loop errors in output amplifiers and correct compensation for non-linear passive crossover network loading can lead to a significant decrease in system resolution lost. However, of course, this all means jack when you listen to Pink Floyd.

I agree about Pink Floyd, - a day does not go by without listening to at least parts of ‘The Wall. In fact my recent and monstrous speaker project is all about being ‘…one with the band, while pushing it to 11…’ Oh well…

I think that higher order crossovers, i.e. not minimum phase in a conventional sense, receive a rather bad rap and undeservedly so. Jon is correct when he says that we have no idea how our hearing really works and so achieving perfect transient response is not all that important. Jon says and I agree,

I've designed and built true transient perfect loudspeakers, capable of excellent pulse reproduction (on axis), and my personal conclusion and finding was that the compromises and side effects of doing this with dynamic drivers didn't necessarily result in the expected improvements compared with non time correct systems.

I think as long as you can control the signal settling you should have great sound. This can be done with higher order system particularly if active crossovers are used. I also think that a compromise that first order system offer is not that great, since they are not nearly steep enough for the most driver implementations. So, in my view when it comes to the minimum phase system the cure (perfect transient) is worst then the disease (driver interaction).

Victor