| hifiZen |
Here's an interesting paper about the effects of PIM (pasive intermodulation) as it pertains to RF applications. Note in particular the distortion levels being discussed (-153dB!) as well as the suggested remedies.
| quote: | | Tests have shown that nickel plate under gold on the center contact will typically result in a 40 to 50 dB increase in PIM. Stainless Steel in the body will usually give a 10-20 dB increase in PIM. |
This paper provides some interesting validation for the claimed subjective differences between various cables and connectors, and at the distortion levels being discussed, suggest a reason why these effects have not been easily observed in many attempts to measure such differences.
Here's the link: http://www.amphenolrf.com/simple/PIM%20Paper.pdf |
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| Jonathan Bright |
| Thanks for the link=interesting. |
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| Steve Eddy |
| quote: | Originally posted by hifiZen
This paper provides some interesting validation for the claimed subjective differences between various cables and connectors, and at the distortion levels being discussed, suggest a reason why these effects have not been easily observed in many attempts to measure such differences. |
Interesting paper.
But I don't see how it validates anything along the line of claimed subjective differences. Seems to me those sorts of calims can really only be validated by demonstrating actual audibility.
se |
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| hifiZen |
Well, perhaps 'validation' was not the right word. 'Correlation' is more along the lines of what I meant.
I am by no means taking sides in this issues. I have always been, and shall remain, skeptical of any subjective claim which doesn't at least have a plausible theory to explain it, or better, some strong scientific evidence. But, I also try to be open minded about such things. This paper is obviously just one small piece of the picture, but I think it provides some interesting food for thought. |
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| TNT |
The frequency band where this is discussed is far from the audiable range. I wonder what it looks like in the 0-100khz region?
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| Steve Eddy |
| quote: | Originally posted by hifiZen
Well, perhaps 'validation' was not the right word. 'Correlation' is more along the lines of what I meant.
I am by no means taking sides in this issues. I have always been, and shall remain, skeptical of any subjective claim which doesn't at least have a plausible theory to explain it, or better, some strong scientific evidence. But, I also try to be open minded about such things. This paper is obviously just one small piece of the picture, but I think it provides some interesting food for thought. |
I keep an open mind as well. Just that the way I see it, until actual audibility is established, all this other stuff is meaningless except perhaps in an academic sense.
People have been spinning theories and speculations for decades. But until audibility is established, you can't really put those theories to the acid test. But then I think that's precisely why some sit around and do nothing but spin theories. :)
se |
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| FLZapped |
First of all, look at the levels being discussed. Also look at the depth of the conducting surface in the frequency range mentioned. A lot of power in very little material. 0.002 mm as compared to 0.5mm at 20kHz. That's a 250:1 disparity. Add to that the fact you must maintain strict impedances within the connectors and you have a compounded problem because you cannot just randomly increase the contact surface area as you can in audio.
Second, the concern here is interference to other services. When you have a 100 watt transmiter(+50dBm) and a co-located recever with -120dBm sensitivity, it isn't hard to figure out that a -150dBc spurious signal is at -100dBm absolute level, or 20dBm above the base sensitivity of the receiver! The receiver becomes nearly useless if that spurous signal falls in its channel bandwidth except for very strong signals. Not too likely with cellphones transmitting only a couple hundred milliwatts. (+20dBm for 100mw) (Provided they even radiate all their power, which they don't by a long shot)
This is a real and defined problem, especially in multi-channel trunked sites and multi-channel cell sites that have their signals all combined onto a single antenna. Any non-linearity outside the isolation system and you have the potential for a serious nearly unresolvable interference problem. All non-linearities we are concerned with in audio are inband, unlike rf.
Sorry, but there is no corellation to the audibility question with regards to audio systems.
-Bruce |
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| john curl |
| I think that this input on PIM is important. I learn from it, but then I design hi end audio equipment for a living, so I don't easily dismiss distortion generation from any potential source. It is attention to details, such as whether you use a cheap audio connector that is made of magnetic materials and / or has nickel plating just under the gold plating. We have evaluated components at this level, for many years. In fact, we can change the sound of an audio component by just changing the connectors. Can't measure much however. Probably, it is because of limitations in our test methods and equipment. |
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| janneman |
It is indeed an interesting paper. To put it in perspective, I note the following:
The problem of PIM in passive components is increased by the 50 Ohm impedance levels in the RF bands discussed. If those impedance levels would be much higher, the impedance variation effects that lay at the root of the problem would me much less also, decreasing greatly the PIM. That would mean for audio that the problem could be present in the power amp/loudspeaker interface, but not in signal level interfaces.
If I understand the paper correctly, the problem is also acerbated by mismatch caused by the contact variations, which causes termination reflections and extra PIM. In audio, this will not happen as the cabling length is always very much less than the signal wavelength so impedance matching is a non-issue. For the same reason the skin-depth in audio is much greater than in cell phone equipment, which seems to imply that microscopic contact variations have less overall impact than at rf with very low skindepth.
The levels discussed (some -150dB below the signal) are at least a factor 100 to 1000 below the levels of known distortion mechanisms in contemporary audio technology. It seems therefor extremely unlikely that this is a problem in audio. Nevertheless, it is another lesson that contact quality and reliability is important. We should all clean and re-seat our connectors at least a few times per year, especially in dusty and/or industrial areas and/or smoking venues.
Jan Didden |
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| dimitri |
some thoughts
http://www.angelfire.com/ab3/mjramp/golopid/wire.html
Here you can find measured nonlinear characteristic I-V for a coaxial switch
www.estec.esa.nl/conferences/03C26/papers/a022.pdf
Some simple design rules from http://www.astrolab.com/13.asp
Use of semi-rigid cable with a seamless outer conductor in place of flexible cable.
Use of a solid center conductor in place of a stranded center conductor.
Directly attach the outer conductor to the connector body by soldering or clamping in lieu of crimping.
Limit the number of parts in the current path.
Eliminate contaminants in the current path.
Use high quality machining in the connector parts with a smooth surface finish.
Avoid contaminants in the plating solutions.
Ensure adequate and uniform plating thickness.
Avoid use of magnetic materials in the current-carrying-path.
Ensure adequate contact pressure.
Contact surface of female contact fingers should cover as close to 360° as possible (i.e. narrow slots or slotless).
Use connector interfaces with radial dimensions as large as possible |
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| FLZapped |
| quote: | Originally posted by dimitri
some thoughts
Some simple design rules from http://www.astrolab.com/13.asp
Use of semi-rigid cable with a seamless outer conductor in place of flexible cable.
Use of a solid center conductor in place of a stranded center conductor.
Directly attach the outer conductor to the connector body by soldering or clamping in lieu of crimping.
Limit the number of parts in the current path.
Eliminate contaminants in the current path.
Use high quality machining in the connector parts with a smooth surface finish.
Avoid contaminants in the plating solutions.
Ensure adequate and uniform plating thickness.
Avoid use of magnetic materials in the current-carrying-path.
Ensure adequate contact pressure.
Contact surface of female contact fingers should cover as close to 360° as possible (i.e. narrow slots or slotless).
Use connector interfaces with radial dimensions as large as possible |
These are recommendations for microwave frequencies. You'll note that this company manufactures other assemblies that have braided shields and crimped connections.
At audio, some of these are a non-factor: such as solid, seamless shields. Others are just common sense.
-Bruce |
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| dimitri |
Yes, Bruce, they are just common sense.
The only thing, that seamless shield is more preferable - see Henry Ott book
http://www.hottconsultants.com/
solid center conductor – this can be much more esoteric, but I preferred solid conductors instead of multiple-strand |
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| john curl |
| I hate to see this thread 'die' because of lack of interest in what can be very useful to improve audio design. Yes, THESE numbers are low in value, but they seem to accumulate with added contributions, and become easily audible in real systems. |
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| RHosch |
Yes, I suppose if you have a few hundred thousands of such connections in your audio system, their summed contribution might be worth worrying about.
:xeye: |
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| john curl |
| Unfortunately, it is a lot less than that. Listen for yourself, if you have a quality hi end audio system. |
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| fdegrove |
Hi,
| quote: | | THESE numbers are low in value, but they seem to accumulate with added contributions, and become easily audible in real systems. |
Absolutely.
The gold over nickel plating is one good example where you probably won't notice the presence of a single such connector.
However it becomes annoyingly obvious when you use those throughout a system: a harsh kind of peak in the lower highs that makes you wonder what the heck is wrong with the system.
About a year ago when one of our members was organizing a groupbuy of RCA connectors, I did advise against choosing an otherwise well reputed brand for the exact same reason as is being discussed here....
After talking to the manufacturer and several other people in the audio manufacturing business several years ago already my and no doubt many other peoples' pointing to the goldplating process as the cullprit was confirmed and they consequently redesigned the whole thing.
This is just a good example of how compounding small errors of the same nature can yield an audible result of what would normally be considered way outside the audible range, hence a non sequitur for any audio application.
Similar in behaviour is the use of a component with a typical colouration (how do you measure that one anyway?) that seems innocent when used on it's own but will greatly define a systems "colour" when it's being used throughout.
Nothing's ever perfect but repeating the same shortcomings throughout a system is like repeating (cascading it if you like) a circuit topology over and over; it's failings will become more and more obvious to the discerning listener.
When it comes to advancing the state of the art in audio it is of paramount importance to find out exactly what pitfalls to avoid, regardless of whether these are readily measurable or not...
You can only hope that one somehow someone out there will develop a fine enough device that's capable of measuring what it is we're hearing.
Cheers,;) |
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| RHosch |
| quote: | Originally posted by john curl
Unfortunately, it is a lot less than that. Listen for yourself, if you have a quality hi end audio system. |
I have. Not only did I not hear any differences, but neither has anyone else I know ever been able to do so, despite their claims of being able to hear all sorts of inhumanly minute things, such as the direction of an interconnect or the type of insulation on a speaker cable. Of course, perhaps their inability to see what they were listening to had something to do with that?
| quote: | Originally posted by fdegrove
When it comes to advancing the state of the art in audio it is of paramount importance to find out exactly what pitfalls to avoid, regardless of whether these are readily measurable or not... |
Why don't we first worry about things which are actually audible, and only then determine whether they are readily measurable or not?
| quote: | | You can only hope that one somehow someone out there will develop a fine enough device that's capable of measuring what it is we're hearing. |
Impossible, as what you hear is only partially (and in some cases not even strongly) determined by the sound waves hitting your ear drum. Thus, if what you hear is determined in some part by things that happen only inside your head and have absolutely no relationship to the signal being reproduced, there is no labarotory instrument that will ever be able to detect them. |
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| fdegrove |
Hi,
| quote: | | Why don't we first worry about things which are actually audible, and only then determine whether they are readily measurable or not? |
If it were not audible then there's nothing to worry about anyway....
Except perhaps for those people that won't trust their own ears and need absolute proof rendered by some measuring device.
Unfortunately that approach is too time consuming which is why some of us leave it as is and move on.
| quote: | | Thus, if what you hear is determined in some part by things that happen only inside your head and have absolutely no relationship to the signal being reproduced, there is no labarotory instrument that will ever be able to detect them. |
That wasn't the point in the first place. See above.
Cheers,;) |
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| RHosch |
| quote: | Originally posted by fdegrove
If it were not audible then there's nothing to worry about anyway.... |
Except in the case of certain manufacturers/designers/salesmen/forum members/etc. claiming that their designs/products/theories/whatever are valuable and/or "better" than someone else's designs/products/theories/whatever. If I'm trying to decide if a particular cable is worth the thousand dollars being asked for it, then whether or not the explanations offered for said cable's claimed audible superiority refer to things that are actually audible is certainly something for us to worry about.
| quote: | | Except perhaps for those people that won't trust their own ears and need absolute proof rendered by some measuring device. |
Human ears are perfectly suited for detecting the supposed audibility of some change, if used properly.
| quote: | | That wasn't the point in the first place. See above. |
And I'm afraid you missed my point entirely. How did you and John come to the conclusion that the effect of connecting plating becomes audible thousands of times sooner than the measurements would indicate? Precisely.
If, however, you are someone who wishes to spend money in all cases where a minutely measurable effect can be found, and indeed even in cases where an effect may only be postulated (hopefully on some sound principle), for the cause of preventing any possible chance that such effects will ever become audible, regardless of whether the level of the effect is remotely near human detection limits or not, then that is your perogative and I support you in your pursuit. Some people have more money than others, different hobbies and pleasures than other, or more spare time than others. I don't wish to discourage you from doing what you enjoy. |
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| analog_sa |
| quote: | | something for us to worry about |
At least you don't have to worry much. Apparently any mid-fi system will many times exceed the resolution of your hearing. Now, that's what i call lucky! |
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| fdegrove |
Hi,
| quote: | | And I'm afraid you missed my point entirely. |
It's become obvious that I did...
Your point being that you fail to understand the justification for the steep asking price for some of the toys out there.
That's however totally irrelevant to the discussion here which is merely about some people's claim that goldplated connectors can sound unpleasant presumably due to the way the plating process is done.
An issue that potentially can bring down prices on some fancy cable even though I doubt very much it will.
That's simply human nature and the laws of economics I'm afraid.
To cheer you and other people up this is DIYaudio where some of us are creative enough to find ways to outperform with our own homebrewn cables a good deal of the offerings on the market.
I even recall someone going through the trouble of making their own RCA connectors (not that you have to stick with RCAs) out of silver....
| quote: | | How did you and John come to the conclusion that the effect of connecting plating becomes audible thousands of times sooner than the measurements would indicate? |
While I can't speak on behalf of John I'm pretty certain it's not just us having noticed this phenomenon.
The fact that a company actually did some measurements came after I arrived to this conclusion and I'm certain to be not the only one either.
The way you detect this is mere experience in my case.
With a little effort and practice most people are capable of hearing differences between various small details in a system.
In fact I notice time and again that even people claiming no experience whatsoever and lousy hearing beforehand often do distinguish small differences perfectly well most of the time, much to their own surprise.
At the end of the day all that matters is how much you enjoy your system. Not how much it costs.
Cheers, ;) |
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| RHosch |
| quote: | Originally posted by fdegrove
Your point being that you fail to understand the justification for the steep asking price for some of the toys out there. |
I'm afraid you completely missed my point once again. There is no question as to the reason for the steep price of many "toys" on the market - simple supply and demand (which isn't always a simplistic relationship, but none-the-less even bizarre cases can be adequately explained by basic economic principles). I've never challenged the right of a company to price a product however they please... I might comment "are you serious?" but for the most part am perfectly happy with people spending their money as they see fit.
I do have a problem with companies using fraudulent and deceptive advertising (more than the simply overzealous and misleading advertising used by practically all companies). I also have a problem with a certain phenomenon being claimed as audible when all evidence suggests otherwise.
As I said previously, however, you enjoyment is what matters and the means through which you achieve that is no concern of mine. If it means "fooling yourself" into better sound, so be it. I'll leave you to it, and continue to focus on the companies who peddle products that are bordering on pixie dust. |
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| fdegrove |
Hi,
| quote: | | I'm afraid you completely missed my point once again. |
I'm also afraid you're barking up the wrong tree...
| quote: | | I do have a problem with companies using fraudulent and deceptive advertising (more than the simply overzealous and misleading advertising used by practically all companies). |
Well I can't think of anyone who actually enjoys being deceived but let's face it : 95% or more of all publicity IS deceptive.
That can come pretty close to fraudulent in some cases but as long as the law isn't broken what do you expect your fellow forum members to do about it other than not buy the stuff we don't actually believe in ????
If you can put the product to the test at your own convenience and you find the claims made about it don't justify the asking price or are simply false, well don't buy it. It's as simple as that.
If you don't notice the distortion of gold over nickel plated connectors then that's fine by me too.
I don't hear it on every single such connector either and you'd need a system with high resolving power to notice it anyway...
Really, I don't see why you need to complain about this simple fact of life on a DIY audio forum of all places...
| quote: | | I'll leave you to it, and continue to focus on the companies who peddle products that are bordering on pixie dust. |
You appear to be assuming quite a lot...
To the best of my knowledge no one has even mentioned a single company in this entire thread.
Guess one of us is missing the point again and it ain't me.:angel:
Cheers,;) |
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