Not the speakers themselves are the concern here, Joshua, rather the side-effects of RF leaking into the amp via the normally unshielded speaker wires -- especially when the amp is a typical global NFB design. Output inductors don't help much unless they are split into two parts, one per each single wire.
http://www.diyaudio.com/forums/showthread.php?postid=1419373#post1419373
- Klaus
http://www.diyaudio.com/forums/showthread.php?postid=1419373#post1419373
- Klaus
Joshua_G said:
It doesn't directly, but the speakers and cables are an easy way for RF pickup to be directed back into the amplifier.
It's called IIM distortion, also studied and written about by Matti Otala, (and me) about 32 years ago.
PMA said:
... except that RF ingress via the speaker cables is not interface intermodulation in this context.
See
http://www.aes.org/e-lib/browse.cfm?elib=2817
and
http://www.aes.org/e-lib/browse.cfm?elib=11887
... and I guess John refers to this:
http://www.aes.org/e-lib/browse.cfm?elib=3765
The AES lists only one conference paper with John Curl as co-author here:
http://www.aes.org/e-lib/browse.cfm?elib=2229 which is not related to IIM.
Jan Didden
dimitri said:
This is the same article as the 2229; one is the conference paper, the other is the JAES article. 😉
I think there are some more articles on TIM and IIM with John as (co) author, possibly IEEE? John?
Jan Didden
Omitted factors in audio circuit design
Curl, J.
Acoustics, Speech, and Signal Processing, IEEE International Conference on ICASSP '78.
Publication Date: Apr 1978
Volume: 3, page(s): 263- 266
Curl, J.
Acoustics, Speech, and Signal Processing, IEEE International Conference on ICASSP '78.
Publication Date: Apr 1978
Volume: 3, page(s): 263- 266
I have no access to IEEE papers.
Edit: What are the omitted factors? Can you quote the abstract?
(I did find out recently that I can become a member of the local university library that will give me that access. It's on my to-do list😉
Jan Didden
Edit: What are the omitted factors? Can you quote the abstract?
(I did find out recently that I can become a member of the local university library that will give me that access. It's on my to-do list😉
Jan Didden
Jan, I worked twice again with Matti Otala, AFTER my sojourn to Finland in 1976.
I also returned to Finland for a month in Mar 1977, to work with Matti on new projects. I, therefore, became aware of what was going on and updated on the latest research. I did not stay in Finland any further, even though I was asked to work there, as I had pressing problems in Switzerland and in California.
I had also worked for HK for about 1 year when Matti joined us at HK, in Plainview, NY. I worked on IIM measurements from my California office as well. on a new power amp that Matti wanted to make. I MEASURED IIM potential from one horn loudspeaker actually modulating another and produced Polaroid pictures of the same measurement at HK in 1978 at a formal meeting on the subject, (and others) with Matti Otala present.
Now, I wish that I could just put this sort of thing in 'short form' without having to elaborate, but obviously many here are prone to challenge my credentials, and my taking proper credit on occasion. I will not challenge you, Jan, since I don't really what you have contributed to audio in this way, but it does give me a chance to 'brag' in detail when confronted.
When it comes to 'credits' Matti and I had a 'tiff' about that. He became annoyed when 'Audio' removed his and the Centre's acknowledgment at the end of the original IEEE paper when we modified it slightly for publication in 'Audio' in 1979. At the same time, (you can verify this with Bob Cordell) Bob Cordell's article titles on TIM were modified, and this caused concern with Matti and Walt Jung, and this helped to promote our 'rebuttal to Cordell' in 1980.
Matti responded by reducing any acknowledgment's of me for a time. We did not always get along, you know.
I also returned to Finland for a month in Mar 1977, to work with Matti on new projects. I, therefore, became aware of what was going on and updated on the latest research. I did not stay in Finland any further, even though I was asked to work there, as I had pressing problems in Switzerland and in California.
I had also worked for HK for about 1 year when Matti joined us at HK, in Plainview, NY. I worked on IIM measurements from my California office as well. on a new power amp that Matti wanted to make. I MEASURED IIM potential from one horn loudspeaker actually modulating another and produced Polaroid pictures of the same measurement at HK in 1978 at a formal meeting on the subject, (and others) with Matti Otala present.
Now, I wish that I could just put this sort of thing in 'short form' without having to elaborate, but obviously many here are prone to challenge my credentials, and my taking proper credit on occasion. I will not challenge you, Jan, since I don't really what you have contributed to audio in this way, but it does give me a chance to 'brag' in detail when confronted.
When it comes to 'credits' Matti and I had a 'tiff' about that. He became annoyed when 'Audio' removed his and the Centre's acknowledgment at the end of the original IEEE paper when we modified it slightly for publication in 'Audio' in 1979. At the same time, (you can verify this with Bob Cordell) Bob Cordell's article titles on TIM were modified, and this caused concern with Matti and Walt Jung, and this helped to promote our 'rebuttal to Cordell' in 1980.
Matti responded by reducing any acknowledgment's of me for a time. We did not always get along, you know.
John,
Nobody wants to challenge your credentials (at least not me) but it is difficult to recall what happened 30+ years ago, even if you were there. That is why we (at least I) always ask for papers or at least some back up for statements. Not that papers are infallible, but at least they allow you to follow the reasoning and measurements and form your own opinion in view of contrasting views. Seems to me a sensible thing to do.
And for the record, my 'contributions to audio in this way' are not up to par to yours by a long shot. You know that. But that doesn't mean I should accept any off-the-cuff statement without back-up from any authority.
Jan Didden
Nobody wants to challenge your credentials (at least not me) but it is difficult to recall what happened 30+ years ago, even if you were there. That is why we (at least I) always ask for papers or at least some back up for statements. Not that papers are infallible, but at least they allow you to follow the reasoning and measurements and form your own opinion in view of contrasting views. Seems to me a sensible thing to do.
And for the record, my 'contributions to audio in this way' are not up to par to yours by a long shot. You know that. But that doesn't mean I should accept any off-the-cuff statement without back-up from any authority.
Jan Didden
Personally, what is it to you, Jan, except for an attempt to reduce my credibility on this website?
'J'Accuse' and I am getting tired of it.
I have (fortunately) a very good memory for certain periods of my life, especially when I continually changed countries to do my research. Certainly you can remember details of your life, when you are were a special vacation for example? It is the same for me, as vivid details come back when I think of working on projects in different locations, over the years. I can still see, in my mind's eye, the beautiful 'rear-end' of one of Matti's office associates, that almost got me to work there for a year or so. One word of encouragement from her, might have done it.
'J'Accuse' and I am getting tired of it.
I have (fortunately) a very good memory for certain periods of my life, especially when I continually changed countries to do my research. Certainly you can remember details of your life, when you are were a special vacation for example? It is the same for me, as vivid details come back when I think of working on projects in different locations, over the years. I can still see, in my mind's eye, the beautiful 'rear-end' of one of Matti's office associates, that almost got me to work there for a year or so. One word of encouragement from her, might have done it.
Please send him the darned paper, Dimitri. Or I will forced to.
I don't think it shows anything about IIM, but it is still useful.
I don't think it shows anything about IIM, but it is still useful.
john curl said:
John, I explained several times that I am not out to reduce anybodies credibility. I couldn't care less one way or another. I just try to get the facts straight.
It boils down again to being able to recognize technical arguments and to realize that those are not arguments about persons or personalities, and that responding with ad hominum attacks is self-inflicting loss of credibility.
Example:
Question: "Why do you think that TIM is caused by the phase of the moon?"
Answer: "Well you pitch-fork wielding villager, don't you know I worked with Dr. BlaBla personally?"
Who do you think reduces who's credibility?
Jan Didden
Rather poor response, an apology would be more appropriate. However, my 'off the cuff' remark could be taken wrong, because it was ambiguous. I did not actually say that I specifically wrote anything about IIM, but that could be implied. I meant to imply that I had done some independent research on the subject. That is why I put commas (...) around my self reference.
RF pickup
Getting back to RF entering the amp thru the output, has anyone tried using sheilded speaker cable such as coaxial RF cable? RG-8 comes to mind as one choice. Would a sheilded speaker cable help, or are the voice coils themselves acting as loop antennas?
Getting back to RF entering the amp thru the output, has anyone tried using sheilded speaker cable such as coaxial RF cable? RG-8 comes to mind as one choice. Would a sheilded speaker cable help, or are the voice coils themselves acting as loop antennas?
John's answer is probably a little too curt.
1) The voice coil is actually pretty well shielded inside the magnet structure.
2) The speaker cable is a poor antenna meaning that it isn't too good at getting rf. However if there is a lot it will pick it up.
3) Most modern audio products that must meet CE will be pretty resistant to EMI and RFI, at the cost of networks at all input and output points.
However this adds to the ever growing pile of difficult technical challenges to making good audio. It also brings a new host of possible changes to the sound in places we weren't looking at.
Examples of these challenges:
1) iPod docs with FM tuners will not have digital amps because the digital amp causes too much interferance.
2) Made for iPhone requires a test to make sure the TDMA RF doesn't affect the audio of the accessory or the phone. That is a real challenge.
Translating these requirements to our level of audio sensitivity illustrates how hard it can be to make good audio co-exist with the 21st. century.
1) The voice coil is actually pretty well shielded inside the magnet structure.
2) The speaker cable is a poor antenna meaning that it isn't too good at getting rf. However if there is a lot it will pick it up.
3) Most modern audio products that must meet CE will be pretty resistant to EMI and RFI, at the cost of networks at all input and output points.
However this adds to the ever growing pile of difficult technical challenges to making good audio. It also brings a new host of possible changes to the sound in places we weren't looking at.
Examples of these challenges:
1) iPod docs with FM tuners will not have digital amps because the digital amp causes too much interferance.
2) Made for iPhone requires a test to make sure the TDMA RF doesn't affect the audio of the accessory or the phone. That is a real challenge.
Translating these requirements to our level of audio sensitivity illustrates how hard it can be to make good audio co-exist with the 21st. century.
What I mean is that cable just like HEAVY DUTY COAX has been made and used for this application in the past. 1979, I believe, by the Japanese. It had other problems, like excessive capacitance, to make it worthwhile, except in EXTREME environments, such as radio stations.
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