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In Reply to: RE: the late Al Sekela's choke tweak and True ribbon tweeter posted by JBen on January 13, 2015 at 23:03:22
JBen, I am a big fan of the chokes and I also understand the benefits of using a cap/resistor in parallel to the tweeter. The attenuation of the inductor does extend into the audible but is negligible (about 0.4 db at 20 kHz and 0.1 db at 10 kHz). My setup is definitely not flat to 0.4db :). This is not to say that there is no audible difference with and without the chokes, it is just that those differences are not due to 1st order attentuation of the signal.
I am not sure why you are getting benefit from the chokes on your woofers as these already have a LP filter but if it works for you that's great.
I don't think there is any need to bring up Davey's personal quirks, as it were, into the discussion. I have learned a lot from Davey (as I did from Al) and I listen to the meat and leave the gravy on the side.
P.S. I thought you were on supervised leave from the Asylum :).
Edits: 01/14/15Follow Ups:
LOL! Neo, I may take a leave from the "leave" at times like this. If I turn on the Android tablet while waiting in a doctor's office, I may discover compelling items -- such as this one -- in the forum.I see that you remembered the reason why adding chokes on my MMG's mid/bass driver may make sense (the bi-amp). I should add that limited testing with a regular xover and chokes on all drivers also delivered some SQ goodies. They were less palpable, though still appealing to me. Line-level multi-amping paints the SQ gains (from the chokes) on a better canvas. The differences are more clearly perceived.
Your effort to moderate our reactions here are much appreciated, as always. I got more, far more, from Al Sekela than from Davey. The fact is that well beyond the chokes, Al's suggestions are very key to the additive gains that made my MMG's what I like so much versus other speakers, even some pricier Maggies. Being a trained musician, I may know a thing or two about good music sound. As I evaluated, tested and measured some of his ideas, it was clear that Al Sekela knew a thing or two also.
Speaking of measurements, I found it intriguing that the ribbon tweeters in your IIIA seem to have reacted less sharply attenuated by the chokes than what I've seen QR tweeters do. Here is something that I posted a few centuries ago. At the time, I was evaluating and measuring various types of chokes. Please note that these two sweeps below are quite different. However, the impact on frequency response from two kinds of chokes can be clearly seen inside the hearing range (1st chart). Aside from their lack of sufficient improvement on 3D imaging, the toroidal chokes attenuation at the top was always annoyingly dull to my ears. Of course, some engineers would have said that 10uH is always 10uH and sounds the same no matter what choke design. Neither my ears nor the microphone would agree.
LEFT MMG Speaker Standing Straight, bi-amped
Blue=no choke, Green= 5502 choke, Red=Toroidal choke.
Chart at 1db scale
(chokes at negative tweeter terminal plus a 5502 choke at negative of low panel)
Calibrated microphone at speaker 78" away, vertical & horizontal center
----------------------------------
Both speakers, MMG reverted to stock xover: Red=no choke, Green= 5502 choke. 8db scale.
(choke at negative speaker terminal NOT at tweeter jumper)
Microphone at center from seating position
Edits: 01/15/15
The attenuation I reported (0.4 db at 20 Khz, 0.1 db at 10 Khz) is calculated not measured which is why I said that the affect you are getting from the chokes is not due to simple attenuation. I am not a subjective v. objective purist when it comes to things audio but I do get nervous trying to argue against the math. The difference that you got with toroidal and standard chokes is another example of reality screwing with our heads. Perhaps we should study string theory to see if there is another construct which will explain things audio.
You should be more than nervous when arguing against the math. :) (And that's not to say everything we hear is measurable or not measurable.) But if you measure something that simply shouldn't be there it warrants a raised eyebrow and further investigation. It's been my experience that a culprit can usually be found.
At this point, JBen is so hard over in his defensive posture that he appears incapable of even considering alternative explanations.
Oh well.
Dave.
Davey, in your first post in this thread you said:
"An attenuating resistor actually lowers the signal level in the tweeter range..... a 10uH inductor does not. " (my italics)
Then, I just showed that a calibrated MICROPHONE, not just my head or my ears, can sense the changes by the 10uH choke, within the audible range. I also showed that even chokes of the same value but different design may yield different results. So, I already presented some real-world data to partly account -- again, for PART OF -- what may affect perception. I took these measurement in 2009, not now. They were not the only ones I made, just what I posted then. You just said to Neo: "But if you measure something that simply shouldn't be there it warrants a raised eyebrow and further investigation." Well, I agree. I did some due diligence and conducted other tests. I no longer have the measurements of real-world phase response and group delay that I once made but they suggested ways in which perceived benefits could be real. I even had several chokes matched for true value because they DO vary from nominal value.
Who, then, is "so hard over in his defensive posture that he appears incapable of even considering alternative explanations"?
(coming soon, a reply to what you just posted while I wrote this one)
Hi. Neolith;
I'm a "no tech" old guy, but I would like to take a shot at why JBen uses a choke on his woofers.
JBen bi-amps his MMGs using a Passive Line Level XO. That would take the speaker level choke out of the circuit, as you know.
I'm also a fan of Al's choke idea.
On your "meat and gravy" observation....Just change the "gravy" to vinegar...IMO
Take care...old guy
I totally forgot that JBen biamps his MMG's despite numerous conversations by email with him on this point. Maybe it's because I am older than old guy :).
Edits: 01/14/15
Quirks aside, I'm super conservative on this issue (and most others.) I like the idea of having a proper termination on the amplifier at frequencies higher than the audio band. There are so many disparate amplifiers and amplifier combinations out there.......and maybe audiophile X lives close to a talk radio station transmitting at 50,000 watts. :)
Magnepan's have much lower inductance transducers than conventional speakers, but who's to say an inexperienced user might decide to try the choke "tweak" on some other combination and run into trouble.
I know this choke "tweak" seems really simple on its face, but there are possible pitfalls.
When people make blanket recommendations regarding audiophile "tweaks" I get nervous.
Cheers,
Dave.
I have a class D amplifier (PS Audio Trio C-100). Presumably it has a pretty robust HF filter on its output.
I am using the choke tweak with a 1.5 ohm resistor in series (Magnepan 3.6 in a room with hard floors). I am not convinced I heard anything from the choke itself; obviously the attenuation resistor had a significant effect.
I wonder if this is because a class D amp already needs to have a filter?
By the way, can the Zobel network be used in the series port for the Magnepan tweeter attenuator?
FWIW, I use Class D amps (W4S ST-500) as did Al Sekela (Gilmore Raptor). Whether you get noticeable results or not depends on your set-up and environment. You might not have a problem with RFI. In any case if you are up to tweaking, I suggest making an RC network (across the speaker terminals) and see what happens. Values are not critical, 10 ohm resistor and 0.18 to 0.27 uF cap will do.
Edits: 01/16/15 01/16/15
Your setup raises some good questions and, dare I say it, an objective testing opportunity. :)
What is the switching frequency and amplitude level of the Gilmore Raptors? What does the internal filter network look like and how much attenuation of the switching frequency does it provide the load? How much further attenuation of the switching frequency does the extra 10uH inductor provide when you create an L/C/L T-network?
The Maggie tweeter drivers are low inductance and a switching amplifiers switching frequency could easily excite resonances in those drivers. (The ribbon drivers primarily.....probably not so much with the quasi-ribbon drivers.)
In the case of a conventional speaker system (with dome tweeter) there may (or may not) be a local RC Zobel downstream of the crossover network as part of the crossover design. Since a conventional tweeter has high inductance relative to a ribbon driver it effectively functions as its own "choke tweak".....assuming a typical audio band RC Zobel is not used. :)
This brings up the topic (indirectly) of high-resolution audio and whether our playback systems should be able to reproduce harmonics above the normal audio band. With Maggie ribbon tweeters we have a driver that is capable of that, and that begs the question......that if you do believe reproduction capability that high is a good thing, then why would you deliberately roll-off that capability with a series inductor?
Hopefully the RC network will not make any audible difference. In that case, it's probable you didn't have an issue to begin with. And the reverse is true. If it does make an audible difference, it's probable you did have some issue with frequencies above the audio band making it back into your amplifier and interacting with its operation. I hope that concept is clear to everyone.
I'm sorry, but these are the kind of things I think about. :)
Dave.
Switching amplifiers are an interesting case because there's already an output filter employed.
However, I would suggest a choke tweak would be even less advised because when those amplifiers become unloaded at high frequencies the LC output becomes a fairly effective resonant circuit without a load resistance shunting the capacitor. It's hard to say how well amplifiers will tolerate that load inconsistency without objective testing. I suspect most would be fine.
My point with this recommendation is that the RC shunt accomplishes the objective with no downside, but the series L has a potential downside. A series inductor unloading an amplifier might not be a problem, but it's unknown without some testing.
No, you can't insert the RC network in the tweeter attenuator spot. That's a series connection input spot.
I think some of the posters have actually lost sight of what the original objective of the "choke tweak" was. It might be good for those folks to review.
Cheers,
Dave.
Davey, you are reaching, I believe, when you say: " A series inductor unloading an amplifier might not be a problem, but it's unknown without some testing."
Well, test it. You keep this floating dark cloud as the source of your warning against Al's chokes. We could use a range of risk. I certainly have looked into it, to a limited but practical degree.
I have never driven tube power amps hard with the chokes on. However, over 21 SS power amps and receivers have been driven hard in my room. Some with Zobels, BTW. With or without the chokes, I failed to damage anything. Not exactly great proof, I am sure. Yet, if it CAN happen, then the risk if very low compared to other things we try as tweaks.
In contrast, you and I -- plus the really talented tweakers in this forum -- can recommend tweaks with vastly more potential for damage. Hell, I always fear that adopting a PLLXO may blow up someones gear if they are not careful. I am sure that the same crossed your mind. You and I can abuse the QR tweeters but...true-ribbons? Folks like, GL, Neolith and Andy must have iron b... nerves, LOL!
I suggest that you are vastly overplaying the risk card. Let them TRY IT, just let them draw their own conclusions.
(Gone to have dinner and to enjoy music for hours...received some got nice CD's as gift. Back at midnight Eastern : - ))
"Well, test it."
How can I test YOUR setup? :) You've completely lost focus on the issue. I'm talking about variables that could be different for every single setup out there. Isn't that obvious by this point? My goodness.
Since you won't go back and review the discussion Al and I had regarding this, try going back over the last few months and review the discussions you and I had regarding this. Take note of the suggestions I made to you regarding testing without acoustic or listening tests.......both of which are fraught with variables.
I will stipulate the 10uH coil effect is right there at the top of the audio band. Some variables can certainly come into play when you get that close. However, the theoretical numbers don't lie.....Neo has shown you those. Apparently you don't believe them?
Also, consider the possibility this whole issue has nothing to do with RFI and the audible result is simply the low-pass filtering action of the coil reducing out-of-band behavior in the tweeters. Al never even considered that. :) Materials science might be a fun topic to venture into. :)
I know you want to believe this is all so simple and "if it sounds good do it" is all the evaluation required, but I ALWAYS consider the big picture (worst-case) in all situations. Maybe that makes me overly risk-averse.....if so, I'm comfortable with that. In my day job, and also with audio gear, I don't believe in playing fast and loose with the engineering. Sorry.
Dave.
Davey, you are in denial. And once again, you are twisting what I said.
Of all the people here, I am one of the few who care to try and reconcile perceptions with measurements. Spare me the excuses; real-world objective measurements are key to fine tuning an audio system, despite the limitations.
I have just spent over 4 glorious hours listening to 2 modded MMG's play full orchestral music alone. Music poured grandly, full of real instrumental textures, of superb 3D positioning, on a huge, larger-than-room stage, with arresting orchestral richness & inner detail. I've enjoyed chromatic delicacy in a wide and dynamic range that covers almost ribbon-tweeter top transparency down to almost sub-woofer territory bass. These are Maggies that shake things, that slam without a subwoofer, that can make you dance to impactful rhythm and can make you cry with tuneful delight. I could go on and on describing in detail the virtues of this system and the specific attributes with each type of music. I can still taste the rushing flavor of the experience, while lamenting that I live in an apartment. It is past midnight but I would have loved to keep listening like, forever.
This system is largely not of my own making and not due to much virtue of my own. I just accepted the input from others, evaluated it subjectively and, when practical, TESTED objectively by measuring it. A very substantial portion of the delightful sound that I now enjoy is due to Al Sekela's advice long ago. And it was not just the chokes, BTW, other ideas of his were very useful.
Therefore, I can't stay quiet and allow you to soil his reputation simply because you fear testing the ideas. Or because engineering has still not found all the explanations that you seek.
So, here's the deal, show me the beef. Davey, walk the talk, SHOW US YOUR REAL-LIFE ACOUSTIC MEASUREMENTS. Imperfect as you may call them, they will certainly tell a good part of the story that you seem to be hiding.
OR....at least help us to understand that you can FEEL the music emanating from your system. If your system were sounding as great as your engineering knowledge suggests, we would hear about. You would share the delight, the pride and the overwhelming urge to tell about it. At least something! Like telling us about a certain musical experience every now and then. Many of us have such a moment frequently and often ache to share it. I can't find any indication of it ever happening to you. Clearly, something is amiss.
If you are to try and disqualify Al Sekela, I will take delight, and my time, to undo some damage. I owe to him a decent effort to that effect. To those who have ears to hear it will be shown by the music, not by engineering formulas.
I'm hiding a story now? I have some sinister agenda to bad-mouth Al's memory? You must be kidding.
I had a number of offline conversations with Al regarding this topic....but mostly about bi(tri)-amping and his reluctance to even consider trying it. I even offered to customize one of my active crossover units and send to him for an unlimited evaluation. He declined.
I found him to be a really nice guy and enjoyable to chat with but just not that intellectually curious about some of the technical aspects. Nothing wrong with that.....he's not alone in that regard. But underlying, I never had a sense he wasn't 100% enthused about his audio interest. I respect that.
He also had enough respect for me that we could agree to disagree on our audio outlook. If, in your mind, you think I'm attempting to soil/damage his reputation, then I think the problem is looking at you in the mirror. Mature people can have meaningful discussions on topics in which they disagree. Sadly, that doesn't appear to be possible with you.
I haven't said anything here regarding this "choke tweak" that I didn't say when Al was still with us.
I sense the same audio enthusiasm in you that Al had but, unfortunately, some of the same closed-mindedness with regards to the technical details.
It's obvious I'm not going to be the one to convince you to consider the larger picture when evaluating audio gear. That's fine, maybe somebody else will have better luck.
Cheers,
Dave.
Ok, Davey but where's the beef? I mean, the real beef. "The larger picture when evaluating audio gear." has to lead to the beef at some point.
Have a great weekend, you all.
....a pescetarian actually. I guess that explains why my opinions have no meat and smell fishy.
Wow, you finally figured me out Sherlock. :)
Well done.
Thanks for the clarification on that foul odor wafting from your posts.
It smacked of vinegar and bull scat to me. No offense. :)
Wow, what a pathetic response. Very nice.
Dave.
You wrote
"Wow, what a pathetic response. Very nice."
Thanks for the "very nice", but I don't deserve it because I only mirrored your pathetic "silly" original post titled "I'm a vegetarian", Sherlock. :)
Cheers
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