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In Reply to: RE: the late Al Sekela's choke tweak and True ribbon tweeter posted by Davey on January 14, 2015 at 08:24:42
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?
Follow Ups:
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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