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The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long

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Posted on March 20, 2015 at 11:22:35
JBen
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  Since: July 26, 2010
 Around mid 2013, inmate Old Guy 42 and myself decided to try some tweaks & stuff that was implemented on my original 1999-style MMGs, adapted to his newer MMGs, vintage 2008. We started this process towards the end of 2013 thinking that it would go fast, like in months. Well, it did not all go as planned.

Oh! It started well. That November, OG42 took some acoustic measurements of his MMGs before we made any changes, to compare later. He then applied the first set of tweaks. After doing this, he measured again and then he spent quality time to give these changes a good listen, as he should. Ok, fine; except that we got stuck there.

On one hand, he took his sweet time on doing this listening. (LOL! The "slacker" was enjoying his CDs all over again, we joked.) Meanwhile, I also delayed things by testing a local cardiac ICU in December. (Neat! Look at those scope traces of my pulse. Darn,..says here a "flat response" ain't good on these :-) Yet, during my recovery in early 2014, I was getting bored. With so much extra time, I began to look more closely at several of the measurements that we had taken of OG42's MMGs so far. This led to a surprising discovery. Duh! I had failed to notice a higher-than-normal amount of harmonic distortion in one of OG42's MMGs. This was the one on the right (when as tweeter-in).

Damn it! Why did I not think of looking into these details before? Did the mods cause this? We then looked at ALL the sweeps, including the initial ones taken before the new tweaks. We found that the distortion had been there all along, probably since the MMG were new. That speaker's "extra" distortion is generally in the 90-150Hz region, largely as 2nd harmonics. This probably is the reason why OG42 would not perceive the distortion as "bothersome". Any other tube gear lovers among us?

After discovering this issue last year, we have made some tests and tried fixes. Nothing helped. We still have other ideas to try. Then we'll go on to the next tweak; to biamp the MMGs (via PLLXO). I did consult with Magnepan in 2014. The outcome of this inquiry? Nothing was offered as possible cause, or fix. Huh? hmmm...

Then, a sudden and amusing thought came to our minds recently. Could this conceivably be a "design feature". Could Magnepan have decided to allow some "pleasing" 2nd harmonics to stay? "Hey, let's allow them to sound more 'tubey'! "

Gang, it is simply an amusing thought; that our dear company has a "dirty little secret", LOL!

Anyway, perhaps a few of you have ventured into measuring distortion in your MMGs or other Maggies -- or can do so? If you did, please lets share. It would be interesting if we find a pattern where one of the Maggies always exhibits high 2nd harmonic distortion.

All this said, however, neither of my old MMGs have this distortion. Nor have I found it in 1.7s for which I have suitable measurements. Bummer, just as I thought we had clinched a Magnepan "conspiracy theory"!

Apart from the snapshot below, we are including a link below to a set of Flash slides (with far more details than most sane folks would really care for)




 

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RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 21, 2015 at 05:42:11
Davey
 Except for the 20.X series, the speakers are asymmetrical, so a certain amount of even-order distortion is inherent and expected. This is an aspect of the speakers that's been well understood for many years.
In this case it looks like one of the speakers had a problem needing repair and/or you were simply measuring the inherent difference in the left/right speakers because of button tuning.
I see no harmonic distortion conspiracy......or even a theory for it.

Dave.

 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 01:53:27
JBen
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  Since: July 26, 2010
 Evidently you missed the humor intent; fine -- I guess I'd starve as a comedian.

OTOH, there was that word: "mostly". I'll say this again so you don't miss the serious part:
- Magnepan did not feel it was a defect, nor did they admit it was. In fact, not even a solution or option was offered. "Gee, your MMGs are out of warranty but if you send the MMG to us at your cost, we'll have a look." or "Yes, send us the sweeps, let's take a look". Nothing of the sort was said. BTW, I am not really "accusing" Magnepan. Overall, they still do far better on customer service than many companies.

In addition -- to my knowledge -- there is NOT a widespread issue of OVERLY high distortion.

What there is, however, is the possibility that some folks are asking us for solutions to some problems that are really reflections of what happens to OG42's MMG, or other issues that measurements could catch.

Would you really mind if folks learned of a diagnostic resource? One which could also help many of them make their system sound much better?










 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 07:30:43
Davey
 I got your humor intent. Actually you're doing pretty well as a Magnepan humorist. :)

You're clearly implying there is a "defect" in this aspect of the Magnepan performance.....you did it three times in your post. Maybe you'd like to elaborate on your assertions vice all the silly rhetoric? I gave you a couple of hints regarding the reasons for the distortion.

I think the members here are more interested in your solution to this distortion issue/problem/conspiracy. Or at least your explanation of why Magnepan doesn't feel this problem is a defect.
If you've got something, please offer it up.

Dave.

 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 09:01:15
old guy 42
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  Since: August 26, 2012
 Let's just cut to the chase, shall we.

Inmate JBen made it clear in the OP that this "bump" in second harmonics did NOT appear in either of his 1999 MMGs nor did they appear in a set of 1.7's that he has suitable measurements. I have changed-out Amps, pre-amps, speaker cable, ICs etc., and the "bump" remains on the same MMG. Also, I checked for de-lam and loose XO parts, etc., but no dice on my 2008 MMGs.

So the question is...do you, or anyone on this board have a similar experience with the "bump" on an MMG? If you would like to share your experience, please do. If you don't want to share, that's OK too.

Let's please stop with the tennis match.

Respectfully...old guy

 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 09:09:16
JBen
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  Since: July 26, 2010
 I agree, on the "solutions" part. In fact, I had hoped you would ask from the start, instead of trying to dismiss the subject altogether. I shall get back to this later simply because it was part of the plan all along.

For now, let me just bring some some stuff that I deleted from the previous post, trying to keep it focused. I kept the separate draft which I shortened after pasting because a few things were already implied or because I -- mistakenly -- thought they would not be needed.

1. Original first sentences: For the record, we do believe that something is not quite right with that particular MMG. In fact, Old Guy 42 thought of the buttons long ago. We don't want to mess with them for now, so they have not been touched. We have looked into other areas, and even found other suspects elsewhere. But the buttons certainly remain a suspect.

2. Cut from further down:
"YOU may have accepted a high harmonic distortions as "inherent and expected" on many Maggies. Some others may also done so. That's fine if they know what they are buying into.

3. Further down:
However, others may only know that their speakers are not sounding as great as they expected, or glary, or too bass-poor, or too soft/bland, etc. Some of us can provide a wider range of diagnostic resources, along with ideas on how to deal with an issue.

4. Original closing:
If you want to bury your head under the ground because you can't tell or hear the difference, I have no qualms. If you want to ignore measurements because of your engineering application dogma, don't come implying that a reality is unproven. Above all, do not deny others a chance to learn. Ultimately, whether THIS ONE issue is a defect or it is part of the factory design, it is of less importance. There are now more resources for those willing to walk the extra mile and find things out. THAT is a more important thing.

Now, back to the replacement that I used for the paragraph above:
"Would you really mind if folks learned of a diagnostic resource? One which could also help many of them make their system sound much better?"

Please answer this simple question above.

 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 09:11:38
Davey
 It's not a tennis match. It's just silly rhetoric from JBen.

It seems fairly clear one of your speakers had an actual issue/problem. To couch that problem in language that intimates Magnepan has some sort of "conspiracy" to build-in distortion to their transducers is just silly.

To answer you question: No, I don't have a similar experience. All of the Maggie drivers I've measured distortion from were similar left/right and with other sets.

So, it seems you have/had a bad driver. It's not a difficult conclusion to come to. Why is all of this nonsense from JBen necessary? That's my question. :)

Dave.

 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 09:16:46
JBen
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Posts: 3082
Location: South FL
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  Since: July 26, 2010
 Ooops! Sorry Old Guy 42...we posted at the same time. I am duly chastized, I guess. Now humbly picking the balls off the court and back on the can, I'll try to stay more focused.

LOL, we should also tell then gang about the "staple count"!

 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 09:26:43
old guy 42
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 WOW, you really DON'T get it do you. Do you understand what "tongue-in-cheek" means??? There is NO conspiracy. Now you are trying to make something out of nothing. Talk about "silly"!!!

If you had just answered JBen's question in the OP, that would have been quite sufficient.

On the rest of your post...thank you for your info....

 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 09:32:47
Davey
 A mostly tongue in cheek Harmonic Distortion Conspiracy Theory that's not really a conspiracy. Got it. :)

Isn't it obvious that my "engineering dogma" is interested in the part that's NOT tongue-in-cheek? :) My goodness.
What did you do to solve this problem? Or are you still experiencing it? Those are the real questions here.
If I had the transducer in my listening room I could certainly find the issue for you, but it's a bit difficult to troubleshoot via forum messaging with all sorts of irrelevant information included.

He did make mention that your two tests were done on different days. It's possible that may have invalidated your testing scheme. This type of thing requires a strict discipline in testing if valid conclusions are to be made. So, it's possible your transducer has no problem.....just the inherent distortion.
Make sense?

Dave.

 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 09:39:18
old guy 42
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Posts: 388
Location: Eastern Pa
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  Since: August 26, 2012
 Hi. J

I meant no offense, J. To me, you are the biggest gentlemen in these here parts.....

 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 10:18:44
JBen
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  Since: July 26, 2010
 None taken, thank you.

 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 10:29:13
old guy 42
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 You know Dave, if your "engineering dogma" is NOT interested in "tongue-in-cheek" why did you not cut to the chase and answer JBen's OP???


As far as irrelevant info. goes...What part of " I checked for de-lam and I also checked for loose XO parts" qualify for irrelevant info??? Are you just taking pot shots at other posters??? I thought you were only interested in "engineering dogma".

Other things I have tried is to add rope caulk to the frame/driver. I also noticed an odd placed staple on the top of the one in question. I have plans to loose the staples and find another way to fasten the driver to the frame.

ALL my sweeps were done in the same spot, and at the same height. I think JBen's OP tells the story pretty well with my experience.


If you want to continue, how about just the "engineering dogma" part of this thread, OK???

 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 10:37:58
JBen
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  Since: July 26, 2010
 Davey, let's just get to the park's cafeteria and have a coolin' drink, my treat.

Yes, if I had that MMG here it would have been easier to apply more resources and find out sooner. As it is, OG42 has done a remarkable set of measurements and tests without the benefit of more resources. At the very least we know some fundamental measurements. The latter are not just the REW ones but also some structural items of interest. We will detail them as best we can soon. I need to take care of other things today.

Now, you added an edit even as I replied. Your last paragraph is new, and I am glad you added it for it also speaks to our level of transparency. On the part where you say " This type of thing requires a strict discipline in testing if valid conclusions are to be made. So, it's possible your transducer has no problem.....just the inherent distortion."

Yes. I may have shortened things on edit and accidentally dropped mentioning that these are far from the only, or best, measurements that we took since we began. They were simply the ones "at hand" and with enough common elements. The ones on March 13 got partially corrupted and I though I would show what can happen when noise is ignored. Importantly (in this case) despite the noise intrusion on March 13, even the noise cannot hide the distortion that we have always found in cleaner measurements. Old Guy 42 did take an extra read of the sine wave ditortion at 115Hz on March 15, which I included first, on the post itself.

I tried to include relevant details -- even those that may seem as "invalidating". Tests were repeated along time precisely because the vagaries of in-home measurements do present challenges and easy mis-direction. We have no anechoic chambers. Personally, for critical items, I can only be sure after testing several times along time. This is one of those rare instances when -- despite notable environmental changes -- it keeps looking like a duck and quacking like one all the time.

 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 11:30:18
Davey
 I'm not sure what the "cut to the chase" answer you're looking for is. You guys are the ones who had the firsthand experience, made the measurements, and determined the higher distortion. It's not clear to me what the cause of that issue is.....or whether it was an issue at all. I could make something up if you want. :)

Checking for delam....noting odd-placed staples....trying rope caulk....investigating better fastening. All good steps and that IS good relevant information. It's information that is interesting/valuable and helps to possibly narrow the issue. "Engineering dogma" were not my words....I hope you caught that.

Why is it so difficult for JBen to approach Magnepan discussions/postings without resorting to strawman arguments, or looking down his nose at my engineering discipline, or taking cheap shots at my hearing ability, or etc? It's a mystery to me.

I'm glad to help you guys if I can....and I don't having my technical statements and technical speculations questioned. But please don't insult my intelligence with the other stuff.

Cheers,

Dave.

 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 12:09:59
old guy 42
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Posts: 388
Location: Eastern Pa
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 WOW...In a previous post to me you posted that you never experienced this "bump" in an MMG, correct? If you re-read JBen's OP you will find that he posted his 1999 MMGs did NOT have this "bump" either. He asked if
anyone with experience with this, to post their findings. Why did you NOT "cut to the chase" and tell him what you told me without all your prose.

No one is insulting you, Dave. It's clear to me you have an ax to grind. That's sad, truly sad. This Planar Asylum is a GREAT source of info for me, but I dislike your posts to inmate JBen.

Anyway, thanks for the info and I'm "over and out"...old guy




 

RE: The MMG Harmonic Distortion Conspiracy Theory...mostly tongue-in-cheek, long, posted on March 22, 2015 at 13:37:08
Davey
 No, I said I haven't noticed higher distortion levels between left/right speakers and/or different sets. I said nothing about "bumps."
That doesn't totally address your possible issue/problem noted here....just relating my distortion experience....which is what you asked me about.

I think maybe you better look at the other (not mine) posts in this thread to experience all the "prose." :)

If you can't see the insults then you're blind....or dense...or something else.

Dave.

 

OK weird.... me too., posted on March 23, 2015 at 06:33:46
BigguyinATL
Manufacturer

Posts: 3475
Joined: April 10, 2002
 Right speaker (tweeter in) distortion at 80dB 125Hz 13% Left speaker just 1.6% The distortion is only high at a specific narrow frequency band - So I suspect it is a resonance that is causing it - loose or Delam wire.
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius

 

RE: OK weird.... me too., posted on March 23, 2015 at 08:28:26
Davey
 For everybody:

You actually don't need any fancy test equipment if you really want to audibly experience the distortion these panels can produce. Buy/borrow an audio signal generator with a continuous (manual) adjustment capability. (Something with rotary potentiometer on the front that gives you complete control.)

You'll hear all kinds of various noises/buzzes/resonances you might not have expected to hear. :) It will easily allow to localize delamination or frame buzzes or various other issues.
This is not unusual with speakers of this type. Apogee's and others will do the same thing.

Cheers,

Dave.

 

RE: OK weird.... me too., posted on March 23, 2015 at 10:35:24
JBen
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Joined: May 18, 2008
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  Since: July 26, 2010
 Hey Bigguy! Before I forget, every time I see your Confucius quote it reminds me of Schrödinger's cat.

Anyway, it sounds to me like you are right. If it is narrow band, it could be what you think. Some sweeps that I've done when a wire segment was loose on mine in the past, did show that way. Visually, they spike alone, unlike what we see on OG42's sweeps (a wide range of frequencies.)

Good luck with this.

Oh! If you are going to disrobe that MMG, would you mind counting the staples and letting us know? This would be the total count or, better yet, each row, horizontal & vertical. As part of our diagnostic effort, we found that OG42's MMGs have less staples than mine. At this stage is just a curious thing. Too early to tell but this line of exploration led him to other promising suspects.

 

RE: OK weird.... me too., posted on March 23, 2015 at 16:36:59
Tom §.
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Posts: 744
Location: Iowa
Joined: September 30, 1999
 If you have a smartphone and a 3.5mm-to-RCA cable, then you're already there. There are many signal generator apps available.

 

RE: OK weird.... me too., posted on March 23, 2015 at 17:17:54
JBen
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Posts: 3082
Location: South FL
Joined: May 18, 2008
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  Since: July 26, 2010
 Y'r absolutely right, Tom! Many are free, too. Thanks for the reminder!

And if you later add the proper audio software and, ideally, a <$20 calibrated mic, you get a half-decent measuring setup also. One that I like is "Audio Tools", available for Androids & iThings - phones and tablets.

At a grander scale, REW (Room EQ Wizard) is free and a rather impressive audio measurement package for the various PC/Mac. A normal set of audio hookup cables and presto! Signal generator and more. Then, add the same <$20 microphone that I mentioned for the droids/iThings and you're in serious business.

 

RE: OK weird.... me too., posted on March 23, 2015 at 18:01:35
Davey
 Yes, understood. I have a setup for my phone too. I still prefer a generator with a knob though because you can narrow the range of interest very quickly and go back/forth conveniently to isolate.

My main point was that a person doesn't need any acoustic measuring equipment....microphone....REW.....etc, etc. to identify problems like this. Your ears will work just fine in this application....with the right signal generator.

Dave.

 

RE: OK weird.... me too., posted on March 24, 2015 at 02:31:40
old guy 42
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Posts: 388
Location: Eastern Pa
Joined: August 12, 2012
Contributor
  Since: August 26, 2012
 Hi. Bigguy;

Thank you for taking the time to look at the measurement chart that JBen so kindly posted for me from my modest measuring gear. I was hoping for a loose wire, but that was not the case. I might have found something promising yesterday, but my plate is full the rest of the work week, so maybe this weekend I will know.

Thanks again....old guy

 

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