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The REAL Problem of March Audio's Sointuva WG (Review, Measurements and Reinforcements with Klippel device)

Nuyes

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I am not good at English. Therefore, this post was written with the translation help of many people in Korea. I am very grateful to them.

I am an audiophile publishing speaker reviews to audio communities. Currently, I am using Klippel Distortion Analyzer 2, Earthworks M30 mic, and a DIYed turntable to measure directivity(quasi-anechoic measurement) and nonlinear distortion for my reviews.

I’ve recently reviewed March Audio Sointuva WG and I’d like to report some problems I found and share some thoughts here, although I am not a native speaker of English.

01.jpg



In a nutshell,

1. The Sointuva WG I received turned out to have rather high levels of THD at 85dB SPL. Also, the distortion rate was lower at 95dB SPL than it was at 85dB SPL, unlike any other typical speakers in which nonlinear distortion increases proportionally as output dB increases.

2. Unusually, in Erin's Sointuva WG review, the 86dB SPL THD data seems to be missing.
There is something I would like to correct about this.


That's my apology to Erin, located at the bottom of the post above.


3. It has questionable build quality regarding sealing, internal wiring, non-uniform component qualities, unassembled parts, etc.

Let’s look at the details.
Below is the very first measurement data.

(I would not attach multi-tone and compression test results in order not to make it too lengthy. If you want to see them, please refer to my original review. https://gall.dcinside.com/mgallery/board/view/?id=speakers&no=243813 )

The acoustical axis used in measurement wasn’t set on the tweeter but the middle of the tweeter and woofer.

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So the real problem begins here.
Some community users pointed out that my THD level at 85 dB SPL, 1m, is approximately the

same as the 96dB SPL data of Erin’s.
It was strange enough, because mine was even higher.


10.png

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At this point one of the community users sent an email to March Audio about this issue, and got this reply.

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Alan claimed that their quality control was seamless, But I thought further tests were needed as we already noticed some problems.

In the first place we suspected deviation between samples, and as I had only one of the pair, I asked the owner to send me the other speaker, and he kindly did so.

13_with Sample B.jpg


1. Sample A&B nearfield measurements (A is the one first measured and thought to have some issues)


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In particular, the measurement results were very different at the passive radiators, so I decided to disassemble this piece (Sample A) in order to exchange the radiator (which was suspected to be defective).



I added a description to this post using the link below.

There is a lot of information missing as it is a huge task for me to compile and post this thread.

So people reading this may be confused.


Please understand.


 
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OP
Nuyes

Nuyes

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2. Binding post leakage
While disassembling Sample A, I was flabbergasted.

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There was no sealing at all at the binding posts, and I could literally see some light coming from the gaps between the binding posts and the speaker enclosure.

This caused substantial noise, and when I used banana plugs which were tightly fit in the binding posts, the noise level dropped significantly.



22_with banana.png
23_without banana.png
24_comparison.png







Nearfield measurements data at the binding posts

This problem is clearly noticeable when playing bass, and any sensitive listener would notice it.











Please refer to the link of the video.
The above link is a temporary Youtube account that is created specifically for this report.




I can’t just ignore this issue, so I tried some simple sealing tests.



26.jpg











After confirming that the noise was reduced with sealing, I sealed completely around the binding posts.

When I raised this noise issue to Alan March, he said “they were working perfectly.” That’s ridiculous...

and the community user who sent the email received another response from Alan March.




28_1.png








He claimed the awful distortion we talked about was in fact found in every speaker using Purifi speaker drivers. He claimed that he had a know-how regarding how to minimize it. And March Audio asked us about the tightness of the front bolts.










However, from my perspective, after thoroughly disassembling Sointuva WG, the degrees of tightness of all the bolts were varying. Some bolts were well tightened, but some were loose enough to be tightened with my fingers. I doubt that this is what March Audio’s claimed “know-how” but if that’s the case I have to disagree with it.

So I ignored the reply of March Audio and proceeded with further tests.
 
OP
Nuyes

Nuyes

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3. Can it be seen as a non-linear distortion by the speaker unit’s motor?

I thought that this problem was not related to the speaker driver unit and performed another simple measurement.

I measured distortion by the output level of that specific problematic frequency. (passive radiator near field measurements)


28_Distortoin.png

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It showed the highest distortion at 3.8~4.0V, and decreased overall afterwards.
If this problem was being caused by the driver, it should have “increased” proportionally to the output.

I even tried to turn Sointuva WG into sealed speakers, or to check the radiator with a stroboscope(because 2nd harmonics is high) but no more significant improvements were made here.

Rather, the distortion was higher when it was sealed.



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So next to that, I suspected the resonance of the enclosure and added more acoustic absorber.

I put the absorber as much as double the usual amount in one Sointuva WG and below is the measured data set after that.




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Distortion by output is significantly reduced.

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and THD is radically reduced too.

At this point I was confident that the main reason for all the issues was ridiculously poor absorption inside of the enclosure.
 
OP
Nuyes

Nuyes

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4. A sealing issue in the tweeter-waveguide assembly?
When I was performing the measurement I could hear the sound coming out near the tweeter part.

36.jpg



and performed another nearfield measurement as in the picture above.


37_2_83V.jpg
38.png



And as you might already have expected there was a leak or resonance and I took action accordingly.
 
OP
Nuyes

Nuyes

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5. In this whole situation Alan kept claiming that the problem is caused by the inherent characteristic of Purifi drivers and that he could solve it.


39_0.png


Picture above is the response of Alan March to the owner who brought up the issue. Alan March said that it is not the problem of resonance so it cannot be solved by additional absorbers. However as you all have already seen on this post, we solved it by adding the absorbers.


Also, Alan March said he got confirmation by the Purifi audio engineer that the problem is created by resonance at the magnet of the woofer and resonance at the woofer unit frame, but I doubt that they are the main causes of high THD as much as 1% at 85dB SPL.

39.jpg






To prove this, I did nearfield measuring at the woofer's frame and magnet joint.




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When I saw the measured data of the woofer's frame and magnet joint along with the other data of the driver like nearfield measurement data of the woofer cone, I could not see any single particular problem related to frequency range that had an issue.

So Alan March's claim was totally wrong.
 
OP
Nuyes

Nuyes

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6. Improvements

I sealed the tweeter parts.

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Regarding insert nuts.
The insert nuts at the unit joint just fell out when pushed physically and thus caused leakage.

So I sealed it myself. (Picture below.)




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There are more issues I found during the improvement process.





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Usual insert nuts have a tube at the end and seals a bit when it is pulled




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But I found some insert nuts without those sealing tubes.


I cannot confirm whether or to what extent this contributed to leakage of enclosure but the inconsistent use of materials is enough to be criticized.

Another jaw dropping issue was that





52_4.jpeg








Insert nuts should be installed like the picture above, but when I disassembled the other Sointuva WG piece which didn’t have an issue,



52_5.jpeg







I found an unassembled insert nut.
A clear apology and follow up actions is required from the manufacturer.




Organizing the internal wiring.

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The existing wiring was not fixed and might have caused a noise by vibration so...




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I organized it as above.
 
OP
Nuyes

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7. Conclusion of the improvements
First, I measured a level of sound leaking from the gaps between the tweeter and waveguide joint.


56_TWTnWG.png
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It was a simple sealing process but turned out to be very effective, and made clear improvements.


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Additionally, there were improvements of 3rd harmonics at high frequency too though it was not intentional.








Comparison of THD




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Improved a lot.
The distortion by output problem is also clearly solved.



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As you can see from the data of June 4 - the final day of improvement.


62_1m farfield.png




This is the result from the same test, but at far-field.

Likewise, we could see THD level increase proportionally per output and this is how it is supposed to be. (so it is normal)

Below is the absorber that was inside the Sointuva WG.


63.jpg



and there were five of them.


So I added 2 pounds of additional acoustic micro fiber as an absorber.

64.jpg
 
OP
Nuyes

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Final measure data


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There was change in bass region as above


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THD reduced a lot



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As well as the THD, the multitone test result of the mid - bass frequency is also improved.

Finally all of the improvements were done, and “Sointuva WG - DC speaker gallery version” was safely returned to the owner’s hands.




So, to summarize, there is a problem caused by internal resonance which is worsened as it leaks through the gaps. But this could be drastically improved with sophisticated sealing at the binding posts and insert nuts, and additional absorption at the inside of the enclosure.

Last mystery:
Why did Erin unusually not include 86dB SPL THD data to Sointuva WG’s review?


- The End -






+ 01.07.2022

Regardless of the core problem of the Sointuva WG, I want to confess my mistakes and make things right.



It is true that I had strong suspicions about Erin at the time I was fixing issues with Sointuva WG.



And already one of my friends asked Erin about this question, and Erin gave him an appropriate answer... but I didn't believe it.



A cowardly excuse... I use templates for most of my measurements while using Klippel software.

This led to strong suspicions that only certain processes were missing from his measurements.



I doubted him without exact grounds, and he made no effort to believe it.

This is very wrong.



And this has resulted in many people being suspicious of Erin.



And also this totally ruined one man's happy weekend.



It's all my responsibility and my fault for people to doubt and slander him, at least on issues related to this thread.







I apologized to he timidly, and he asked me to post this apology on ASR for everyone to see.



Its contents are as follows:






Hello, Erin.



I am the person who posted that review on ASR.



I would like to sincerely apologize to you for this.



I should have asked and wrote about the missing 86dB SPL at 1m THD data in the first place, but I didn't.



And my stupid rashness totally ruined one man's pleasant weekend.




-----





Apart from this, you have always been a great help to me.


The data you've accumulated has given me the confidence of the public as well as cross-validation of my reviews by reviewing the same speakers.



I am fully aware of the difference between my measurement data and the anechoic chamber measurement data using Klippel NFS, and it's limitations.



But despite that, the THD of the Sointuva sample I received was higher than the 96dB data you measured, a symptom not found with other speakers I've run.



So, using the Klippel DIS module(as you know), I tested the harmonic distortion of that resonant band and found that it had a maximum value at about 85dB SPL at 1m.



Coincidentally, I also found that 86dB SPL data was missing from the Sointuva WG only in your review series.



That made me suspicious of you.



Explaining all of this may sound like an excuse for my atrocities, but I think all I can do is tell the truth.



Once again, I sincerely apologize.











I don't want anyone innocent to suffer because of my faults.

I was wrong. Sorry to everyone.
 
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SDC

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Tks

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Man, talk about thorough.. Not only was there a demonstration of the issues, but also fixes that demonstrates the false claims of the manufacturer..

Also, on a sidenote, I always wondered why internal resonances were ever a problem in speakers to the degree they are. And why manufacturers just don't seal the damn thing up with a heavy does of absorbers since I've never seen performance regression on that front when one does so.
 

SDC

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Been following this thread before uploaded here in ASR (In S.Korea Dcinside forum). The effort Nyu put in this product was a hell lot. Hope more people see this and product gets fixed. Great job everybody!
 
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SDC

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I didn’t psychoanalyse the emails but it seems like Alan was curious with skepticism not necessarily calling any of this bullshit.

Yeah I used strong wordings, my apology. But this project has been done for very long time and his response was... disappointing.
 

SDC

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Can you share which sealant you used for the binding posts? And is it reversible?

I'm quite sure he used bluetack. Not sure if it is reversible but pulling all that out of the copper pipe would be a hard job.
 

abdo123

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I'm quite sure he used bluetack. Not sure if it is reversible but pulling all that out of the copper pipe would be a hard job.
I mod a lot of vintage speakers and turn them into nice looking subwoofers so I’m interested in a sealant that is more or less reversible incase I decide in the future i want them to function as full range speakers again.
 

eddantes

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Looks like something, a liberal application of hot glue, would fix during construction... That is if disassembly was a something one wanted to give up. Perhaps theres a "rubber cement" type application of hot glue?
 
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