Jump to content
The Klipsch Audio Community
Langston

Iron-core versus air-core woofer inductor intermod test (Continued).

Recommended Posts

The only person in the house that will hear what he’s measuring is the dog. 
 

Also, the only iron core in this group is the one made by UT, everything else is steel laminate. 
 

I won’t use the small Erse or the Sledgehammer from Madisound. The laminated plates slide out with vibration. Don’t believe me, just grab them and tap them on the table. I got a pair of Chorus II nets that Crites had built, and some of plates had slid a quarter of the way out of the thing. 
 

The best coils are dipped in wax or varnish so there is no air between the windings, and so they don’t move against each or on the core.

 

Coils are measured on the board/in-network, and the values massaged until you get the desired results. If you did your job right - mutual inductance is part of the design, and moving them apart changes the response. 

  • Like 4

Share this post


Link to post
Share on other sites

Cranky soldermeister is right! At least the first part - I'd have to see some of your solder work to opine on the other (meister is German for master) : )

 

You just answered a question I've had about some Danley passive crossovers I replaced with my own a few years ago. They used ERSE 14awg IXQ steel plate cores that add mounting holes through the plates at either end, but they mounted them on a bed of silicone glue with wire ties and filled those holes. Why fill the holes? I think you nailed it - to keep the plates from shifting.

 

1218544586_SM100Xover.thumb.JPG.5f6a185939ed6a9dfec95c24357cc1e2.JPG

 

I disagree with you about mutual inductance being purposeful, 'cause it's bad. How bad from an audibility point of view will vary, but I bet that input cup mounted three way crossover in my Heresy II's screws up the mids audibly. If you mean by "mutual inductance" the presence of nearby ferrous material or unmodulated magnetic fields (driver magnets), you're probably right and it's on the dog.

 

Mutual inductance between (air core especially) inductors can be a big deal when modulated by audio. My measurements thus far show the skirts of mid and high pass passive networks beginning to fall apart -30dB to -50dB below the passband primarily due to poorly placed low pass inductor(s). You may say that's not audible, and I'd agree, but the crosstalk is different in phase, not just amplitude AND it's imbedded throughout the adjacent passband, not just the skirts, even if it's not apparent in the trace.

 

That also means if you can hear some of the crosstalk, it'll be like IMD - unmusical - ugly - my guess is "grainy". Can you imagine a preamplifier or amplifier or active crossover manufacturer trying to sell a product that included the same kind and level of crosstalk between channels? They'd be bankrupt quicker than a knife fight in a phone booth (unless they plated the turd in gold and gave it a name like "Jupiter" or something.)

 

Refrain: Why not do the best with what we have to work with?

 

BTW, the Sledgehammer will arrive today (it looks to be ERSE IXQ OEM, TBD) that'll allow me to finish the shootout with the final (3) inductors.

 

Cranky measurementmeister - Langston : )

Share this post


Link to post
Share on other sites
11 minutes ago, Langston said:

I'd have to see some of your solder work to opine

It's purdy.

  • Like 1
  • Haha 1

Share this post


Link to post
Share on other sites
Posted (edited)

Today's Contenders

1473818183_InductorsGroup2.thumb.jpg.f79d5e3b93c37dbc4c49691f0699cbad.jpg

 

                         L (1kHz)  Q (1kHz)  DCR      Price

1. Crites E-Core:        4.077mH   17.8      0.4626Ω  $19.00
2. Madisound 15awg SH:   3.963mH   33.0      0.2473Ω  $20.70
3. Jantzen 14awg C-Coil: 3.478mH    9.2      0.0690Ω  $54.98

                         (Keysight U1733C LCR meter)

 

Inductance values 15% off spec better not be normal for Jantzen. Both C-Coils were labeled 3.9mH, one was as above, the other was 3.327mH.

 

Conclusions
1. The 15awg Madisound Sledgehammer is an OEM ERSE IXQ inductor and it is the best performer by a large margin. If available with an acceptable DCR for your design, I doubt you'll find better regardless of cost (yes Virginia, that is a challenge). These are the only cored inductors to date that I'd consider as an alternative to air core in mid and high passbands. Secure them with stainless #10 bolts through the holes provided at either end and you're good to go.

 

2. My personal favorite is the Crites inductor that Bob worked with Universal Transformers to produce. They are tied with the IXQ as smallest and easiest to place, and the Crites seems completely immune to nearby ferrous material - which also means it transmits little magnetic interference. The build quality is second to none and with the varnish they're dipped it in it'll last a lot longer than any loudspeaker. The downside in my application is the DCR of 0.46Ω which would cost me a little over 1dB from the Klipschorn bass cabinet compared to the inductor I selected.

 

3. In highly efficient loudspeakers any of the (6) inductors I've reviewed will do well and their measurable differences will very likely be inaudible if placed properly in the system. With the ERSE IQ series, I'd heed Deang's warning and arrange a way to keep the plates from shifting (actually I'd just spend a little more for the IXQ). In less efficient loudspeakers where the inductor will pass peak currents exceeding a couple of amps, I suspect the distortion differences will become noticeable.

 

THD
You know the drill, this a marketing dept. measurement (for inductors) that I use to ballpark maximum current capability. One thing that the THD sweep was helpful for in this case was revealing a tiny resonance near 600Hz in the IXQ when passing an insane 16.6 amps (1.1kW into 4Ω) through it. The second IXQ sample had the resonance centered around 450Hz at that same "Honey! Get the fire extinguisher!" level. It's all quiet on the Western Front at lower levels. Fastening the units with stainless #10 bolts to stiffen the plates didn't help (or hurt). Finally, the C-Coil showed something similar around 1.2kHz.

 

467299686_THDAmpsGroup2.thumb.png.fffe28dc6f52c36a048296853a37449c.png

 

696233419_THDWattsGroup2.thumb.png.2e8346aa6d2512db89194fac7ac046bb.png

 

IMD
I'd be very happy with any of these coils in my system. Again, my threshold of acceptance is 0.5% for this nasty and prevalent form of distortion. In my case I went with the Jantzen because of its near zero DCR.

 

1248912578_IMDGroup2.thumb.png.c7d88df1aff3e419fc135a2354167b77.png

 

Multitone
Multitone was born from engineers that wanted to take two-tone IMD to the next level, thus it's not surprising to see the results below tracking what we saw above.

 

1239195533_MultitoneGroup2.thumb.png.8bdcb8e19dcc328a850342c57c4a2105.png

 

If you really want to know what's going on here you'll have to read through my earlier posts in this thread. I didn't repeat myself. Well, not that much. : ) I'm amazed at how hard it is to find objective comparisons of loudspeaker inductors or even objective data on them. I hope I filled in some gaps for you, it certainly did for me.

 

God bless you and your precious family - Langston

 

If someone separated the art of counting and measuring and weighing from all the other arts, what was left of each (of the others) would be, so to speak, insignificant. - Plato

Edited by Langston

Share this post


Link to post
Share on other sites

Hi @Langston

 

I am watching with interest your topic on the coils 👍

 

I myself modestly made a filter with a Jantzen coil 4N 18AWG for the HF103 Faital medium from my Cornwall.

 


I also love your amps: the Italian Powersoft and the US Benchmark AHB2. I myself have ordered a more modest but interesting handcrafted German handcrafted amp, the Pas-Audio 2002PCA, a class AB mosfet.

 

🤪

  • Like 1

Share this post


Link to post
Share on other sites

I’ve heard good things about the Benchmark, but why are all of the measurements done at 1kHz?

Share this post


Link to post
Share on other sites
On 5/29/2021 at 10:15 PM, Langston said:

Hello:

 

My first post here. Incredibly impressive forum on two counts - some genuinely serious audio (Chris A. and others) and secondly, rare for today, allowing some difficult conversations without censorship.

 

I spent a few decades in pro audio (concert production) with the intent on bringing the best sound in the world to my audiences. Of course I rarely pulled it off, but I enjoyed the pursuit. : )

 

Much of the endeavor involved modifying the weakest link in the chain: loudspeakers. My hero in the realm is Dick Heyser and he did a review on the mighty Klipschorn in a 1986 Audio Magazine article and ever since then I wanted to purchase a pair and have a go at making them all they could be without violating PWK's vision. Now I'm retired and have the time to make a mess of home audio, so I found a very nice pair of 1974 vintage Klipschorns, Polk SDA SRS 1.2TL's, Martin Logan CLS II's and some other stuff. I'm into inverse filtering per Dave Gunness's work and I'm also a huge Tom Danley fan though and may end in his court, we'll see.

 

---

 

What's my first post about? My stubbornness to stay with passive crossovers per the original Klipschorn design and thus have to deal with something I avoided with professional loudspeakers: cored inductors. Something this "simple" ended up taking much of a month to figure out and I'd like to share my findings. Sure, air core is the way to go as long as you keep them away from ferrous materials and magnetic fields. That's not so hard with the smaller values required for mids and highs, but at low frequencies, reasonable DCR is a challenge.

 

I thought it would be easy getting a high quality 4mH cored inductor with less than 0.5Ω DCR for the Crites cast frame woofer (replaced the square magnet K-33P), but even some of the best of these generate too much distortion for my taste.

 

---

 

What do I mean by distortion? To begin with, THD is a poor, but not quite useless distortion measurement for devices that exhibit natural low-pass characteristics; such as inductors and horn loaded bass cabinets. THD is all about comparing the unwanted odd and even harmonics to a fundamental, and the harmonics are largely filtered out! Thus you can get good THD numbers and still have audibly unacceptable levels of distortion with low pass devices. The solution is to measure distortion components within the passband of the device, and that can be done with intermodulation techniques that use two or more simultaneously generated tones within the passband to generate sum and difference frequencies as well as harmonics of the (two or more) fundamentals.

 

I chose Audio Precision's "MOD" IMD measurement technique as well as a high resolution, low frequency Multitone stimulus to compare 4mH inductors loaded by a 4Ω power resistor. 4Ω is what the Klipschorn and a great majority of low frequency systems use, thus 8Ω wattage specifications tend to be marketing ploys IMO. Inductors are current limited animals, not wattage limited. An inductor that is clean at 10 amps into 4Ω behaves identically at 10 amps into 8Ω. Ohm's law states that Amps(squared) times resistance equals watts, thus the 8Ω load will provide the marketing department with twice the wattage specification compared to the more realistic 4Ω.

 

---

 

It has been a personal endeavor to select a low DCR woofer inductor for my 2nd order (electrical) low pass filter. There is a 12awg copper foil air core inductor that boasts a 0.3Ω-ish DCR, but I wanted to learn about cored inductors, thus purchased the following 4mH coils (that's what their nominal spec's were, but the truth turned out to be 3.4mH - 4.2mH).

 

1. ERSE SuperQ 16awg
2. ERSE SuperQ 14awg
3. ERSE IQ 18awg
4. Jantzen C-coil 14awg
5. Madisound Sledgehammer 15awg
6. Crites Steel Core 0.46Ω DCR (don't know the awg yet, either 18 or 20)

 

I won't have inductor #5 until 2 June.

 

Would the results of my testing be of interest?

 

God bless you and your precious families - Langston

Heck YEAH! (this is the polite version). The uncensored version would have the HE double hockey sticks before the Yeah!!

  • Like 1

Share this post


Link to post
Share on other sites
Posted (edited)
On 6/6/2021 at 8:49 AM, Deang said:

I’ve heard good things about the Benchmark, but why are all of the measurements done at 1kHz?

 

I really like John Siau's audio philosophy, so when the Benchmark amp came out, it wasn't a question of whether to buy it, but how to get him to sign it! : )

 

369854648_AHB2Bottom.thumb.jpg.0935e4dbf8ba7f332ed33229bd8d7466.jpg

 

The truth is I haven't had efficient enough loudspeakers to be able to use the amp enough to really get to know it, so I use it mainly to measure stuff. I love the fact that it has clip LED's! Like most amps these days, it'll throttle itself to prevent more than about 1% THD when overdriven, but I hate the idea not knowing when the amp is beginning to act like a compressor/limiter. I also love heavy symphonic music at live levels (OK, maybe a bit too live) and these '74 Klipschorns I've been working on recently probably won't take the AHB2 amp out of idle. With the Klipschorn, the high power portions of my inductor testing are silly, but I wanted to learn.

 

I've actually never heard Klipschorns in my life, but I'm getting close - a couple of days from now and I'll find out what all the fuss is about. : )

 

On the 1kHz testing - I'm sure you're referring to the LCR meter results. I also looked at 100Hz, 120Hz, 10kHz and 100kHz, but I didn't think that was very enlightening. Everybody specs them at 1kHz - but I'm new at these things - let me know if you'd like to see the other frequencies for mH and Q. Another thing is that I've studied Q and know what it means and even how to calculate it without an LCR meter, but I still don't see how it applies in passive loudspeaker crossover applications. Please clue me in - I'd love to learn. Complex transfer function measurements agree with LTSpice simulations (of perfect inductors) at these "low" audio frequencies without the need to know anything other than mH and DCR. Above audio frequencies, I see why Q is a big deal.

 

Thanks!

Edited by Langston
  • Like 1

Share this post


Link to post
Share on other sites

No, sorry, I was referring to Benchmark’s stated specifications.

Share this post


Link to post
Share on other sites
Posted (edited)
2 hours ago, Deang said:

No, sorry, I was referring to Benchmark’s stated specifications.

 

Good question. Even the excellent link provided by the cool Frenchman with a taste for American cars is 1kHz oriented. I'll fix that and start another thread for it. : )

Edited by Langston
  • Like 3
  • Thanks 1

Share this post


Link to post
Share on other sites
On 6/6/2021 at 12:53 PM, Langston said:

 

Good question. Even the excellent link provided by the cool Frenchman with a taste for American cars is 1kHz oriented. I'll fix that and start another thread for it. : )

 

@Langston, I have an odd thought for you.  Is it possible to put these inductors in a Faraday cage to help eliminate coupling and cross talk?  That would be interesting to see.

 

Would a small(ish) ferrous metal box that surrounds the inductor do the same thing in the magnetic spectrum that a traditional copper mesh cage does for the electrical fields? 

 

Or did I misunderstand what you said above?:  If you mean by "mutual inductance" the presence of nearby ferrous material or unmodulated magnetic fields (driver magnets), you're probably right and it's on the dog.

 

 

Share this post


Link to post
Share on other sites

Reality, the difference between air vs iron is minimal at best and I serious doubt anyone can A/B test the difference between the 2. Measurable difference yes but that is the case with straight pieces of wire of different materials. Fact is Klipsch engineer's use iron for cost savings realizing no real audible difference. Many here build beautiful expensive crossovers that are more eye candy then sound candy. I say go for it if it makes you happy and have the money to waste. 

Share this post


Link to post
Share on other sites
Posted (edited)
6 hours ago, henry4841 said:

Reality, the difference between air vs iron is minimal at best and I serious doubt anyone can A/B test the difference between the 2.

 

I'm leaning in that direction given certain assumptions that resulted from what I learned from the measurements.

 

Which measurements would most likely expose the devices' audible defects in use and how to simulate that setup took me about a month to figure out. It is for my '74 Klipschorn project. In the past I wouldn't have even considered passive crossovers, but now that I'm so comfortable with inverse filtering (removing selected resonance and transfer function aberrations through FIR convolution), that I think I can achieve audibly indistinguishable results using passive crossovers and a single amplifier channel. It's a heck of a lot harder, and that's a huge plus. : )

 

Assumptions

1. Cored inductors are selected that don't change characteristics due to vibration.

2. Cored inductors are selected that remain low in IMD up to the peak current that will pass through them in a given circuit.

3. That inductors of any type are located so that none receive more than -50dB crosstalk from any other inductor.

 

This is fairly easy stuff to achieve and the fact that most pictures I see of passive crossovers violate at least #3 tells me that you're right - many people listen with their eyes and manufacturers listen to their accountants.

 

I think beauty follows function. Anybody that's been married a long time will tell you that. : )

 

God bless you and your precious family - Langston

Edited by Langston
  • Like 1

Share this post


Link to post
Share on other sites
Posted (edited)
6 hours ago, Oicu812 said:

I have an odd thought for you.  Is it possible to put these inductors in a Faraday cage to help eliminate coupling and cross talk?

 

We're both odd! : ) I tried that using steel and copper plates and got small improvements out of it, like an additional 3dB or so crosstalk reduction, but it would have been a hassle to implement, so it failed the hassle/benefit ratio. Moving an inductor an inch or two, or changing its angle relative to the other inductors will change things by 10dB at least, sometimes much more. I've been able to easily exceed my goals in crosstalk reduction in this project by inductor location, angle and height (to align their centers).

 

Here's early peek at the final design where you can see different thickness boards under the two air-cores to get maximum cancellation with the large iron-core toroid. The air-cores are aligned in the worst possible manner with each other so they would ignore the beast, so I used distance to reduce the crosstalk between them. I'll do a separate thread when the time comes for this Klipschorn mod, but the passive crossover's worst crosstalk is -72dB, and that's the larger air-core talking to the smaller air-core. Also, the smaller air-core is part of a CLR impedance compensation network parallel with the driver, thus less critical. Every other crosstalk combination results in less than -100dB. : )

 

God bless you and your precious family - Langston

 

1851076574_KHFPXovers1.thumb.jpg.bd21c455f2aa2eaa589643bc305e82c2.jpg

 

Edit: I just noticed that I should have swapped locations of the "beast" with the smaller air-core. That may have dropped the -72dB figure another 6dB or so. I'm definitely not gonna fix it. Fails the hassle/benefit ratio.

Edited by Langston
  • Like 1

Share this post


Link to post
Share on other sites

The main problem one could encounter using and iron core inductor is saturation. Hardly any issue when used in a crossover. We are dealing with really low averages going to speakers compared to some active electronic components. Never a problem with saturation. But anyone can go for it if one desires to have the best. Done that, been there before I learned better. 

Share this post


Link to post
Share on other sites
8 hours ago, Oicu812 said:

 

@Langston, I have an odd thought for you.  Is it possible to put these inductors in a Faraday cage to help eliminate coupling and cross talk? 

 

 

Not a Faraday cage. Mu-metal.

  • Like 2
  • Thanks 1

Share this post


Link to post
Share on other sites
1 hour ago, henry4841 said:

The main problem one could encounter using and iron core inductor is saturation. Hardly any issue when used in a crossover. We are dealing with really low averages going to speakers compared to some active electronic components. Never a problem with saturation. But anyone can go for it if one desires to have the best. Done that, been there before I learned better. 

 

I used two methods to determine cored inductor current saturation levels; the classic scope method using a variable pulse rate and width generator I made and by observing knees in the distortion traces with sweeps and a big amp. I noticed that the sweep method is more appropriate because the knee occurs before you can see it on the scope. My tough IMD acceptance threshold of 0.5% occurs much lower (maybe a tenth) of the current saturation spec. (mfg's use the scope/pulse method). I'm not saying it's a law of nature that you can divide the inductor current saturation level spec by 10 to figure out IMD or anything else. The good news is that my measurements showed huge variations between differing cored inductor designs with some of the least expensive coming out on top.

 

IMO, given that extremely good performing inductors are inexpensive, it seems silly not to optimize this element of our addiction.

 

My inductor torturing pulse generator (the inductors get hot) and schematic with notes: (link to designer's page)

 

256801372_LSatInternal.JPG.18d684cfe927ea445ab16673f7018a9c.JPG

 

1425960286_LSatSchematic.thumb.png.8151296b79404d1bf2bdb0403d081d47.png

  • Like 1

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...