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B&C 21-IPAL Driver and Measurements Discussion

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Thanks for the link. I just read it with translate. They did an excellent job on the build.

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Hey.

I was digging deeper in some speaker parameters and detailed relations of voice coil work.

It has been said for some B&C drivers, that they used Aluminium voice coil winding instead of Copper, to get more turns in the gap, to get greater motor force.

That is easy to say, but it doesn´t seem that easy to do.

For example with 21SW115 vs 21DS115. IPAL drivers also have Aluminium voice coils (wire) for that reason. The motor force is there, yet I still cannot wrap my head around it due to “apparent physics” of things.
One needs to have 1,6x of wire area/volume of Aluminium to get to the conductivity per length compared to Copper.
Then Accounting for Bl, (21SW115 vs 21DS115), on top of that, one needs double the wire length to get to the adequate outcome of Bl in slightly wider magnetic gap.
Then the 21DS115 has longer coil with smaller Resistance, which again means, more wire. We´re talking about 3,5x more wire volume here. How come it works? It looks like to me like it cannot work "just like that". Even worse, the Mms of the Aluminium "aided" driver is more. IPALs are the same thing. Even greater motor force, but at least half of it can be attributed to greater flux density in the gap. It is not the case with other drivers.

Can anybody help me solving this obvious thing mathematically (Resistance, wire length and volume) so the outcome makes sense?

Thanks.

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The short version is that the answer is not as simple as that.

Have you ever done modeling of electromagnetic circuits, or tried to design and model a speaker motor and voice coil system?

The wire material, total length, number of turns, wire gauge, etc...All matter, but that is only part of the puzzle. The gap geometry, amount of wire in the gap, magnet size, shape, grade, steel grade, shape, etc all have an effect. It's a complex set of tradeoff's and compromises. If you modify one thing it affects many others. Copper and aluminum are both useful. Copper becomes very heavy and is more expensive for long xmax, large diameter voice coils like those required for modern sub drivers.

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That short version of your answer is not that bad at all. I actually wanted to hear something like that, because only "more wire in the gap" didn´t work well in my book.

I touched some modeling, getting custom transformers made. Sometimes counted, sometimes physically "iterated" to expected performance. My nature is of "random electronic engineering". I might not know precisely, but at least there is some imagination. 🙂

All those compromises are understandable, but there is this main representative claim, that this advancement between virtually identical drivers with identical motor structures happened by replacing copper wire for Al wire (like 21SW115 and 21DS115, while IPALs don´t have these copper counterparts). That is my image of things, and how these are portrayed.

Once it was claimed, I started to count for real, and it looks to me the way the wire easily cannot fit in the gap to make this change....

Like if B&C left one piece of some magic fact in that claim away from readers/listeners. It possibly is not just the wire, which is what you wrote. Then, I´m keen on finding what is it then...

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I would not assume that those motors are identical...Most of the B&C bass drivers used 2 layer coils, inside/ outside wind with split winding on the outside layer only. Quasi / mini LMT design basically. Some pro woofers still utilize single layer coils. Note that they make a big deal of stating it's a 4 layer coil on the DS's. Gap size could different for the 2 layer coil and 4 layer. It probably would be. Wire gauge is probably different. Length of wire in the gap??? It's a guess without more information. 

Speaker motor and coil design is a DEEP rabbit hole. 

Car audio drivers have been using 4, 6 and 8 layer coils for years. I've even seen some drivers with 12 and 16 layer winds. 

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I think that even that one about same motors have been claimed, but I might dig too long to even find it. It would make sense if it was little different, even when not counting on gap widths.

It is true that coils of those speakers might not be specified precisely, and that can be why I cannot make it work. I only saw Quasi-split voice coil mentioned in 21SW152 specs on B&C site, but not for other speakers. Who know which models are made that way, which models are not, and what differences might be in the same coil topologies between drivers.

It would definitely mess up some of my guesses about wire lengths and so on.

One other thing flew over my mind. Copper is more diamagnetic, while Al is more paramagnetic material. Can it be, that the Aluminium actually alters the flux in the gap some more, compensating for some of the losses in greater gap? Just an idea. And also less back EMF.

Yes, I fell into this deep rabbit hole for last month. It seems that I have no real use for it - Knowledge of speaker behavior as an "user" is enough to develop stuff. Yet human mind has this bad habit of exploring all kinds of rabbit holes. We even like to play with things that can easily kill us...

16 layer winds? OMG, how large magnet this one needs....

 

//repaired mistake in magnetism part

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Bennett chimed in on another forum. It´s what you expected - different coil topology, possibly slightly different motor assy. Then with resting aspects offsetting the "apparent mathematical issue" make things doable. Thank you for all that technical chat and unwrapping my head from the maddness...

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I have a question regarding the 21Ipal driver failures. Is there any of you guys having any problems with them? 

I had some problems with my drivers in the past year. 4 of them had a strong noise in the suspension, 2 had them right from the beginning, 2 developed it after 5-10 minutes of use. 2 others had one of the two layers unglued and unfortunately it was the one underneath so I had to sent them back. Another one had the suspension not glued straight , one could clearly see a 2-3 mm difference on one side .

Please tell me about your experiences.

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Hello.

Depends what does it mean "problems" in some cases. Unglued coil is quite obvious, other issues might not be that obvious. I believe B&C speakers takes this seriously. Everytime I have slightest issues with those drivers, they requested serial numbers to check things up, and they were most helpful to solve the issue directly, so I didn´t even had to deal with the seller.

Strong noise in suspension is very broad claim. Could you document it somehow, and specify more in detail?

Aluminium four layer coil is probably hard to make reliable. It has lower melting point, it has more thermal expansion, and four layers with additional motor force also add trouble to the adhesives on voice  coil, former and spiders.

Anyway, I recommend you to deal with B&C, as we might not be of great help with already damaged product. I haven´t seen single damaged product from B&C in any similar way yet. Only second hand stories from far away, which sounded like miraculous occurrence.

Also B&C Is one of those brands, which are copied by eastern countries a lot. Make sure you get original reliable product made by B&C Speakers.

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@Crashpc thanks for the quick reply. All the drivers were sent back to the factory and repaired under warranty. The problem is they didn't recognize there is a problem with the driver. It happened to me just with the Ipal, none of the others had that problem. 

The noise is a strong ticking sound coming from the spider suspension and a rumble like that of a diesel engine, in tandem with excursion. It is present no matter what level and it increase directly proportional with it. 

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The company is big, the other drivers work very well and very hard with no problems. Bennett was very helpful with me, but this problem keeps appearing. 

I reevaluated my settings, the enclosure, measured temperature, working conditions, changed enclosure , all sorts of things. 

I have 2 working well right now, they have played for over 150 hours at very high levels on all sorts of program, including having ATB and Lost Frequencies playing on them. No issues so far. 

2 21ID drivers were used in the other SKhorn XL enclosure with no issues for the same amount of time. Settings and limits were identical (relative to each other's impedance) 

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Paul,

We briefly discussed this before but I did receive a pair of 21Ipal's that had a ticking sound coming from inside the motor. It was the first pair I ever received. Sounds exactly like you described almost like diesel a engine and got worse with level. Also that pair had a different gasket material and the BL was quite a bit below spec on them. Almost like an old production run or something. My second set did not behave the same way. BL was up where it should be and no ticking sounds. Bennett exchanged the first set of drivers after I sent some video and explained it to him.

I still don't know for sure what the ticking sound is. I've never had an issue with any other B&C woofer.

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Hey Paul,

I might be slow on things -  If they repaired yours under the warranty, while they didn´t find the issue, what was the solution then? (recone, replacement of drivers), and do you have your repaired driver back in fully working order without those issues?

Was the original issue repeatable with free air driver, so B&C got better chance of finding it?

I had small ticking noise with 18SW115 due to terminal leads, and maybe something with 21DS115, but only under very extreme conditions, while it solved itself after burn-in or with slight bending of those leads. Nothing like "diesel engine" as you guys describe it. I´m so used to B&C quality that I might feel childish butt-hurt at first, when I´d found less than flawless product from these...

Anyway, I would blame the enclosure on first sight, but again, it´s hard to tell. You might need to do more detailed break-in procedures from now on, and break down all your steps between getting those drivers shipped and getting to the failure, to get to the issue.

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The noise was present right out of the box, at any level in free air. Breaking in didn't help, as a matter of fact it made things worse. Enclosures had nothing to do with this, the other drivers behave excellent in there. The solution was recone , but the delivery terms are way too big for what I can handle. I sent them and they repaired them all, but after a long time... 

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Right there, in the first step. Welp, there is probably no way to blame the box, or driver break-in, or material fatique. It´s the driver.

Then I possibly have nothing in my hands to help. At least product support is good. Hope it is solved for good at B&C.

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