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The elusive "i" ???

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Posted on April 6, 2021 at 16:05:00
Joe Schmo
Audiophile

Posts: 518
Location: Palm Beach
Joined: April 21, 2008



This is by no means official or confirmed, just my own thoughts and observation. Could I have stumbled upon a few clues as to what revisions were made to the 1.7 to elevate it to the "i" designation?

I have a pair of new 1.7i speakers in house, so using the trusty flashlight trick, I thought I'd take a look at the crossover through the sock to see if there are any obvious differences. I found a pic of the original 1.7 crossover in an old post using Google for comparison.

Here's what I can see:

A. The 1.7 had a solder tab on the far right that joined the yellow super tweeter wire to a red wire that was connected to the rear fuse/jumper plate. That solder tab is gone in the 1.7i and the yellow super tweeter wire now goes straight to the fuse/jumper plate.

B. The 1.7 had two black Axon True Cap capacitors that are now white capacitors of a different vendor/model that I haven't identified. I also cannot determine by looking through the sock if the values are the same as those values previously posted for the 1.7. Obviously I can't measure them yet either.

C. The red wire that connected the solder tab on the far right has been eliminated along with the solder tab. The yellow super tweeter wire now goes straight to the fuse/jumper plate.

The inductor connections look the same through the sock, but again I cannot verify the value or DCR of the 1.7i inductor without complete access which will come later on. ;)

All of the other wiring connections look the same tracing them with difficulty through the sock. Again though, that is my preliminary observations doing this with limited access.

I know my 1.7i crossover pic looks like a 1950s UFO shot. It's the best I could do through the sock. Clear access will come soon enough!

So, there are some mechanical crossover revisions that I can see, but I don't know if any component values are different. It does appear that two of the crossover capacitors are from a different vendor?

This is just fun speculation on my part. Nothing more, nothing less.





-Joe

They're not that big!

 

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RE: The elusive "i" ???, posted on April 9, 2021 at 13:20:11
emailtim
Audiophile

Posts: 5393
Joined: July 2, 2017
 "... The 1.7 had two black Axon True Cap capacitors that are now white capacitors of a different vendor/model that I haven't identified. ..."

I believe the white capacitors are RTI caps.

I found this:

"... Most boutique American brands are actually fabricated by RTI Electronics of Anaheim, California, though their high-end audio cap production is now a subsidiary of Electrocube. ..."

"...
RTI F Series
Metalized Polypropylene Film
1.0uF/200VDC = $20.00

As previously mentioned, RTI claims to be the OEM for 75% of the boutique audio caps on the market. Their F Series is sonically identical to the Auricap, above, and the same comments apply. While available for bulk purchase only, for a $5,000 minimum order, RTI will be happy to put your name on them instead of their own.
..."

http://www.laventure.net/tourist/caps.htm

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2022/03/30 Historical Records CENSORED

 

RE: The elusive "i" ???, posted on April 10, 2021 at 06:32:34
Gforcegerry
Audiophile

Posts: 27
Location: Suffolk
Joined: January 27, 2004
 Thanks Joe.
Interesting and I look forward to updates.
I have 1.7s so always keen to know what the difference is.

 

RE: The elusive "i" ???, posted on April 11, 2021 at 14:48:04
Joe Schmo
Audiophile

Posts: 518
Location: Palm Beach
Joined: April 21, 2008
 I agree. The white capacitor in the 1.7 appears to be made by RTI from what I can see in that top photo. Apparently RTI was sold to API Tech in 2012. It does not appear that RTI audio capacitors were made under that name/spec after that time. This was about the same time, or shortly thereafter that the "i" designation appeared on the 1.7 and 3.7 speakers.

I don't see any visible markings through the sock on the three white caps that have replaced the RTI and Axon caps of the 1.7, so who knows where they are sourced from, but they are different.

On closer examination, the inductor is different looking too. The one in the 1.7 looks identical to an Erse IXQ model. The one that is now in the 1.7i has a different looking bobbin. Could the "i" designation be as obvious as a different spec inductor? LOL

The blue axial lead bipolar electrolytic cap and the black Erse Pulse X cap from the 1.7 look unchanged in the 1.7i.

The crossover in the 1.7 is definitely not the same as the crossover in the 1.7i. It's a slightly different layout and different components. Everything else besides the crossover appear to be identical between the two models. Based on these observed differences, I believe that the "i" revision was the crossover.








-Joe

They're not that big!

 

RE: The elusive "i" ???, posted on April 11, 2021 at 14:51:39
Joe Schmo
Audiophile

Posts: 518
Location: Palm Beach
Joined: April 21, 2008
 I'll eventually remove the sock to get a better look, but the crossover appears to be where the "i" revision took place.
-Joe

They're not that big!

 

RE: The elusive "i" ???, posted on April 11, 2021 at 17:17:55
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 I thought that had been settled at that time, that the crossover was the change. I think Magnepan would 'upgrade; for a fee....the 'Non-I' issue.

As for inductors?

First? there are 2 main types. Aircore and Ironcore. Any of the solids qualify fo that.

Such inductorss can be made over a wide range of configurations for any given inductance value. In general? Number of layers.....and number of turns PER LAYER.

But in order to fit the speaker, you may choose one type over another. This means you also choose wire size based only in part on maximum power handling. Resistance of the inductor also plays no small part.

An Example? My MG1.6 uses an ironcore in the low-pass circuit. It is 16ga wire and 0.40Ohms while being 3.5mh in value.
The last? I can't rmember offhand.
But when I was thinking to UPGRADE my crossover, I discovered that nobody made that exact value, but would instead DEWind a higher value for me.
So I did some research.

And I discovered the OPTIMIUM INDUCTOR has the same number of turns per layer as layers. Typically, an airfare has a LOWER Resistance than Iron for the same inductance. At least the ones sold use THAT a a 'selling point. But what if you want the new within say..... 5% of the old? DIY is the answer.
And don't forget that changing the inductor resistance will ALSO change the frequency balance. Lower DCR of the inductor results in a louder output. Thicker wire just means you will NEVER be able to over power this inductor while and ironcore can saturate....BOOOOO

I ran many siulations thru an online calculator. I found that I could get the same reisitivity out of an aircore and have thicker wire AND a reasonable overall size......Aircore can be gigantic, under certain condtions.
I used in my model, STOCK PVC sizes. Nut / bolt an axle with 'side plates' to limit the width. Add a couple feet for leadouts.

Copper Magnet Wire is getting expensive. But you want wire that has NOT bee 'respooled' and potentially nicked or abused.
Too much is never enough

 

RE: The elusive "i" ???, posted on April 11, 2021 at 18:49:42
emailtim
Audiophile

Posts: 5393
Joined: July 2, 2017
 " ...
And I discovered the OPTIMIUM INDUCTOR has the same number of turns per layer as layers. ... "

How do copper foil inductors fit into that picture ?
.

2022/03/30 Historical Records CENSORED

 

RE: The elusive "i" ???, posted on April 11, 2021 at 20:08:38
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Why would you want a foil inductor? A personal prejudice? Also, the field around a wire is symetric. Not so with a flat conductor.

If the height of coil is the same as width, that is the maximum possible flux density, so should be about the same as a wire wound inductor.

I'm a big fan of epoxy, too. And a low temp oven bake to outgas. Must stay will below the insulation temp rating.
Too much is never enough

 

RE: The elusive "i" ???, posted on April 11, 2021 at 20:48:36
emailtim
Audiophile

Posts: 5393
Joined: July 2, 2017
 "... Why would you want a foil inductor? ..."

They used to be quite popular and have a considerable following in various varieties (poly,wax,etc).

FWIW, I have seen square and rectangular mag wire. I wonder if that works any better than round wire (presumably less gaps when wrapped laid side-by-side. Foil would also have less air gaps if that makes any difference.


.

2022/03/30 Historical Records CENSORED

 

Here is one set of "pros and cons", posted on April 11, 2021 at 21:20:55
emailtim
Audiophile

Posts: 5393
Joined: July 2, 2017
 Here is one set of pros and cons that I see parroted in other write-ups between wire and foil.

Questions are:

1) How much is marketing hype ?
2) Do these deltas present in the audio band ?

https://positive-feedback.com/Issue6/goertz.htm
.

2022/03/30 Historical Records CENSORED

 

RE: The elusive "i" ???, posted on April 11, 2021 at 21:46:42
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Over my pay grade.

BUT? I think the dominating principle is that the coil be SQUARE. For round, that's as many turns per layer as layers. Without regard to the diameter of the CORE.

When I did my noodling? I kept varying the size of hte CORE using standard PVC sizes until I got close than varied another parameter.

I eventually got a 'square' coil of DCR within 5% of the Magnepan stock coil......so no increase in bottom end, by even a db or so.....

A POTENTIAL problem with SQUARE is that the EDGE is vulnerable. Nick? And loss of insulation. This is not a good thing, if taken to extremes.
Too much is never enough

 

RE: Here is one set of "pros and cons", posted on April 11, 2021 at 21:52:23
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 All that skin effect and 'what he noticed' is Just Gas until coils are compared and matched based
on DCR.

the typically LOWER DCR of the foil coil (not meant to match whatever coil is coming OUT except for MH value...)will play a LITTLE louder because the total DCR of that part of the circuit is lower.....but the driver is STILL the same.

I'd compare like to like. And the photos I've seen of those coils tell me they are NOT optimized.....But wound on a standard core until the correct value is reached.
The goal is lower DCR which SELLS....+
Too much is never enough

 

RE: The elusive "i" ???, posted on April 12, 2021 at 07:31:16
Joe Schmo
Audiophile

Posts: 518
Location: Palm Beach
Joined: April 21, 2008
 "I thought that had been settled at that time, that the crossover was the change. I think Magnepan would 'upgrade; for a fee....the 'Non-I' issue."

Well, yes and no.

Yes, Magnepan did offer to perform the "i" revision to existing 1.7 and 3.7 speakers for a reasonable cost, but safely packing the speakers for shipping and all shipping cost both ways were the owners responsibility. Some thought that was a fair deal others did not.

The main debate however, that continues to this day as far as I know, is that Magnepan would not reveal what the "i" revision entailed. Sighting proprietary trade secrets, their official statement on the revision was that their listening panel unanimously concluded that the revision improved the speakers performance, but that they felt the change did not warrant a full .8 designation. They stated that the .7 and 20.7 models already included the "i" design changes and would not need an "i" identifier. They made the offer to owners of 1.7 and 3.7 speakers to perform the revision at the factory at the owner's own discretion.

Following that there has been a great deal of speculation as to what the "i" revision was, with very little direct, verifiable evidence. I have made a reasonable attempt to do that here.

We will most likely never know for sure.


-Joe

They're not that big!

 

RE: The elusive "i" ???, posted on April 12, 2021 at 10:28:03
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 I see the ONLY potential path forward to be IF you can locate an origina pair of 1.7 OR th 3.7 and to a teardown side-by-side with the 'i' revision model......
Count Dem Staples!

Various measurments may be part of this.

As for the DIY crowd? If they are going to modify the crossover anyway? Probably just as well to start with the Non-i version which would be less $$$ to purchase.....
Too much is never enough

 

RE: The elusive "i" ???, posted on April 12, 2021 at 23:58:10
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 I'd doubt 'pictureguy caps' would sell!
Too much is never enough

 

why squares?, posted on April 16, 2021 at 15:50:08
DrChaos
Audiophile

Posts: 2063
Location: San Diego
Joined: July 13, 2009
 I bet it's for better mechanical properties.

There are forces on magnetic systems, like magnetostriction. I think the square wires will lie better and deal with those vibrations better(which can result in nonlinearities electrically as geometry is changing), so useful in inductors & motors I think.

 

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