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Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6

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Posted on April 11, 2015 at 12:33:01
nicoff
Audiophile

Posts: 47
Location: USA
Joined: April 20, 2003
 I broke the ribbon tweeter in one my 20.7 speakers. I will be ordering a replacement next week.

But since I also have the 3.6 maggies, I wondered if the ribbon tweeter in the 3.6 would fit the 20.1.

I searched this forum and there seemed to be differing opinions. Some folks referred to Magnepan's web site which shows the specs for each speaker to show differences; others pointed out that several listed specs were incorrect which means that the information listed may not be entirely accurate.

So I decided to do a hands-on testing. I took out the damaged tweeter out of the 20.7 and a good tweeter from one of the 3.6. I compared them side-by-side. The dimensions (length, width) are exactly the same. The holes for the screws that hold them in place are also exactly at the same location. The ribbon and the end connections also look the same.

Then I installed the tweeter of the 3.6 into the 20.7. The result? It works perfectly. So unless I am missing something, both speakers use the same ribbon tweeter. Extrapolating, and now with a high degree of certainty, I believe that the ribbon tweeters in the 3.6, 3.6R, 3.7, 3.7i, 20.1, and 20.7 are all the same.

Perhaps this is common knowledge, or perhaps I am missing something.

 

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RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 11, 2015 at 12:57:53
Norman M
 If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.

 

RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 11, 2015 at 14:49:00
wazoo
Audiophile

Posts: 4062
Location: Middle GA
Joined: December 6, 2006
 It's a superb tweeter. Your observation makes plenty of sense, especially for a manufacturer that values cost containment, like Magnepan.

I disconnected my 3.7s this week - I'll probably have to put them away for a while (not permanently - due to a temporary room reconfiguration). I tried my daughter's Def Tech Mythos ST speakers. They will fit better and they sound quite good, but the Maggie ribbon would be sorely missed. It really is a superb tweeter.

 

Roof, posted on April 11, 2015 at 16:10:34
slapshot
Audiophile

Posts: 2248
Joined: January 9, 2006
 Wazoo, what are you doing to the roof?

 

the word in question ends with an 'm', not an 'f' ;-), posted on April 11, 2015 at 17:50:58
wazoo
Audiophile

Posts: 4062
Location: Middle GA
Joined: December 6, 2006
 The room reconfiguration is a bit of a long story, but the mancave will also serve as my sleeping quarters for a year, or two. At any rate, I doubt the 3.7s will be workable in the new arrangement. For the time being, I'll live with conventional speakers. Well, the MMGs will remain in use in the house.

Hey, it'll give me an opportunity to dig into the 3.7s. I might even build them a set of hardwood frames.

 

RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 11, 2015 at 18:46:39
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 You are correct the tweeters for the "3 series -- 3.3, 3.5, 3.6, 3.7 -- and for the 20 series are identical.
The tweeter for the IIIa came in two forms - one identical to the III with an impedance of 3.0 ohms and then as as a 2.2 ohm version. The ribbon for the IIIa requires a 60" slot and the current ribbon requires a 60.6" slot. I routed out the extra 0.6" in my IIIa's and am using the current tweeter. Initially Magnepan would not sell the "newer" ribbon for the IIIa because it didn't fit the frame but if you explain that you are modifying the frame then they are happy to accommodate.



"Our head is round in order to allow our thoughts to change direction." Francis Picabia

 

RE: the word in question ends with an 'm', not an 'f' ;-), posted on April 11, 2015 at 19:25:47
slapshot
Audiophile

Posts: 2248
Joined: January 9, 2006
 Ah, well, place them side by side--double bed you can sleep on! :)

"Conventional" speakers sounds so, um, conventional!

 

RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 11, 2015 at 19:37:57
Green Lantern
Audiophile

Posts: 16952
Location: San Diego, Ca
Joined: November 12, 2002
Contributor
  Since: June 17, 2003
 not meaning to pry but would it be possible to shed some light on how the tweeter was damaged?

Glad the swap worked out for you!









 

RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 11, 2015 at 21:26:27
nicoff
Audiophile

Posts: 47
Location: USA
Joined: April 20, 2003
 The tweeter got damaged because I switched sources and due to a handshake delay I thought that the volume was too low and raised the volume. When the preamp resolved the handshake and connected to the new source, the volume was too high and broke the tweeter. It was my fault. But I have to say that this new preamp takes much longer to resolve hdmi handshakes than my previous one.

 

RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 11, 2015 at 22:15:32
Norman M
 Then the all too obvious, no fuses or with fuses?

 

RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 12, 2015 at 05:44:16
nicoff
Audiophile

Posts: 47
Location: USA
Joined: April 20, 2003
 With fuses. The fuses did not break. This is NOT the first time that I have had a broken tweeter and the fuse did not break. I have asked Magnepan why the fuse did not break and never got a good answer.

 

thanks for the info, posted on April 12, 2015 at 05:49:01
Green Lantern
Audiophile

Posts: 16952
Location: San Diego, Ca
Joined: November 12, 2002
Contributor
  Since: June 17, 2003
 Every now and then I'll hear digital artifact in-between songs which sounds a lot like a needle being gouged on a LP (now there's irony for you).

Doesn't happen that often and I'll be damned if I can prevent it, but when it does-it sure makes the hair on my neck stand on end.









 

RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 12, 2015 at 06:39:58
Davey
 I wouldn't blame Magnepan too much for lack of an explanation. Fuses are just not an optimum solution for this application.
This isn't the first time the ribbon protected the fuse and it won't be the last. :)

The right set of transient conditions can easily create a situation where the fuse element can not heat/react fast enough.

There are better solutions for this issue nowadays....resettable poly-switch being one....but Magnepan seems slow to adopt something else.

Dave.

 

nuisance opens - question, posted on April 12, 2015 at 08:26:45
wazoo
Audiophile

Posts: 4062
Location: Middle GA
Joined: December 6, 2006
 A resettable poly-switch with a markedly faster reaction time will need an adjusted current rating. I experimented with pico fuses, which open very fast, and using the stock fuse current rating resulted in nuisance opens once every month or two. As I have no concern over going fuseless, I upped the rating an ampere and didn't have one blow over a three month period (not conclusive, I know). By that time, I was tired of fiddling around and stripped the connector plates down to just the binding posts.

I guess I'm about to have plenty of time to fiddle with them now. Although, I'm currently very busy with other, more pressing projects.

 

RE: nuisance opens - question, posted on April 12, 2015 at 09:08:10
Davey
 Yes, sorry for not elaborating. You would probably not select an equivalent current rating if replacing a fuse with a polyswitch or different type of protection device. An alternative would be a much faster reacting device and higher "rating" would be appropriate.

Dave.

 

RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 12, 2015 at 10:02:39
Norman M
 I'm indeed sorry to learn about your ribbon loss. Instances of the ribbon having saved the fuse have been mentioned here many times. In all such instances in which I switched into a source set to play at a too high level, the fuses always blew before ribbon damage occurred. And this happened innumerable times in the 20+ years I've had my Tympani IV-As. So my fuses must have indeed saved both my ribbons and my ass. Magnepan must have heard about instances in which the ribbons died before the fuse many, many times.

I suppose Magnepan didn't have a "good answer" to your question because in reality it amounts to a design flaw on their part, (especially because 'Davey' in this thread describes a way to avert this from happening). I'm not a techie, so I don't know how practical Davey's solution might be. That is to say, can it be built into their ribbon speakers, or is it an after market solution which can only be done on a user's part?

 

RE: nuisance opens - question, posted on April 12, 2015 at 14:42:08
macmagman
Audiophile

Posts: 501
Location: NW Indiana
Joined: October 17, 2010
 This has happened to me more than once also. If there is an alternative as Davey mentioned with a poly switch which would eliminate this problem I am all ears.

 

RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 12, 2015 at 15:25:21
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 We have discussed this before and I think it is "safe" to conclude that a fuse will not protect a tweeter and a polyswitch is a better solution. However, I am wondering if the tweeter blew not because of high current but rather because of extreme excursion. In other words, did the ribbon rip apart or did it melt. I suspect it ripped and, if so, then a polyswitch may not help either. Perhaps a close look at the tweeter will reveal signs of melting or signs of a rip.
Since most tweeters fail because of clipping, the best approach IMO is go to a line-level XO (biamp) since this isolates the tweeter from the clipping amp (much more likely to be the bass amp than the tweeter amp). Again however if the tweeter ripped because of large excursion, then this approach will not work either.



"Our head is round in order to allow our thoughts to change direction." Francis Picabia

 

RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 12, 2015 at 15:59:49
Davey
 Yeah, I think it's possible it was excursion related. There are usually capacitors in the signal path, but it's still possible to create decent currents at low frequencies with the odd transient from the power amp. In this case he's noting a sudden resumption of the signal at high volume caused the issue. :)

I'm not meaning to suggest that polyswitches will guarantee tweeter longevity in all cases, but I think they will perform better, relatively speaking, than fuses in both the protection aspect and the "sound" aspect. Fuses are a fairly non-linear device and not what I would want in series with my drivers.

However, these ribbon drivers are fragile and power amps can store/deliver a lot of energy. There is some inherent risk no matter what type of safety approach is taken. :)
As has been noted previously, it's not that expensive to replace one of these tweeters and some users see an occasional failure as the price of doing business.

Dave.

 

RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 13, 2015 at 17:25:32
Norman M
 Whether a ribbon melted or ripped (from excursion) wouldn't a lot of 'juice' have been sent its way before either took place? It doesn't appear that too many listeners here might ruin a ribbon as a consequence of clipping, at least not during the course of normal music listening. It's unfortunate that fuses can't break before either 'melting' or extreme excursion happens. While it might not be terribly expensive to get a new ribbon, it wouldn't be easy for me to install one. I have in fact watched my dealer's workers doing that (while in my home) and to top it off on one occasion a soldering joint eventually failed and they returned and did it a second time. If they didn't get it right the first time around, my chances are next to zero.

 

RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 13, 2015 at 20:27:45
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 Actually clipping is probably the main reason why tweeters (cone or ribbon) go bad. Clipping causes a lot of high frequency noise (current) that causes the tweeter to fry. Ideally the fuse should limit the current but in reality that does not happen. You might want to read the article by Rod Elliott (http://sound.westhost.com) on why tweeters blow. My point about excursion of the ribbon is that it may not be a thermal event that afflicted the OP and in that case a thermal protection device, either a fuse or polyswitch, will not help.
As far as replacing the tweeter, it really isn't that hard but good soldering techniques are needed. Try practising your skills before you tackle the ribbon. It really won't take that long to get adept. Remember to use an iron that is hot enough and make sure the surfaces are clean. Also create a mechanical connection before making the electrical connection.



"Our head is round in order to allow our thoughts to change direction." Francis Picabia

 

RE: Difference Between Magnepan Ribbon Tweeters: Mg 20.7 vs 3.6, posted on April 13, 2015 at 23:48:09
Roger Gustavsson
Audiophile

Posts: 2054
Location: Huskvarna
Joined: February 12, 2010
 Is it the ribbon end connections that need more space in the later ribbon drivers? The ribbon cage is indentical. I have both the earlier version (T-IVa) and the current ribbon drivers (3.6).

 

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