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Magnepan XO-1 on MG-3.5R's?

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Posted on October 17, 2011 at 13:34:46
Planarguy
Audiophile

Posts: 15
Joined: October 17, 2011
 I just got off the phone with Magnepan and they were confused too. In the manual for the MG-3.5R, it tells you you can use the XO-1 line level electronic crossover unit for that model, but refers you to the XO-1 instructions for details. The XO-1 instructions do not list the MG-3.5R's.
Ha!
So, have any of you done this, and if so, how what formula did you use to calculate the capacitor value for the MG-3.5R and your amplifier?

Thanks for your input.

 

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The XO-1 is *not* an "electronic XO". It is simply ..., posted on October 17, 2011 at 14:46:16
andyr
Manufacturer

Posts: 12548
Location: Melbourne
Joined: September 2, 2000
 a collection of passive parts to allow a primitive style of passive biamping.

If you want to biamp your 3.5s (which IMO is an excellent thing to do), do it right ... get an active XO that allows you to have asymmetric slopes and level controls on both frequency bands. (Marchand make one, if you're not into DIY.)


Regards,

Andy

 

RE: Magnepan XO-1 on MG-3.5R's?, posted on October 17, 2011 at 14:59:35
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 The XO-1 is just a first order high pass filter and a potientiometer to reduce the gain of the bass amplifier to match the mid-treble amp. Magnepan assumes that the amp with the greater gain will be used on the bass which is not necessarily the case. Greater power does not equate to greater gain.
In any case the value for the cap is C = 1/(2*pi*f*R) where R is the input impedance of the mid-treble amp and f the -3db cutoff frequency of the hp filter.

Using the XO-1, creates a PLL hp filter and you continue to use the external xo (speaker level) for the bass. Sort of a bastardized line-level/speaker-level XO. As Andy says it's really not suitable for the 3.5.



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

 

RE: Magnepan XO-1 on MG-3.5R's?, posted on October 17, 2011 at 17:26:34
Planarguy
Audiophile

Posts: 15
Joined: October 17, 2011
 I am rather experienced in these sorts of things, so am aware of the simplistic design of the XO-1. I have designed and built true active crossovers in the past(anyone remember ProSonics?), but my vision and hand control is not what it once was. Scratch the building project. I consider Marchand and others to be grossly over priced, so scratch that idea too. Besides, line level is cleaner.
In any case, the XO-1 should certainly work equally as well(as poorly?) with the 3.3, 3.5, 3.6, etc, as it did on the 3 and 3a's as well as the Tympani's. The manual for the 3.5 even states the XO-1 can be used with them, just no details on the what specific formula you should use. The XO-1 manual lists 2 different formula. 1 for the MG3, and one for the Tympani. These are different; so I don't think Andy's approach would necessarily be correct here for this model, although do appreciate the suggestion.
Unfortunately, the lady at Magnepan who had the paperwork for this - retired, and Wendell doesn't know what happened to the info.
As far as matching and or adjusting output via the potentiometers, yes, It was a poor assumption that the more sensitive amp. would be used with the bass level control. A couple of ways around that, but the easiest thing to do is to make sure the assumption is correct.
I was hoping someone else had already invented this wheel, but looks like I'll be doing that myself. I'll report back to the group, with the correct formulas for the MG-3.5R, or scrap the idea and go back to my reference speakers; Bose 301's........;) Let's see, where did I put that The Mama's and the Papa's 45...?

 

RE: Magnepan XO-1 on MG-3.5R's?, posted on October 17, 2011 at 18:13:10
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 Did not mean to talk down to you but you did ask for the formula. I would shoot for a cutoff frequency around 200 hz in which case the formula simplifies to C = 0.8/R with R being in Kohms and C in mfd. The formula that was in the IIIa's manual was 0.318/R as the target frequency was 500 hz.
I had been using the XO-1 for my IIB's and it sounded very good but the IIB had a 1st order HP filter so it made a lot of sense. I bought those speakers and the XO-1 in 1980.
I continued to use it when I got my IIIa's but quickly changed to a Marchand XM-44 which was available in kit form for ~$500. That was ~10 years ago.
I suggest that you get a few caps that get you somewhere between 180 and 300 hz and see which one sounds the best.



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

 

RE: Magnepan XO-1 on MG-3.5R's?, posted on October 17, 2011 at 19:42:09
Planarguy
Audiophile

Posts: 15
Joined: October 17, 2011
 The problem lies not in that formula, but rather in determining the proper crossover frequency to plug into it.
We all know the Magnepan crossover topology as used in their passive x'overs and the contradictory advice of using EITHER asymmetric crossover points and slopes OR 6 db per octave slope when going to active(or line level) filters - both advised by Magnepan.
This being the case, we have to decide what the actual filter frequency is, or should be here? There in lies the formula PROBLEM - not really formula but more of a question - what is the best compromise frequency to plug into the formula? Now, in the 3.5 manual, they present it as different formula for two different model systems. Of course that's not really the case, but I stayed with their presentation.
When I talked to Wendell, he went so far as too say, it isn't critical! Too me, this is too tough to swallow without a bit more chewing first.
So, fear not, you haven't shot anything down. I just didn't make myself clear enough I suppose. Reasons I am beginning to hate the Internet; Too much written communication, misunderstandings and time lags, all compressed into small venues and a limited amount of time to sort it out, as there are always more pressing matters, specially these days.

So, enough time spent on this! As previously stated, I'll work it out iteratively and get back to the group - when and as time permits.

 

RE: Magnepan XO-1 on MG-3.5R's?, posted on October 18, 2011 at 06:15:06
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 I am a little surprised that Wendell said the xo frequency didn't make that much difference, since in other cases he has told inmates to carefully conserve the DCR of any upgrade inductors. I suppose small differences of 10-15 Hz would not be that noticeable considering the normal error in the component values.
Getting the right -3db frequency is just trial and error since you will be replacing a 2nd order filter with a 1st and the slopes will be different regardless. The native filter has a -3db of ~200 Hz so I would shoot for about 50 hz higher since the slope is not as steep.
If you let me know the input impedance of your amp, I will try to work out a PLL 2nd order filter. These can be a bit tricky since the Q values are usually low but the 3.5 mid HP also has a low Q (0.45) so it may work out.

In a way, internet communication can be a good thing. While it's a PITA, it requires precision and discipline of thought to get across what we actually want to say. Unfortunately, it's a skill few of us have (including myself) but don't blame it on the internet. Just think of how precise and eloquent the letters of 18th century had to be since it would take 2 weeks or more between posts.



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

 

RE: Magnepan XO-1 on MG-3.5R's?, posted on October 18, 2011 at 10:27:23
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 We can use Colin's work on his 3.3 to build the XO

If you use a 1st order rather than a second you can get it right with a higher XO frequency. The manual says 2nd order 200hz or 250 hz at 1st order.

Try a 1st order with caps in your PLLXO portion for 200hz to 300hz - which is similar the range that worked for colin on his 3.3 relative to the recommended value - which has a higher XO where he got 660 hz or something like that- over the 500 hz spec.

The bass XO has to be active. Colin did a 3rd order electronic XO for his bass LP. There are plenty of these available in the pro audio used market and they usually have great bass. Car audio electronic XOs at 3rd order are available too.

If you want EQ and such on your bass, you can use a Behringer DCX2496 which is entirely good on bass. You can fix your room modes some with its parametric EQ and match phase with the top section.

 

Xover frequency, posted on October 18, 2011 at 12:57:03
sbrians
Audiophile

Posts: 1455
Joined: March 4, 2002
 My active crossover guy believes that Magnepan crosses over the 3 series too low and uses 500Hz. I thought that was possibly too high theoretically, but am enjoying it.

 

RE: Magnepan XO-1 on MG-3.5R's?, posted on October 18, 2011 at 13:44:40
Planarguy
Audiophile

Posts: 15
Joined: October 17, 2011
 For PASSIVE crossovers, watching the dcr of inductors is a good idea. NOTE: sometimes speakers are designed with deliberately high series resistance for purposes of tuning. I've seen people totally screw up their beloved before mods speakers that way, only to put them back to stock, yet end up hundreds of dollars poorer. Dahlquist owners are particularly well known for this.

So, once again, to be clearer (yet...) Wendell indicated the exact value of the capacitor, as used in the XO-1 box was not terribly important. Hopefully we are on the same page now?
Absolute precision shouldn't be necessary for answering a simple question. As in the question _ Dear, is dinner ready? Answer - Well, because of the sunspots, the distance of the moon from the Earth, the rats over breeding in new Zealand, and market price on fish in New York..etc. My response to her- Look here wife! A simple Yes, or No will do.
In my case, I just wanted to know if anyone else had tried it, and if so, the value of the capacitor for their amplifiers input impedance. A question which I have answered to my satisfaction BTW.

Again, thank you for your time and attempt to help.

 

RE: Magnepan XO-1 on MG-3.5R's?, posted on October 18, 2011 at 13:46:19
Planarguy
Audiophile

Posts: 15
Joined: October 17, 2011
 Thank you. If I go truly active, I'll look into these ideas.

 

RE: The XO-1 is *not* an "electronic XO". It is simply ..., posted on October 18, 2011 at 13:52:36
Planarguy
Audiophile

Posts: 15
Joined: October 17, 2011
 The XO-i IS an electronic, line level crossover, or actually filter; it's just not an ACTIVE(with gain) electronic crossover.
Yes, poorly constructed, and primitive. They discontinued making them too.
Seems to be a warranted move. Can't believe they made them to start with in that silly unshielded plastic box!

 

RE: Magnepan XO-1 on MG-3.5R's?, posted on October 18, 2011 at 14:12:27
Planarguy
Audiophile

Posts: 15
Joined: October 17, 2011
 Last post on this subject, at least for me:

I'm using a 682(6800pf, or ,oo68uf) cap. I gleaned from an old HF radio chassis I had laying about. The value seems about right into the 47K input impedance of my amplifier, although I may try a lower value cap.i.e. .0047. or. 0056, when time permits. Ordering a few caps from Magnepan which are sure to be higher quality then what I had laying around from 30 years ago.

More then likely, I'll build an active crossover for this to do it correctly and will perhaps try much sharper slopes too as part of the design. So may have 6/12/18/24 and be able to select from Butterworth,L/R, and bessel function which I'm especially fond of. Did I happen to mention that in the early 70's, while working on early robotics systems for defense contractors, I built active crossovers on the side for my audiophile friends?

well, that was a long time ago, and few of those brain cells, remain at my age as I'm sure is clear from my grumpy and befuddled posts.. and throw in a good measure of arthritis too.

Thanks again to all.

 

Everyone undertaking a new XO.... , posted on October 18, 2011 at 19:03:00
play-mate
Audiophile

Posts: 948
Joined: November 21, 2008
 ....should consider to find the slope values via a digital crossover unit first !

The modest price of such units can give much insight into the merits on the complex task of filter design.
Buy one and do some listening on different settings, before committing to any particular design first, and one will be surprised how many variables there are in different rooms & setups.

just my 2 cents


kind regards






Hysolid // Mytek Brooklyn // Spectron Musician III // Analysis Audio Omega

 

RE: The XO-1 is *not* an "electronic XO". It is simply ..., posted on October 18, 2011 at 21:33:24
Davey
 :)

I can't believe how misunderstood this topic is.......even after all these years.

The XO-1 is no more "electronic" than a passive speaker level crossover is.

And active electronic crossovers don't necessarily have gain. "Active" just means the crossover needs some power to run.

Cheers,

Dave.

 

RE: The XO-1 is *not* an "electronic XO". It is simply ..., posted on October 26, 2011 at 00:24:09
Planarguy
Audiophile

Posts: 15
Joined: October 17, 2011
 The "Electronic" term was and often is used to differentiate a LINE LEVEL UNIT from a high level, or one BUILT IN TO THE SPEAKER. Without that common usage of the term, the question easily gets lost in mix. A piggy backed unit behind and wired into the speaker qualifies as high level.
Sure, the XO-1 still uses the bass section of the passive, but with the bass level controls, and the high pass filtering, it's close enough for ME.

I disagree with your definitions limitations even though technically you are right of course. However, the question was a simple one, and I was looking for a simple answer, not an uncalled for lecture. I haven't ALWAYS been just an Audiophile, and I've been at this since 1963. So, please save your haughty responses for someone 40 years younger sonny! I'm NOT confused, I'm just grouchy and impatient!

It's moot at this point - I sold the speakers. Brought home a pair of 3.7's, and they were back at the store the next day.
My old MG-3a's sounded much sweeter to my ears... Really wish they'd quit fixing what isn't broken, or at least keep the old models in the line up! OK, maybe it's my old ears, but then why do my B&W 802's sound so darn good? Anyway -

I'm DONE with this thread -AGAIN !

 

RE: The XO-1 is *not* an "electronic XO". It is simply ..., posted on October 26, 2011 at 04:22:23
tyu
Audiophile

Posts: 963
Joined: April 19, 2011
 It's moot at this point - I sold the speakers. Brought home a pair of 3.7's, and they were back at the store the next day.
My old MG-3a's sounded much sweeter to my ears... Really wish they'd quit fixing what isn't broken, or at least keep the old models in the line up! OK, maybe it's my old ears, but then why do my B&W 802's sound so darn good? Anyway -

I'm DONE with this thread -AGAIN !


Facks an just the facks,Most people here cant do this thay have to judg others.I got a pr of MG1.7 an i to think that magnepan took the roung step.But dont tell people here thay can take it.
Thay dont have the speaker but if Magnepan made it got to be right. Had Magnepan for 30years .
This should kill the post,the truth...

Thanks for your time

 

RE: Magnepan XO-1 on MG-3.5R's?, posted on October 17, 2015 at 08:52:38
soundshotter@gmail.com
Distributor or Rep

Posts: 1
Location: CA
Joined: October 17, 2015
 there are 2 or 3 different XO-1 Magnepan crossovers, they are all different, the two i have dealt with are, one that is metal with wood side panels, comes as a pair and works with the mg3 series. the second i believe(unconfirmed)works with the mg2b's and c's and is a single unit all black(plastic I believe) and has to do with bi-amping and level control, i know because unfortunately i bought a pair that the seller did not include pics of and was not for my mg3a's....
paul

 

RE: Magnepan XO-1 on MG-3.5R's?, posted on October 17, 2015 at 09:37:05
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 The Elliot Sound Products webpage lists an active which meets your requirements.
Well regarded stuff, it is customizable by the builder. (you)
Add a PS and you're good to go.

I don't know if it'll convert to balanced or you are stuck with single ended.

The OTHER solution which is becoming much more available and less expensive would be some form of DSP product. Almost INFINITLY flexible, you can test crossover points and slopes until you turn purple, and all without a soldering iron. Do it all in SOFTWARE!

Link is to what I'm aiming at for my panels.
Too much is never enough

 

RE: Magnepan XO-1 on MG-3.5R's?, posted on October 19, 2015 at 08:36:06
Norman M
 I have used both Magnepan's XO-1 and the Marchand XM44-2 to bi-amp a 3.6 and Tymp IV-A. There is no different as night and day result in the sound no matter how I conducted the comparison. One way was to listen and quickly as possible switch XOs (and re-wire) and the other was to listen for several weeks using one of the XOs to become very familiar with the sound, and only then, switch the the other. If there is any difference to be heard, I *think* prefer using the passive XO-1, however the resultant sound is so very much the same, I wouldn't swear on it. Being only the hobby which it is, IMO everyone inclined to bi-amp should carry out the test and report their findings here. Regardless of theory and mathematics, it's only the sound which is of importance. If in fact differences result, but which can't be heard, what difference does it make which type of XO one ends up using. I believe that in this thread 'Davey' brought to attention that the internal XOs are passive, but so are all of Magnepan's external XO boxes.

 

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