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In Reply to: RE: Old glue formulation or newer formulation posted by macmagman on April 13, 2016 at 22:38:26
I think Magnepan switched to the new glue in 2004. You will need about the same power for bass and mid/tweeter. The mids are not very well protected as they operate at rather low frequences with a first order crossover. The mid foil conductor is thinner than any foil used for the QR-tweeters!
Follow Ups:
Thanks Roger,
that explains a lot, what's the use of having the fuse then? that's a poor design by Magnepan, I rarely blow midrange fuses, I've blown a few tweeter fuses but an exchange tweeter for $100 is one thing, seems that Magnepan want's to sell $1200 panels instead thats a VERY POOR business practice, and this is my second one!!
Would I be better off with the Magtech on the mid-tweeters until I can get a second one?
The midrange crossover freq and slope (1st order vs 2nd order in a few MG20.x and T4 iterations) is coupled with the lower mass mylar and thinner foil are related issues. The power handling of the midrange is reduced as you go down in mylar thickness and thinner foil/wire gauge. The lower crossover freq and lower order XO also reduce the midrange's robustness as it is allocated more of the lower frequency load.It is a long struggle of many planar makers to provide at the same time
1. higher power handling (higher XO, thicker mylar or tougher diaphragm like kaladex, Neo magnets and thicker foil)
2. higher resolution (thinner mylar thinner foil/wire, lower HP freq)
3. enhance coherence.. (lower XO freq so that midbass fundamentals are carried by the lower mass mids)Genesis and Infinity using BG RD75 or RD50 drivers or EMIMs with Al foil on Mylar, had provided the user with the option of adjusting the mid XO from appx 100hz for low output music to appx 200 hz for louder music. That provided better coherence and resolution at lower volumes and sufficient power handling at higher volumes.
I think magnepan had taken the crossover freq slightly too low and are facing the same problem that Genesis and Infinity reached and should have provided the loud playing user with the option of either switcing the speaker to a higher crossover freq. on the 20.1 or 20.7 or ordering the 20.7 with a higher XO freq.
Since the 20.1 can be crossed over electronically, the crossover can be switched to a higher freq (for both LP and HP) - following the Infinity and Genesis example I would suggest you do just that and put the XO freq up one octave. Very easy to do with a Marchand or Pass crossover.
For the 20.7 you can do exactly the same with internal mid HP cap halved and bass LP coil halved in either a replacement strategy or as a hot switchable option. That would allow playing at higher volume without burning your midrange drivers.
The solution I picked was to go out from the Mylar and ferrous magnet construction chosen by Infinity Magnepan and the BG RD series (and Wisdom) and go for a Neo8 line array that uses a polyamide or imide kaladex that can withstand higher temperatures and Neo magnets that allow a thinner metal foil. The result is higher sensitivity, higher ultimate output and higher resolution. As a result I gradually lowered my XO from the "just to be safe" 300hz 4th order to 250 hz 1st order and now even 150 hz 1st order. In an accident a few years back I clocked my mids running 126 db.
I don't know if the Neo8 line array is a solution for 20.1 owners even if the drivers were still available. The AMT Pro 8" drivers can't be driven as low as the Neo8 and will likely require 4-500hz high pass. Or 300 hz with a high order slope.
Edits: 04/15/16
Great info Satie;
But way over my head,I am using a Marchand XM44 my question to you would be should I back off on the high setting on it?
Get Phil at Marchand to build you new boards with the same slope but the crossover frequency (actually both HP and LP freq would be doubled) one octave higher, or keep the same crossover frequency but go for a steeper crossover - say a symmetrical LR4. Then you plug in the new boards and can play more loudly - and can swap back the original boards for low volume playback if you end up lacking detail with the new boards.
I would personally go for the LR4 choice since it is not that bad in a 2 way biamp setup and would allow you to keep an octave's worth of the midrange driver's higher resolution.
Thanks Satie;
I am pretty ignorant when it comes to the technical side of this hobby, Phil did send me some other boards.
This is what I have installed now 300HzHP6, and 135HzLP18
This is what he sent also 200HzHP24, and 200LP24
Using your suggestion translated with these numbers what do I ask Phil for?
Many thanks for all of your help....
Since you already have them, the 200 hz LP24 boards should help you by taking out low freq drive requirements from your mids. Plug those in and you should have less congestion in the midrange when playing hard and be less likely to burn them again.
If I were making fresh boards I would have taken 250 hz on a "just to be safe" driven choice.
Read how to replace the boards, it is easy but you need to do it correctly and plug the new LP board where the old one was and the HP board where the old HP board was.
For future improvement you will want to swap the caps on the boards with better foil caps as the LR24 have many of them so the difference in SQ is significant. .
Sure wish there was a way Phil could design the mother board to accept those mods so one could simply select them via selector switch on front rather than manually inserting them.
My complaint is the same - after desoldering and resoldering the boards so many times I was beginning to lose the loops on the circuit board. I was looking at vacuum and air variable capacitors to make changing freq and slope easy rather than deal with the potentiometers' familiar problems in transparency and tracking, but it seemed to have equivalent problems as the potentiometers and those are cheaper and far smaller in size. I used wire wound pots for the PLLXO for a while.
the cards on these boards are fairly small. See pix on link below of an example. you mention foils to mod the cards, what specific foils have you tried that will fit the cards and could you elaborate on the actual audible improvements. I have added a link to this topic from the past.
thanks image link http://www.canuckaudiomart.com/details/649258631-marchand-xm44-crossover/images/1175005/
Edits: 04/16/16 04/16/16
were first of all in smoothness at the top end while retaining the sparkle on high hats triangle and the metallic sheen of brass, just that these were now more realistic and less electronic sounding. The second was that it sounded fuller in the mids when the bandpass boards were done. The slight bit of upper mid/low treble shrillness was gone as was the slight thinness in tone. Imaging improved, particularly in the depth dimension and it tightened the bass a bit further.
I used mostly 0.01 uF Dayton foils but also RTE polystyrenes and platinum caps from sonicap.
I used both sides of the boards to get the real estate required. Smaller values would be easier to fit on one side. But the smallest Dayton foil is 0.01uF and that is the best value in foil caps.Absolute results are just a notch or two below the best foils from Jantzen and Duelund.
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