My used Magnepan 1.6's are missing sparkly treble. Why?

Are the jumpers that connect the high and low in place? Is the fuse okay?
http://www.magnepan.com/pdfs/manual/MG_1.6.pdf

At some point the speakers were modified to remove the fuse. That whole panel shown in the manual doesn't exist. There is just an aluminum panel across the speaker with plugs for the wires. The seller represented that was a modification to improve the sound along with better stands.  I wanted to attach a picture but couldn't figure out how to.  Is there a trick to that or are JPEGs not supported in this forum?

You cannot directly attach pictures or forms unfortunately.
You have to add a link to say a Dropbox location of the picture for example.

Thanks for the tip. Lets see if this dropbox link to the JPEG of the back of the speaker works.

https://www.dropbox.com/s/3qaj08yrow0nat0/IMG_0017.JPG?dl=0

Yes the link works perfectly.
However it raises more questions than answers and all of them appertain to just what the heck the seller did behind that panel.......

You definitely should NOT be lacking in upper treble on these.

You may have to remove those panels just to try and figure out what has been done in the way of wiring.

Here are some pictures of what is behind that aluminium panel.  I assume the other speaker is the same.

https://www.dropbox.com/s/x5tt7tqscfu77om/IMG_0019.JPG?dl=0
https://www.dropbox.com/s/qoraem5mzc07lte/IMG_0022.JPG?dl=0

You should post your question at Planar speaker asylum! I'm sure you will get some information over there!
https://www.audioasylum.com/cgi/etv.mpl?forum=mug

pinwa, should you figure out the cause of the problem please share it with us.

Maybe Almarg might have a better idea?

any demag type of disk may help.  The Shefield or others.  

I don't know what a Shefield demag disk is.  Are you talking about this:

https://www.amazon.com/Sheffield-Xlo-Test-Burn-CD/dp/B000025RLX

Although that seems like an interesting, if wildly overpriced, product I can't imagine why it would fix anything in the speakers.

The fuses should never be bypassed. Asking for trouble. I hope your problem is something simple.

I think the previous owner did some unsanctioned surgery.
When in doubt, call Magnepan or email.
You could also call or PM Johnny Rutan (Audioconnection). He knows and sell Maggy's and might be able to give you some good (and free) advice.
Though he is a dealer, he is a really great guy who can help without trying to sell you something.
You can trust me on that...
Bob

Whatever it is it's bad and obscene. 

You will probably have to remove that plate be to see how they were wired .

I'm not sure if this is simply confirmation bias or what but I did find  several different demagnetizing tracks on YouTube and after playing them I think the treble response is improved.  It is still somewhat muted but better than it was.  I don't think the problem with the speakers has anything to do with the removal of the fuse or a tear in the ribbons either of which ought to pretty much eliminate the high end response and that isn't what is going on.  I found a couple of 20Hz to 20KHz audio sweep on YouTube  https://www.youtube.com/watch?v=H-iCZElJ8m0 .  I stopped hearing anything around 11KHz which was also my limit listening with my Ananda headphones and that might be about all my 62 year old ears can hear anyhow.  So the 1.6's are responsive to at least that level.  I think the high end is just softer/quieter than it should be.  Maybe time to look into an equalizer?

most of the demag/burn-in disks can be had used on ebay or other sources.  There is a clarity of sound after using them that does fade with time.  

Seems a bit telling that you can't hear above 11k with your headphones too?  You may want to get your hearing tested and get that equalizer as well.  Maybe the hearing test will help you set up the equalizer?  Or go to a stereo store and see if you can't hear higher treble on other speakers. 

11K is about it for me.  I'm curious how high you hear?  Assuming this tone generator is accurate you should be able to get a pretty precise measure of the limits of you hearing.

https://www.szynalski.com/tone-generator/

Well I can hear up to 14k maybe a bit higher according to the tone generator.  It is a pretty annoying tone at 14k and I would like to say I can hear it at 15k too but maybe not so much.

I would go to a dealer in my area and see if the dealer has a pair that has the same tweeter in another speaker or ask the dealer if you can do a side by side comparison of both speakers, then if there is no dealer in your area. send them back to magnepan and let them restore them back to the speaker they was and you can ask them if they can send you a box for them. they did for me when i had a bad pair and they did a rebuild. which was a waste of time. the speaker fell apart.

I thought I should provide an update to my original post.  Since I wasn't sure what was going on with the 1.6's and there was a very good used 1.7 for sale locally at a good price I ended up getting that also.  Overall I liked the 1.7 better and the treble might have been a bit better but still not what I expected.  However, I kept playing around with the placement of the speaker and positioning the 1.7's tweeter on the inside and a little more toed in and that definitely improved the over all sound but cymbals and top hats still seemed to be somewhat lacking.  Reading more posts about how others had placed their Maggies I noticed many users thought they were better tilted forward slightly.  So today I made that small adjustment by sliding a CD case just under the rear stands.  And that definitely made a big difference in the overall sound and especially the high end.  The 1.7's now sound realistically bright and closely match what I'm hearing if I listen on the Ananda headphones.  And that also may explain why the 1.6's seemed so disappointing since they were actually set up to be tilted back by about the same amount as my 1.7's are now tilted forward.  I feel like I mostly have the 1.7's dialed in now but it is amazing how sensitive they are to small changes in positioning.  That fussiness is probably why they aren't more popular.

Tilted back?
Oh heck no...lol
My baby Maggies gave me a huge improvement in SQ when i played with positioning but mostly due to me tilting them forward.
And yes tweeters on the inside gave best results.
There likely then is not much wrong with the 1.6 to start with

I think you are probably right about the 1.6's being fine although I'm probably not going to go to the trouble of hooking them up again to find out.  I'll put them up for sale soon and hopefully somebody else will fall in love with them.  At the used prices these Maggies are one of the great values in the HiFi world.

I totally agree with you OP on vfm.
My pair of $500 Maggies bested an $8500 pair of Josephs in my room with my gear.
Thats obviously not implying they were better, just  a better fit with my gear, room and my ears.

But my present Spatial Audio ob speakers are another huge step forward over the Maggies for me.

The Spatial Audio speakers look very interested.  I think if a used pair of M3's or X5's came up I would probably give them a try.