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In Reply to: RE: Help needed: Tympani IVa midrange driver problem posted by Roger Gustavsson on April 08, 2021 at 13:09:54
Thanks, I've written to Gary at Magnepan. I'm thinking even if the mid panels normally have some warp to them, that this example may be a bit extreme.
My other channel (with the higher output) seems to be pretty flat.
Mine looks like this, about 1 mm warp/curve/bend.
Thanks for the photo, very helpful. I just heard back from Gary at Magnepan, and he indicated a slight bow (about 1/8") was typical.
Mine is over twice that, so I plan to do some measurements this weekend comparing the panel as it is now and with some braces holding it closer to flat to confirm that raises the level.
My mids differ in output by about 3 dB. The distance Mylar to magnets is too large in one of them. I will rebuild mine, sand down the spacers so a flat surface will face the Mylar in order to make a secure contact with the double-sided foam tape.
Since my mids were recently rebuilt at the factory, I'm planning on another approach (that doesn't require replacing or re-wiring the mylar) to move the magnet/perforated panel closer to the mylar (and closer to flat). This weekend I'll be testing to see if adding cross bars at 2 or 3 locations to the rear of the panel, pushing it closer to flat (but not quite there, per Magnepan). If that raises the output level, I'll route out some grooves in the MDF panel to mount the bars, which will also help hold the panel in place.
I'll post my progress.
I would've thought 4 positions would be necessary, for the stiffness & length of the mid panel?
And presumably these crossbars should not be made of steel?
"I would've thought 4 positions would be necessary, for the stiffness & length of the mid panel?
And presumably these crossbars should not be made of steel?"
Why not steel if stiffness is required? The slightly curved back of my T-IVa mids are stiffer than any other of my Magnepan drivers.
But now I think about it, Roger ... Magnepan used steel crossbars on my Maggie bass panels - so it can't be a problem!
I'll experiment with the number of braces. Aluminum is usually my choice when doing metal work, as it's easier to machine. As a side benefit, it's not magnetic.
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