[Hobbsmeerkat]

It's to keep the drivers acoustically in phase.

If you wired the mid normally, it would be 180° out of phase from both the mid and tweeter, causing a big holes at the crossover point.

[ketchup]

Thanks again.

I'd like to burn these crossovers in for a few hundred hours before installing them in my system.  What are my options?  Can I connect them to a full range amplifier output and put some resistors in place of the speaker drivers in the circuit? 

I have an Audiodharma cable cooker.  Has anyone burned crossovers in with one of those?

[Hobbsmeerkat]

You'll need some high wattage (30-50W) resistors to keep them from burning up, or a bundle of lower wattage resistors in parallel.

Maggies typically are 4ohm speaker, and if you go the parallel route, you will need either 2x 8ohm, 3x 12ohm, 4x 16ohn
10W resistors will get you 20, 30 or 40W of max load
20W Resistors will get you 40, 60 or 80W of max load.

For a dummy load, you can get away with cheap resistors. Just make sure they dont get too hot for the arrangement you use.

[dan2023]

It's to keep the drivers acoustically in phase.

If you wired the mid normally, it would be 180° out of phase from both the mid and tweeter, causing a big holes at the crossover point.

out of curiosity, what causes the phase shift?

[Hobbsmeerkat]

The crossover components & driver placement, but for Maggies, it's typically the components.

Every component added to the circuit will shift the phase one way or another, especially at the crossover point.

Which is why even if two drivers have a good roll-off on their own, they can still be 90° out of phase, (causing no summing or cancelation) or even 180° out of phase. (causing full cancellation)

90° phase rotation is harder to work with, as it requires more parts to rotate the phase further to bring them in phase or 180° and then flip the polarity.

[ketchup]

I would replace that stack on the tweeter to a 18uF vcap odam. This is a significant improvement and worth every cent. Bypass if you like a warmer sound the 0.01 pure copper duelund cap.

For the mids I'd use 25uF sonicap gen 1s. I personally would bypass these with 0.1 miflex pure copper caps. Made a difference even though a shunting cap for my nx otica.

Resistors I'd use path audios resistors. Some had magnetic problems but I've bought 9 of them and none have an issue at all with neo magnets. Way better sounding than the other "Premium" resistors in my test.

I would wire with solid core wire, Danny's wire on his website is a good deal and good wire.

Inductors I would foil inductors on the mids as they are in line of the signal and air core on the tweeter if you wanted to save money. Personally I'd do all copper foil. Dayton or Janzen inductors are good for this project.

I'm revisiting this thread as I prepare to order some parts. 

Badd99, what's the thought process behind bypassing the tweeter cap with a pure copper Duelund and bypassing the mid driver cap with a Miflex pure copper cap?  Just curious why you'd use these two types of caps in these locations.

If anyone else wants to chime in, please do.

[ketchup]

18uF is about 6% larger than 17uF, and most budget  caps have a variance of +/- 10%, so in the grand scheme of things, it will mean slightly lower extension on the tweeter. It's more important than your caps are matched into pairs than if the value is +/- a few percent in one direction.

High-end caps typically offer +/- 5% variance so an 18uF can be as low as 17.10uF or as high as 18.90uF soif you have the opportunity, get them matched into pairs.

Another question.  The closest I can get to 17uF for the tweeter cap is 18.6uF.  The factory cap has a tolerance of +/-5%, so 18.6uF will be beyond the upper limit of the factory range of 17.86uF.  Is it a bad idea to use 18.6uF in this situation?

[Hobbsmeerkat]

That's right at the edge of the +10% side, (around 9.4%) so you'll be getting lower extension out of the tweeter panel, which could cause issues.

Another option to consider will be two 8.2uF caps in parallel which will get you much closer to the 17uF you need, (~16.4uF) especially if they read closer to the 8.4-8.6uF range.
of course it means you will need 4 matched caps instead of 2 but it if gets you closer to the stock +/-5% tolerance then you'll be in good shape.

[ketchup]

That's right at the edge of the +10% side, (around 9.4%) so you'll be getting lower extension out of the tweeter panel, which could cause issues.

Another option to consider will be two 8.2uF caps in parallel which will get you much closer to the 17uF you need, (~16.4uF) especially if they read closer to the 8.4-8.6uF range.
of course it means you will need 4 matched caps instead of 2 but it if gets you closer to the stock +/-5% tolerance then you'll be in good shape.

Thank you.  It's a ribbon tweeter.  Does that change your opinion at all?

[Hobbsmeerkat]

They are more sensitive to damage from too much output down low, so I would go the two 8.2uF route in this case to get a closer match to your desired 17uF value,.

[emailtim]

The ribbon has a shallow slope which means it extends quite low.  If you use a steeper slope, you can take some of the stress off the ribbon by preventing it from extending so low into the midbass region.  It will sound more "relaxed" as well.  You will also have to redesign the rest of the XO network accordingly. 

FWIW, I redesigned mine so no 3 drivers are playing on top of each other.

Magnepan 3.6 Ribbon (from Stereophile):


Magnepan 20 Ribbon (from Stereophile):