How close together can drivers be? (face to face / magnet to magnet?) - AVS Forum
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post #1 of 3 Old 08-22-2013, 08:48 AM - Thread Starter
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Hey all,

I'm sure this is a daft question but, hey, I'm not afraid to look silly tongue.gif lol


I'm currently attempting to design boxes for dual SI18s.

To make them as compact as possible I should make them a 2 x Front Firing design, but I would like to try them in a Push-Pull configuration to see if it can make them sound even cleaner than they are already supposed to be.


I have therefore progressed through some designs to one where I could stack the boxes on top of each other or run them side by side (to give me options for the single location that I can easily place boxes within my room).

These designs are dual opposed boxes that are standing up - i.e. so I could perhaps disguise them as side tables if I move house. The current design is the driver at the bottom facing in / spider out (with a baseplate at the very bottom to protect the magnets) and the driver at the top facing out of the box in the usual way but without a protective top plate at this moment in time.


So, my question is...

If I was to stack them, how much gap would I need between driver cone and driver cone? (assuming I put some supports between them and stack them so the drivers which are facing out are pointed directly towards each other)

Would I need to work out a driver's displacement, divide it by the circumference of the drivers (as that is where the air can 'escape' when pressed together between the drivers, and I'm assuming you would want it to flow freely out and not be compressed), then make sure there is that many inches between the resting point of the cone and the halfway point between the cones? (if that makes sense??)

Or can I just stack them and have, in my current workings, 4 inches between the top of the driver surrounds, so there is probably 2" to 3" 'gap' between the outer edge of the cones when they're at XMax of c.23.5mm?

Would that create too much pressure for the cones themselves and risk damaging them??


- Or, If I stack them the other way round, so the inward-facing drivers are now back-to-back with only about 5" between the base of the magnets, is that too close? Will the magnetic fields interfere with each other and risk damage to the drivers/magnets?


Like I say, probably dumb questions... biggrin.gif lol

Many thanks in advance for any help!! smile.gif
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post #2 of 3 Old 08-23-2013, 10:57 AM
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5" is fine, that should be far enough that they won't demagnetize in our lifetimes.

As for the cones, at some point it will act like a port, just make sure the air velocity is below audibility and you should be just fine.
2" should be sufficient in nearly all cases.
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post #3 of 3 Old 08-26-2013, 08:36 AM - Thread Starter
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Thanks very much for your reply! smile.gif

I may tweak my current design slightly as I think I might risk reducing the gap between the cones to only about 1.5" if I run over XMax and near to XMech at very low Hz (I'm hoping for extension down to about 5Hz but WinISD suggests XMech at about 2.5Hz, assuming my signal chain doesn't roll off massively by that point) and that 'feels' too little.

Just a bit of a pain because I'll have to add extra stuffing because I'll need to reduce box size to make it all work!
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