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Old 3rd September 2007, 04:31 AM   #1
Ap is offline Ap
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Default Push - push subwoofer spacing.

Have finally settled on my new sub desing, its using two 10" drivers mounted back to back in push-push configuration.
Just wondering if anyone knows if there is a limit to how close the magnets can be too each ohter, I'm hoping 20mm is Ok - any idea?
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Old 3rd September 2007, 05:08 AM   #2
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Default Re: Push - push subwoofer spacing.

Quote:
Originally posted by Ap
Have finally settled on my new sub desing, its using two 10" drivers mounted back to back in push-push configuration.
Just wondering if anyone knows if there is a limit to how close the magnets can be too each ohter, I'm hoping 20mm is Ok - any idea?
Thats ver similar to my new design, except I have 18's and the W and D of the box is a bit greater.

It will depend to an extent on how much power you're going to play through them and whather they have vented polepieces, As an idea, my drivers are rated for 1000W, and the sims indicate 40Hz at extremely high levels will be <100W/driver, heat won't be an issue. Run very hard, I'd put the driver motors on the outside for cooling.
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Old 3rd September 2007, 05:58 AM   #3
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You get most advantage of push-push if the magnets are tightly wedged against each other... this may pose an issue if your drivers have those pesky pole-piece vents.

Do make sure you get something between the magnets so they are tightly coupled.

dave
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Old 3rd September 2007, 06:59 AM   #4
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Thanks Dave,
the drivers have vented pole pieces - can you suggest a suitable material to wedge - MDF Ok?
Andrew.
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Old 3rd September 2007, 07:07 AM   #5
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Quote:
Originally posted by Ap
Thanks Dave,
the drivers have vented pole pieces - can you suggest a suitable material to wedge - MDF Ok?
Andrew.
MDF is kinda squishy... a piece of hardwood is most practical.

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Old 3rd September 2007, 11:21 AM   #6
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I have heard of people successfully implementing push push designs and getting much lower levels of distortion. This makes sense based upon the fact that the equal and opposite forces should cancel. I have been doing this in my designs for a long while now and have found that if your box is not properly designed, placing the magnets directly against each other will lead to further benefits, and yes MDF will be fine contrary to some other's beliefs. In my experience, hardwood is much more deformable than MDF. In my humble opinion this is a good design and I would love for you to share your results with us!

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Old 3rd September 2007, 01:49 PM   #7
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Actually, with both magnets facing eachother, this design is more of a bipole than push-pull. I'm not too sure that a bipole setup would eliminate distortion all that much. Maybe some because two drivers working together would be doing half the work of one driver at the same freq and output, but that's it.

A true push-pull design would be like my sub or some of the larger M&K subs where one driver is mounted normally with the basket inside the enclosure and the second driver mounted inverted with the basket outside the enclosure. This inverted driver would also be wired 180* out of phase but would remain mechanically in phase.

The cancellation of even order harmonics comes from both drivers moving in opposite directions of eachother, cancelling out their own distortions from the motor, suspension and cone.


This is a small piece taken from Dan Marx's website... http://www.danmarx.org/audioinnovation/theories.html

"According to M&K who specialize is push/pull subwoofers claim that this approach cancels out even ordered harmonics. So take your pick. Either way, harmonic distortion is reduced in that any anomalies or variations in the two driver's spider, cone or suspension characteristics are canceled out by the other driver's inversely proportional anomalies and variations. The sound is as accurate and pure as it can possibly be with each driver "correcting" the other driver."


When I first built my sub, I had both drivers mounted normally with their magnets facing eachother. They sounded pretty good that way, but then someone on here recommended that I invert one driver due to what I just mentioned above, and the subs improved! Much cleaner, purer sounding bass with more detail.

Just my 2 cents.
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Old 3rd September 2007, 01:52 PM   #8
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You are on about push-pull. Everybody else is on about push-push.

The advantage of push-push is cancellation of sub walking. The advantage of push-pull is cancellation of harmonics.
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Old 3rd September 2007, 01:57 PM   #9
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Quote:
Originally posted by richie00boy
You are on about push-pull. Everybody else is on about push-push.

The advantage of push-push is cancellation of sub walking. The advantage of push-pull is cancellation of harmonics.

Oh yeah, you're right! LOL!!!!

I guess my eyes read what they wanted to read this morning, instead of what was actually written.

Oh well, I think I still made a valid point though.


Doing a push-pull design would also cancel out the sub(s) walking as the cones would still be moving into and out of the enclosure together. Remember, one driver is mounted and wired inverted.
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Old 3rd September 2007, 02:06 PM   #10
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Yes that would be push-pull on opposite sides. Good idea.
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