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Push pull double 18

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Mark Wilkinson:
Got this idea from a thread on the diyaudio forum http://www.diyaudio.com/forums/subwoofers/177905-thread-ppsl-enclosures.html

They call it a push-pull-slot-loaded sub.  The inverted driver in the slot is wired in reverse polarity, so both squeeze into the slot at the same time.
The slot is basically made as small as possible, and then you build whatever  kind of box you want around the slot/driver module.

I chose a bass reflex box, because I had already built a successful single 18 with the drivers, and could simply  double the net box size for two 18s, after accounting for the extra driver module volume inside the overall box.  Pretty easy design really. Ended up 49Hx21.75Wx31.25D

What's really cool about it IMO, is the wonderful reduction in cabinet vibration.  Opposed drivers really do reduce vibration it appears.
This was the primary reason I tried this design....I absolutely love the single 18's I built other than how much they can walk/jump around.
The single 18's are well braced, but it seems it's weight that matters.  I watch orbitshifters and th-118s want to walk around too....

Supposedly, the design reduces 2nd order harmonic distortion too.  We'll see....   
I can say it sounds very, very, clean, kinda like a labsub (which btw doesn't move much either...opposed drivers again)

Anyway, here's a pict and measurement taken this morning. 
Measurement is raw other than the 3 peq's shown in table.
The slot provides a heck of a boost in the high 100'sHz, that has to be knocked down.
I'd put efficiency at 101-102 @ 2.83v after the knockdown.

Scott Holtzman:

--- Quote from: Mark Wilkinson on March 19, 2018, 01:32:36 pm ---Got this idea from a thread on the diyaudio forum http://www.diyaudio.com/forums/subwoofers/177905-thread-ppsl-enclosures.html

They call it a push-pull-slot-loaded sub.  The inverted driver in the slot is wired in reverse polarity, so both squeeze into the slot at the same time.
The slot is basically made as small as possible, and then you build whatever  kind of box you want around the slot/driver module.

I chose a bass reflex box, because I had already built a successful single 18 with the drivers, and could simply  double the net box size for two 18s, after accounting for the extra driver module volume inside the overall box.  Pretty easy design really. Ended up 49Hx21.75Wx31.25D

What's really cool about it IMO, is the wonderful reduction in cabinet vibration.  Opposed drivers really do reduce vibration it appears.
This was the primary reason I tried this design....I absolutely love the single 18's I built other than how much they can walk/jump around.
The single 18's are well braced, but it seems it's weight that matters.  I watch orbitshifters and th-118s want to walk around too....

Supposedly, the design reduces 2nd order harmonic distortion too.  We'll see....   
I can say it sounds very, very, clean, kinda like a labsub (which btw doesn't move much either...opposed drivers again)

Anyway, here's a pict and measurement taken this morning. 
Measurement is raw other than the 3 peq's shown in table.
The slot provides a heck of a boost in the high 100'sHz, that has to be knocked down.
I'd put efficiency at 101-102 @ 2.83v after the knockdown.

--- End quote ---

That's interesting.  Is the vent in the back for the top sub or is there a waveguide down the back to the bottom vent?

Mark Wilkinson:

--- Quote from: Scott Holtzman on March 19, 2018, 01:47:28 pm ---That's interesting.  Is the vent in the back for the top sub or is there a waveguide down the back to the bottom vent?

--- End quote ---

Hi Scott,  both drivers vent into the same back chamber, just like a regular double 18 BR.
So the port at the bottom is handling duty for both drivers. 

The port shelf on mine is currently just screwed in place, and without it's bottom brace tying it to the cabinet.
Needed to make sure of tuning before gluing and bracing it in.
It definitely began to flap some at 30Hz as i turned up the juice !

Dave Garoutte:
What's the advantage of having the both aimed up?
Compared to if they were aimed together and not reversed polarity?

Art Welter:

--- Quote from: Mark Wilkinson on March 19, 2018, 01:32:36 pm ---Supposedly, the design reduces 2nd order harmonic distortion too. 

The slot provides a heck of a boost in the high 100'sHz, that has to be knocked down.

--- End quote ---
Mark,

The extra upper boost the plenum (slot) provides helps make up for the reduced even order harmonics the push pull arrangement provides ;^).

Looks svelte!

Cheers,
Art

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