Re some of the other comments...
1/ it is important that the braces (which i would consider required) should not be dead centre
2/ one of the braces should support/brace the driver magnet
3/ holey braces work well...
4/ i wouldn't it out of MDF... well braced 18/19 mm plywood (but i'd also be doing push-push so mechanical energy into the box would be dramaticallyless)
dave
1/ it is important that the braces (which i would consider required) should not be dead centre
2/ one of the braces should support/brace the driver magnet
3/ holey braces work well...
4/ i wouldn't it out of MDF... well braced 18/19 mm plywood (but i'd also be doing push-push so mechanical energy into the box would be dramaticallyless)
dave
Member
Joined 2002
I;m confused on how come push-push subs work well. Don;t they fight each other causing problems ? Isn't it better to have one in each box alone. ie ported sealed etc etc.
jleaman said:
The purpose of opposing push-push is to overcome "any" tendency to walk, as the opposing forces cancel out. It also (I believe) has the effect of canceling out a small amount of nonlinear behavior of the drivers. They can be fore and aft (bi-pole) or, and this would be my preference, side firing (side-to-side) with perhaps a plate amp at the rear.
All in all, elimination or curtailing of any movement on the part of the cabinet is a much to be desired goal.
Best Regards,
TerryO
Member
Joined 2002
jleaman said:
Terry did a good explain...
Acoustically the drivers are working in parallel (just like any dual woofer speaker), mechanically they are in opposition and the majority of the mechanical energy that would otherwise pass into the box is actuvely cancelled.
In a "normal" box at least 70% of the unwanted energy is passed into the box mechanically (and in reality probably closer to 95% in any box with a "port". In a push-push woofer -- depending on how tightly coupled -- you are actively removing at least 90% of that energy.
dave
in order to cancel nonlinear behavior the cones have to be moving in opposite directions with respect to their motor structures. This is done by mounting the woofers on opposite sides of the box and by having one magnet enclosed within the box and one facing the outside, then wiring them out of phase.
tade said:
Tade,
What you state has always been my understanding. What I'm getting at is that push-push can "normalize" the driver's differences, perhaps not to the extent that some form of Isobaric loading will. But OTOH, I've been wrong before
Best Regards,
TerryO
65 litres tuned to 22 Hz (10 cm port/68 cm long)
67 litres sealed (Q=0.5)
41 litres sealed (Q=0.57)
22 litres sealed (Q=0.707)
How big a box can you live with? (double the above for 2 drivers)
Note that you are exceeded max linear excursion pretty quickly. I'd go with 44-60 litres sealed push-push (a SMALL box for a pair of 12s). Attached is a pic of a 44 litre push-push extremis sun (and it is a 7" driver -- it will go lower thou
dave
67 litres sealed (Q=0.5)
41 litres sealed (Q=0.57)
22 litres sealed (Q=0.707)
How big a box can you live with? (double the above for 2 drivers)
Note that you are exceeded max linear excursion pretty quickly. I'd go with 44-60 litres sealed push-push (a SMALL box for a pair of 12s). Attached is a pic of a 44 litre push-push extremis sun (and it is a 7" driver -- it will go lower thou
dave
Attachments
TerryO said:What I'm getting at is that push-push can "normalize" the driver's differences, perhaps not to the extent that some form of Isobaric loading will. But OTOH, I've been wrong before
No the cones and motors have to be working mechanically in reverse for cancellation to occur. Push-push will simply add non-linearities just the same as if both drivers were on the same panel. So what Tade is saying holds.
richie00boy said:
You can arrange push-push in a push-pull configuration, it is just harder to get the mechanical coupling required.
If you have a linear enuff driver, then push-pull makes little difference. push-pull (unless you do some serious enclosure gymnastics -- requires a magnet facing out into the room, with the attendant possibility of a thumbs down from the SO. Also if the woofer has a vented pole-piece mounting it magnet out can be problematic. Given all that, i usually just do regular push-push... but one of these days i would like to try a push-push push-pul isobarik just for fun....
dave
Attachments
Getting this thread back on track I have been going through a redesign. The drivers will still be independant enclosures or the same external volume, but the enclosure makeup has chnaged.
Now designed to use standard 18mm MDF, with a double skin on all sides. The bracing has been changed so that none of it if centred and also used 18mm MDF, it joined on all sides at its fixing ends by the inner skin of the enclosure.
The rounded vertical edges has shrunk from 25mm radius to 18mm to fot the material and tooling available.
3D CAD drawings to follow to illustrate.
Now designed to use standard 18mm MDF, with a double skin on all sides. The bracing has been changed so that none of it if centred and also used 18mm MDF, it joined on all sides at its fixing ends by the inner skin of the enclosure.
The rounded vertical edges has shrunk from 25mm radius to 18mm to fot the material and tooling available.
3D CAD drawings to follow to illustrate.
Image of exploded parts:
An externally hosted image should be here but it was not working when we last tested it.
Image of assembled parts:
An externally hosted image should be here but it was not working when we last tested it.
Cutaway section:
An externally hosted image should be here but it was not working when we last tested it.
No need to draw the driver in, or more accurately, be able to draw up an accurate model of the driver. I could do a basic model, but I can't see it would benefit in anyway. The bracing and front baffle have been drawn for it to fit correctly.
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