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Force cancellation woofers
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Old 8th March 2017, 08:22 PM   #21
scottjoplin is offline scottjoplin  Wales
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Those poor little woofers are having to work soooo hard...
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Old 9th March 2017, 08:44 AM   #22
chris661 is offline chris661  United Kingdom
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Originally Posted by scottjoplin View Post
Those poor little woofers are having to work soooo hard...
They'd have a much more difficult life trying to produce bass in a dipole system.

Chris
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Old 9th March 2017, 03:33 PM   #23
scottjoplin is offline scottjoplin  Wales
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That is very true, I suggest you don't use them for that...ha ha
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Old 9th March 2017, 03:40 PM   #24
jplesset is offline jplesset  United States
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About 20 years ago, I built a sub with 4 12" drivers. No, I don't remember exactly which ones. Regular box, about 6 cu ft. One woofer per side and a table-top. Bracing from side to side. The box is very stable, to the point where my wife was willing to put fragile glass sculpture on top AND she likes it loud....
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Old 22nd February 2019, 07:45 AM   #25
Bon is offline Bon  Australia
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Time for an update to my original enquiry about the effectiveness of force cancelling woofer techniques. I started with a sub using 400mm plastic drainage pipe. I used 2x12" Peerless XLS drivers for a home theatre sub. This was a trial to evaluate the principle. The 600mm pipe length had a central circular brace but I don't consider it was really necessary. The end baffles were a drop-in fit, glued and screwed to the pipe. 5mm threaded steel rods through the woofer holes have nuts Araldited on one end and a long nut for tightening the other end. The saucer of water balanced on the cylinder with no ripples is amazing verification of the lack of cabinet vibration. Having confirmed the effectiveness, I next implemented force-cancelling in a 4-way active speaker project. The sealed sub-woofer sits below the 3-way sealed enclosure with drivers mounted close to the floor to assist bass output (<100 Hz). Drivers are SB Acoustics SB23MFCL45-8. Threaded 4mm stainless rod are the largest to fit the woofer holes. The results exceed my expectations. I will try and use this method in future projects whenever feasible. The only downside is that side-mounted drivers restrict the possible speaker room positions. Avoid side-walls and nearby furniture.
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Old 22nd February 2019, 02:20 PM   #26
phivates is offline phivates  United States
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I think we undervalue the vibrating mass aspect of low frequency reproduction, and over focus on the acoustic pressure in the box. I witnessed this by loading a refoamed woofer in an open box (U frame it would be known as these days) and watched everything on or near the speaker rattle and move around while I heard nothing during break-in (25 Hz).
It's cultural: we westerners are always looking for the single significant factor, and second place is for losers. In reality all problems have two parents four grandparents etc.
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Old 22nd February 2019, 02:30 PM   #27
badman is offline badman  United States
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Quote:
Originally Posted by phivates View Post
I think we undervalue the vibrating mass aspect of low frequency reproduction, and over focus on the acoustic pressure in the box. I witnessed this by loading a refoamed woofer in an open box (U frame it would be known as these days) and watched everything on or near the speaker rattle and move around while I heard nothing during break-in (25 Hz).
It's cultural: we westerners are always looking for the single significant factor, and second place is for losers. In reality all problems have two parents four grandparents etc.
Well put. I know that for me, I'll not likely ever build another non-force-cancelling subwoofer setup again. It's just too much benefit to ignore, and isn't that hard to design in.
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Old 22nd February 2019, 08:00 PM   #28
Bon is offline Bon  Australia
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Quote:
Originally Posted by phivates View Post
I think we undervalue the vibrating mass aspect of low frequency reproduction, and over focus on the acoustic pressure in the box. I witnessed this by loading a refoamed woofer in an open box (U frame it would be known as these days) and watched everything on or near the speaker rattle and move around while I heard nothing during break-in (25 Hz).
It's cultural: we westerners are always looking for the single significant factor, and second place is for losers. In reality all problems have two parents four grandparents etc.
My speaker building has evolved over decades. The importance of enclosure rigidity and damping cannot be overemphasised. The force cancelling technique was the last important element to implement after previously taking materials, bracing, constrained-layer-damping to extremes. As the enclosure and driver size increase, force cancelling is a game changer IME. Testing the sub with 15 Hz, doors, windows, furniture in the room were shaking violently. If you have every had a LARGE helicopter go overhead at low altitude, you would have an impression. The saucer of water balanced on the sub did not show even a ripple. Later, it was discovered that the plasterboard (wall board) nails had "popped" at several locations. BTW, the subs are sealed.
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Old 22nd February 2019, 10:14 PM   #29
phivates is offline phivates  United States
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Right. Get all the elements working together. I can't imagine a glass of water on top of an OB would be calm when driven to reasonable levels of bass - unless slot loaded.
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Old 23rd February 2019, 04:55 AM   #30
kazap is offline kazap
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Quote:
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I started with a sub using 400mm plastic drainage pipe.........

Looks excellent. Where did you source the 400mm plastic drainage pipe in Australia? I wonder if there are any tubes with ID of 445mm as then 18" woofers would fit straight on with no sawdust.
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