Push - push subwoofer spacing.

[planet10]

Originally posted by richie00boy
Yes that would be push-pull on opposite sides. Good idea.

This becomes a push-pull arranged as a push-push. A bit trickier getting the tight coupling , but a very valid approach if your woofers aren't all that linear.



more here http://www.t-linespeakers.org/projects/steve/index.html (althou this example is not what i'd call well coupled)

dave

[Saturnus]

I too can wholeheartedly recommend mounting the drivers magnet to magnet. It gives a wide range of benefits. Greater sensivity and greater cabinet stability among some.

I would not recommend using a wedge between the magents. It's important that the magnets are fitted tight together to get the full benefits of the design. It's a much better idea to drill or cut a suitable hole(s) in the dust cap instead if the drivers have pole vents, and a non-permeable dustcap.

Please note however that some drivers have both pole vents and holes in the voice coil former, and in that case you should just let the VC former holes vent all the compression behind the dustcap.

[Brett]

Originally posted by Saturnus
I too can wholeheartedly recommend mounting the drivers magnet to magnet. It gives a wide range of benefits. Greater sensivity and greater cabinet stability among some.

I'm curious to know where the increased sensitivity comes from.

[planet10]

Originally posted by Brett
I'm curious to know where the increased sensitivity comes from.

There is a tiny potential for increased sensitivity because 1 magnet can reinforce the other, but in practise this is not significant (at least based on measures done with a pair of magnet to magnet RS 40-1197s). Of much greater import is that if you get the magnets that close you end up with a compound woofer that is magnetically "shielded".

dave

[Fore]

I don't understand this need to support/couple facing magnets together. Air is made by the cone's excursion and I was thinking that the magnets moved along with the cone, so you can't have them touching anything. Obviously I'm wrong...so how's this work?

[planet10]

Originally posted by Fore
I don't understand this need to support/couple facing magnets together. Air is made by the cone's excursion and I was thinking that the magnets moved along with the cone, so you can't have them touching anything. Obviously I'm wrong...so how's this work?

In an ideal world the woofer/magnet is fixed in space and only the cone moves.

But the momentum of the cone causes and equal & opposite momentum in the driver basket/magnet. By having 2 drivers in intimate contact, but pushing in opposite directions the momentums of the basket/magnets of the 2 drivers cancel. In a single woofer system this momentum is transfered to the box, which all too often you can hear, and in the case of a sub it can exhibit as woofer-walk (ie the woofer starts moving around). By actively cancelling this you dramatically reduce the energy passed to the box (making it sound better) and further increase the downward dynamic range.

dave

[Brett]

Originally posted by planet10
There is a tiny potential for increased sensitivity because 1 magnet can reinforce the other, but in practise this is not significant (at least based on measures done with a pair of magnet to magnet RS 40-1197s). Of much greater import is that if you get the magnets that close you end up with a compound woofer that is magnetically "shielded".

dave

Ta, I thought I was missing something.

Magnetic shielding won't be an issue, as nothing needs to be shielded. Sensitivity sin't a problem either for me; two pairs of 18" pro drivers. Muuhahahaha!

At current design, I'm going to build the box push-push and will experiment with push-pull later to see if I can hear any difference.

[buggsson]

This front and back firing as I suppose this solution will be, does it have any implications as to positioning the box in the room? That is, distance to back wall etc.

[Fore]

I see now. That makes sense too. Thanks for the explanation Planet10. So either have the box's internal width be exact to have both magnets touching each other, and if that's not possible, then wedge a piece of wood between them eh?

Originally posted by planet10


In an ideal world the woofer/magnet is fixed in space and only the cone moves.

But the momentum of the cone causes and equal & opposite momentum in the driver basket/magnet. By having 2 drivers in intimate contact, but pushing in opposite directions the momentums of the basket/magnets of the 2 drivers cancel. In a single woofer system this momentum is transfered to the box, which all too often you can hear, and in the case of a sub it can exhibit as woofer-walk (ie the woofer starts moving around). By actively cancelling this you dramatically reduce the energy passed to the box (making it sound better) and further increase the downward dynamic range.

dave

[planet10]

Originally posted by Fore
So either have the box's internal width be exact to have both magnets touching each other, and if that's not possible, then wedge a piece of wood between them eh?

In practise you can rarely get the magnets right against each other, so you purposely add a coupling brace as illustrated in this woofer (this 3D was a quick & nasty to illustrate -- it is actually 2 16" cubes i already had modeled merged together.

dave