Push-pull woofer alignment questions

[planet10]

Originally posted by navin


Dave what would be the volume required in this box?

I would assume it would be the same as one woofer in a sealed box.

Same net volume as 1 driver -- you do need to account for the extra volume the 2nd internal driver takes up...

box could be sealed, ported, TL...

dave

[3-LockBox]

Originally posted by john k...
Well there is certainly a lot of misinformation in you post. First, if by PP you means two driver mounted in the same box but with the motor structure in the box and one flipped so the motor is out of the box and the driver wired out of place electrically (in phase acoustically) then the required box volume doubles as effectively Vas doubles.

The distortion issues are a little more complex. The common assumption is that because the drivers are electrically out of phase even order distortion generated in the motor will cancel. This seems true at first glance and is basically true for an infinite baffle or a dipole configuration. However, when a box enters the picture the loading of the box side of the driver changes the situation. When the box compliance is considered the forces acting on the driver include the pressure force on the box side of the cone and there is not guarantee that the even order distortion will cancel.

Yes, by push-pull I was referring to your description in paragraph one. M&K use to sell a subwoofer with a variation on the PP theme. Vance Dickason's LSD Cookbook 6th Ed. talks of the PP woofer alignments, but indicates that Vas is halved. Perhaps its a misprint. I've seen other sites that indicate that Vas is halved as well, but just as many more repeat what you've said about it doubling. M&K's subwoofers are in a sealed cabinet and they tout cancelation of odd ordered harmonics.

I believe Linkwitz has also stated the same thing concerning your statements on dipoles versus box loading. His Orions employ PP alignment in a dipole, open baffle. His Orions also employ an intricate divider/EQ network, which boosts the bass considerably to achieve a flat response.

[planet10]

Originally posted by 3-LockBox
I've seen other sites that indicate that Vas is halved

Vas is halved only when the 2 drivers are used isobarikally... if you use them as normal Vas (for the pair) doubles.

dave

[Svante]

Originally posted by planet10
.... B & D are the same.

Well, not in terms of net reaction force on the box.

[planet10]

Originally posted by Svante
Well, not in terms of net reaction force on the box.

I addended myself in a later post... as far as push-pull goes they are topologically the same, D has the advantage of being push-push (but extra effort needed to couple the drivers)

dave

[3-LockBox]

Originally posted by planet10


Vas is halved only when the 2 drivers are used isobarikally... if you use them as normal Vas (for the pair) doubles.

dave

Well then my pipe dreams are dashed!





Or...maybe not

[newpaton2]

hello planet 10, Just to get this straight.
Diagram C requires double volume? so therefore it isnt isobarik?

[mdocod]

holy resurrection!