Push-push phase
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 23rd February 2007, 12:16 PM #1 rick57 diyAudio Member   Join Date: Dec 2002 Location: dry ol Melbourne Australia Push-push phase My aim is to mimimise or cancel driver non-linearities. I've been searching on this, and understand that push-push is more effective than push-pull. Thanks to Dave's good drawing at www.t-linespeakers.org/FALL/push-push.html, push-push construction is clear. Box modelling is as per a single woofer, apart from effective Vas doubling. Cone excusion halves. with the 'normal': - connected in parallel: impedance halves, sensitivity + 3 dB - connected in series: impedance doubles, sensitivity - 3 dB Am I right that the wiring is simply normal stereo electrical in-phase? Thanks
planet10
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Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Re: Push-push phase

Quote:
 Originally posted by rick57 My aim is to mimimise or cancel driver non-linearities. Box modelling is as per a single woofer, apart from effective Vas doubling. Cone excusion halves. with the 'normal': - connected in parallel: impedance halves, sensitivity + 3 dB - connected in series: impedance doubles, sensitivity - 3 dB Am I right that the wiring is simply normal stereo electrical in-phase?
To get non-linearity cancelation you need push-pull where when one driver's cone is moving away from the motor, the other is moving towards the motor.

Referring to the attached diagram, normal push-pull is arranged as in #4.

Push-push is an arrangement where the drivers are oriented such that the newtonian motion of 1 driver is actively cancelled by another. The most effective way to achieve this is when the magnets are rigidly coupled as in #2.

#3 is an arrangement of push-pull that, if you couple the 2 drivers together mechanically with ready rod bolts or carefully placed braces, gets you most of the push-push advantage of #2. (one could mount the drivers such that they fire into a holey PVC pipe the same diameter as the driver)

#4 is the ultimate push-push push-pull. it also gives you a box that is 1/4 the size of 2, 3 & 4 (which all have the same box volume despite what you might gather from the cross-section). It also gives added isolation from waves coming back thru the cone.

In each case the drivers are wired so they all push on the boxes internal volume the same way.

2 drivers can be treated as a single driver with 2x the Vas (and 2x the Sd).

When wired in parallel, efficiency is increased by 3 dB and -- if driver by a true voltage source -- sensitivity goes up 6 dB (3 dB increase in efficiency + 3 dB due to the amp delivering 2x the power)

When wired in series, efficiency is increased by 3 dB and -- if driver by a true voltage source -- sensitivity stays the same (3 dB increase in efficiency - 3 dB due to the amp delivering half the power)

Sensitivity is a specification i'd like to see binned -- there are lots of amplifiers (tube amps of almost any ilk for instance) that do not satisfy the criteria of being a true voltage source.

dave
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 24th February 2007, 02:28 PM #3 rick57 diyAudio Member   Join Date: Dec 2002 Location: dry ol Melbourne Australia dave (I'd moved to an option that might not have been the better one for the situation) Which do you think is a more useful to cancel, non-linearity or the newtonian motion? If the drivers aren't that good (current situation - some that i got for \$20 each at a car boot sale, for a PC's sub) - probably better to cancel non-linearity, via push- pull? While if the drivers are good, eg Peerless CSX (I also have), better to cancel the newtonian motion (push-push)? And when you have 4 drivers (i have a set of 4 from a cancelled plan): #4 (push-push push-pull) - what is the effective Vas and effects on dB & ohms? Cheers
planet10
frugal-phile(tm)
diyAudio Moderator

Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Quote:
 Originally posted by rick57 Which do you think is a more useful to cancel, non-linearity or the newtonian motion? ... the drivers aren't that good
A little ingenuity with the box bracing and #3 will give you all of the non-linearity cancellation, and most of the newtonian motion cancellation.

Quote:
 While if the drivers are good, eg Peerless CSX (I also have), better to cancel the newtonian motion (push-push)?
Yes. And gain the WAF. When i talked with Nick (Llambda) about these concepts he said that if using his drivers, there would be next to no gain doing push-pull.

Quote:
 And when you have 4 drivers (i have a set of 4 from a cancelled plan): #1 (push-push push-pull) - what is the effective Vas and effects on dB & ohms?
I tend to like pairs of woofers so i would look at 2 push-push woofers, but when you have 4 drivers in isobarik configuration, except for the doubling of the volume inside the box that they take up, you treat them as a single driver. Vas, Qt, Fs is all the same. Efficiency goes up 3 dB, and assuming series/parallel we end up with a sensitivity increase of 3 dB.

dave
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 25th February 2007, 12:34 AM #5 rick57 diyAudio Member   Join Date: Dec 2002 Location: dry ol Melbourne Australia Thanks Dave, when I read of this some time ago with the with hand built bass drivers and the bolt thru the pole piece http://www.t-linespeakers.org/FALL/push-push.html I was thrown off the benefits, but now the applications are clear Cheers
planet10
frugal-phile(tm)
diyAudio Moderator

Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Quote:
 Originally posted by rick57 but now the applications are clear

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