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Author Topic: Push pull double 18  (Read 10350 times)

Kevin McDonough

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Re: Push pull double 18
« Reply #10 on: March 20, 2018, 09:16:02 am »


In this case, a positive voltage on the input terminals makes both cones (forward and reverse facing) move forward, so it doesn't have the same advantages as the OP's design where the two cones move in different directions and therefore reduce cabinet vibration.


I've never heard of anyone mention that a PPSL cab reduces cabinet vibrations, just distortion. To be clear, the way it works is one driver is cone side into the little chamber, and one is magnet side. With a very small chamber you almost have the magnet sitting inside the cone of the other driver.

then one is reverse wired, so that when signal is applied they both move into the chamber at the same time, and away from the chamber at the same time.  (if they were wired normally they'd cancel each other out!)

As someone says, the theory is that the distortion artefacts caused by cone breakup and non-linearity are the opposite for each driver cancel each other out with their opposing movements and it seems to hold in practice, most people report they have a much "cleaner" sound.  (though this is occasionally a detriment to people who are used to the bit of distortion added by other cabs and are used to that sound, think it sounds louder because of it!  ;D)

user DJK on speakerplans and DIYaudio has posted a lot of good info about them and their design if people want to search for more info.

K
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Mark Wilkinson

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Re: Push pull double 18
« Reply #11 on: March 20, 2018, 09:29:12 am »

The lab sub does not use opposed drivers.

The reason for the minimal movement of the lab sub is the horn loading, and small back volume.

Hi Ivan, The labsub has opposed drivers...about 8" apart directly facing each other...that's a fact.
Not sure by what you mean, that it doesn't use them..

How much cabinet vibration dampening is due to horn loading and rear chamber volume, and how much is due to opposed drivers....who knows?? 
Next time I have one out, I'll unhook one driver and see how much cabinet vibration goes up... I'm certain it will increase at least some..

Before I began this current sub, I took a pair of single 18's and faced them about 10" apart.  I clamped four 1"x 4"s to the subs connecting their cabinets together. 
Then I really cranked some tunes, running only one sub, and then running both.
I sat on the one sub, and vibration was very noticeably reduced when both were running....even with this half-ass clamped together connection.
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Mark Wilkinson

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Re: Push pull double 18
« Reply #12 on: March 20, 2018, 09:44:30 am »

I've never heard of anyone mention that a PPSL cab reduces cabinet vibrations, just distortion. To be clear, the way it works is one driver is cone side into the little chamber, and one is magnet side. With a very small chamber you almost have the magnet sitting inside the cone of the other driver.

then one is reverse wired, so that when signal is applied they both move into the chamber at the same time, and away from the chamber at the same time.  (if they were wired normally they'd cancel each other out!)

As someone says, the theory is that the distortion artefacts caused by cone breakup and non-linearity are the opposite for each driver cancel each other out with their opposing movements and it seems to hold in practice, most people report they have a much "cleaner" sound.  (though this is occasionally a detriment to people who are used to the bit of distortion added by other cabs and are used to that sound, think it sounds louder because of it!  ;D)

user DJK on speakerplans and DIYaudio has posted a lot of good info about them and their design if people want to search for more info.

K

Thanks for the further explanation Kevin,


I've been after a reduced vibration sub design.....it's part of a modular lounge strategy I'm playing with, that's easier to stack and tie down without excessive vibration.

As I was reading through DJK's and others' posts about PPSL, it became clear that any opposed design, whether push-pull inverted, or push-push, would counteract inertial driver force transmitted to the cabinet.   So adding in the possibility of a distortion reduction, I went for a PPSL.

Plus, as DJK mentioned somewhere, if you don't like the sound of the PPSL (like some people don't like low distortion horn loaded), you can always flip the inverted driver around in the slot, and switch it to a push-push, and get back the distortion.
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Ivan Beaver

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Re: Push pull double 18
« Reply #13 on: March 20, 2018, 12:38:17 pm »

Hi Ivan, The labsub has opposed drivers...about 8" apart directly facing each other...that's a fact.
Not sure by what you mean, that it doesn't use them..


I guess it depends on what is considered "opposed" and push pull.

I agree about the placement of the drivers in the lab12.

But they are both moving in the same direction at the same time.

I would call that more "tandum".

I was considering "opposed" drivers as meaning that as one moves into its basket, the other moves out.

But I guess it just depends on how you look at what the term means.
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Mark Wilkinson

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Re: Push pull double 18
« Reply #14 on: March 20, 2018, 02:24:14 pm »

I guess it depends on what is considered "opposed" and push pull.

I agree about the placement of the drivers in the lab12.

But they are both moving in the same direction at the same time.

I would call that more "tandum".

I was considering "opposed" drivers as meaning that as one moves into its basket, the other moves out.

But I guess it just depends on how you look at what the term means.

Yep, I hear where you were coming from.

I think the speaker building community, at least the DIY community, uses the term 'opposed' to describe relative cone-to-cone movements.

I mean, take the labsub's cones.... I wouldn't say they move in the same direction...

Since both move into the throat at the same time, it means one moves to the right, and one moves to the left (for a lab standing up), or up vs down, ...opposite directions no matter how viewed...



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Rob Spence

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Re: Push pull double 18
« Reply #15 on: March 20, 2018, 02:39:09 pm »

Yep, I hear where you were coming from.

I think the speaker building community, at least the DIY community, uses the term 'opposed' to describe relative cone-to-cone movements.

I mean, take the labsub's cones.... I wouldn't say they move in the same direction...

Since both move into the throat at the same time, it means one moves to the right, and one moves to the left (for a lab standing up), or up vs down, ...opposite directions no matter how viewed...

Same direction is relative to the frame of the driver. Ie, both out or both in.



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Art Welter

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Re: Push pull double 18
« Reply #16 on: March 20, 2018, 03:39:05 pm »

As I was reading through DJK's and others' posts about PPSL, it became clear that any opposed design, whether push-pull inverted, or push-push, would counteract inertial driver force transmitted to the cabinet.   So adding in the possibility of a distortion reduction, I went for a PPSL.

Plus, as DJK mentioned somewhere, if you don't like the sound of the PPSL (like some people don't like low distortion horn loaded), you can always flip the inverted driver around in the slot, and switch it to a push-push, and get back the distortion.
Mark,

PP only reduces even order distortion. In my quick test with LAB 12 drivers in a sealed and ported configuration, at high drive levels odd order distortion actually increased slightly PP compared to standard.

The test you previously posted appears to have the distortion components less than the noise floor, so can't really provide useful information.
I'd suggest 2 meters for testing distance considering your proximity to structures if your test mic can handle the SPL.

Will be interesting to see the results when the cabinet bracing is completed.
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Mark Wilkinson

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Re: Push pull double 18
« Reply #17 on: March 20, 2018, 04:03:26 pm »

Same direction is relative to the frame of the driver. Ie, both out or both in.


No, i don't think that's correct....at least not in the context of trying to define "opposed"
« Last Edit: March 20, 2018, 04:34:34 pm by Mark Wilkinson »
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Mark Wilkinson

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Re: Push pull double 18
« Reply #18 on: March 20, 2018, 04:23:57 pm »

Mark,

PP only reduces even order distortion. In my quick test with LAB 12 drivers in a sealed and ported configuration, at high drive levels odd order distortion actually increased slightly PP compared to standard.

The test you previously posted appears to have the distortion components less than the noise floor, so can't really provide useful information.
I'd suggest 2 meters for testing distance considering your proximity to structures if your test mic can handle the SPL.

Will be interesting to see the results when the cabinet bracing is completed.

Hi Art,  I saw your post about the test with the Lab 12's, and I get it's only about even order distortion,.... and even then maybe only about drivers that show significant inductance asymmetry in and out.

Yep, I saw the noise floor later, too.  Good idea on testing closer with REW for distortion, although I want to test at 130dB levels...
I'm looking forward to distortion testing the PPSL directly vs the bass reflexes. 
I don't really expect much, don't really care much honestly.
But am very curious about it.

Here's a distortion sweep at 120dB made the same day, that gets above the noise floor a little. 
Look at the port shelf talking  ;D   It's why i stopped...

« Last Edit: March 20, 2018, 04:43:07 pm by Mark Wilkinson »
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Art Welter

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Re: Push pull double 18
« Reply #19 on: March 20, 2018, 04:44:38 pm »

Hi Art,  I saw your post about the test with the Lab 12's, and I get it's only about even order distortion,.... and even then maybe only about drivers that show significant inductance asymmetry in and out.

Yep, I saw the noise floor later, too.  Good idea on testing closer with REW for distortion, although I want to test at 130dB levels...
I'm looking forward to distortion testing the PPSL directly vs the bass reflexes. 
I don't really expect much, don't really care much honestly.
But am very curious about it.
Mark,
I'd like to do some 130 dB distortion testing of my newest subs, but the neighbors don't  :-[
 Had not heard of inductance asymmetry, but suspension and Bl (motor) asymmetry are common, and back when DJK came up with PPSL the drivers he used had a lot more of those problems than the drivers you are using.

My take away was I couldn't detect the difference with the LAB 12's until after they exceeded Xmax, and then the PP sounded a little worse. If you tend to push the drivers past Xmax, having them sound worse when they do help you "put on the brakes" before they break ;^).
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