ProSoundWeb Community

Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Subwoofer Forum => Topic started by: Mark Wilkinson on March 19, 2018, 01:32:36 pm

Title: Push pull double 18
Post by: Mark Wilkinson on March 19, 2018, 01:32:36 pm
Got this idea from a thread on the diyaudio forum http://www.diyaudio.com/forums/subwoofers/177905-thread-ppsl-enclosures.html

They call it a push-pull-slot-loaded sub.  The inverted driver in the slot is wired in reverse polarity, so both squeeze into the slot at the same time.
The slot is basically made as small as possible, and then you build whatever  kind of box you want around the slot/driver module.

I chose a bass reflex box, because I had already built a successful single 18 with the drivers, and could simply  double the net box size for two 18s, after accounting for the extra driver module volume inside the overall box.  Pretty easy design really. Ended up 49Hx21.75Wx31.25D

What's really cool about it IMO, is the wonderful reduction in cabinet vibration.  Opposed drivers really do reduce vibration it appears.
This was the primary reason I tried this design....I absolutely love the single 18's I built other than how much they can walk/jump around.
The single 18's are well braced, but it seems it's weight that matters.  I watch orbitshifters and th-118s want to walk around too....

Supposedly, the design reduces 2nd order harmonic distortion too.  We'll see....   
I can say it sounds very, very, clean, kinda like a labsub (which btw doesn't move much either...opposed drivers again)

Anyway, here's a pict and measurement taken this morning. 
Measurement is raw other than the 3 peq's shown in table.
The slot provides a heck of a boost in the high 100'sHz, that has to be knocked down.
I'd put efficiency at 101-102 @ 2.83v after the knockdown.

Title: Re: Push pull double 18
Post by: Scott Holtzman on March 19, 2018, 01:47:28 pm
Got this idea from a thread on the diyaudio forum http://www.diyaudio.com/forums/subwoofers/177905-thread-ppsl-enclosures.html

They call it a push-pull-slot-loaded sub.  The inverted driver in the slot is wired in reverse polarity, so both squeeze into the slot at the same time.
The slot is basically made as small as possible, and then you build whatever  kind of box you want around the slot/driver module.

I chose a bass reflex box, because I had already built a successful single 18 with the drivers, and could simply  double the net box size for two 18s, after accounting for the extra driver module volume inside the overall box.  Pretty easy design really. Ended up 49Hx21.75Wx31.25D

What's really cool about it IMO, is the wonderful reduction in cabinet vibration.  Opposed drivers really do reduce vibration it appears.
This was the primary reason I tried this design....I absolutely love the single 18's I built other than how much they can walk/jump around.
The single 18's are well braced, but it seems it's weight that matters.  I watch orbitshifters and th-118s want to walk around too....

Supposedly, the design reduces 2nd order harmonic distortion too.  We'll see....   
I can say it sounds very, very, clean, kinda like a labsub (which btw doesn't move much either...opposed drivers again)

Anyway, here's a pict and measurement taken this morning. 
Measurement is raw other than the 3 peq's shown in table.
The slot provides a heck of a boost in the high 100'sHz, that has to be knocked down.
I'd put efficiency at 101-102 @ 2.83v after the knockdown.

That's interesting.  Is the vent in the back for the top sub or is there a waveguide down the back to the bottom vent?
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 19, 2018, 02:02:19 pm
That's interesting.  Is the vent in the back for the top sub or is there a waveguide down the back to the bottom vent?

Hi Scott,  both drivers vent into the same back chamber, just like a regular double 18 BR.
So the port at the bottom is handling duty for both drivers. 

The port shelf on mine is currently just screwed in place, and without it's bottom brace tying it to the cabinet.
Needed to make sure of tuning before gluing and bracing it in.
It definitely began to flap some at 30Hz as i turned up the juice !
Title: Re: Push pull double 18
Post by: Dave Garoutte on March 19, 2018, 05:50:46 pm
What's the advantage of having the both aimed up?
Compared to if they were aimed together and not reversed polarity?
Title: Re: Push pull double 18
Post by: Art Welter on March 19, 2018, 05:56:26 pm
Supposedly, the design reduces 2nd order harmonic distortion too. 

The slot provides a heck of a boost in the high 100'sHz, that has to be knocked down.
Mark,

The extra upper boost the plenum (slot) provides helps make up for the reduced even order harmonics the push pull arrangement provides ;^).

Looks svelte!

Cheers,
Art
Title: Re: Push pull double 18
Post by: Don T. Williams on March 19, 2018, 06:02:03 pm
What's the advantage of having the both aimed up?
Compared to if they were aimed together and not reversed polarity?

One explanation that I have seen is that differences in linearity in the cone movement "out" vs. movement "in" will be out of phase and thus cancel.  The result should be lower distortion.  That's the theory.  Has anyone out there measured and confirmed the theory? 
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 19, 2018, 06:32:11 pm
One explanation that I have seen is that differences in linearity in the cone movement "out" vs. movement "in" will be out of phase and thus cancel.  The result should be lower distortion.  That's the theory.  Has anyone out there measured and confirmed the theory?

Art, thank you !

Dave, yep, what Don is saying...

Don, I think Art has done more homework on this than anywhere I've seen.
I have a pair of single 18's, same drivers, and very close to same bass-reflex build in terms of volume and ports. 
I hope to measure distortion side by side and compare directly.

Below is a distortion test I ran with REW's swept sine this morning, but only at 110dB @ 1 meter equivalent, because my port isn't glued in yet and rattled alot at 120dB.
This was at 10 meters, so +20dB
Looks great so far i think....
 
Title: Re: Push pull double 18
Post by: Jeremy Young on March 19, 2018, 07:30:17 pm
Very cool Mark!


My EAW FR250z 2x15" subwoofer is another example of a push/pull arrangement design, but in this case it's in two separate sealed portions of the same front-loaded reflex cabinet. 

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 can't say as I've ever unplugged one woofer and measured to see whether distortion changes, but the concept seems sound to me and it does sound good for its price/class.   

This past summer I A/B'd that sub against an Orbit Shifter Pro during an impromptu outdoor shootout and well..... let's say they are in different classes.  The OS Pro was much more transparent, but let's not forget it cost me about 20% of what the OS Pro did, and it's considerably smaller in size.

Sorry no measurements of that, it was far too casual for any measurements to mean anything in a formal post.  Up until that day I always thought it sounded pretty good, but I only ever use it in small-ish rooms where positioning and room-modes can have just as much affect.
Title: Re: Push pull double 18
Post by: Ivan Beaver on March 20, 2018, 07:51:23 am

Supposedly, the design reduces 2nd order harmonic distortion too.  We'll see....   
I can say it sounds very, very, clean, kinda like a labsub (which btw doesn't move much either...opposed drivers again)


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.
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 20, 2018, 09:12:45 am
Very cool Mark!


My EAW FR250z 2x15" subwoofer is another example of a push/pull arrangement design, but in this case it's in two separate sealed portions of the same front-loaded reflex cabinet. 

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.



This past summer I A/B'd that sub against an Orbit Shifter Pro during an impromptu outdoor shootout and well..... let's say they are in different classes.  The OS Pro was much more transparent, but let's not forget it cost me about 20% of what the OS Pro did, and it's considerably smaller in size.



Thanks Jeremy, 
Yeah, I saw the FR250z mentioned in the diyaudio thread, but like you say, it is considered more of a regular dual-driver bass reflex, only with one driver mounted backwards. I couldn't glean any clear consensus on what folks thought EAW was trying to accomplish...

Interesting you compared your sub against an OS.  I have a pair of OS's and use one to compare against the diy 18's I'm making.
Here's a past thread, 1 OS  vs 2 diy 18's.  http://forums.prosoundweb.com/index.php/topic,163594.0.html
Having used the boxes for a while, I've really come to consider 2 of the single 18's as an equivalent to 1 OS  in terms of output.

If all continues to turn out as designed with the new dual 18 PPSL in this thread, it should directly equal a pair of my single 18's....
which in my mind, means this new box should equal an OS.   When I'm certain it does, I'm most likely putting my JTR rig up for sale....going totally DIY i think :)
Title: Re: Push pull double 18
Post by: Kevin McDonough 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
Title: Re: Push pull double 18
Post by: Mark Wilkinson 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.
Title: Re: Push pull double 18
Post by: Mark Wilkinson 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.
Title: Re: Push pull double 18
Post by: Ivan Beaver 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.
Title: Re: Push pull double 18
Post by: Mark Wilkinson 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...



Title: Re: Push pull double 18
Post by: Rob Spence 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.



Sent from my iPad using Tapatalk Pro
Title: Re: Push pull double 18
Post by: Art Welter 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.
Title: Re: Push pull double 18
Post by: Mark Wilkinson 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"
Title: Re: Push pull double 18
Post by: Mark Wilkinson 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...

Title: Re: Push pull double 18
Post by: Art Welter 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 ;^).
Title: Re: Push pull double 18
Post by: Ivan Beaver on March 20, 2018, 05:39:24 pm

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 ;^).
But that is ONLY if you are paying attention to the sound.

Many people don't pay any attention, until it stops.  And then it is to late. :(
Title: Re: Push pull double 18
Post by: David Morison on March 21, 2018, 04:07:17 am
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...

Hi Mark,
Could you help interpret that a little please?

The curves seem to show that 2nd harmonic has the highest distortion, followed by 3rd etc, pretty much as expected.
However the trace IDs below that have an oddly high percentage figure for the 4th harmonic even though that trace appears lower than 2nd & 3rd - is there an explanation for that please?

Thanks,
David.
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 21, 2018, 08:51:09 am
Hi Mark,
Could you help interpret that a little please?

The curves seem to show that 2nd harmonic has the highest distortion, followed by 3rd etc, pretty much as expected.
However the trace IDs below that have an oddly high percentage figure for the 4th harmonic even though that trace appears lower than 2nd & 3rd - is there an explanation for that please?

Thanks,
David.

Hi David, I don't really have a good interpretation, other than the observation the box was audibly buzzing/rattling at the bottom of REW's sine sweep. 
The shelf port was just screwed in, albeit fairly tightly, for tuning verification (30Hz target). 120dB isn't that loud, but it was obvious it was loud enough to rattle the port without bracing or glue. The buzz rattle sounded like low 100Hz ish....maybe 4th order??   
I only took the two sweeps posted, one at 110dB, then at 120. If 120 had stayed clean, I would have tried for 130 just being anxious to get a preliminary look.. 
It was kinda silly for me to post any distortion plots before bottling her up, but all the 2nd order reduction talk lured me in  :)

I swear, I think I spend as much time and work doing bracing and cursed grills, as box design/construction.  What a comparative pain.
Hope to finish up port bracing today.

But hey, the second nicest thing I like about this about this sub, is the driver grill is only 12 1/2" x 20" !!!
Maybe I'll finally get one not to rattle first try ...

Do you have any particular techniques you like for discerning resonances?  Slow manual sine sweeps is about the best technique I've found so far.
Title: Re: Push pull double 18
Post by: Uwe Riemer2 on March 21, 2018, 10:33:28 am
Mark,
you are putting a lot of effort into this design, but did you consider the effect of gravity on the drivers in the long run?

I would, because I have considerable experience in repair of a triple chamber bandpass design with the same driver orientation. The loss of center position of otherwise fine drivers hurts every time I see it.

Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 21, 2018, 01:38:38 pm
Mark,
you are putting a lot of effort into this design, but did you consider the effect of gravity on the drivers in the long run?

I would, because I have considerable experience in repair of a triple chamber bandpass design with the same driver orientation. The loss of center position of otherwise fine drivers hurts every time I see it.

Hi Uwe, thanks for the heads up. I've wondered if cone sag might be an eventual problem.

How do you tell when there is a loss in center position?

Do you think loss of center occurs when in storage, when playing, or both?
It's made me wonder how manufactures store their drivers in the wharehouse.....

If this is an issue, and anybody with experience here please do chime in...

I've had the idea that I could build the next ones with slot ports on top and bottom, so the subs could stand on either end, and rotate the hang direction. 
Or I could run the slot vertically, but I'm hoping to minimize width, and going vertical would make the box substantially wider.
But I like what I have unless.......

Title: Re: Push pull double 18
Post by: Art Welter on March 21, 2018, 02:19:48 pm
I've wondered if cone sag might be an eventual problem.

1)How do you tell when there is a loss in center position?
2)Do you think loss of center occurs when in storage, when playing, or both?
3)It's made me wonder how manufactures store their drivers in the wharehouse.....
4)If this is an issue, and anybody with experience here please do chime in...
Mark,

I had already mentioned cone sag to you prior to your construction on 3/3/18, was a bit surprised when you oriented the cones horizontally in your PPSL. "Done is done", but  since Uwe brought it up again..
1) You will see the sag in the surround after time stored horizontally.
Distortion will increase as the cone is harder to push up than down. After sag, the driver will require more power to achieve Xmax in the up stroke than the down stroke. Eventually, the driver may hit Xlim (flap, clack, or break) on the down stroke with far less power than in it's original state.
2) Gravity (and rust) never sleeps.
3) Warehouse storage is usually for as short a term as possible, but often the wrong way (horizontally). There are examples of "new old stock" with 1/2" sag posted on line.
4) The softer  and heavier the suspension, the more the problem, and the sooner it becomes problematic.

Your drivers have a fairly light, stiff suspension, but if you have a choice, follow my prior advice re-posted below.

Otherwise, rotate the drivers when you notice a few mm of sag.

Cone sag can also occur vertically, the diagonal sag eventually causing voice coil rubbing problems.
Oh, well...

Cheers,
Art





Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 21, 2018, 04:19:49 pm
Mark,

I had already mentioned cone sag to you prior to your construction on 3/3/18, was a bit surprised when you oriented the cones horizontally in your PPSL. "Done is done", but  since Uwe brought it up again..
1) You will see the sag in the surround after time stored horizontally.
Distortion will increase as the cone is harder to push up than down. After sag, the driver will require more power to achieve Xmax in the up stroke than the down stroke. Eventually, the driver may hit Xlim (flap, clack, or break) on the down stroke with far less power than in it's original state.
2) Gravity (and rust) never sleeps.
3) Warehouse storage is usually for as short a term as possible, but often the wrong way (horizontally). There are examples of "new old stock" with 1/2" sag posted on line.
4) The softer  and heavier the suspension, the more the problem, and the sooner it becomes problematic.

Your drivers have a fairly light, stiff suspension, but if you have a choice, follow my prior advice re-posted below.

Otherwise, rotate the drivers when you notice a few mm of sag.

Cone sag can also occur vertically, the diagonal sag eventually causing voice coil rubbing problems.
Oh, well...

Cheers,
Art

Hi Art,  the reason I said I've been wondering about cone sag is because of your prior post, I remember it well... :)

This box isn't a done-is-done situation.  It's a prototype for an eventual 4 boxes, to let me see how well the PPSL idea works.
Letting the plenum bolt up directly to the cabinet walls made for really easy construction.  Heck, sawdust is barely over two weeks old. 
Whether I have to build 3 more of the same, or 4 from an altered design, doesn't really matter much at the margin. 

I do like the width and the way the box handles though.
But enough warning about horizontal orientation, and I'll certainly go vertical....

or split the slot port in two, half on top, and half on bottom, where I just rotate the sub every so often...
What do think about that idea?   Thx

Title: Re: Push pull double 18
Post by: Uwe Riemer2 on March 21, 2018, 04:48:47 pm

How do you tell when there is a loss in center position?

Do you think loss of center occurs when in storage, when playing, or both?
It's made me wonder how manufactures store their drivers in the wharehouse.....

I've had the idea that I could build the next ones with slot ports on top and bottom, so the subs could stand on either end, and rotate the hang direction. 
Or I could run the slot vertically, but I'm hoping to minimize width, and going vertical would make the box substantially wider.
But I like what I have unless.......

Some baskets allow a parallel look along the spider, this is the easiest way to spot it.

Loss of center position occurs in storage and playing, I have no data, what is more severe.
But the benefit of push/pull might be outweighted by the asymmetrical load of gravity.

Build one box with the slot vertically and then compare the two designs,
or use the existing design on the side.

Title: Re: Push pull double 18
Post by: Art Welter on March 21, 2018, 05:17:27 pm
I do like the width and the way the box handles though.
..or split the slot port in two, half on top, and half on bottom, where I just rotate the sub every so often...
What do think about that idea?   Thx
If you like the box ergonomics the way it is, build more of the same, and flip 'em every once in a while when stored when you notice sag.

Splitting the bass reflex port would also work OK, and stiffen up the cabinet a bit, but then you have two dirty bottoms instead of one, and upside down plugs half the time...




Title: Re: Push pull double 18
Post by: Ivan Beaver on March 21, 2018, 06:36:56 pm
If you like the box ergonomics the way it is, build more of the same, and flip 'em every once in a while when stored when you notice sag.


The old Maryland Sound "clams" (Karlson couplers) would exhibit bad cases of cone sag.

On one side they would be hanging out of the basket, and on the other side they would be depressed into the basket-because of the mounting angles.  Especially in clubs where the were installed (like the old Hammerjacks in Baltimore for example.)
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 21, 2018, 08:13:22 pm
The old Maryland Sound "clams" (Karlson couplers) would exhibit bad cases of cone sag.

On one side they would be hanging out of the basket, and on the other side they would be depressed into the basket-because of the mounting angles.  Especially in clubs where the were installed (like the old Hammerjacks in Baltimore for example.)

Yep, I can find lot's of stuff about older drivers having sag problems, but I have to wonder if newer suspensions haven't improved.

Hey, what's your guess on the driver mounting angle of the TH-118, off horizontal ? It looks more horizontal than not ??
 
I'm starting to look around to see if I can find current prosub designs that are more horizontal than not....also asked BMS what they think about horiz for this driver....



.
Title: Re: Push pull double 18
Post by: Jeremy Young on March 21, 2018, 08:53:11 pm
I'm not going to pretend to be anywhere near the level of experience that you guys are.    This is just my take on the issue being discussed.

There are numerous commercially available pro audio subwoofers with drivers mounted similar to Mark's design.  Or designed to be stored in that orientation. Take any front-loaded reflex subwoofer with rear casters, or boxes like the EAW SB1000 series where the casters are on the rear/bottom and could be stored drivers-up.  Even the EAW FR250z I referenced earlier in this thread has four rear casters and has been sitting with grille-up for about 12 months straight in my storage. 

I would think this would be a bigger problem on mid/high boxes or home hi-fi stuff where the spiders are much softer than a pro audio woofer.  Then again, my home theatre subwoofer is facing downward and I've owned it over a decade and the foam surround seems to be holding up just fine.

What did EV do with their MTL-4 design to address this?

As for storage, if it's an issue worth concern, and the transport/deployment logistics make sense to move ahead similar to your prototype, why not just put a tiny sticker on each end, label one summer and one winter (or colour code them) and flip it over once every 6 months?  In summer, store with red upward, in winter, store with blue upward or something like that.  It could be recessed into a pocket where the foot of another cabinet would reside when stacking, so it's discrete.

My two cents...take with a grain of salt when in this company though.  I'm not a speaker designer, just user/fixer.  Keep up the good work Mark!
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 22, 2018, 10:32:15 am
Hi Jeremy, thanks for the moral support !

BMS kindly replied back already, and said although possible, they don't recommend horizontal mounting....that sag will occur sooner or later.
Same thing Art and Ewe were saying...(thx again guys)

But I still have the same thoughts you do....real world usage, both in many designs that are either outright horizontal, or significantly off vertical, are definitely out there.  And there is the storage issue you mention....

Pure speculation makes me wonder if horizontal storage sag isn't minor compared to being driven, though.  All the high power 18" drivers I briefly checked, have a moving mass of a little over 1/2 lb.....I never quite internalized before how much force it must take to oscillate that much mass.....it would seem the dynamic strain on the suspension if motor looses full controll would dwarf stain at rest.....but time does take its toll.....who knows....   
Maybe a bigger issue than mounting orientation, is always keeping driver excursion within full motor control...?

Anyway, if the box I've built shows the same full power vibration reduction and distortion measures well at high level, I'll probably put slot ports on both ends where I can periodically flip the box.
Title: Re: Push pull double 18
Post by: Marc Sibilia on March 22, 2018, 11:11:05 am
Pure speculation makes me wonder if horizontal storage sag isn't minor compared to being driven, though.  All the high power 18" drivers I briefly checked, have a moving mass of a little over 1/2 lb.....

If you are concerned about it, you can apply about 0.6 VDC of the correct polarity to them while stored, and let the voice coil carry the weight.  1/2 lb is about 2.2 newtons.  With BL of 25 T-m, 0.1 A will carry the weight.  Power is trivial at (0.1 A)^2 * 5.6 ohm = about 60 mW, so heating is a non-issue.

You could make up a storage harness hooked to a wall wart.  You can run it all year for a pair of PPSL subs (4 drivers) for about 30 cents of electricity.  It is cheap insurance for $2800 worth of drivers and you don't have to scrape up the top of your cabinets.

Marc

P.S.  Never mind.  Seemed like a good idea until I thought about the internal wiring.  The upper driver needs to be pulled into the cabinet and the lower needs to be pushed out of the cabinet.  That is the opposite of how they are wired for audio output.
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 22, 2018, 12:48:00 pm
If you are concerned about it, you can apply about 0.6 VDC of the correct polarity to them while stored, and let the voice coil carry the weight.  1/2 lb is about 2.2 newtons.  With BL of 25 N-m, 0.1 A will carry the weight.  Power is trivial at (0.1 A)^2 * 5.6 ohm = about 60 mW, so heating is a non-issue.

You could make up a storage harness hooked to a wall wart.  You can run it all year for a pair of PPSL subs (4 drivers) for about 30 cents of electricity.  It is cheap insurance for $2800 worth of drivers and you don't have to scrape up the top of your cabinets.

Marc

P.S.  Never mind.  Seemed like a good idea until I thought about the internal wiring.  The upper driver needs to be pulled into the cabinet and the lower needs to be pushed out of the cabinet.  That is the opposite of how they are wired for audio output.

Marc, I think its a very interesting idea !   Thank you.
Yeah, I saw I'd need to be able to switch between push-pull and push-push wiring to use your idea.  Easily doable, just need to think through the "what ifs" when switch is in wrong position  ;D
Title: Re: Push pull double 18
Post by: Marc Sibilia on March 22, 2018, 01:21:40 pm
Marc, I think its a very interesting idea !   Thank you.
Yeah, I saw I'd need to be able to switch between push-pull and push-push wiring to use your idea.  Easily doable, just need to think through the "what ifs" when switch is in wrong position  ;D

If you run the drivers out separately to 1+- and 2+- on an NL4, you could just use a specially wired plug for storage.
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 22, 2018, 01:52:37 pm
If you run the drivers out separately to 1+- and 2+- on an NL4, you could just use a specially wired plug for storage.

Yep, been thinking about that solution also.  I would need a specially wired plug for normal operation too, to connect the drivers together.....since my subs are fed from a NL2 breakout from my mains (like the way kf 650s work).  If I can determine no harm can occur from a switch being wrong, a switch sounds like a lot less parts to implement.

Having the voice coil carry the mass while in storage is a really clever idea  .... thx again
Title: Re: Push pull double 18
Post by: Don T. Williams on March 22, 2018, 03:00:31 pm
I'm just curious if anyone is reporting problems with speaker oriented in the vertical position during use or storage have misaligned voice coils or skewed cones from their orientation?  Gravity works 24/7 and transporting gear in a truck or trailer can be a rough ride and could exacerbate the problem! 

I've had several KW181's with magnets that broke loose and pinched the voice coils.  They travel horizontally when on their casters.  My suspicion with these failures was that people were "flipping" the cabinets down off the caster into their vertical use position very hard.  These were all from rentals, and we all know how people treat equipment they don't own.
Title: Re: Push pull double 18
Post by: Scott Holtzman on March 22, 2018, 03:15:24 pm
I'm just curious if anyone is reporting problems with speaker oriented in the vertical position during use or storage have misaligned voice coils or skewed cones from their orientation?  Gravity works 24/7 and transporting gear in a truck or trailer can be a rough ride and could exacerbate the problem! 

I've had several KW181's with magnets that broke loose and pinched the voice coils.  They travel horizontally when on their casters.  My suspicion with these failures was that people were "flipping" the cabinets down off the caster into their vertical use position very hard.  These were all from rentals, and we all know how people treat equipment they don't own.

I have 12 181's and have seen that exact failure mode 3 times now. Once the magnet broke loose and was rattling around in the cabinet.
Title: Re: Push pull double 18
Post by: Marc Sibilia on March 22, 2018, 04:13:34 pm
  If I can determine no harm can occur from a switch being wrong, a switch sounds like a lot less parts to implement.

Since both drivers are in a common chamber, bad things can happen because it is like having the speaker in free air with no stiffness contribution from the air in the cabinet.  If you applied significant audio power with the switch in the wrong position, you will see over-excursion.  If they were in separate chambers, it would be safe, but make almost no sound.
Title: Re: Push pull double 18
Post by: Art Welter on March 22, 2018, 04:27:25 pm
Since both drivers are in a common chamber, bad things can happen because it is like having the speaker in free air with no stiffness contribution from the air in the cabinet.  If you applied significant audio power with the switch in the wrong position, you will see over-excursion.  If they were in separate chambers, it would be safe, but make almost no sound.
Marc,
The OP's cabinet is vented, so there is virtually no "air stiffness" other than at Fb. Assuming the same Fb, dual chambers are functionally identical to a single and free air.

Even a "sealed" cabinet leaks over time, otherwise barometric pressure change would cause major cone offset.

Art

Title: Re: Push pull double 18
Post by: Art Welter on March 22, 2018, 04:47:21 pm
1)  All the high power 18" drivers I briefly checked, have a moving mass of a little over 1/2 lb.....I never quite internalized before how much force it must take to oscillate that much mass.....it would seem the dynamic strain on the suspension if motor looses full controll would dwarf stain at rest.....but time does take its toll.....who knows....   
2)Maybe a bigger issue than mounting orientation, is always keeping driver excursion within full motor control...?
3)Anyway, if the box I've built shows the same full power vibration reduction and distortion measures well at high level, I'll probably put slot ports on both ends where I can periodically flip the box.
1) Something else to "internalize"- assuming the driver's suspension and magnetic forces were symmetrical, the cause of the cabinet "walking" you want to avoid is actually the result of asymmetrical wave-forms presented to a single vertical driver. Dual opposed drivers cancel any of those causes of asymmetrical weight shift.
2) Unless you implement the DC offset scheme, or rotate the drivers, suspension sag will offset the driver to a bias towards one or the other ends of the motor linearity range.
3) OK. Sag on PA drivers is so slow, pick a designation for even and odd years ;^).

Title: Re: Push pull double 18
Post by: Art Welter on March 22, 2018, 04:55:44 pm
The old Maryland Sound "clams" (Karlson couplers) would exhibit bad cases of cone sag.

On one side they would be hanging out of the basket, and on the other side they would be depressed into the basket-because of the mounting angles.  Especially in clubs where the were installed (like the old Hammerjacks in Baltimore for example.)
They fixed that with the "Bearclaw" quad Karlson, vertical cone orientation- probably dumped the singles in those clubs.

Damn, we're old...

Wish I could rotate some of my sagging skin ;^).
Title: Re: Push pull double 18
Post by: Marc Sibilia on March 22, 2018, 05:17:25 pm
The OP's cabinet is vented, so there is virtually no "air stiffness" other than at Fb. Assuming the same Fb, dual chambers are functionally identical to a single and free air.

That is almost true. There is no stiffness below Fb, but above Fb there is. Mark will normally have processing (HPF) to control excursion below Fb.  Now he may get into excursion trouble between Fb and the normal excursion maximum above Fb where the system is relying on the air compliance.  The system will no longer have an excursion minimum at Fb because there is no net pressure change in the box to drive the port air velocity.  The excursion will just keep climbing as frequency goes down as if it were an open baffle until it hits the HPF.

Marc
Title: Re: Push pull double 18
Post by: Ivan Beaver on March 22, 2018, 08:39:08 pm
They fixed that with the "Bearclaw" quad Karlson, vertical cone orientation- probably dumped the singles in those clubs.

Damn, we're old...

Wish I could rotate some of my sagging skin ;^).
I had some "half clams" by Maryland sound.  They had 2x 15" JBL 2205s in each.
I used them a lot for small/medium gigs with the 4560s and 2" gauss horns for mids and highs .

You can see them in the photo.  The next to the end stacks.  Those stacks and the 2 large Altecs in the middle were the only cabinets I didn't build in the photo.
Title: Re: Push pull double 18
Post by: Scott Holtzman on March 22, 2018, 09:05:47 pm
I had some "half clams" by Maryland sound.  They had 2x 15" JBL 2205s in each.
I used them a lot for small/medium gigs with the 4560s and 2" gauss horns for mids and highs .

You can see them in the photo.  The next to the end stacks.  Those stacks and the 2 large Altecs in the middle were the only cabinets I didn't build in the photo.

The ones that look like a pair of jeans unzipped?  That's an unusual opening.
Title: Re: Push pull double 18
Post by: Ivan Beaver on March 23, 2018, 11:40:05 am
The ones that look like a pair of jeans unzipped?  That's an unusual opening.
That would be the ones.

The design was a Karlson Coupler.  There were lots of "claims" made about it-back in the day.

There was even an HF device, called "The Tube".  I have one in my office

Here is a link to some photos

https://www.google.com/search?q=transilvania+tube+horn&client=firefox-b-1&tbm=isch&source=iu&ictx=1&fir=9FXDe3kxVv4Z4M%253A%252CvLx8m7f9IBRWzM%252C_&usg=__V7YbsElIUjVoxcuxvMR-tBTyaho%3D&sa=X&ved=0ahUKEwig3N-h44LaAhVPuVMKHYmIBEEQ9QEIUjAE#imgrc=_
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 23, 2018, 02:06:03 pm
1) Something else to "internalize"- assuming the driver's suspension and magnetic forces were symmetrical, the cause of the cabinet "walking" you want to avoid is actually the result of asymmetrical wave-forms presented to a single vertical driver. Dual opposed drivers cancel any of those causes of asymmetrical weight shift.
2) Unless you implement the DC offset scheme, or rotate the drivers, suspension sag will offset the driver to a bias towards one or the other ends of the motor linearity range.
3) OK. Sag on PA drivers is so slow, pick a designation for even and odd years ;^).

1) Never saw it that way, thx.

3) Yes, but perhaps akin to certain female anatomy, ....sag, although slow in early years, may accelerate greatly in later years,
necessitating more periodic rotation..... or better yet, new units !   ..sorry.... ;D

Switching gears.....a little more conversation with BMS leads me to think storage and transport are the culprits being sag, much more so than playing however mounted.  I even heard half jokingly that in a perfect world, drivers would be playing 24/7, with the motor holding the voice coil in place.
Makes Marc's idea seem all the more valuable.  A battery powered version might even be a great idea for boxes suspected to have transport problems..

Title: Re: Push pull double 18
Post by: Tim McCulloch on March 23, 2018, 04:01:32 pm
The old Maryland Sound "clams" (Karlson couplers) would exhibit bad cases of cone sag.

On one side they would be hanging out of the basket, and on the other side they would be depressed into the basket-because of the mounting angles.  Especially in clubs where the were installed (like the old Hammerjacks in Baltimore for example.)

Gee thanks, Ivan.  I'd put those memories away and hoped to keep them there.  Charm City, indeed.
Title: Re: Push pull double 18
Post by: Scott Holtzman on March 24, 2018, 05:49:34 pm
That would be the ones.

The design was a Karlson Coupler.  There were lots of "claims" made about it-back in the day.

There was even an HF device, called "The Tube".  I have one in my office

Here is a link to some photos

https://www.google.com/search?q=transilvania+tube+horn&client=firefox-b-1&tbm=isch&source=iu&ictx=1&fir=9FXDe3kxVv4Z4M%253A%252CvLx8m7f9IBRWzM%252C_&usg=__V7YbsElIUjVoxcuxvMR-tBTyaho%3D&sa=X&ved=0ahUKEwig3N-h44LaAhVPuVMKHYmIBEEQ9QEIUjAE#imgrc=_
Sounds laser, that is hilarious.  Very unusual too, great collectable.


Sent from my VS995 using Tapatalk

Title: Re: Push pull double 18
Post by: Craig Hauber on March 24, 2018, 08:45:26 pm

What did EV do with their MTL-4 design to address this?


I ended up storing them on their backs.

When I discovered the issue it hadn't progressed too far so I simply rotated the drivers and let gravity correct the issue for a bit before swapping them to the side drivers.
We handled them with forklifts so it didn't matter which way they were setting on a pallet.  They were essentially a cube so it didn't affect truck-pack or warehouse racking. 

The mid-high box  was the main reason for the forklift (anyone who has used those can understand why) and luckily the 10's in those were all mounted vertical.  any cone sag at all in those would be noticeable quickly due to the phase plug -which I doubt that there would be any in such a small driver that still used the same spider as it's larger 18" sibling. 
I actually had bigger issues with recone-errors in those where a slightly off-center dustcap could reduce excursion significantly due to collision with the phase plug.  (You wouldn't believe how many reconers I've encountered that just eye-balled the placement of those!)

Back on-topic, I also found humidity has quite a bit to do with cone sag too. 

Storage doesn't seem to affect sag as much as heavy use.  With the low-Xmax drivers in the EV subs you always found Xlim quickly then backed-off to just a bit before it and held it there all night :) 
I think the constant straining of the driver's suspension really aggravated the sag issue.  Lightly used installed versions didn't seem to have as bad a problem.

Nightclubs with fog machines are another situation.  I have one client with manifold type boxes mounted sideways where the driver's spiders are saturated in condensed fog fluid -probably due to the constant drawing of air through them while the driver is pumping.  Just awful sag issues -to the point where the coils are almost resting on the back-plate.  Many times the glue holding them to the basket lets-go  I have to change them out often and this is with modern very well built heavy-duty B&C, Radian and RCF drivers. 
The DJ's pound on the system, it's in a humid area (an ocean shoreline) and the excessive fog use just make it a woofer torture chamber. 
Title: Re: Push pull double 18
Post by: Jeremy Young on March 26, 2018, 07:24:26 pm
Thanks Craig, that answers my question and more, thank you for sharing your experiences.  I sure am learning a lot, which is why I keep coming back to these forums.
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 27, 2018, 01:28:25 pm
Craig, I'd like to thank you too.  Very real world info.

Between your post and more digging, I've decided the only way I'll build horizontal, is with some rotation scheme in mind,
and/or possibly going on with the Marc S coil-holding idea.

I've begun making distortion tests on the push-pull I posted, along with testing it swapped to push-push (clamshell like).
I've found I need to get a little more experience with REW's sine sweeps, or better yet it's stepped-sine tests, before I have confidence to trust (or post) what I'm measuring. 
Listening to sweeps and pink, the two are a little different, but I don't know how to describe that yet, or what it means for music.

Clamshell would make rotation very easy, just swap the drivers every now and then.....I'm almost hoping I can't hear or measure an improved difference against push-pull  lol 
Reduced cabinet vibration, and sounding like my single 18 vented diys,  is all I've really been after...
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 28, 2018, 08:46:38 pm
Got a nice day of testing in......

Since the whole idea of push-pull is 2nd order harmonic distortion reduction,
I decided to test push-pull inverted, vs push-push (clamshell) using the same box.
I mean, why not just flip the driver in the plenum around and make a direct comparison, right ?!

REW has a stepped-sine harmonic distortion routine that is really cool. 
It spends a couple of seconds at each sine step to determine distortion.
You set how many sine steps per octave the neighborhood can stand  ;)   I used 12.

First plot is push-pull.
Second is push-push.
Both were at 2 meters, so add 6dB to SPL.

I don't see enough of a clear case for push-pull.................?? 
Plus, the suspension and coil vent noise below 35Hz, was much louder with the pull driver when exposed in the plenum, than when the driver rests in the cabinet as a push driver like its brother.

So, I'm going with push-push.   
This gives the vibration reduction (which is dramatic vs a regular dual 18), and allows for a very easy rotation of drivers to get over the horizontal sag stuff.

Last plot is a transfer for the push-push.  Dark green is raw, blue is processed.
My SPL Leq method of finding sensitivity gives 101.3 dB 2.83v at 1m, with the processing in place.
THD hit 10% right at 130dB 1m.

Happy camper!!

Title: Re: Push pull double 18
Post by: Art Welter on March 29, 2018, 07:22:32 pm

My SPL Leq method of finding sensitivity gives 101.3 dB 2.83v at 1m, with the processing in place.
THD hit 10% right at 130dB 1m.

Happy camper!!
Mark,

Very low distortion- the BMS 18N862 sure is clean!
I see it is available 4 or 8 ohms.
What is your nominal cabinet impedance?
What was the voltage of the test signal?
Did you happen to measure excursion during any of the tests?

Your test results here show the fundamental both at 119.6 dB, on the DIY site, they read 120.9 for push-pull, 121.2 push-push at 2 meters.
Only a 1.6 dB difference, but distortion going from around 3% to 10% with what could be a 4.4 dB change or a 2.8 dB change  (or something different) makes the detail a bit more "interesting" since

Your cabinet response has a 10 dB peak around 150 Hz, what is the "SPL Leq method of finding sensitivity"?

Art
Title: Re: Push pull double 18
Post by: Ivan Beaver on March 29, 2018, 08:53:50 pm

Last plot is a transfer for the push-push.  Dark green is raw, blue is processed.
My SPL Leq method of finding sensitivity gives 101.3 dB 2.83v at 1m, with the processing in place.
THD hit 10% right at 130dB 1m.

Happy camper!!
What sort of processing were you using?

It appears to have a boost at the lower freq.  So how was the 2.83V determined?

Is it at the boosted freq? or some other freq?

Any boost at lower levels to flatten freq response, will have to be deducted at higher calculated SPLs, because there will be more power at those freq (assuming flat impedance)
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 29, 2018, 08:55:45 pm
Mark,

Very low distortion- the BMS 18N862 sure is clean!
I see it is available 4 or 8 ohms.
What is your nominal cabinet impedance?
What was the voltage of the test signal?
Did you happen to measure excursion during any of the tests?

Your test results here show the fundamental both at 119.6 dB, on the DIY site, they read 120.9 for push-pull, 121.2 push-push at 2 meters.
Only a 1.6 dB difference, but distortion going from around 3% to 10% with what could be a 4.4 dB change or a 2.8 dB change  (or something different) makes the detail a bit more "interesting" since

Your cabinet response has a 10 dB peak around 150 Hz, what is the "SPL Leq method of finding sensitivity"?

Art

Hi Art,

I'm using two 8 ohm.  An impedance curve is attached, however it's in-room next to other subs....

The distortion sine-stepped measurements were probably averaging right around 25v rms. 
I didn't grab voltage averages, because I had 100ms of cool down waiting in between each sine step.

Differences between SPL on distortion graphs here and on DIY, are simply due to freq of cursor when I captured the graphs.
I put graphs up here in distortion %, as it's the more common language.
And on DIY in dB relative, as that's more common there. Didn't try to match, or even know, where cursor freq was.

Hey, if I reran distortion using final push-push processing, it shouldn't make a damn what freq i choose ! ;)

The "SPL Leq method of finding sensitivity" is very simply.....put processing in place (as per blue trace posted)....simultaneously meter SPL LEQ and average RMS voltage. 
Do the math and bring it to 2.83v at 1m.

An aside.....I really, .....really, want to hear what's wrong, or more fair, than that method for a sub sensitivity spec......
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 29, 2018, 09:00:33 pm
What sort of processing were you using?

It appears to have a boost at the lower freq.  So how was the 2.83V determined?

Is it at the boosted freq? or some other freq?

Any boost at lower levels to flatten freq response, will have to be deducted at higher calculated SPLs, because there will be more power at those freq (assuming flat impedance)

Hi Ivan,
see reply to Art, it should answer your question as to how 2.83v was determined.
Which you will see is not at any any freq, but at an average of all, of the processed response.

Processing is a custom FIR setup.



Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 29, 2018, 09:02:08 pm
delete modify attempt that misposted
Title: Re: Push pull double 18
Post by: Ivan Beaver on March 29, 2018, 09:37:24 pm

An aside.....I really, .....really, want to hear what's wrong, or more fair, than that method for a sub sensitivity spec......
I feel that loudspeakers should be measured (at least as far as sensitivity and response) with NO processing of any type.

Just the measurement system into the amp, and to the speaker.

It gives a much better indication of the natural raw capability of the loudspeaker.

Anybody can add eq to bump up a part of the response to tame the peaks as needed.

Assuming the generator is flat, and is using a swept sine wave, you can easily measure the applied voltage.  2.83V is suggested.

I never measure at 1m, it is to close to get numbers that translate to other distances.  It is better to get several meters away.  I prefer to increase the drive voltage at the same dB as the distance takes away.  10m=20dB is a easy one to remember and the voltage increase is simply 10x more.

Another advantage to this method is that any power compression will be present, which gives an idea of real world numbers in usage.
Title: Re: Push pull double 18
Post by: Art Welter on March 30, 2018, 12:26:52 am
Hi Art,

I'm using two 8 ohm.  An impedance curve is attached, however it's in-room next to other subs....

The "SPL Leq method of finding sensitivity" is very simply.....put processing in place (as per blue trace posted)....simultaneously meter SPL LEQ and average RMS voltage. 
Do the math and bring it to 2.83v at 1m.

An aside.....I really, .....really, want to hear what's wrong, or more fair, than that method for a sub sensitivity spec......
Mark,

Thanks for the explanation, had to look up the meaning of "Leq", so I re-learned an acronym I'd forgot...

Traditionally, a sensitivity rating was considered to be 1 watt at one meter, and the manufacturer would use the appropriate drive voltage for the nominal impedance of the speaker- 2 volts for a nominal 4 ohm, 2.83v for 8, 4v for 16 ohm, etc.
BMS, JBL, EAW still are traditional in that sense, others require math, using 2.83 volts for 4 ohm or even 2 ohm speakers, six dB more "sensitive"!

Without an impedance graph, "sensitivity" is ambiguous- your cabinet could have been anything from a nominal 2 to 16 ohms given it is available in 4 or 8 ohms. If you are going to the effort to "do the math and bring it to 2.83v at 1m" I'd prefer you'd do the math for "1 watt at one meter" so I don't have to do more math converting...

With your explanation and the impedance graph, it appears your sensitivity is more or less "fair".

That said, how "average RMS voltage" is determined- lowest and highest voltage divided by 2, or logarithmic average, the frequency range the average is done over all introduce variability and potentially ambiguous results compared to "put in X volts and graph what happens".

I do appreciate your work!

Thanks,
Art



Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 30, 2018, 12:22:21 pm
I feel that loudspeakers should be measured (at least as far as sensitivity and response) with NO processing of any type.

Just the measurement system into the amp, and to the speaker.

It gives a much better indication of the natural raw capability of the loudspeaker.

Anybody can add eq to bump up a part of the response to tame the peaks as needed.

Assuming the generator is flat, and is using a swept sine wave, you can easily measure the applied voltage.  2.83V is suggested.

I never measure at 1m, it is to close to get numbers that translate to other distances.  It is better to get several meters away.  I prefer to increase the drive voltage at the same dB as the distance takes away.  10m=20dB is a easy one to remember and the voltage increase is simply 10x more.

Another advantage to this method is that any power compression will be present, which gives an idea of real world numbers in usage.

Thx for the reply Ivan,
I agree with much of what you say, particularly using voltage as a reference and not power. 
Also measuring at a distance, with more voltage..... 28.3v at 10m makes a ton of sense, for the reasons you give. 

But I feel we need to see both raw and processed curves to know what we can expect. 

I also feel measurements are better than judgement calls for defining specs.

With processing in place we get to see manufacturer claims against intended usage.
Let the HPF and LPF used be stated.  Let any eq be stated.

If they claim an unrealistic low freq response, and use too low a HPF, the efficiency spec will suffer greatly using the method I prescribed.
If they use an unrealistic high response, and use an obviously too high LPF, their game playing sticks out.
If eq is used to raise low areas of response, it will lower measured efficiency, as in real world.
If eq is used to lower peak areas, it will also lower efficiency, as in real world.
(Both of those uses of eq are appropriate processing IMO)

Personally, I try to flatten sub response within its intended passband, and then compare that to other subs similarly set up.
I mean, in the end, I care more about processed performance than raw.
And I have a simple intuitive way of measuring those comparisons....works for me anyway :)


 
Title: Re: Push pull double 18
Post by: Mark Wilkinson on March 30, 2018, 12:40:30 pm
Mark,

Thanks for the explanation, had to look up the meaning of "Leq", so I re-learned an acronym I'd forgot...

Traditionally, a sensitivity rating was considered to be 1 watt at one meter, and the manufacturer would use the appropriate drive voltage for the nominal impedance of the speaker- 2 volts for a nominal 4 ohm, 2.83v for 8, 4v for 16 ohm, etc.
BMS, JBL, EAW still are traditional in that sense, others require math, using 2.83 volts for 4 ohm or even 2 ohm speakers, six dB more "sensitive"!

Without an impedance graph, "sensitivity" is ambiguous- your cabinet could have been anything from a nominal 2 to 16 ohms given it is available in 4 or 8 ohms. If you are going to the effort to "do the math and bring it to 2.83v at 1m" I'd prefer you'd do the math for "1 watt at one meter" so I don't have to do more math converting...

With your explanation and the impedance graph, it appears your sensitivity is more or less "fair".

That said, how "average RMS voltage" is determined- lowest and highest voltage divided by 2, or logarithmic average, the frequency range the average is done over all introduce variability and potentially ambiguous results compared to "put in X volts and graph what happens".

I do appreciate your work!

Thanks,
Art

Hi Art,  yeah, what a tower of confusion traditional measures of efficiency are, using power against nominal impedance.
I agree, an impedance graph is a must.

I do like sensitivity referenced to voltage not power,
in a way because it almost forces us to do a little math and give impedance  some thought.
Nominal's  meaning is so dang limited....IMHO.

You know, average impedance could be measured though. 
Pretty dang easy really,..... over the same time  period that SPL LEQ and averaged rms voltage are taken, also take an average current reading.

A little Ohm's law and we get measured average impedance, to go with measured SPL sensitivity against voltage.
Heck,  we even get a real 1 watt spec.........

To hell with tradition !!
Title: Re: Push pull double 18
Post by: Chris Grimshaw on April 10, 2018, 04:55:30 pm
<snip>

REW has a stepped-sine harmonic distortion routine that is really cool. 
It spends a couple of seconds at each sine step to determine distortion.
You set how many sine steps per octave the neighborhood can stand  ;)   I used 12.

<snip>

Last plot is a transfer for the push-push.  Dark green is raw, blue is processed.
My SPL Leq method of finding sensitivity gives 101.3 dB 2.83v at 1m, with the processing in place.
THD hit 10% right at 130dB 1m.

Happy camper!!

Hey Mark,

Just wondering if you can share how to set up REW to do this testing routine. I've gone through the help file and can't find much.

130dB at 10% THD is excellent.

Chris
Title: Re: Push pull double 18
Post by: Ivan Beaver on April 10, 2018, 07:07:27 pm
Hey Mark,

Just wondering if you can share how to set up REW to do this testing routine. I've gone through the help file and can't find much.

130dB at 10% THD is excellent.

Chris
Here is a good document on how to do it.

It is real easy and quick.  But be SURE to calibrate the mic to get useful results.

http://www.brentbutterworth.com/cea-2010-measurement-manual.html
Title: Re: Push pull double 18
Post by: Mark Wilkinson on April 11, 2018, 10:05:20 am
Hey Mark,

Just wondering if you can share how to set up REW to do this testing routine. I've gone through the help file and can't find much.

130dB at 10% THD is excellent.

Chris

Hi Chris,

First, as you've probably already discovered, that's a great article Ivan linked,.... full of real world instruction. 
It also made me realize REW is set up to do CEA-2010, in addition to stepped sine.

As far as stepped-sine....I couldn't find much in the REW help file, or on the support forums either.
I spent 2 days wondering how to even get the thing to work, because after making a stepped sweep, the RTA page housing the stepped sine initiation, and the output graph,.... didn't show any harmonics ????
Then, I finally noticed, every time you run a stepped sine, it adds a new measurement on the main REW page, just as if you ran a normal measurement. 
That's all there is to it !!! I was such a dope lol.

Do pay attention to FFT length per the help files if you're trying to measure way low.  And averages if you have a noisy environment.
The only other caveat i can think of right now, is that I kept blowing my circuit breaker trying to test around Fb, at high volume.
I had to move the mic closer to turn down the juice to a PL340 running bridge. 

I'm going to try CEA-2010 next time out....it has to be safer than stepped sine, since it only runs 6.5 cycle bursts. 
Will be interesting to see how they compare
Title: Re: Push pull double 18
Post by: Mark Wilkinson on April 13, 2018, 02:12:55 pm
If you are concerned about it, you can apply about 0.6 VDC of the correct polarity to them while stored, and let the voice coil carry the weight.  1/2 lb is about 2.2 newtons.  With BL of 25 T-m, 0.1 A will carry the weight.  Power is trivial at (0.1 A)^2 * 5.6 ohm = about 60 mW, so heating is a non-issue.

You could make up a storage harness hooked to a wall wart.  You can run it all year for a pair of PPSL subs (4 drivers) for about 30 cents of electricity.  It is cheap insurance for $2800 worth of drivers and you don't have to scrape up the top of your cabinets.

Marc

P.S.  Never mind.  Seemed like a good idea until I thought about the internal wiring.  The upper driver needs to be pulled into the cabinet and the lower needs to be pushed out of the cabinet.  That is the opposite of how they are wired for audio output.



I've ended up settling on a horizontal push-push box (clamshell) as per pict below,
and I think Marc's idea to stop cone sag has become very easily doable.

If I haven't screwed up, a single 4-pole double-throw switch, can allow speakon connection on one side of the switch, and low voltage DC connection on the other. 
I'm going to use a mono TRS jack to feed 1.6vdc to the 2 drivers in series.
Parts Express has a nifty cheap 12vdc to 1.6v converter, that will allow plug into a power pack or trailer harness. 
Circuit is below....if anyone spots an error or 'what if' problem, thanks for pointing it out.

I measured cone sag, horizontal vs no-sag vertical, and it's about 1mm. 
I put the 1.6vdc on the two drivers (0.8v each) it looks like the 1mm is fairly exactly offset, but I can't measure as close as I'd like.
Marc, you recommended 0.6v....I'm hoping 0.8 is close enough that I'm not making a small 'reverse sag problem' .  The mass is supposed to be 267 grams.....thx.
Title: Re: Push pull double 18
Post by: Mark Wilkinson on May 09, 2018, 05:35:29 pm
Here is a good document on how to do it.

It is real easy and quick.  But be SURE to calibrate the mic to get useful results.

http://www.brentbutterworth.com/cea-2010-measurement-manual.html

Thanks again for this link.... yes, it really is easy and quick !!
REW makes both CEA-2010 and stepped sine measurements so simple. 

The CEA-2010 test, which uses only 6.5 cycle bursts at 1/3 octave points,  seems to me to be about measuring distortion on peak transients.....
whereas stepped sine (as posted earlier) seems more about measuring distortion at high continuous SPL levels.

Anyway, I hauled one of the push-push double 18"s out into the grass today.
Below are the SPLs @ 2m that passed CEA.  These SPLs are as read by REW, and are not adjusted to 1m.
 
Clearly, if +6db is added to adjust those 2m SPLs to 1m, the levels are peak, plain and simple.
I'd call them peak RMS I guess... ;)


The high CEA numbers don't surprise me a bit. 
The pair I've built so far, are a real joy to listen to.

The "anti-sag" hook up appears to be working great, so no concerns there.... 
A standard powerpack with a 12v output looks like it would hold both subs against gravity for about a month before needing recharging.

I've added a pict below of a finished sub, with the modular ground stack top boxes been making.



Title: Re: Push pull double 18
Post by: Don T. Williams on May 10, 2018, 12:53:03 am
Thanks for sharing.  It looks great!
Title: Re: Push pull double 18
Post by: Mark Wilkinson on May 10, 2018, 10:10:50 am
Thanks for sharing.  It looks great!

Thanks for the kind words Don

One thing I'd like to add about the CEA test, is that I think it might be a good help in sizing an amp to a sub.
I first ran the test off a single channel of a PL380.  When I hit the end of the amps output at 80Hz and up, CEA was still showing pass.
So I switched the amp to bridge and ran again.  Fail levels came within trying for only another dB on all three 1/3 oct centers, 80, 100, and 125Hz.....

The 6.5 cycle burst is modulated as below, so I'm thinking it probably represents the shortest peak worth trying to have enough amp for..??
I can't see why I would want a bigger amp than a single channel PL380, even for transients.  (Drivers are 8 ohm 1500w AES in parallel.)

Now I have no idea what the weighting formula is for pass/fail, or how applicable it is for what we hear at high sustained levels,
but it was easy to see that pushing the slider up was not increasing SPL linearly...so compression and distortion were appearing in sync.

What I really like about the short pulses, is they are much less scary to push to the edge, to listen for distortion and compression, than any test signal I've found. And you can test a sub at any specific freq.  REW can generate the bursts at any freq, not just 1/3 octave centers.
I can see using them just for listening tests...dialing in HPF filters..setting peak limiters...etc.


Title: Re: Push pull double 18
Post by: Mark Wilkinson on May 08, 2019, 08:28:10 pm
It's been a year since i built these subs...thought I should give a follow up post.

I absolutely love them. 
Easy to handle, dig crazy deep, clean as in squeaky clean, and plain ole loud.
Opposed clam shell mounting doesn't walk or even vibrate the cabinet much, you have to really crank before they would toss a beer..
Just pulled the drivers out to check them for sagging, since they are in a horizontal mounting position.
The "anti-sag" DC voltage described earlier in this thread, that i keep on them when not in use, has apparently worked fine...couldn't tell any difference in any drivers. (Thx again for the idea, Marc S.)

I know the following traces don't work for live because they entail 64ms latency, but damn, look how clean they are for playback.
No smoothing, either mag or phase
Title: Re: Push pull double 18
Post by: David Morison on May 09, 2019, 08:06:33 am

I know the following traces don't work for live because they entail 64ms latency, but damn, look how clean they are for playback.
No smoothing, either mag or phase

Damn, now that's just showing off!
Great work man 👍
Title: Re: Push pull double 18
Post by: Mark Wilkinson on May 09, 2019, 11:35:17 am
Damn, now that's just showing off!
Great work man 👍

Thanks David !! 
And yeah, you're right about the showing off part, sorry :-[
Over zealous sometimes....

Hey, check out at my latest piece of experimental insanity, sitting on top of one of the push-push subs..
24 cheap 3.5" drivers that i have being driven with 6 amp channels powering 4 drivers each.
Separate DSP on each channel .... purely for playing with line array theory...shading, steering, etc, etc..   
Not much $ in the whole project for what I've been learning....biggest learning has probably been, despite nice looking transfers, I don't really like the sound of the line lol
But it is really cool to move the sound around...


Title: Re: Push pull double 18
Post by: Roland Clarke on May 09, 2019, 11:44:15 am
Interesting project Mark!   :)
Title: Re: Push pull double 18
Post by: Douglas R. Allen on July 24, 2019, 08:56:05 pm
Is there plans available for your design here? I went to the DIY site and tried to plow through the 85 pages. Having to sign up before looking at pictures wasn't something I felt like doing.
Thanks;
Douglas R. Allen
Title: Re: Push pull double 18
Post by: Chris Grimshaw on July 25, 2019, 05:43:43 am

Not much $ in the whole project for what I've been learning....biggest learning has probably been, despite nice looking transfers, I don't really like the sound of the line lol
But it is really cool to move the sound around...

I found similar.

That, and the variable HF balance with distance as the array goes between point and line source. The best I came up with was a shaded array, with only the top few drivers playing above 5kHz. At that point, you might as well just reach for the compression drivers and be done with it.
Lower-mid power handling wasn't great, either, but you have more cone area than I did.

Chris
Title: Re: Push pull double 18
Post by: Mark Wilkinson on July 25, 2019, 12:34:57 pm
Is there plans available for your design here? I went to the DIY site and tried to plow through the 85 pages. Having to sign up before looking at pictures wasn't something I felt like doing.
Thanks;
Douglas R. Allen

Yeah, the DIY site's super long threads are a bear to get through....and the signup requirement to see picts annoys me too...

One of our forum members, Kyle F., has been working on putting the measurements I passed to him, into plans.
Here's a couple of 3D models he sent, on the way to making plans...
One of us will post them here when done.
Thank you Kyle  :)
Title: Re: Push pull double 18
Post by: Mark Wilkinson on July 25, 2019, 01:00:22 pm
I found similar.

That, and the variable HF balance with distance as the array goes between point and line source. The best I came up with was a shaded array, with only the top few drivers playing above 5kHz. At that point, you might as well just reach for the compression drivers and be done with it.
Lower-mid power handling wasn't great, either, but you have more cone area than I did.

Chris

@ Roland,  a belated thanks for your May comment...I forgot about this thread (have had my head down deep in the DIY hole  :-[

@Chris, yep, I found the straight-line array to be a can of worms sonically. I could make very nice, very pleasing sound,... move the sound up, move it down, bow it in or out.  But I dunno, I just kept getting the feeling I was listening to sound through a diffusion or something.....

But one part of the line-array experiment that turned out better than hoped was the CBT conversion. It was pretty easy to move the drivers/baffle between the straight and curved boxes. The CBT version was remarkably room position independent in how it sounded and measured.  Hat's off to Don Keele..
I tried to amplitude and delay shade the straight-line to match the CBT...got close..but the continuous geometric curve of the CBT clearly was better.

I guess I need to try the frequency shading you mentioned (before I junk the arrays  ::)
But that will have to wait...giving a go at my first synergy effort..

Title: Re: Push pull double 18
Post by: Douglas R. Allen on July 25, 2019, 06:52:49 pm
Yeah, the DIY site's super long threads are a bear to get through....and the signup requirement to see picts annoys me too...

One of our forum members, Kyle F., has been working on putting the measurements I passed to him, into plans.
Here's a couple of 3D models he sent, on the way to making plans...
One of us will post them here when done.
Thank you Kyle  :)


Thanks for posting these. Looks simple enough a Doug could do it. I haven't dipped my toes in DIY for years (Snail Horns years ago)  but these look like something I can build and can put some 18's I have in storage to work.
Looking forward to the design.

Kindest Regards;
Douglas R. Allen

Title: Re: Push pull double 18
Post by: Mark Wilkinson on September 04, 2019, 02:56:04 pm
Hi all, PDF plans for the sub can be found at the link below.
Courtesy of forum member Kyle Forbes ! :)

There isn't any internal bracing shown, which is obviously needed. 
Different folks like to go to different lengths with bracing, so it's left up to you.
Kyle made nice handle locations/drawings.  More handles always help, huh
I just used two handles up high in the back side corners, which gets bye, but only because
the box is  easy to handle since the driver weight is centered.


https://drive.google.com/file/d/1fgvpuvMumpqZhwfjS32CkI1obfxhYBOt/view?usp=sharing
Title: Re: Push pull double 18
Post by: Kyle R Forbes on September 05, 2019, 12:14:44 pm
I hope to post some cut sheets to get the most out of a 4' X 8' sheet. I'm pretty excited to make a (hopefully) positive contribution as a newbie/weekend warrior ;D

Thanks Mark!