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Author Topic: Push pull double 18  (Read 23756 times)

Art Welter

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Re: Push pull double 18
« Reply #40 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

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Art Welter

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Re: Push pull double 18
« Reply #41 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 ;^).

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Art Welter

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Re: Push pull double 18
« Reply #42 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 ;^).
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Marc Sibilia

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Re: Push pull double 18
« Reply #43 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
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Ivan Beaver

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Re: Push pull double 18
« Reply #44 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.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

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Scott Holtzman

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Re: Push pull double 18
« Reply #45 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.
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Scott AKA "Skyking" Holtzman

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Ivan Beaver

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Re: Push pull double 18
« Reply #46 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=_
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Mark Wilkinson

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Re: Push pull double 18
« Reply #47 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..

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Tim McCulloch

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Re: Push pull double 18
« Reply #48 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.
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Scott Holtzman

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Re: Push pull double 18
« Reply #49 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

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Scott AKA "Skyking" Holtzman

Ghost Audio Visual Solutions, LLC
Cleveland OH
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Re: Push pull double 18
« Reply #49 on: March 24, 2018, 05:49:34 pm »


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