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Author Topic: Push pull double 18  (Read 17728 times)

Mark Wilkinson

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Re: Push pull double 18
« Reply #30 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....



.
« Last Edit: March 21, 2018, 08:19:46 pm by Mark Wilkinson »
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Jeremy Young

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Re: Push pull double 18
« Reply #31 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!
« Last Edit: March 21, 2018, 09:18:16 pm by Jeremy Young »
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Brown Bear Sound
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Mark Wilkinson

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Re: Push pull double 18
« Reply #32 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.
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Marc Sibilia

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Re: Push pull double 18
« Reply #33 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.
« Last Edit: March 22, 2018, 04:15:51 pm by Marc Sibilia »
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Mark Wilkinson

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Re: Push pull double 18
« Reply #34 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
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Marc Sibilia

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Re: Push pull double 18
« Reply #35 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.
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Mark Wilkinson

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Re: Push pull double 18
« Reply #36 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
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Don T. Williams

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Re: Push pull double 18
« Reply #37 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.
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Scott Holtzman

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Re: Push pull double 18
« Reply #38 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.
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Scott AKA "Skyking" Holtzman
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Marc Sibilia

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Re: Push pull double 18
« Reply #39 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.
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