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Old 31st January 2005, 11:40 PM   #1
APi is offline APi  Finland
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Question Does hybrid dipole bass move diaphragm?

I am thinking of building a hybrid ESL with dipole bass.

Since dipole bass cause huge pressure difference between front and back of the speaker, it will also move ESL diaphragm more or less. I am afraid that ESL could misbehave because of that.

How can I avoid intermodulation distortion as well as diaphragm being to close to stators in all possible case? Does anybody have any experience about that?
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Old 1st February 2005, 11:12 PM   #2
Calvin is offline Calvin  Germany
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Hi,

You´re right. Any bass in close proximity to an ESL-Panel can blow the diaphragm into the stator. So does a dipole-bass.
R. Sanders named this phenomen acoustic coupling.
Solutions:
-move the bass farther away from the panel
-when using dipoles a ´slot ´ between Panel and woofer, used as kind of a pathway, helped
-use highest possible diaphragm tension
-use higher -but still smallest possible- d/s spacing.

jauu
Calvin
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Old 1st February 2005, 11:37 PM   #3
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Makes you wonder what happens to the cone of a sealed mid-range driver. Wouldn't a woofer cone moving forward cause the mid-range cone to move backward?

Is this a form of distortion that no one has yet recognized?
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Old 2nd February 2005, 12:40 AM   #4
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Quote:
Originally posted by Bill Fitzpatrick
Makes you wonder what happens to the cone of a sealed mid-range driver. Wouldn't a woofer cone moving forward cause the mid-range cone to move backward?

Is this a form of distortion that no one has yet recognized?
There are many designs where the midrange and bass drivers are in different enclosures.
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Old 2nd February 2005, 01:13 AM   #5
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Of course a cone midrange has to be in a separate enclosure.

Perhaps other readers will know what I mean.
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Old 2nd February 2005, 01:53 AM   #6
Stocker is offline Stocker  United States
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Bill, do you mean, pushing on the midrange from the outside?

I would think that theoretically it would be possible to have this affect the sound quality. By that level of volume, it seems likely also that the eardrums are moving so much, along with the lungs and walls and windows etc. that the difference would be hardly heard....

Good point though, I think.
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Old 2nd February 2005, 02:36 AM   #7
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Quote:
Originally posted by Stocker
Bill, do you mean, pushing on the midrange from the outside?
Yes, that's what I meant. And this would apply to a tweeter as well.

So there is a situation of dynamically changing air pressure in front of mid relative to the rear. It would seem to me that the mid would have a more difficult time pushing against a high pressure (>15psi) than it would against a low pressure (<15psi) and that some of the T/S parameters, for example, would keep changing in response to the woofer output, notably Cms and Qms. I need to read about this acoustic coupling as noted by Sanders.

Who has some additional input?
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Old 2nd February 2005, 03:07 AM   #8
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Your question is not in vain. It is a problem. I backed into this by having my subwoofers slap the diaphragms in my Magneplanars against the screen. Having a quad-amped system, and knowing that the amp powering the woofer panels was off at the time (I was testing some changes to the subs), it was clear that the subs alone were bottoming the woofer panels.
Not just vibrating the membranes...bottoming them.
I'd say that would cause a little tiny, itsy bit of IM distortion.
The subs were three or four feet behind the woofer panels at the time. I later brought the subs forward into the room in order to cure a resonance and discovered by accident that it reduced--but did not eliminate--the problem. My subs are sealed enclosures, so all the pressure originates from the front.
I have also noticed the same thing with my midrange driver modulating my tweeter, so it's not just in the bass.
What to do about it, I don't know. But, yes, I'd say it was a problem--one that doesn't get recognition. On the other hand, perhaps everyone is mum because there's nothing that can be done so there's no point in getting worked up about it. I drag the problem out and meditate on it from time to time, but I've got too many other things on my plate to give it my full attention, so it just kinda hangs around like a bad smell in the air.

Grey
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Old 2nd February 2005, 03:39 AM   #9
Stocker is offline Stocker  United States
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The solution is easy! Coaxial, with horns in the middle!

Or, 2" diameter, 1" throw full-range drivers.

or, well...don't tubes cause more distortion than this?

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Old 2nd February 2005, 03:48 AM   #10
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Default Martin Logan Statement 2

The Martin Logan Statement 2 has a line source dipole ESL, a dipole line array of 6.5" Scan Speaks separated by a physical gap from the ESL panel, and a separate bipole subwoofer array that was placed far away from the panels that could have a radiation pattern aimed perpendicular to the ESL and still pressurize the room.

ML apprears to have used all of the techniques mentioned in this thread to reduce the effects of low frequency sound waves modularing the ESL panel.....physical gap to midrange line array and separate bass cabinet aimed away from the ESL.
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