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PostPosted: January 9th, 2018, 11:14 pm 
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It should reduce 2nd harmonic distortion due to asymmetries in the cone suspensions since the restoring force of the suspension will not be exactly symmetrical (not purely kx where x is the displacement and k the spring constant).


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PostPosted: January 10th, 2018, 12:10 am 
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Since my HX300-8OB amps were originally for a 3x8" OB servo array and these are now OB 2x12's, the amps have to be modified to the HX300-12OB model. They are now going to be shipped to Rythmik Audio for modification. Hope to get them shipped this week and back by the end of Jan.

At least I know the subs are working with both amps at this point. Now to get them packed and on the way.


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PostPosted: January 10th, 2018, 8:32 am 
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brombo wrote:
It should reduce 2nd harmonic distortion due to asymmetries in the cone suspensions since the restoring force of the suspension will not be exactly symmetrical (not purely kx where x is the displacement and k the spring constant).


That reminds me of J. Gordon Holt’s experiment on audibility of absolute phase. He found that one can identify the polarity reversal only in the drivers that do not have linear excursion on both sides.

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664BEFB6-1ACA-4ED3-857F-00C80821752F.jpeg [ 63.21 KiB | Viewed 932 times ]


https://www.stereophile.com/content/absolute-phase-fact-or-fallacy

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PostPosted: January 10th, 2018, 8:37 am 
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Deleted.

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PostPosted: January 10th, 2018, 9:53 am 
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Cogito wrote:
brombo wrote:
It should reduce 2nd harmonic distortion due to asymmetries in the cone suspensions since the restoring force of the suspension will not be exactly symmetrical (not purely kx where x is the displacement and k the spring constant).


That reminds me of J. Gordon Holt’s experiment on audibility of absolute phase. He found that one can identify the polarity reversal only in the drivers that do not have linear excursion on both sides.

Attachment:
664BEFB6-1ACA-4ED3-857F-00C80821752F.jpeg


https://www.stereophile.com/content/absolute-phase-fact-or-fallacy


A servo controlled driver should have the same excursion characteristics for both directions if the servo circuitry is doing its job.


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PostPosted: January 10th, 2018, 10:05 am 
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It always better to make the mechanical part of the system as perfect as you can before correcting its deficiencies electrically.


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PostPosted: January 10th, 2018, 11:38 am 
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Very true, but the servo if properly designed and executed it is another tool that can help get better results. The fly in the ointment is the cost of producing a good servo is often more than the cost of an additional driver. The servo is not going to work properly when the excursion puts the VC beyond the XMag point as the motor strength has dropped significantly. A good servo design takes that drop into account otherwise the amp would be directed to put destructive levels of power into the driver which cannot correct because there is insufficient motor strength. The voice coil at that point becomes a toaster. So the range of correction available to the servo is limited by the characteristics of the driver.

On the other hand, starting with a good driver, the distortion should be below 1% until you approach XMax. By using the money spent on the servo, you can usually buy a second driver which will give you double the linear volume displacement before the distortion rises. The second driver can be put in the reversed position and driven 180 degrees out of phase so the acoustic output is in phase. You get lower distortion, more linear displacement, higher sensitivity but wind up with double the enclosure size. It is always a trade off.


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PostPosted: January 10th, 2018, 12:05 pm 
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tomp wrote:
Very true, but the servo if properly designed and executed it is another tool that can help get better results. The fly in the ointment is the cost of producing a good servo is often more than the cost of an additional driver. The servo is not going to work properly when the excursion puts the VC beyond the XMag point as the motor strength has dropped significantly. A good servo design takes that drop into account otherwise the amp would be directed to put destructive levels of power into the driver which cannot correct because there is insufficient motor strength. The voice coil at that point becomes a toaster. So the range of correction available to the servo is limited by the characteristics of the driver.

On the other hand, starting with a good driver, the distortion should be below 1% until you approach XMax. By using the money spent on the servo, you can usually buy a second driver which will give you double the linear volume displacement before the distortion rises. The second driver can be put in the reversed position and driven 180 degrees out of phase so the acoustic output is in phase. You get lower distortion, more linear displacement, higher sensitivity but wind up with double the enclosure size. It is always a trade off.


Adding a second driver firing in the reverse direction is not going to correct the non-linearities of the driver of either driver, but it spreads the non-linearities to both phases and mask them with linear content (from driver firing forward), which might be less objectionable.

BTW, we are not saying HAL's drivers have the non-linearity issues.

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PostPosted: January 10th, 2018, 12:15 pm 
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Since the 6x12 servo subs sound great with the line arrays using the same techniques, I know how these will sound after having the same sub section with a P-Audio coaxial for years.

Going to be a good match with the Neo3/Neo10 planars in a triamp setup.


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PostPosted: January 10th, 2018, 2:30 pm 
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Cogito wrote:
tomp wrote:
Very true, but the servo if properly designed and executed it is another tool that can help get better results. The fly in the ointment is the cost of producing a good servo is often more than the cost of an additional driver. The servo is not going to work properly when the excursion puts the VC beyond the XMag point as the motor strength has dropped significantly. A good servo design takes that drop into account otherwise the amp would be directed to put destructive levels of power into the driver which cannot correct because there is insufficient motor strength. The voice coil at that point becomes a toaster. So the range of correction available to the servo is limited by the characteristics of the driver.

On the other hand, starting with a good driver, the distortion should be below 1% until you approach XMax. By using the money spent on the servo, you can usually buy a second driver which will give you double the linear volume displacement before the distortion rises. The second driver can be put in the reversed position and driven 180 degrees out of phase so the acoustic output is in phase. You get lower distortion, more linear displacement, higher sensitivity but wind up with double the enclosure size. It is always a trade off.


Adding a second driver firing in the reverse direction is not going to correct the non-linearities of the driver of either driver, but it spreads the non-linearities to both phases and mask them with linear content (from driver firing forward), which might be less objectionable.

BTW, we are not saying HAL's drivers have the non-linearity issues.


Shashi:

I don't think that is correct. As I said I am not an expert on the mechanism but you might want to look at this patent:

US 5537479 A

Here is what the author claims. I can't verify that myself. It might be an interesting test if I ever get time.

This push-pull configuration is a prior art concept in which the major even-order distortion harmonics (which contain the 2nd harmonic, usually the largest of all distortion harmonics) are greatly reduced because they are intentionally caused to be precisely out-of-phase as radiated, as between a normally mounted driver (or drivers) and an axially inverted mounted driver (or drivers)


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