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Author Topic: JTR Orbit Shifter ("Live Sound" version)  (Read 11582 times)

Art Welter

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Re: JTR Orbit Shifter ("Live Sound" version)
« Reply #20 on: July 16, 2010, 08:38:57 pm »

Jeff Permanian wrote on Fri, 16 July 2010 16:56

Art Welter wrote on Fri, 16 July 2010 13:24


Jeff,

30mm is an impressive X max figure !

The 23mm Xmax Growler appears to hit Xmax ( 10% harmonic distortion generated) with a 29 volt 45 Hz sine wave, though at 50 Hz and above can handle 85V with low (around 10% or less) distortion.

The Orbit Shifter, with it’s much longer horn and larger mouth area must go much lower than the Growler before exceeding  Xmax.

Have you done any testing so far to determine the Orbit Shifter's maximum input voltage without exceeding  Xmax  ?

Art Welter


The Growler is no where near its Xmax at 29 volts. The harmonic distortion is due to the driver displacing a large percentage of the rear chamber's volume.



Interesting, must be a tiny rear chamber volume for a 12” driver with an Xmax of 23 mm (about 1165 cc,  0.04 cubic feet displacement) to displace a large percentage of it’s volume.

Does the Orbit Shifter’s driver also displace a large percentage of it’s rear chamber volume ?

Art Welter
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Phil Lewandowski

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Re: JTR Orbit Shifter ("Live Sound" version)
« Reply #21 on: July 18, 2010, 10:40:34 pm »

Art Welter wrote on Fri, 16 July 2010 20:38

Jeff Permanian wrote on Fri, 16 July 2010 16:56

Art Welter wrote on Fri, 16 July 2010 13:24


Jeff,

30mm is an impressive X max figure !

The 23mm Xmax Growler appears to hit Xmax ( 10% harmonic distortion generated) with a 29 volt 45 Hz sine wave, though at 50 Hz and above can handle 85V with low (around 10% or less) distortion.

The Orbit Shifter, with it’s much longer horn and larger mouth area must go much lower than the Growler before exceeding  Xmax.

Have you done any testing so far to determine the Orbit Shifter's maximum input voltage without exceeding  Xmax  ?

Art Welter


The Growler is no where near its Xmax at 29 volts. The harmonic distortion is due to the driver displacing a large percentage of the rear chamber's volume.



Interesting, must be a tiny rear chamber volume for a 12” driver with an Xmax of 23 mm (about 1165 cc,  0.04 cubic feet displacement) to displace a large percentage of it’s volume.

Does the Orbit Shifter’s driver also displace a large percentage of it’s rear chamber volume ?

Art Welter


That is interesting.  And the Growler does not have a big rear chamber, so that makes sense.


I am curious, what is the reason that displacing a large amount of a rear chamber's volume causes distortion?


Thanks,
Phil
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Tim McCulloch

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Re: JTR Orbit Shifter ("Live Sound" version)
« Reply #22 on: July 19, 2010, 03:03:04 pm »

The driver excursion encroaches the "nominal" cubic volume of the rear chamber as you play louder and lower.  The non-linearity of loading creates the distortion.

It changes the loading ratio more dramatically for a small chamber than a large one.

Or I'm completely wrong in my understanding of these things and should be sitting on the sidelines...  Either way, your posts with Art in the distortion thread, coupled with this one, have been great exercises.  Thanks for documented work and the discussions that have followed.

Have fun, good luck.

Tim Mc
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Phil Lewandowski

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Re: JTR Orbit Shifter ("Live Sound" version)
« Reply #23 on: July 19, 2010, 04:48:46 pm »

Tim McCulloch wrote on Mon, 19 July 2010 15:03

The driver excursion encroaches the "nominal" cubic volume of the rear chamber as you play louder and lower.  The non-linearity of loading creates the distortion.

It changes the loading ratio more dramatically for a small chamber than a large one.

Or I'm completely wrong in my understanding of these things and should be sitting on the sidelines...  Either way, your posts with Art in the distortion thread, coupled with this one, have been great exercises.  Thanks for documented work and the discussions that have followed.

Have fun, good luck.

Tim Mc


Gotcha, ok that is starting to make sense.  Thanks Tim.


And no problem, it has been a great learning experience for me.  Nothing beats actually getting out there and measuring and playing.  Smile


Take Care,
Phil
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Art Welter

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Re: JTR Orbit Shifter ("Live Sound" version)
« Reply #24 on: July 19, 2010, 06:35:56 pm »

Tim McCulloch wrote on Mon, 19 July 2010 13:03

The driver excursion encroaches the "nominal" cubic volume of the rear chamber as you play louder and lower.  The non-linearity of loading creates the distortion.

It changes the loading ratio more dramatically for a small chamber than a large one.



Tim,

At what driver excursion to chamber size percentage does it  “encroach” the  cubic volume of the rear chamber ?

What aspect of the loading is non-linear ?

Why does the “non-linearity of loading” create  distortion ?

In the example of the Growler driver, the maximum linear displacement is .04 cubic foot.
If the compression chamber was only one half cubic foot (a very small box for a 12” driver) that would be a ratio of .04/.5.
8% does not normally qualify as a “large percentage”.
Of course, Jeff said the Growler is not near Xmax at 29 volts at 45 Hz, so the percentage would be smaller if that is true, and I would be quite surprised to find the compression chamber to be only one half cubic foot, it probably is closer to 3 times that size, putting the % of displacement to chamber size below 3% when driven to Xmax.

Below the cut off frequency of the horn, the acoustic resistance of the horn is zero, so the driver acts as it would in a small sealed chamber. As the driver is driven at frequencies below the horn cut off, excursion rises rapidly, while output reduces rapidly. Excursion above Xmax results in higher distortion, which increases rapidly with small increments of excursion past Xmax.

In each case of measured distortion in horn loaded cabinets, the distortion increased below the horn cut off. The bigger horns, with lower cutoff frequencies, have less distortion to lower frequencies.

Inquiring minds await you or Jeff's alternative explanations of the causes of low frequency distortion in straight horns.

Art Welter
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